Class 8 School Science

Chapter 7 The Microbial World Short Answer Type Questions

Question 1. What are microbes?
Answer:

Microbes:

The term microbe is short for microorganisms, which means extremely diverse small organisms. A microbe is any living organism that spends its life at a size too tiny to be seen with the naked eye.

Microbes include bacteria and archaebacteria, protists, and some fungi. Viruses and the recently discovered prions are also considered microbes.

Question 2. What is a virus?
Answer:

Virus:

A virus is an acellular infectious agent that replicates only inside the living cells of other organisms. Viruses can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea.

Question 3. What are bacteria?
Answer:

Bacteria:

Bacteria are microscopic prokaryotic organisms whose single cells have neither a membrane-enclosed nucleus nor other membrane-enclosed organelles like mitochondria and chloroplasts.

Question 4. What are protozoa?
Answer:

Protozoa:

The name ‘proto-zoa’ literally means ‘first animals’ and early classification systems grouped the protozoa as members of the animal kingdom.

However, they were recognized as a discrete assemblage based on their unicellularity and were assigned to the kingdom Protista. Protozoa are eukaryotic organisms that exist as structurally and functionally independent individual cells.

Question 5. What are fungi?
Answer:

Fungi:

A fungus (plural: fungi) is any member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms.

Read And Learn More WBBSE Solutions For Class 8 School Science Short Answer Type Questions

These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, protists, and bacteria. One major difference is that fungal cells have cell walls that contain chitin, unlike the cell walls of plants and some protists.

Question 6. Which contains cellulose, unlike the cell walls of bacteria What are algae?
Answer:

Algae (singular: alga) are any of numerous groups of chlorophyll-containing, mainly aquatic eukaryotic organisms ranging from ‘ microscopic single-celled forms to multicellular forms, distinguished from plants by the absence of true roots, stems, dried Leaves.

Question 7. Write two characteristics of the virus.
Answer:

Characteristics of the virus:

Obligate intracellular parasite composed of nucleic acid (either DNA or RhlA) and protein coat.

Multiply inside living cells using the host cell machinery.

WBBSE Solutions For Class 8 School Science Long Answer Type Questions	WBBSE Solutions For Class 8 School Science Short Answer Type Questions
WBBSE Solutions For Class 8 School Science Very Short Answer Type Questions	WBBSE Solutions For Class 8 School Science Review Questions
WBBSE Solutions For Class 8 School Science Solved Numerical Problems	WBBSE Solutions For Class 8 School Science Experiments Questions
WBBSE Solutions For Class 8 Maths	WBBSE Class 8 History Notes
WBBSE Class 8 History Multiple Choice Questions	WBBSE Solutions For Class 8 History
WBBSE Solutions For Class 8 Geography

 

Question 8. State for example the useful and harmful role of viruses.
Answer:

Useful Role Of Viruses:

Viruses have very clever ways of attacking all types of cells, including bacteria. Scientists are trying to find ways of using these viruses to kill bacteria, instead of antibiotics.

Harmful Role Of Viruses:

Viral infections can cause disease in humans, animals, and even plants. Respiratory viruses can induce rubella, measles, mumps, influenza, and the common cold.

Question 9. How viral infection can be prevented?
Answer:

Prevention Of Viral Infection:

Viral infections can cause disease in humans, animals, and even plants. However, they are usually eliminated by the immune system, conferring lifetime immunity to the host for that virus.

Antibiotics do not affect viruses, but antiviral drugs have been developed to treat life-threatening infections. Vaccines that produce lifelong immunity can prevent some viral infections.

Chapter 7 The Microbial World Short Answer Questions

Question 10. Write two characteristics of bacteria.
Answer:

Characteristics Of Bacteria:

1. Prokaryotic organisms with cytoplasm and nucleic acids (both DNA and RNA).
2. Membrane-bound cell organelles are absent.

Question 11. Write briefly about useful bacteria.
Answer:

Useful Bacteria:

Some bacteria degrade organic compounds for energy, and without bacteria, the earth would have no soil in which to grow plants.

Bacteria living in the gut(E. coli, Lactobacillus, Streptococcus, etc) can help animals break down food. These so-called ‘good bacteria help maintain the conditions necessary for food digestion.

Ammonifying bacteria (eg. Bacillus ramosus) release ammonia in soil by decay and putrefaction. Nitrifying bacteria (Nitrobacter) convert ammonia to nitrites.

Symbiotic (eg. Rhizobium) or nonsymbiotic (eg. Azotobacter) bacteria fix up atmospheric nitrogen into the soil to increase soil fertility.

1. Bacitracin, a source of antibiotics, is extracted from Bacillus subtilis.
2. Bacillus subtilis, Clostridium tertium etc help in extraction of fibre from jute, hemp and coir.

For the curing of tea and tobacco, My coccus cardigans and Bacillus megatherium are used.

Question 12. Write briefly about harmful bacteria.
Answer:

Harmful Bacteria:

There are many types of harmful bacteria, some of which are deadly, while others only cause minor illnesses. One of the most dangerous is Yersinia pestis, which caused the bubonic plague, and which still afflicts small portions of the world’s population.

A less dangerous, but still inconvenient, form is Campylobacter, which is responsible for most cases of food poisoning, causing severe intestinal discomfort and often vomiting.

Other bacteria may be an inconvenience if treated, but deadly if left on their own, such as the different types of Streptococcus that are responsible for strep throat and pneumonia.

Denitrifying bacteria convert nitrates to free nitrogen gas in soil with excessive water and poor aeration resulting in a reduction of soil fertility, eg. P. denitrificans, etc.

Food poisoning is caused by Clostridium botulinum, Micrococcus pyogenes, etc.

Bacteria also cause some harmful plant diseases like the soft rot of potatoes, angular leaf spots of cotton, plant tumors, etc.

Question 13. State two characteristics of protozoa.
Answer:

Characteristics of protozoa:

1. Protozoa are eukaryotic microorganisms lacking the capability of photosynthesis.
2. Protozoa are notable for their ability to move independently (by pseudopodia/ cilia/ flagella), a characteristic found in the majority of species.

Question 14. Name the microbes that are employed in
Answer:

1. conversion of lactose to lactic acid
2. synthesis of Vit. B12
3. sewage treatment
4. tanning of leather
5. production of protein-rich powder or protein cakes
6. Lactobacillus (bacteria)
7. Clostridium (bacteria.)
8. Chlorella or Chlamydomonas (algae)
9. Lichens
10. Yeast (fungi)

Question 15. Write briefly about useful protozoa.
Answer:

Useful Protozoa:

Some protozoans live in the body of other organisms and help them. Termites, for example, have protozoans (Triconympha) living in their body.

1. The protozoans digest the cellulose in the wood eaten by termites and convert it into carbohydrates that the termites can use.
2. A large number of protozoa living in polluted water feed upon waste organic matter and thus purify it.
3. The skeletal deposits of foraminiferans and radiolarians are associated with oil deposits.

Question 16. Write briefly about harmful protozoa.
Answer:

Harmful Protozoa:

Some protozoans cause diseases. The protozoan Entamoeba causes amoebiasis (amoebic dysentery) in human beings, while Plasmodium causes malaria.

1. Trypanosoma, a parasitic protozoan that lives in the bloodstream of human beings, cattle, and other animals, causes a dangerous disease called sleeping sickness.
2. About 200-300 varieties of protozoa live in the soil, feed on nitrogen-fixing bacteria, and reduce the fertility of the soil.
3. Drinking water in natural conditions is made unpalatable by the reproduction of some free-living protozoa in it.
4. Protozoans living in the gut of termites indirectly help in the destruction of wooden articles.

WBBSE Class 8 Science Important Short Answers

Question 17. State two characteristics of fungus.
Answer:

Characteristics of fungus:

Most fungi grow as tubular filaments called hyphae. An interwoven mass of hyphae is called mycelium. The walls of hyphae are often strengthened with chitin.

Fungi are not capable of producing their own food (due to lack of chloroplastid), so they get their nourishment from other sources.

Question 18. Write briefly about useful fungi.
Answer:

Useful Fungi:

Fungi, together with bacteria, are responsible for most of the recycling which returns dead material to the soil in a form in which it can be reused.

1. Fungi are also important directly as food for humans. Many mushrooms are edible and different species are cultivated for sale worldwide.
2. Yeast is used in baking bread, Penicillium came Berti is used in cheese to give flavor and shine to butter, etc.
3. Fungi are used in the biological control of pathogenic bacteria and certain nematodes.

Question 19. Write briefly about harmful fungi.
Answer:

Harmful Fungi:

Some fungi are harmful as they cause disease: rusts and smuts on farm crops and orchards, athletes’ feet, oral thrush, ringworm disease, etc. Aspergillus, and Rhizopus infect food grains and make them unfit for consumption.

Question 20. State two characteristics of algae.
Answer:

Two Characteristics Of Algae:

1. Algae are eukaryotic organisms that have no roots, stems, or leaves.
2. Algae have chlorophyll and other pigments for carrying out photosynthesis.

Question 21. What are harmful algae?
Answer:

Harmful Algae:

Phytoplankton blooms, micro-algal blooms, toxic algae, red tides, or harmful algae, are all terms for naturally occurring phenomena.

Several hundred species of micro-algae are reported at times to form mass occurrences, so-called blooms. Nearly one-fourth of these species are known to produce toxins.

Short Answer Questions for Class 8 Microbial World

Question 22. Write briefly about useful algae.
Answer:

Useful Algae:

Humans use algae as food, for the production of useful compounds, as biofilters to remove nutrients and other pollutants from wastewaters to assay water quality, as indicators of environmental change, in space technology, and as laboratory research systems.

1. Nostoc and Anabaena are good nitrogen fixers.
2. Chara is used as larvicidal to destroy mosquito larvae.
3. Chlorella is an antibiotic extracted from chlorella.

Question 23. What is a vaccine?
Answer:

Vaccine:

A vaccine is a biological preparation that provides active acquired immunity to a particular disease.

Question 24. What is immunity?
Answer:

Immunity:

In biology, immunity is the balanced state of having adequate biological defenses to fight infection, disease, or other unwanted biological invasions, while having adequate tolerance to avoid inflammation, allergy, and autoimmune diseases.

Question 25. What is vaccination?
Answer:

Vaccination:

Vaccination is the administration of antigenic material (a vaccine) to stimulate an individual’s immune system to develop adaptive immunity to a pathogen. Vaccines can .prevent or ameliorate morbidity from infection.

Question 26. What is an antigen?
Answer:

Antigen:

An antigen is any substance that causes your immune system to produce antibodies against it. An antigen may be a foreign substance from the environment, such as chemicals, bacteria, viruses, or pollen. An antigen may also be formed inside the body, as with bacterial toxins or tissue cells.

Question 27. What is an antibody?
Answer:

Antibody:

An antibody is a protein produced by the body’s immune system when it detects harmful substances, called antigens.

Question 28. What are antibiotics?
Answer:

Antibiotics:

Antibiotics or antibacterials are a type of antimicrobial used specifically against bacteria, and are often used in the medical treatment of bacterial infections.

They may either kill or inhibit the growth of bacteria. Several antibiotic agents are also effective against a number of fungi, and protozoans and some are toxic to humans and animals.

Question 29. What is symbiosis?
Answer:

Symbiosis:

Symbiosis is close and often long-term interaction between two or more different biological species. Some symbiotic relationships are obligate, meaning that both symbionts entirely depend on each other for survival.

For example, many lichens consist of fungal and photosynthetic symbionts that cannot live on their own. Others are facultative, meaning that they can, but do not have to live with the other organism.

Question 30. What is parasitism?
Answer:

Parasitism:

Parasitism is a non-mutual symbiotic relationship between species, where one species, the parasite, benefits at the expense of the other, the host.

Question 31. What are saprophytes?
Answer:

Saprophytes:

Saprophytes are living organisms that feed on dead organic matter. They are considered extremely important in soil biology, as they break down dead and decaying organic matter into simple substances that can be taken up and recycled by plants. The term is usually used to refer to saprophytic fungi or bacteria.

Question 32. What is food processing?
Answer:

Food Processing:

Food processing is the transformation of raw ingredients, by physical or chemical means into food, or of food into other forms.

Food processing combines raw food ingredients to produce marketable food products that can be easily prepared and served by the consumer.

Question 33. What is the canning of food?
Answer:

Canning Of Food:

Canning is a method of preserving food in which the food contents are processed and sealed in an air-tight container.

Question 34. What is food preservation?
Answer:

Food Preservation:

Food preservation usually involves preventing the growth of bacteria, fungi (such as yeasts), or other microorganisms (although some methods work by introducing benign bacteria or fungi to the food), as well as retarding the oxidation of fats that cause rancidity.

WBBSE Chapter 7 Microbial World Study Guide

Question 35. What is pasteurization?
Answer:

Pasteurization:

Pasteurization is a heat-treatment process that destroys pathogenic microorganisms in certain foods and beverages. It is named after the French scientist Louis Pasteur,

who in the 1860s demonstrated that abnormal fermentation of wine and beer could be prevented by heating the beverages to about 57° C for a few minutes.

Pasteurization of milk requires temperatures of about 63° C maintained for 30 minutes or, alternatively, heating to a higher temperature(72° C)and holding for 15 seconds (and yet higher temperatures for shorter periods of time).

Question 36. What is fermentation?
Answer:

Fermentation:

Fermentation is a metabolic process that converts sugar to acids, gases, and/or alcohol. It occurs in yeast and bacteria, but also in oxygen-starved muscle cells, as in the case of lactic acid fermentation.

Question 37. What is retting?
Answer:

Retting:

Retting is a process employing the action of microorganisms and moisture on plants to dissolve or rot away much of the cellular tissues and pectins surrounding bast-fiber bundles, and so facilitating the separation of the fiber from the stem.

To extract fine fibers from the jute plant, a small stalk is harvested for pre-retting. Usually, this small stalk is brought 2 weeks of harvesting time. If the fiber can easily be removed from the Jute hurd or core, then the crop is ready for harvesting.

Question 38. What is Nitrogen fixation?
Answer:

Nitrogen Fixation:

Nitrogen fixation is a process in which nitrogen in the atmosphere is converted into ammonium. Atmospheric nitrogen or molecular nitrogen

(NJ is relatively inert: it does not easily react with other chemicals to form new compounds. Nitrogen fixation, natural and synthetic, is essential for all forms of life because nitrogen is required to biosynthesize the basic building blocks of plants, animals, and other life forms.

Question 39. What are Nitrogen-fixing bacteria? Nitrogen-fixing bacteria are microorganisms capable of transforming atmospheric

Answer:

Nitrogen-Fixing Bacteria:

Nitrogen into fixed nitrogen, inorganic compounds usable by plants. More than 90 percent of all nitrogen fixation is affected by them.

Two kinds of nitrogen fixers are recognized: free-living (non-symbiotic) bacteria, including the Cyanobacteria (or blue-green algae)

Anabaena and Nostoc, and such genera as Azotobacter, and Clostridium; and mutualistic (symbiotic) bacteria such as Rhizobium, associated with leguminous plants, and Spirillumlipoferum, associated with cereal grasses.

Question 40. What is nitrification?
Answer:

Nitrification:

Nitrification is the biological oxidation of ammonia or ammonium to nitrite followed by the oxidation of the nitrite to nitrate. Nitrification is an important step in the nitrogen cycle in soil.

Short Answer Resources for Class 8 The Microbial World

Question 41. What is denitrification?
Answer:

Denitrification:

Denitrification is a microbially facilitated process of nitrate reduction (performed by a large group of heterotrophic facultative anaerobic bacteria) that may ultimately produce molecular nitrogen (NJ through d series of intermediate gaseous nitrogen oxide products.

Question 42. What is ammonification?
Answer:

Ammonification:

The process of ammonification is the result of the breakdown of organic matter such as dead animals and plants or waste materials like excrement.

This breakdown is accomplished by scores of microorganisms that utilize dead organic material for energy and produce ammonia and related compounds as a byproduct of their metabolisms.

Ammonification classically occurs in the soil, in an aerobic environment which gives the bacteria and other microorganisms oxygen to work with.

Question 43. What is the salting of food?
Answer:

Salting Of Food:

Salting is the preservation of food with dry edible salt. It is related to pickling (preparing food with brine, that is, salty water) and is one form of curing. It is one of the oldest methods of preserving food.

Question 44. What is pickling?
Answer:

Pickling:

Pickling is the process of preserving food by anaerobic fermentation in brine or vinegar. The resulting food is called pickle.

Question 45. What are methanogenic bacteria?
Answer:

Methanogenic Bacteria:

Methanogenic bacteria are a large and diverse group that is united by three features:

1. they form large quantities of methane as the major product of their energy metabolism,
2. they are strict anaerobes, (Hi) they are members of the domain archaea or archaebacteria.

Question 46. What is biogas?
Answer:

Biogas:

Biogas typically refers to a mixture of different gases produced by the breakdown of organic matter in the absence of oxygen.

Biogas can be produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, or food waste.

Biogas can be produced by anaerobic digestion with anaerobic bacteria, which digest material inside a closed system, or fermentation of biodegradable materials.

Biogas is primarily methane and carbon dioxide and may have small amounts of hydrogen sulfide. Biogas can be compressed, the same way natural gas is compressed to CNG, and used to power motor vehicles.

Question 47. Write the Differences between bacteria and virus
Answer:

The Differences between bacteria and virus:

Points of differences	Bacteria	Virus
Ribosomes	Present	Absent
Cell wall	Peptidoglycan/Lipopolysaccharide	No cell wall, a Protein coat is present instead.
Living attributes	Living organism	Opinions differ on whether viruses are a form of life or organic structures that interact with living organisms.
Number of cells	Unicellular; one cell	No cells; not living
Structures	DNA and RNA float freely in the cytoplasm. Has a cell wall and cell membrane.	DNA or RNA is enclosed inside a coat of protein.
Treatment	Antibiotics	Vaccines prevent the spread and anti-viral medications help to slow reproduction but cannot stop it completely.

 

WBBSE Class 8 Science Practice Questions on Microbes

Question 48. Write the differences between fungi and bacteria.
Answer:

The differences between fungi and bacteria:

1. Fungi are eukaryotes while bacteria are prokaryotes.
2. Bacteria are single-celled whereas most fungi are multicellular except for yeast.
3. The compositions within their cell walls are different.
4. Fungi are heterotrophs while Bacteria can be autotrophs or heterotrophs.
5. Bacteria have 3 distinct shapes furg have various shapes.

Bacteria reproduce sexually via binary fission whereas fungi are capable of reproducing both sexually or asexually. (There is no hard and fast rule that the differences should always be written in columns.

The above answer is an example. However, students can arrange them according to columns, if instructed by their teachers.)

Question 49. Write the differences between algae and fungi.
Answer:

The differences between algae and fungi:

Algae	Fungus
1. Cell wall is made up of cellulose.	1. Cell wall is made up of chitin.
2. Cells contain chloroplasts. Hence, these are green in color.	2. Cells do not contain chloroplasts. Hence, these are colorless.
3. These are autotrophic.	3. These are heterotrophic.
4. Cells are uninucleated.	4. Cells or hypha are uninucleated, binucleated, or coenocytic.
5. The reserve food is starch	5. The reserve food is glycogen.

 

Question 50. Write the similarities and dissimilarities between algae and protozoa.
Answer :

Some similarities are:

1. They have nuclei and can reproduce by mitosis followed by cell division.
2. Many in both groups are able to move.
3. Like the algae, some protozoans, like Euglena, are able to do photosynthesis.
4. Both belong to the kingdom Protista.
5. Some differences are

Characteristics	Algae	Protozoa
Nutritional type	Photoautotroph	Chemoheterotroph
Multicellularity	Some	None
Cellular arrangement	Unicellular, colonial, filamentous	Unicellular
Food acquisition	Diffusion	Absorptive; ingestive (cytostome)
Characteristic	Pigments	Motility; some form cysts

 

Question 51. Write the differences between symbiosis and parasitism.
Answer:

The differences between symbiosis and parasitism:

Symbiosis	Parasitism
1. It is a relationship in which two organisms live together in a manner that is beneficial to both.	1. It is a relationship between two organisms that is beneficial to one (the parasite) and harmful to the other (the host).
2. Each partner in the relationship is called a symbiont.	2. The organism which draws food is called the parasite and the one which provides food and shelter is called the host.
3. For example, the relationship between root nodules of leguminous plants and Rhizobium (N2 -fixing bacterium), E. coli present in the human intestine.	3. For example, Cuscuta is a parasitic plant. Plasmodium is a parasite in the body of man and mosquito.

 

Question 52. Write the differences between parasite and saprophyte.
Answer:

The differences between parasite and saprophyte:

Parasite	Saprophyte
1. The organism, which depends upon other organisms for its nourishment and growth, is known as a parasite.	1. The organism, which grows on dead and decaying material for its growth, is known as a saprophyte.
2. It has intracellular digestion.	2. It shows extracellular digestion.
3. It causes harm to the organism.	3. It does not depend on a living host.

 

WBBSE Chapter 7 The Microbial World VSAQs

Question 1. What are microbes?
Answer:

Microbes:

Microscopic living organisms other than plants and animals.

Question 2. What is the whitish layer, formed on the surface of bread during the rainy season?
Answer:

It is a layer of fungus.

WBBSE Class 8 Quick Answers on Microbes

Question 3. What are the most primitive and ancient organisms found on earth?
Answer:

Microbes are the most primitive and ancient organisms.

Question 4. Name one anaerobic microbe.
Answer:

Yeast (or tetanus-causing pathogen) is an anaerobic microbe.

Question 5. What is the term used to denote the organisms living on dead and decaying organic matter?
Answer:

They are called saprotrophs.

WBBSE Class 8 Very Short Answer Questions Microbial World

Question 6. Which microbes can produce their food?
Answer:

Algae can produce their food.

Question 7. What are thermophilic bacteria?
Answer:

Thermophilic Bacteria:

They can grow and survive even at about 100X.

Question 8. What types of bacteria are found in hot springs?
Answer:

Types of bacteria are found in hot springs:

Thermophilic bacteria are found in hot springs.

Question 9. What is staining?
Answer:

Staining:

It is the process of coloring specimens for identification under a microscope.

Question 10. Which cell organelle is present in bacteria?
Answer:

Ribosomes are present in bacteria.

Read And Learn More WBBSE Solutions For Class 8 School Science Very Short Answer Type Questions

Question 11. State the characteristics of bacterial DNA.
Answer:

It is circular DNA, not enclosed within the nucleus.

Question 12. Name a locomotory structure of protozoa, other than pseudopodia.
Answer:

The locomotory structures may be cilia or flagella.

Chapter 7 The Microbial World WBBSE Answers

Question 13. What are the units of fungal mycelium?
Answer:

Units of fungal mycelium:

A large number of hyphae form mycelium

WBBSE Solutions For Class 8 School Science Long Answer Type Questions	WBBSE Solutions For Class 8 School Science Short Answer Type Questions
WBBSE Solutions For Class 8 School Science Very Short Answer Type Questions	WBBSE Solutions For Class 8 School Science Review Questions
WBBSE Solutions For Class 8 School Science Solved Numerical Problems	WBBSE Solutions For Class 8 School Science Experiments Questions
WBBSE Solutions For Class 8 Maths	WBBSE Class 8 History Notes
WBBSE Class 8 History Multiple Choice Questions	WBBSE Solutions For Class 8 History
WBBSE Solutions For Class 8 Geography

 

Question 14. Give an example of a unicellular roundish fungus.
Answer:

Yeast is a unicellular, roundish fungus.

Question 15. Why fungi can not synthesize their food?
Answer:

Because they do not have chloroplasts in their cell.

Question 16. Name colonial algae.
Answer:

Colonial algae:

Volvox is a colonial alga.

Question 17. Why algae can synthesize their own food (autotrophic)?
Answer:

Because they have chloroplasts in their cytoplasm.

Question 18. Which microbes cause smallpox?
Answer:

Smallpox is caused by a virus.

Question 19. Which microorganisms do not have a nucleus and cytoplasm?
Answer:

Viruses do not have a nucleus and cytoplasm.

WBBSE Class 8 Science Very Short Answer Format

Question 20. What type of nucleic acid is found in viruses?
Answer:

The nucleic acid is either DNA or RNA.

Question 21. Which microbes show the characteristic of living only within the body of a host?
Answer:

Viruses behave like living only within the body of a host.

Question 22. Which type of microbes causes amoebiasis?
Answer:

Some protozoal microbes are responsible.

Question 23. How tuberculosis can spread from one person to other?
Answer:

It can spread through cough and sneezing.

Question 24. Which symbiotic bacteria are found in root nodules of leguminous plants?
Answer:

Rhizobium lives in root nodules.

Question 25. Which symbiotic bacteria live in the human intestine?
Answer:

The symbiotic bacteria Escherichia coli live in the human intestine.

Question 26. Which microbial association is found in Lichen?
Answer:

In lichen, an association of algae and fungi is found.

Question 27. What is the term used to denote the mutually beneficial association between two organisms?
Answer:

The term is symbiosis.

Question 28. How the bacteria Azotobacter is helpful?
Answer:

It helps to fix nitrogen in the soil.

WBBSE Class 8 Science Important Very Short Answers

Question 29. What is the function of nitrifying bacteria?
Answer:

It converts ammonia into nitrate and nitrite.

Question 30. Which bacteria help in the formation of curd from milk?
Answer:

The bacteria is Lactobacillus.

Question 31. What is the term used for the process of food preservation in air-tight containers?
Answer:

It is known as canning.

Question 32. By which process, milk can be preserved?
Answer:

It is done by Pasteurization.

Question 33. what are antibiotics?
Answer:

Antibiotics:

These are life-saving drugs produced from microbes.

Question 34. Who first discovered antibiotics?
Answer:

Alexander Flemming first discovered antibiotics in the year 1928.

Question 35. What are antigens?
Answer:

Antigens:

Antigens are foreign substances that may enter our body fluid.

Very Short Answer Questions for Class 8 Microbial World

Question 36. What are antibodies?
Answer:

Antibodies:

Antibodies are protein substances produced by our body’s defense mechanism to fight against antigens.

Question 37. What is vaccination?
Answer:

Vaccination:

Vaccination is the administration of antigenic material (a vaccine) to stimulate an individual’s immune system to develop immunity against a pathogen.

Question 38. Name two diseases that can be controlled, by vaccination.
Answer:

Typhoid, tetanus, polio, diphtheria, smallpox, tuberculosis, etc (any two are to be .. mentioned).

Question 39. Which gas may be produced from the treatment of wastes?
Answer:

Methane gas may be produced.

Question 40. Name algae that is used in space shuttles.
Answer:

Chlorella is used to clean the enclosed air.

Question 41. Name some methods of food preservation.
Answer:

Pasteurization, Pickling, Freezing, etc.

WBBSE Class 8 Science Study Guide Microbial World

Question 42. What are biofertilizers?
Answer:

Biofertilizers:

Biofertilizers are the microbes that can bring about the nutrient enrichment of soil and enhances the nutrient availability to crop plants. Example: Azotobacter, Azolla-anabaena, Rhizobium etc.

Question 43. Name two plant pathogenic fungi.
Answer:

Albugo Candida and Puccinia graminis.

Microbial World WBBSE Class 8 Resources

Question 44. Name two algae that are used as food.
Answer:

Alaria and Laminaria.

Question 45. Name a virus that is used as a biopesticide.
Answer:

Nucleopolyhedrosin virus (NPV).

Chapter 7 The Microbial World Review Questions MCQs

Question 1. Microbes are

1. Living
2. Non-living
3. Inorganic compounds
4. None of these

Answer: 1. Living

Question 2. Microbes are visible by

1. Naked eye
2. Microscope
3. Hand lens
4. Spectacle

Answer: 2. Microscope

Question 3. Bacteria, viruses, and protozoa are

1. Animals
2. Plants
3. Microbes
4. Carriers

Answer: 3. Microbes

Question 4. The application of microbial metabolism to transform simple raw materials into valuable products is called

1. Biocatalysis
2. Tissue culture
3. Genetic engineering
4. Fermentation

Answer: 4. Fermentation

Question 5. An ideal place of survival of microbes

1. Damp places
2. Sunny places
3. Dry places
4. Rocky surfaces

Answer: 1. Damp places

Read And Learn More WBBSE Solutions For Class 8 School Science Review Questions

Question 6. The microbes that can produce their own food

1. Protozoa
2. Virus
3. Algae
4. Bacteria

Answer: 3. Algae

Question 7. Microbes prefer the temperature for growth

1. 0°C-5°c
2. 25°C-35°c
3. 100°C-110°c
4. Sub-zero temperature

Answer: 2. 25°C-35°c

Question 8. For microscope observation, specimens are generally

1. Moist
2. Heated
3. Stained
4. Acidified

Answer: 3. Stained

WBBSE Solutions For Class 8 School Science Long Answer Type Questions	WBBSE Solutions For Class 8 School Science Short Answer Type Questions
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WBBSE Solutions For Class 8 School Science Solved Numerical Problems	WBBSE Solutions For Class 8 School Science Experiments Questions
WBBSE Solutions For Class 8 Maths	WBBSE Class 8 History Notes
WBBSE Class 8 History Multiple Choice Questions	WBBSE Solutions For Class 8 History
WBBSE Solutions For Class 8 Geography

 

Question 9. Which one is not a microbe?

1. Bacteria
2. Fungus
3. Small plants
4. Virus

Answer: 3. Small plants

Question 10. Microbes may be

1. Beneficial or harmful
2. Always Harmful
3. Always Beneficial
4. All of these

Answer: 1. Beneficial or harmful

Question 11. Curd, milk, cheese, and butter are produced with the help of

1. Yeast
2. Acetobacter
3. Penicillium
4. Streptococcus

Answer: 4. Streptococcus

Question 12. Antibiotics are mostly produced commercially from

1. Viruses
2. Saprophytic bacteria
3. Parasitic host
4. All of these

Answer: 2. Saprophytic bacteria

Question 13. Louis Pasteur is famous for the discovery of

1. Bacteria
2. Life
3. Vaccine of hydrophobia
4. Antigen

Answer: 3. Vaccine for hydrophobia

Chapter 7 The Microbial World WBBSE Solutions

Question 14. Bacteria are placed under the kingdom

1. Plantae
2. Monera
3. Protista
4. Akaryota

Answer: 2. Monera

Question 15. Pseudopodia is the locomotory structure of

1. Bacteria
2. Algae
3. Protozoa
4. Virus

Answer: 3. Protozoa

Question 16. Hyphae is a term associated with

1. Fungi
2. Algae
3. Microbes
4. Virus

Answer: 1. Fungi

Question 17. Penicillium is a

1. Fungus
2. Algae
3. Medicine
4. Fertilizer

Answer: 1. Fungus

WBBSE Class 8 Science Important Review Questions

Question 18. An example of colonial algae is

1. Chlamydomonas
2. Volvox
3. Spirogyra
4. Mucor

Answer: 2. Volvox

Question 19. Biofertilizers include

1. Cyanobacteria
2. Mycorrhizal fungi
3. Nitrifying bacteria
4. All of these

Answer: 4. All of these

Question 20. Virus can be seen under

1. Electron microscope
2. Simple light microscope
3. Compound light microscope
4. None of these

Answer: 1. Electron microscope

Question 21. The nucleic acid of the virus is

1. Both DNA and RNA
2. Either DNA or RNA
3. Only rna
4. Only DNA

Answer: 2. Either DNA or RNA

Review Questions for Class 8 Microbial World

Question 22. Viruses are

1. Unicellular
2. Multicellular
3. Acellular
4. Prokaryotes

Answer: 3. Acellular

Question 23. The word ‘virus’ in Latin means

1. Poison
2. Sweet
3. Dangerous
4. Friend

Answer: 1. Poison

Question 24. Which is not a bacterial disease?

1. Tuberculosis
2. Tetanus
3. Cholera
4. Aids

Answer: 4. Aids

Question 25. Which is a protozoan disease?

1. Polio
2. Malaria
3. Ringworm
4. Polio

Answer: 2. Malaria

Microbial World WBBSE Study Guide

Question 26. Diarrhea is transmissible through

1. Air
2. Carrier
3. Water
4. Food

Answer: 3. Water

Question 27. Amoebiasis is caused by a

1. Protozoa
2. Virus
3. Fungus
4. Algae

Answer: 1. Protozoa

Question 28. Rhizobium is a

1. Parasite
2. Symbiont
3. Free-living
4. Host

Answer: 2. Symbiont

Question 29. In humans, e. Coli supplies

1. Vitamin b12
2. Vitamin c
3. Nitrogen
4. Protein

Answer: 1. Vitamin b12

Chapter 7 Microbial World WBBSE Resources

Question 30. Which of the following is not a communicable disease?

1. Cancer
2. Cholera
3. Chickenpox
4. Malaria

Answer: 1. Cancer

Question 31. Saprophytes draw nourishment from

1. Living organism
2. Parasites
3. Dead organic matter
4. Metallic substances

Answer: 3. Dead organic matter

Question 32. Which is not a nitrogen-fixing bacteria?

1. Clostridium
2. E. Coli
3. Azotobqcter
4. Y. Pestis

Answer: 2. E. Coli

Question 33. The breakdown of the nitrogenous compounds to ammonia is

1. Ammonification
2. Nitrification
3. Nitrogen fixation
4. Denitrification

Answer: 1. Ammonification

Question 34. Curd forming microorganisms is

1. Lactobacillus
2. Penicillium
3. Rhizobium
4. Metha no-bacteria

Answer: 1. Lactobacillus

Question 35. Which of the following diseases is not caused by bacteria?

1. Cholera
2. Typhoid
3. Measles
4. Tuberculosis

Answer: 3. Measles

Question 36. Antibiotics may be produced from

1. Microbes
2. Animals
3. Plants
4. Minerals

Answer: 1. Microbes

Question 37. The microorganisms which can multiply and reproduce only inside the cells of other organisms are

1. Protozoa
2. Fungi
3. Virus
4. Bacteria

Answer: 3. Virus

Question 38. Antibiotics are not effective against

1. Bacteria
2. Fungus
3. Microbes
4. Virus

Answer: 4. Virus

Question 39. Which of the following is not an area where microorganisms are employed?

1. Preparation of drugs
2. Recycling of materials in nature
3. Preparation of food by photosynthesis
4. Increasing the fertility of the soil

Answer: 3. Preparation of food by photosynthesis

Question 40. Proper vaccination can prevent the spread

1. Bacteria
2. Virus
3. Protozoa
4. Algae

Answer: 2. Virus

Question 42. Refrigeration helps in food

1. Preservation
2. Degradation
3. Nitrification
4. Preparation

Answer: 1. Preservation

Question 43. A pathogenic protozoan residing in the human digestive tract is

1. T. Gambiense
2. P. Ovale
3. Trichonympha
4. Giardia intestinalis

Answer: 4. Giardia intestinalis

Question 44. Which among the following vitamin is/are produced using microbes?

1. Vit b12
2. Carotene
3. Riboflavin
4. All of these

Answer: 4. All of these

Question 45. Which one is a viral disease ?

1. Mumps
2. Tetanus
3. Pneumonia
4. Ringworm

Answer: 1. Mumps

Chapter 7 The Microbial World Fill in the blanks

 

Question 1. The algae___________is used as food in the space station.
Answer: Chlorella

Question 2. Bread mold is a type of ___________
Answer: Fungus

Question 3. Microbes have survived over ___________ billion years on earth.
Answer: 3.5

Question 4. ___________ microbes can survive in presence of oxygen.
Answer: Aerobic

Question 5. ___________ are the microbes that can produce their own food.
Answer: Algae

Question 6. The process of coloring specimens for microscopic observation is known as ___________.
Answer: Staining

Question 7. An example of the kingdom Protista is ___________.
Answer: Protozoa

Question 8. Bacterial nucleus is known as___________ .
Answer: Nucleoid

Question 9. Membrane-bound cell organelle is absent in ___________.
Answer: Bacteria

Question 10. In 1674,___________ proved the existence of bacteria.
Answer: Leeuwenhock

Question 11. Bacteria are placed under the kingdom ___________
Answer: Monera

Question 12. Pseudopodia is the locomotory organ of some ___________.
Answer: protozoa

Question 13. Yeast is a unicellular ___________.
Answer: Fungus

Question 14. In fungus, a large number of ___________ together form mycelium.
Answer: Hyphae

Question 15. Fungi can not synthesize their food due to lack of ___________.
Answer: Chloroplast

WBBSE Class 8 Science Practice Questions on Microbes

Question 16. Spirogyra is a ___________ filamentous algae.
Answer: Multicellular

Question 17. Algae are ___________ in color.
Answer: Green

Question 18. Hydrophobia is a ___________ disease.
Answer: Viral

Question 19. Mushroom is a ___________.
Answer: Fungus

Question 20. Parasites live in association with ___________.
Answer: Host

Question 21. Vitamin deficiency may be caused by the death of beneficial ___________ within our intestine.
Answer: Bacteria

Question 22. Rhizobium lives in the root nodules of ___________ plants.
Answer: Leguminous

Question 23. Lichen has an association of ___________ and fungus.
Answer: algae

Question 24. In the case of symbiosis both organisms of an association are mutual ___________.
Answer: Benefited

Question 25. The process of surviving on decomposed organic wastes is known as ___________.
Answer: Saprophytes

Question 26. Clostridium is a ___________ fixing bacteria.
Answer: Nitrogen

Question 27. Alcohol is produced from sugar by the fungus ___________
Answer: Yeast

Question 28. Pasteurization is performed to preserve ___________.
Answer: Milk

Question 29. The antibiotic is produced from the fungus ___________ Penicillium.
Answer: Penicillin

Question 30. The natural form of resistance against infection is called ___________.
Answer: Immunity

Chapter 7 The Microbial World Identify As ‘True’ Or ‘False’

Question 1. is not seen by the naked eye.
Answer: True

Question 2. Microbes have most above.
Answer: False

Question 3. The aerobic microbe can survive in absence of oxygen.
Answer: False

Question 4. Bacteria belong to the kingdom Protista.
Answer: False

Question 5. Some microbes can produce their own food.
Answer: True

Question 6. Staining is required for the microscopic observation of specimens.
Answer: False

Question 7. Bacteria, fungi, and plants are microbes.
Answer: False

Question 8. All microbes are harmful.
Answer: False

Question 9. Plastid is absent in bacteria.
Answer: False

Question 10. Rotest Koch discovered the pathogens of malaria.
Answer: False

Question 11. A few protozoa are multicellular.
Answer: False

Question 12. All protozoa possess cilia or flagella
Answer: False

Question 13. Fungi can grow either in the presence or absence of sunlight.
Answer: True

Question 14. Spirogyra is unicellular algae.
Answer: False

Question 15. viruses are acellular.
Answer: True

Question 16. Sibiu. lost’s body viruses behave as inert particles.
Answer: True

Question 17. Influenza and mumps are viral diseases.
Answer: True

Question 18. Ringworm is an animal.
Answer: False

Question 19. AIDS may be transmitted by coughing and sneezing.
Answer: False

Question 20. Rhizobium is a symbiotic protozoan.
Answer: False

Question 21. Lichen is a parasite.
Answer: False

Question 22. Plants can not take atmospheric nitrogen directly from the air.
Answer: False

Question 23. Soyabean is a leguminous plant.
Answer: True

Question 24. Bacteria can convert vinegar to alcohol.
Answer: False

Question 25. The vaccine is an antibiotic drug.
Answer: False

Question 26. Microbes may be used in the treatment of waste materials.
Answer: True

Chapter 7 The Microbial World Match The Column

1. 

Column – A	Column – B
A. Bacteria	1. Fungi
B. Protozoa	2. Plantae
C. Fungus	3. Monera
D. Algae	4. Protista

Answer: A-3,B-4,C-1,D-2

2.

Column – A	Column – B
A. Bacteria	1. living or non-living
B. Virus	2. mycelium or hyphae
C. Fungi	3. pseudopodia or cilia
D. Protozoa	4. cell wall and nucleoid

Answer: A-4,B-1,C-2,D-3

3. 

Column – A	Column – B
A. Malaria	1. Through food
B. Tuberculosis	2. Through vector
C. Amoebiasis	3. Through blood
D. Hepatitis	4. Through cough

Answer: A-2,B-4,C-1,D-3

4.

Column – A	Column – B
A. Plasmodium	1. Saprophyte
B. Lichen	2. Parasite
C. Clostridium	3. Free-living
D. Mucor	4. Symbiotic

Answer: A-2,B-4,C-1,D-3

5.

Column – A	Column – B
A. Barber’s itch	1. Bacteria
B. Diarrhoea	2. Virus
C. Encephalitis	3. Fungi
D. Leprosy	4. Protozoans

Answer: A-3,B-4,C-2,D-1

6.

Column =- A	Column- B
A. Through drinking water	1. AIDS
B.Through vector	2. Amoebiosis
C. Through blood	3. Kalazar
D. Through air	4. Tuberculosis

Answer: A-2,B-3,C-1,D-4

Chapter 7 The Microbial World

What are Microbes?

Microbes:

The term microbe is short for microorganisms, which means small organisms visible only under microscopes. A microbe is any living thing that is too tiny to be seen with the naked eye.

Microbes are the oldest form of life on earth. They may live as individuals or cluster together in communities. Microbes live in the water you drink, the food you eat, and the air you breathe.

Right now, billions of microbes are swimming in your belly and mouth, and crawling on your skin Don’t worry; over 95% of microbes are good for you.

Microbes include bacteria, viruses, fungi, algae, and protozoa. These single-cell organisms are invisible to the eye, but they can be seen with microscopes.

Microbial Characteristics

Many characteristic features are used in classifying and identifying microorganisms. In general, these characteristic features have been divided into several major categories.

Read And Learn More WBBSE Notes For Class 8 School Science

1. Classical Characteristics

The classical type of approach such as morphological, physiological, biochemical, ecological, and genetic characteristics has been widely employed to study microbial taxonomy and it also provides phylogenetic information about microorganisms.

2. Morphological characteristics

Morphological features are important in microbial taxonomy for many reasons. Morphology is easy to study and analyze both eukaryotic and prokaryotic microorganisms.

Many different morphological features are used in the classification and identification of microorganisms. Some of these features are cell size, cell shape, colonial morphology, ultrastructural characteristics, staining behavior, cilia, and flagella, mechanism of motility, color, etc.

3. Physiological and Metabolic characteristics

Physiological and metabolic characteristics are very useful because they are directly related to the nature and activity of microbial enzymes and transport proteins.

Because proteins are gene products, analysis of these characteristics provides an indirect comparison of microbial genomes.

4. Ecological characteristics

Microorganisms are well-associated and growing in terrestrial freshwater and marine environments. The taxonomically important ecological properties are life cycle patterns,

The nature of the symbiotic relationships, and the ability to cause disease in particular hosts and habitat preferences such as temperature, pH, oxygen, and osmotic concentration.

5. Genetic characteristics

Most eukaryotes can reproduce sexually; hence genetic analysis has been of considerable usefulness in the classification of these types of microorganisms.

However, prokaryotes do not reproduce sexually, and chromosomal gene exchange (through transformation and -conjugation) is sometimes useful in the classification of prokaryotes.

The major Characteristics of microbes are

1. Microbes are found almost everywhere, i.e. in deserts, polar regions, saline or brackish water wetlands, and hot streams, and also found in the alimentary canal of humans as well as termites:

2. The majority of microbes require oxygen for survival. However, yeast and tetanus-causing pathogens can survive under low concentrations of oxygen.

3. Damp places are ideal for their growth and survival. Their growth is better in darker places

4. Some of them cannot survive in direct sunlight. Some of them (Saprophytes) collect their food from dead and decaying organic substances.

5. Some of them (Parasites) find shelter in other animals and collect food from different organs or tissues or cells of those animals. Some are able to synthesize their own food (Autotrophs).

WBBSE Class 8 Microbial World notes

6. Generally, the microbes can grow well between 25’Cto 38°C. A few microbes can even grow and survive at- 108C. Some others can grow and survive even above 100°C.

7. The thermophilic (heat-loving) bacteria can grow and reproduce at 100°C. The thermophilic bacteria are found in hot springs and deep-sea hydrothermal vents.

8. Without staining, microbes are invisible to us under the microscope.

Read And Learn More WBBSE Notes For Class 8 School Science

Classification of Microbes

Microbes Are Classified As Follows:

The term microbe is short for microorganism, which means small organisms. To help people understand the different types of microbes, they are grouped or classified in various ways.

Microbes are very diverse and represent all the great kingdoms of life. In fact, in terms of numbers, most of the diversity of life on earth is represented by microbes.

Here is an outline of the major groups of microorganisms:

1. Viruses
2. Bacteria (Monera)
3. Algae (Plantae)
4. Fungi
5. Protozoa (Protista)

Viruses

A virus is acellular and composed basically of a tiny bundle of genetic material (either DNA or RNA) carried in a shell called the viral coat.

They have no boundary wall, cytoplasm, or nucleus. Thousands of different viruses, which come in many shapes, are parasites and disease-causing agents.

Viruses are found on or in just about every material and environment on Earth from soil to water to air. Viruses do not show most of the characteristics of living things outside the living host.

But if they come into contact with a suitable plant, animal, or bacterial cell, they spring into action. They infect and take over the cell like pirates hijacking a ship.

Viruses exist to reproduce only. To do that, they have to take over suitable host cells. The new viral genes then come together and assemble into whole new viruses.

The new viruses are either released from the host cell without destroying the cell or eventually build up to a large enough number that they burst the host cell.

 

Understanding microbes for Class 8

Bacteria

Bacteria consist of only one cell, but they are a very complex group of living things. Unlike viruses, bacteria feed, move, and respire as well as reproduce on their own.

 

WBBSE Chapter 7 summary on microbes

Some bacteria can live in temperatures above the boiling point and in cold below the freezing point. There are thousands of species of bacteria.

Bacteria are classified into 5 groups according to their basic shapes: spherical (cocci), rod (bacilli), spiral (spirilla), comma (vibrios), or corkscrew (spirochaetes). They can exist as single cells, in pairs, chains, or clusters.

Some bacteria can make their own food from sunlight, just like plants. Also like plants, they give off oxygen. Other bacteria absorb food from the material they live on or in. They have no membrane-bound cell organelles.

A single teaspoon of soil contains more than a billion (1,000,000,000) bacteria. Bacteria reproduce by binary fission. In this process the bacterium, which is a single cell, divides into two identical daughter cells. Binary fission begins when the DNA of the bacterium divides into two (replicates).

Differences between bacteria and viruses:

Because bacteria and viruses cause many of the diseases we’re familiar with, people often confuse these two microbes. But viruses are entirely different from bacteria.

For one thing, they differ greatly in size. The biggest viruses are only as large as the tiniest bacteria. Another difference is their structure. Bacteria are complex compared to viruses.

A typical bacterium has a rigid cell wall and a thin, rubbery cell membrane surrounding the fluid, or cytoplasm, inside the cell.

A bacterium contains all of the genetic information needed to make copies of itself—its DNA—in a structure called a chromosome. In addition, it may have extra loose bits of DNA called plasmids floating in the cytoplasm.

Bacteria also have ribosomes, necessary for copying DNA so bacteria can reproduce. Some have threadlike structures called flagella that they use to move.

 

Types of microorganisms Class 8

Algae

Algae are found in fresh and saltwater around the world where they can either be free-floating (planktonic) or attached to the bottom.

They can also grow on rocks and trees and in soil when enough water is available. Algae can exist as single cells, an example of which is Chlamydomonas, or joined together in chains like Spirogyra or made up of many cells, for instance, Rhodymenia (red seaweed).

 

 

All algae contain a pigment called chlorophyll and they make their own food by photosynthesis. Chlorophyll is contained in the chloroplasts and gives many algae their green appearance. Their cell contains a cell wall, nucleus, and other cell organelles.

Fungi

Fungi cannot synthesize their own food as plants do. They have cell walls, nuclei, and other organelles but these do not have chloroplast.

Hence they cannot synthesize food. The cell wall is composed of chitin. Fungi include single-celled living things that exist individually, such as yeast, and multicellular clusters, such as molds or mushrooms.

Yeast cells look round or oval under a microscope. They’re too small to be seen as individuals, but you can see large clusters of them as a white powdery coating on fruits and leaves.

Groups called decomposers to grow in the soil or on dead plant matter where they play an important role in the cycling of carbon and other elements.

Some are parasites of plants causing diseases such as mildews, rusts, scabs, or canker. In crops, fungal diseases can lead to significant monetary loss for the farmer.

A very small number of fungi cause diseases in animals. In humans, these include skin diseases such as athlete’s foot, ringworm, and thrush.

Fungi live in the soil and on your body, in your house and on plants and animals, and in freshwater and seawater. A single teaspoon of topsoil contains about 120,000 fungi. They need moist and warm conditions to grow.

 

Importance of microorganisms in nature for Class 8

Fungi absorb nutrients from living or dead organic matter that they grow on. They absorb simple, easily dissolved nutrients, such as sugars, through their cell walls.

They give off special digestive enzymes to break down complex nutrients into simpler forms that they can absorb. Some fungi are quite useful to us.

We’ve used several kinds to take antibiotics to fight bacterial infections. We use baker’s yeast, to make bread rise and to brew beer.

There are some dangerous fungi that cause diseases in plants, animals, and people. Fungi ruin about a quarter to half of harvested fruits and vegetables each year.

Protozoa

Protozoa are single-celled organisms having one or more nuclei. They come in many different shapes and sizes ranging from an Amoeba which can change its shape to its fixed shape and complex structure.

They live in a wide variety of moist habitats including freshwater, marine environments, and soil. They can live freely or in a colony.

Protozoa mainly feed on bacteria, but they also eat other protozoa, and sometimes fungi. Some protozoa absorb food through their cell tissues.

 

 

Others, surround food and engulf it. Others have openings similar to mouth pores into which they sweep food.
Protozoa can be classified into three general groups based on their shape. One group is the Ciliates, which are generally the largest protozoa. The second group is the Amoebae.

The nutrients from living or dead organic matter that they grow on. They absorb simple, easily dissolved nutrients, such as sugars, third group is the Flagellates, which are usually the smallest of the protozoa.

Most protozoa do us no harm. But there are a few that cause diseases. One type of amoeba can live in human intestines. It feeds on red blood cells and causes a disease known as dysentery.

Another species of protozoa can sicken hundreds of thousands of people when it gets into the tap water. Perhaps the best-known deadly protozoa cause malaria, a terrible disease that leads to about 800,000 deaths each year worldwide.

Nutritional Relationships with Other Organisms

Microbes are related to several other organisms to maintain their life and derive nourishment. Some of these relationships are –

1. Parasitic

They derive their nutrition from the plants and animals on which they grow. Certain enzymes are produced by them which decompose or kill the protoplasm of the host cells.

The interrelationship between the parasitic microbe and the host is called parasitism. Such effects of the parasites on the host become visible to the naked eye as disease symptoms.

Many well-known diseases of human beings like typhoid, tetanus, tuberculosis, pneumonia, and many others are due to parasitic bacteria.

Microbes are also known as pathogenic bacteria. Some bacteria grow well only in the presence of oxygen, while others grow well in absence of oxygen. The former is known as aerobes and the latter are anaerobes.

2. Saprophytic

They grow on dead and decaying plants and animals, dung,’ rotten wood, stagnant water, and many other decaying substances rich in organic matter.

Certain enzymes secreted by the bacteria decompose the complex organic substances of the substrate, converting them into simpler ammonium compounds.

They cause decay and therefore are also known as putrefying bacteria. The souring of milk, the manufacture of cheese, the preparation of butter from milk, and vinegar from sugarcane juice, are various processes completed by the action of certain specific saprophytic bacteria.

Zygomonas ferments glucose-producing alcohol, lactic acid, and carbon dioxide, and plays a significant role in the wine industry.

Acetobacter oxidizes organic compounds to organic acids such as lactic acid thus having a significant role in the vinegar industry. Lactobacillus converts sugars into lactic acid. Canned food is spoiled by some Bacillus and Clostridium bacteria.

3. Symbiotic

Symbiosis is the phenomenon by which two organisms maintain a relationship with each other to be mutually benefitted. In symbiotic mode, organisms develop a special relationship with certain other organisms to obtain nourishment.

Organisms involved in this type of relationship are called symbionts. Rhizobium bacteria is a striking example of this type.

They occur in root nodules of leguminous plants and help in fixing the free nitrogen of the atmosphere in the soil for the plants which in return provides carbohydrates and protection to the bacteria.

Microbial interactions in the environment Class 8

They are also called nitrogen-fixing bacteria and add to the fertility of the soil. Azotobacter and Clostridium are other examples of nitrogen-fixing bacteria.

They are found in chalky soil and obtain energy from the carbohydrates present in the soil. The energy so obtained is used in fixing atmospheric nitrogen into amino acids in the soil which react with the calcium salts, forming nitrites and thereafter nitrates.

Lichens form a very good example of a symbiotic relationship. Lichens are formed by the symbiotic relationship between algae and fungi sharing a single colony.

Fungus provides water, nutrients, and shelter in the form of the network formed by mycelium. Algae synthesize the food for the entire colony through the process of photosynthesis.

Role of Microbes in the Environment

The human body has( 10-100 trillion microbes living on it, making it one giant super-organism. Since the first link between microbes and diseases was made, people have been advised to wash their hands.

Scientists, however, have recently started to investigate more closely how the microbes that call the human body home affect our health. While some microbes cause disease, others are more beneficial, working with our bodies in many subtle ways.

Microbes and Human Health In fact, many of these microbes are actually beneficial. The microbes living in our digestive system break down food and produce useful vitamins.

The millions of microbes that coat our skin and insides form a protective barrier against more dangerous microbes. Without them, our bodies would be open to microbial attack.

In spite of the benefits, a relatively small number of microbes are harmful to humans. Disease-causing micro organisms are called pathogens.

Many diseases and epidemics are caused by microbes: the plague, smallpox, AIDS, influenza, food poisoning, malaria, and anthrax. These diseases result in severe illness or even death.

Those microbial diseases which spread from an infected person to a healthy person through the air, water, food, physical contact, etc are called communicable diseases.

Some of the communicable diseases are cholera, the common cold, chicken pox, Tuberculosis, etc. As scientists learn more about bacteria, fungi, and viruses, they are better able to treat and prevent these diseases. Common treatments include antibiotics that kill bacteria and vaccines that help the body fight off viruses.

2. Microbes and Ecosystems:

Recycling of waste Microbes obtains energy from their environment. Like humans, many microbes do this by eating plant and animal material.

This is called biodegradation. A typical microbe buffet consists of waste from humans and other animals, dead plants and animals, and food scraps.

Bacteria, fungi, and algae all take part in decomposing—or breaking down—this waste material. Without them, the world would quickly be overrun with discarded food scraps, raw sewage, and dead organisms.

Microbial decomposition releases nutrients into the environment that are needed by other organisms. Microbes are also involved in the cycling of many other important compounds in— and between—ecosystems, including oxygen, carbon, and nitrogen.

Many microbes use the energy of sunlight to convert carbon dioxide to oxygen, which we need to breathe. As they do this, they create new organic material— themselves—which is then eaten by other organisms.

In this way, the cycling of nutrients and energy continues. Microbes like methanogenic bacteria produce biogas, an environment-friendly biofuel.

3. Microbes and Food and Agriculture

People have a long history of using microbes in agriculture and food production. Microbes play a part in the production of food, such as yogurt, cheese, wine, bread, vitamins, beans, and chocolate.

Alcohol is produced by microbes like Yeast. In some cases, microbes function as they would in their original environment. For example, bacteria living around the roots of bean plants (Rhizobium, acetobacter, Clostridium, etc) convert nitrogen from the air into a form that the plant can use, like fertilizer.

People have also learned how to use the natural abilities of microbes to create new food, such as by making beer from grains.

4. Industrial Applications of Microbes

Microbes are so efficient at what they do that scientists use them in many industrial applications. Decomposing microbes are active in wastewater treatment plants, composting facilities, and landfills.

They break down food scraps and waste materials into compost or fertilizer that can be used in gardens or in agriculture. Some industrial facilities capture methane gas that is produced during certain types of decomposition.

The methane can then be used to make ethanol for cars or to generate electricity. Microbes are employed to separate jute fiber from jute stem.

Many types of scientific research involve altering the DNA of microbes or using their DNA to alter other organisms. By changing the DNA sequence of microbes, scientists can use them to create compounds that the microbes would not normally produce.

This includes medical products like Insulin or sources of fuel. Microbes are also used to change the DNA sequence of other organisms, such as changing plants to become resistant to insects or viruses.

Microbial Habitat

Microbes live in almost every nook and corner you can think of, from 20 miles beneath the Earth’s surface to 20 miles overhead. They live at temperatures less than -20 degrees Celsius to temperatures hotter than the boiling point.

Microbes thrive on a huge range of food including oil and toxic wastes. Every time you walk on the ground you step on billions of microbes.

Microbes live in the soil, on rocks, inside roots, buried under miles of earth, in compost piles, and toxic waste all over the earth’s surface.

Microbes are found in boiling hot springs and on frozen snow fields. Most animals interact with microbes in important ways, and all animals, as well as all plants and fungi, depend on microbes for their survival.

Microorganisms and their roles for Class 8 students

Microbes live in their digestive systems, in their mouths, and on their skin. Microbes are important for the good health of animals.

Animals provide microbes with food and shelter. That is why animals are called “hosts” to microbes. For example, cows depend on microbes for their food.

Cows and other animals called ruminants have special stomachs called rumens which are host to billions of microbes that help these animals survive.

Also, we depend on microbes to clean up our environment. Without microbes to get rid of all the dung from animals, the world would be a really smelly place. Microbes make this world a cleaner place.

Useful and Harmful Microbes

People often use the word germ instead of microbe, so you might think that microbes are all harmful. But some are useful to us.

Useful microbes

1. Some useful microbes are listed below-
2. Bacillus thuringiensis – a common soil bacterium that is a natural pest-killer in gardens and on crops.
3. Arbuscular mycorrhizas – fungus living in the soil that helps crops take up nutrients from the soil.
4. Saccharomyces cerevisiae – fungus, ba maker’s yeast that makes bread rise.
5. Escherichia coli-one of many kinds of microbes (bacteria) that live in your digestive system to help you digest your food every day.
6. Streptomyces – bacteria in soil that makes an antibiotic used to treat infections.
7. Pseudomonas putida – one of many microbes that clean wastes from sewage water at water treatment plants.

We’ve been using microbes for thousands of years to make products we need and enjoy.

For example, you can thank fungi for the cheese on your cheeseburger and yeast for your bun. Cheese and bread are two microbe-made food people have been enjoying since time began.

In pollution control, researchers are using bacteria that eat methane gas to clean up hazardous waste dumps and landfills.
Fungi and bacteria produce antibiotics such as penicillin and tetracycline.

These are medicines we use to fight off harmful bacteria that cause infections, and other discomforts. Scientists have changed the genetic material of bacteria and yeasts to turn them into medicine.

Harmful microbes

Microbes cause disease when they are able to reproduce in the body. They produce harmful Lactobacillus acidophilus – one of the bacteria that turn milk into yogurt.

There are many other important jobs microbes do. They are used to make medicine. They break down the oil from oil spills. They make up about half of the oxygen we breathe.

They are the foundation of the food chain that feeds all living thin harmful disease-causing microbes in them are infected.

A few harmful microbes, for example, less than 1% of bacteria, can invade our body (the host) and make us ill. Microbes cause infectious diseases There is also strong evidence that microbes may contribute to many non-infectious chronic diseases such as some forms of cancer and coronary heart disease.

Different diseases are caused by different types of microorganisms. Microbes that cause disease are called pathogens.

 

Infectious disease	Microbe that causes the disease	Type of microbe
Cold	Rhinovirus	Virus
Chickenpox	Varicella zoster	Virus
German measles	Rubella	Virus
Whooping cough	Bordetella pertussis	Bacterium
Bubonic plague	Yersinia pestis	Bacterium
TB (Tuberculosis)	Mycobacterium tuberculosis	Bacterium
Malaria	Plasmodium falciparum	Protozoan
Ringworm	Trichophyton rubrum	Fungus
Athletes’ foot	Trichophyton mentagrophytes	Fungus

 

Uses of microorganisms in daily life for Class 8

To cause an infection, microbes must enter our bodies. The site at which they enter is known as the portal of entry. Microbes can enter the body through the four sites listed below:

1. Respiratory tract (mouth and nose) e.g. Influenza virus which causes the flu.
2. Gastrointestinal tract (mouth oral cavity) e.g. Vibrio cholerae which causes cholera.
3. Urogenital tract e.g. Escherichia coli which causes cystitis.
4. Breaks in the skin surface e.g. Clostridium tetani which causes tetanus.

It is important to remember that:

1. A pathogen is a microorganism that has the potential to cause disease.
2. An infection is the invasion and multiplication of pathogenic microbes in an individual or population.
3. The disease is when the infection causes damage to the individual’s vital functions or systems.
4. An infection does not always result in disease.

WBBSE Chapter 6 The Structure Of Living Organisms Long Answer Type Questions

Question 1. Name the characteristics of living things. What is the law of biogenesis?
Answer:

The Seven Characteristics of Living Things

1. Feeding: All living organisms need to take substances from their environment to obtain energy, grow and stay healthy.

2. Movement: All living organisms show the movement of one kind or another. All living organisms have internal movement, which means that they can move substances from one part of their body to another.

Some living organisms show external movement as well—they can move from place to place by walking, flying or swimming.

3. Breathing or Respiration: All living things exchange gases with their environment. Animals take in oxygen and breathe out carbon dioxide.

4. Excretion: Excretion is the removal of waste from the body. If this waste is allowed to remain in the body it could be poisonous.

Humans produce liquid waste called urine. We also excrete waste when we breathe out. All living things need to remove waste from their bodies.

Growth: When living things feed they gain energy. Some of this energy is used for growth. Living things become larger and more complicated as they grow.

Sensitivity: Living things react to changes around them. We react to touch, light, heat, cold and sound, as do other living things.

Reproduction: All living things produce young. Humans make babies, cats produce kittens and pigeons lay eggs. Plants also reproduce. Many make seeds which can germinate and grow into new plants.

Living beings reproduce to form young ones that resemble their parents in the long run. So it is ‘like from like’- referred to as Answer: the law of biogenesis.

Read And Learn More WBBSE Solutions For Class 8 School Science Long Answer Type Questions

Question 2. What is a cell? Who coined the term? How it can be seen?
Answer:

Differences Among Living And Non-Living

An attempt should now be made to distinguish living things from lifeless nonliving or inanimate objects. There is no difficulty in recognising a coconut palm or guinea pig as living objects and rocks in the field or the sand grains in the seashore as non-living bodies.

It may be mentioned here that viruses are an intermediate stage between living and nonliving forms of matter.
The principal points of difference between living and nonliving objects are described in tabular form below:

	Living		Non-living
1	Each kind of plant and animal has a definite form and size, which may vary within very narrow limits in different individuals of the same kind.	1	Non-living objects, such as masses of clouds or collections of stones have neither a definite size nor any precise form
2	A living body is organized of cells, tissues and organs with the division of labour.	2	No such organisation exists
3	Life is an external manifestation of metabolic activities like nutrition, respiration, secretion, circulation, excretion etc.	3	None of the metabolic activities is detected in nonliving objects.
4	The living body increases in bulk by wedging in new particles in between already existing cellular matter.	4	Growth may occur occasionally by deposition of particles only on the outer surface of the body
5	A living body can reproduce its own kind and thus perpetuate its race.	5	There is no power to reproduce its own kind
6	A living body has a definite life cycle.	6	No life cycle is observed. The period of duration is infinite and there is no death.

 

WBBSE Class 8 Structure of Living Organisms Long Answers

Question 3. Write briefly about different types of microscopes.
Answer:

Different types of microscopes:

How a Cell can be seen:

Cells got their name from an Englishman named Robert Hooke in the year 1665. He first saw and named “cells” while he was experimenting with a new instrument we now call a “microscope.

“For his experiment, he cut very thin slices from cork. He looked at these slices under a microscope. He saw tiny box-like shapes. These tiny boxes reminded him of the plain small rooms that monks lived in called “cells”. The smallest objects that the unaided human eye can see are about 0.1 mm long.

A magnifying glass can help you to see them more clearly, but they will still look tiny. Cells are not visible under ordinary magnifying glasses.

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Smaller cells are easily visible under a light microscope. Light microscopes use a system of lenses to magnify an image. The power of a light microscope is limited by the wavelength of visible light, which is about 500 nm. The most powerful light microscopes can resolve bacteria but not viruses.

Light microscopes (optical microscopes) that are commonly used in schools are of two types – compound microscopes and simple or stereo microscopes (also known as dissecting or binocular microscopes).

Left: Stereo microscope; Center: Compound microscope with a binocular head; Right: Compound microscope with a monocular head is greater resolving power than light microscopes, so we can use them to see even more detail than is visible under a light microscope.

 

 

To see anything smaller than 500 nm, you will need an electron microscope Electron microscopes to shoot a high-voltage beam of electrons onto or through an object, which deflects and absorbs some of the electrons.

Resolution is still limited by the wavelength of the electron beam, but this wavelength is much smaller than that of visible light. The most powerful electron microscopes can resolve molecules and even individual atoms.

Some of the specialized types of electron microscopes are – Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), Reflection Electron Microscope (REM), and Scanning Transmission Electron Microscope (STEM).

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Question 4. Write, with diagrams, the special features of RBC and nerve cells.
Answer:

Cell-The Unit of an Organism

Your body, as a whole, is one organism. However, many, many parts make up that whole. First, you notice the entire body. Next, you see that the entire body is made up of parts and organs, and each of those organs is made up of a variety of tissues.

And if, as a pathologist does, you examine a magnified sample of one of the human body’s tissues under a microscope, millions of cells become visible.

Yet you can turn up the magnification for an even closer look, Cells contain molecules that are made up of even smaller components called atoms.

Atoms, molecules, cells, tissues, organs, and organ systems are the body’s building blocks. ‘Schleiden and Schwann together proposed the cell theory in 1839.

Cell theory states that “all plants and animals are composed of cells and cellular products.” Thus, the cell is the basic unit of life.

1. Salient points of cell theory:
2. All living things are composed of cells and their products.
3. All cells arise from pre-existing cells.
4. AII cells are basically alike in chemical composition and metabolic activities.
5. The function of an organism as a whole is the outcome of the activities and interaction of the constituent cells of which the organism is built.

Therefore, all living beings are made up of cells which are the smallest structural and functional unit of the body. Some of them are made up of only one cell and others have many cells.

All living organisms are made up of individual and identifiable cells, whose number, together with their size and type, ultimately defines the structure and functions of an organism.

While the total cell number of lower organisms is often known, it has not yet been defined in higher organisms. In particular, the reported total cell number of a human being is about 37 trillion (one trillion =1,000,000,000,000).

WBBSE Class 8 Science Long Answer Solutions

Question 5. Write briefly about the levels of structural organization of organisms. Does the shape of cells remain the same always?
Answer:

Specialised Cells

The table below shows examples of some specialised animal and plant cells, with their functions and special features.

No A cell changes its shape when it undergoes cell division. Human RBC can change its shape when it moves through arteries, veins and capillaries. A cancer-affected cell also undergoes a change in shape of the cell.

WBBSE Class 8 Science Important Long Answer Questions

Question 6. What are tissues? Name the four principal animal tissues. Write the differences between plant and animal tissues.
Answer:

Levels of organisation:

The Organisation of Cells, Tissues, Organs, Systems and the Organism

From the least complex to the most complex, the organisms are made up of—

1. Atom – The smallest piece of matter that still has physical and chemical properties of matter.
2. Molecule – The smallest piece of a compound that still has the physical and chemical properties of that substance (e.g., water). The molecule is composed of atoms.
3. Cell – The smallest piece of life (some arguments remain about viruses). It is the basic unit of all living beings.
4. Tissue – Collection of cells that work together.
5. Organ – Collection of tissues that work together.
6. Organ System – Collection of organs that work together.
7. Organism – Collection of organ systems that makes up a single life form.

Two or more kinds of tissues together form each of our organs, like the heart or lungs. Many organs together form an organ system, like the digestive or respiratory system.

All the organ systems together form an organism, such as a person, dog or blue whale. The body’s organisation goes from cells to tissues to organs to organ systems to a whole working organism. In unicellular (single-celled) organisms, the single cell performs all life functions.

It functions independently. However, multicellular (many-celled) organisms have various levels of organization within them. Individual cells may perform specific functions and also work together for the good of the entire organism.

The cells become dependent on one another. Multicellular organisms have the following 5 levels of organization ranging from simplest to most complex:

 

Level-1 Cells

Are the basic unit of structure and function in living things. May serve a specific function within the organism.
Examples – are blood cells, nerve cells, bone cells, etc.

 

Long Answer Format for Class 8 Structure of Living Organisms

Level-2 Tissues

Made up of cells that are similar in structure and function and which work together to perform a specific activity.
Examples – are blood, nervous, bone, etc. Humans have 4 basic tissues: connective, epithelial, muscle, and nervous.

 

 

Level-3 Organs

Made up of tissues that work together to perform a specific activity. Examples – heart, brain, skin, etc.

 

 

Level-4 Organ Systems

Groups of two or more tissues that work together to perform a specific function for the organism.
The Human body has 11 organ systems – circulatory, digestive, endocrine, excretory (urinary), immune (lymphatic), integumentary, muscular, nervous, reproductive, respiratory, and skeletal.

 

WBBSE Chapter 6 Living Organisms Study Guide

Level -5 Organisms

Entire living things can carry out all basic life processes. Meaning they can take in materials, release energy from food, release wastes, grow, respond to the environment, and reproduce.

Usually made up of organ systems, but an organism may be made up of only one cell such as bacteria or protists.
Examples – are bacteria, Amoeba, mushrooms, sunflowers, and humans.

 

 

The levels of organization in the correct order are:
cells ⇒ tissues⇒  organs ⇒ organ systems ⇒ organisms

Levels of the body from smallest to largest: Atoms, molecules, cells, tissues, organs, and organ systems.

 

 

Name the associated processes: gaseous exchange and energy production increase

Question 7. Which cell organelle is primarily responsible for maintaining the shape of plant cells? Jow is a bacterial cell different from an onion peel cell?
Answer:

Processes:

respiration reproduction The shape of a plant cell depends on the volume of water inside the cell. Intake or removal of water from vacuoles depends on the volume of water a plant cell can absorb from the soil. Therefore, vacuoles play important role in the formation of plant bodies.

A bacterial cell is prokaryotic in nature while an onion peel cell is eukaryotic in nature having well-developed cellular organisation.

Living Organisms WBBSE Class 8 Comprehensive Answers

Question 8. Draw the longitudinal section of mitochondria. What are grana?
Answer:

Inside chloroplastids, the thylakoids are arranged in stacks like piles of coins called grana. Chlorophyll pigments are present in thylakoids.

Question 9. Describe with a diagram the structures and functions of any one animal cell organelle and any one plant cell organelle. Which kind of plastid is more common in: the roots of plants, Flowers and fruits
Answer:

Cell organelles and their structure and function

An organelle is any specialized structure based on the analogy that cells have their cell, especially one for which a specific organelle is just as complex as a multicellular function can be assigned.

As we mentioned organisms have their livers, kidneys, and stomachs earlier, the name means “little organ” and in other organs.

The Three Main Components of any Plant or Animal Cell:

1. Plasma Membrane / Cell Membrane

Structure – It is a bilipid membraneous layer containing proteins and lipids. There are two outer layers of protein and a middle layer of phospholipid. It is called a unit membrane and is semifluid and dynamic in nature.

Function – The cell membrane separates the cell from its external environment, and is selectively permeable (controls what gets in and out). It protects the cell and provides stability.

Proteins are found embedded within the plasma membrane, with some extending all the way through in order to transport materials.
Carbohydrates are attached to proteins and lipids on the outer lipid layer.

2. Cytoplasm

Structure – It is a colourless, semisolid and jelly-like substance composed of main water and found between the cell membrane and nucleus.

The cytoplasm makes up most of the “body” of a cell and is constantly streaming. The transparent fluid part of the cytoplasm is called cytosol.

Function – Organelles are found here and substances like salts may be dissolved in the cytoplasm. It helps in the exchange of materials between cell organelles and is the active site for metabolic processes like sugar, protein and fatty acid synthesis.

3. Nucleus

Structure – The largest organelle in the cell. It is dark and round and is surrounded by a double membrane called the nuclear envelope/ membrane.

In spots, the nuclear envelope fuses to form pores which are selectively permeable. The nucleus contains genetic information (DNA) on special strands called chromosomes.

The colourless dense sap present inside the nucleus is called the nucleoplasm. One or more round bodies present in the nucleoplasm are called nucleoli. A network of dark-staining fibre in the nucleus is called chromatin.

Function – The nucleus is the “control centre” of the cell, for cell metabolism and reproduction. It regulates the cell cycle and is the storehouse of genes.

2. The Organelles found in both Plant and Animal cells:

1. “ER” or Endoplasmic Reticulum
The Endoplasmic Reticulum is a network of membranous canals filled with fluid. They carry materials throughout the cell. The ER is the “transport system” of the cell.

There are two types of ER: rough ER (RER) and smooth ER. (SER)Rough Endoplasmic Reticulum is lined with ribosomes and is rough in appearance and smooth endoplasmic reticulum contains no ribosomes and is smooth in appearance.

ER gives support to the cytoplasm. It forms an intracellular transport system. SER plays a crucial role in detoxifying many poisons and drugs. It also helps in the formation of proteins and lipids.

2. Ribosomes

Ribosomes are small particles which are found individually in the cytoplasm and also line the membranes of the rough endoplasmic reticulum. Ribosomes produce protein. They could be thought of as “factories” in the cell.

3. Golgi Body / Apparatus

Golgi bodies are stacks of flattened membranous sacs, (they look like pancakes). The Golgi Body temporarily stores protein which can then leave the cell via vesicles pinching off from the Golgi.

In plants, the Golgi apparatus is scattered in the cytoplasm and found in the diffused form. These are known as Dictyosomes.
Secretion is the main function of the Golgi complex. It mainly performs the function of packaging.

The material synthesized near the ER is packaged and dispatched to various targets inside and outside the cell through the Golgi apparatus. It is directly involved in the formation of lysosomes.

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4. Lysosomes

Lysosomes are small sac-like structures surrounded by a single membrane and containing strong digestive enzymes which when released can break down worn-out organelles or food.

The lysosome is also known as a suicide sac. This help to keep the cell clean by digesting any foreign material and worn-out cell organelles.

5. Mitochondria (Singular = Mitochondrion)

The mitochondria are round “tube-like” organelles that are surrounded by a double membrane, with the inner membrane being highly folded.

The mitochondria are often referred to as the “powerhouse” of the cell. The mitochondria release food energy from food molecules to be used by the cell.

This process is called respiration. Some cells ( muscle cells) require more energy than other cells and so would have many more mitochondria.

6. Vacuoles

Vacuoles are fluid-filled organelles enclosed by a membrane. They can store materials such as food, water, sugar, minerals and waste products.

3. Animal Cell Organelles not found in Plant Cells

1. Cilia and Flagella

Both cilia and flagella are hair-like organelles which extend from the surface of many animal cells. The structure is identical in both, except that flagella are longer and whip-like and cilia are shorter.

There are usually only a few flagella on a cell, while cilia may cover the entire surface of a cell. The function of cilia and flagella include locomotion for one-celled organisms and moving substances over cell surfaces in multi-celled organisms.

4. Organelles and other features found only in Plant Cells

1. Cell Wall

The cell wall is a rigid organelle composed of cellulose lying just outside the cell membrane. The cell wall gives the plant cell its box-like shape. It also protects the cell. The cell wall contains pores which allow materials to pass to and from the cell membrane.

2. Plastids

Plastids are double membrane bound organelles. It is in plastids that plants make and store food. Plastids are found in the cytoplasm and there are two main types:

Leucoplasts – Colourless organelles which store starch or other plant nutrients, (for example – starch stored in a potato).

Chromoplasts – Contain different coloured pigments. The most important type of chromoplast is the chloroplast, which contains the green pigment chlorophyll. This is important in the process of photosynthesis.

3. Central Vacuole

The central vacuole is a large fluid-filled vacuole found in plants.

Question 10. Mention the name of an organism whose body structure does not conform to cell theory What are cytoplasmic organelles? What are A, B and C ? Name the layer which lies outside of the cell membrane in a plant cell.
Answer:

Cells make up A; A makeup B; B make up C; C makes up an organism. The body structure of a virus does not conform to the cell theory.

Some specific living components found in the cytoplasmic matrix of all eukaryotic cells and which are concerned with functions of the cell as a whole are called cytoplasmic organelles,

cells A ⇒B ⇒C ⇒Organism (Tissues) (Organs) (Organ system) Cell wall lies outside the cell membrane in a plant cell.

WBBSE Chapter 6 The Structure Of Living Organisms Short Answer Type Questions

Question 1. What is a microscope?
Answer:

Microscope:

Microscopes are instruments which can both magnify and resolve small objects so that they can be used for observing objects which are not visible to the naked eye. The magnification may range from 15 to 20 times (simple microscope) to 107 times (Electron microscope).

Question 2. What is meant by the magnification of a microscope?
Answer:

Magnification of a microscope:-

Magnification is the power of enlargement or ratio of the size of an object observed under the microscope and its actual size seen with the unaided naked eye.

Question 3. What is meant by resolving the power of a microscope?
Answer:

Resolving the power of a microscope:

The ability to distinguish two close points as distinct clear points are called the resolving power or limit of resolution of a microscope.

WBBSE Class 8 Structure of Living Organisms Short Answer Solutions

Question 4. Write the functions of the cell membrane. Important functions are—
Answer:

Functions of the cell membrane:

1. Help in cellular compartmentalization.
2. Bind the semifluid contents of the cell.
3. Protect the cell from injury.
4. Act as a semipermeable membrane between a cell and its environment.

Question 5. Write the functions of mitochondria. Important functions are—
Answer:

Functions of mitochondria:

1. Act as a powerhouse of a cell by forming ATP.
2. Contain several enzymes.
3. Transmit some genetic information from one generation to other.

Read And Learn More WBBSE Solutions For Class 8 School Science Short Answer Type Questions

Question 6. Name the different types of plastids and state their specific roles in the plant body.
Answer:

Three types of plastids and their roles are—

1. Chloroplastid—helps photosynthesis.
2. Chromoplastid—Produce the colour of the flower.
3. Leucoplastid—Store food materials.

Question 7. Write the common function of RER and SER.
Answer:

Common function of RER and SER:

1. Provide a large surface area inside a cell for performing biochemical reactions.
2. Act as a cytoskeletal framework.

Question 8. What is autolysis? State the cell organelle associated with it.
Answer:

Autolysis:

Autolysis is the self-destruction of a cell, tissue or organ with the help of lysosomes. It occurs in ageing, dead and diseased cells.

Question 9. What are vacuoles? How they are formed?
Answer:

Vacuoles:

Vacuoles are non-cytoplasmic areas present inside the cytoplasm. They are believed to be formed by expansion and pinching off from the endoplasmic reticulum.

Chapter 6 Living Organisms Short Answer Questions WBBSE

Question 10. What are cell inclusions or orgastic substances?
Answer:

Cell Inclusions or Orgastic substances:

These are non-living substances present in the cell. They may be organic or inorganic and may be present inside cells in soluble or insoluble states. Cell inclusions are generally of three categories—reserve food, excretory or secretory products and mineral matters.

Question 11. What are the principal types of cells?
Answer:

Principal types of cells:-

Cells are generally of two types—prokaryotic cells (ex-bacteria) and eukaryotic cells (plant and animal cells with true nuclei).

Question 12. Name the double-membraned and membrane-less cell organelles.
Answer:

Double membrane—Mitochondria and chloroplast. Membrane less—Ribosome and centrosome.

Question 13. What is a unit membrane?
Answer:

Unit membrane:

All cellular membranes (like plasma membrane, mitochondrial membrane, Golgi membrane, etc.), are similar in structure and hence it is called unit membranes. It is composed of protein and lipids.

Question 14. What is nuclear reticulum?
Answer:

Nuclear reticulum:

These are network-like structures found inside the nucleus of non-dividing cells. They are formed of DNA and protein. These structures condense during cell division and form chromosomes.

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Question 15. What are the characteristics of mammalian RBCs?
Answer:

Characteristics of mammalian RBCs

Mammalian RBCs are biconcave disc-like cells. They lack a nucleus and hence can hold more haemoglobin. This helps in carrying more oxygen to cope with higher metabolic activities.

Question 16. What are the advantages of multicellular organisms?
Answer:

Advantages of multicellular organisms:

1. Different cell types help in the division of labour.
2. Cells can adjust properly to the changing environment and can perform specialized functions.

Question 17. Write the characteristics of eukaryotic cells.
Answer:

Characteristics of eukaryotic cells:

1. The cells have a definite nucleus.
2. Definite chromosomes are present.

Membrane-bound cell organelles like— Mitochondria, Golgi bodies, etc., are found.

Question 18. Write the similarities between animal and plant cells.
Answer:

Similarities between animal and plant cells:

Both types of cells possess—

1. nuclear membrane,
2. true nucleus and
3. membrane-bound cell organelles like- mitochondria, endoplasmic reticulum etc.

Question 19. What is a tissue?
Answer:

Tissue:

A group of cells of similar origin and function constitute a tissue. Every organ consists of many tissues. For example—our stomach contains epithelial, muscular, nervous and connective tissues.

Short Answer Questions for Structure of Living Organisms

Question 20. What is primordial utricle ?
Answer:

Primordial utricle:

In plant cells, due to the presence of a large vacuole, the nucleus and cytoplasm are pushed towards the periphery of the cell forming a thin layer beneath the cell membrane. This layer is known as a primordial utricle.

 

 

Question 21. Write the differences between a Light microscope and an Electron microscope.
Answer:

Differences between a Light microscope and an Electron microscope:

Points of differences	Light microscope	Electron microscope
1. Illumination	Visible light.	A beam of electrons.
2. Lenses	Glass lenses.	Electron lens
3. Electricity	Not required.	Required.
4. Contrast	Achieved by dyes.	Archived by use of heavy metals.
5. Size	Small and portable.	Large and fixed.
6. Magnification	2000-4000X.	50,000-3,00,000X.

 

Question 22. Write the differences between Unicellular and Multicellular organisms.
Answer:

Differences between Unicellular and Multicellular organisms:

Points of differences	Unicellular	Multicellular
1. Number of cells	Single.	Large number.
2. Function	The same cell performs all functions. Not found.	Different cells perform different functions.
3. Division of labour	Not found.	Well observed
4. Size	Microscopic	Generally macroscopic.

 

Living Organisms Chapter 6 Study Guide WBBSE

Question 23. What is protoplasm? What is middle lamella?
Answer:

Protoplasm:

Protoplasm is the physical basis of life within which occurs all the vital functions of life. It is a viscous substance present inside the cell membrane of all living cells. It consists of cytoplasm, nucleus and vacuoles.

In multicellular plants, cells do not move as they are firmly joined together. The common cementing layer present between two adjacent cells is called the middle lamella.

 

 

Question 24. Write the differences between Mitochondria and Chloroplast.
Answer:

Differences between Mitochondria and Chloroplast:

Points of differences	Mitochondria	Chloroplast
1. Colour	Colourless.	Generally green.
2. Occuranee	All eukaryotic cells.	Only in plant cells.
3. inner membrane.	Become folded to form cristae.	Unfolded and remain attached to thylakoids.
4. Energy source	Convert chemical energy.	Convert light energy.

 

Question 25. Write differences among Chloroplastid, Chromoplastid and Leucoplastid.
Answer:

Differences among Chloroplastid, Chromoplastid and Leucoplastid:

Chloroplastid	Chromoplastid	Leucoplastid
1. Green in colour.	Coloured, other than green.	Colourless.
2. Green chlorophyll pigment present.	Non-chlorophyll pigment is present.	Pigments absent.
3. Found in leaves and stem	Found in flowers, fruits etc.	Found in the root.
4. Help in photosynthesis.	Help in pollination and dispersal of seeds.	Help in food storage.

 

Question Who discovered the nucleus? Draw a typical nucleus showing its structures.
Answer:

Robert Brown first discovered the nucleus.

 

Short Answer Resources for Class 8 Structure of Living Organisms

Question 26. Write the differences between the Cell membrane and the Cell wall.
Answer:

Differences between the Cell membrane and the Cell wall:

Points of differences	Cell membrane	Cell wall
1. Location	Both animal and plant cells.	Only in plant cells.
2. Composition	Protein and lipid.	Cellulose, hemicellulose, lignin, etc.
3. Nature	Thin, elastic, living and semipermeable.	Thin, non-elastic, dead and permeable.

 

Question 28. Write the differences between Nucleoid and Nucleus.
Answer:

Differences between Nucleoid and Nucleus:

Points of differences	Nucleoid	Nucleus
1. Covering membrane	Absent.	Present.
2. Component absent	Nucleolus absent.	Nucleolus present.
3. Chromosome	Absent.	Present.
4. Location	Prokaryotic cell.	Eukaryotic cell.

 

Question 29. Name the organelles which are described by the following-

1. transporting channel of the cell
2. A powerhouse of the cell
3. Digestive bag of cell
4. Control room of the cell

What is a prokaryotic cell?
Answer:

1. ER
2. mitochondria
3. Lysosome
4. nucleus

A cell having intermediate characters of prokaryotes and eukaryotes is called a eukaryotic cell. Ex: Marine photosynthetic dinoflagellates

Question 30. Write the differences between Mesosomes and Mitochondria.
Answer:

Differences between Mesosomes and Mitochondria:

Points of differences	Mesosome	Mitochondria
1. Location	Prokaryotic cell.	Eukaryotic cell.
2. Origin/Formation	From the folding of the cell membrane.	From pre-existing mitochondria.
3. Membrane	Single membrane-bound	Double membrane-bound.
4. Cristae	Absent.	Present.

 

Question 31. Write the Difference between Nucleoplasm and Cytoplasm
Answer:

Difference between Nucleoplasm and Cytoplasm:

Points of differences	Cytoplasm	Nucleoplasm
1. Location	In between the cell membrane and nuclear membrane.	Inside the nuclear membrane.
2. Function	Hold cell organelles.	Hold nucleolus and nuclear reticulum.
3. Division	Divisible into ectoplasm and endoplasm.	No such division.

 

Question 32. Meristematic cells have a prominent nucleus and dense cytoplasm but they lack vacuole-why? What happens when

1. The plasma membrane of a cell breaks down
2. Golgi apparatus is removed from a cell?

Answer:

Meristematic cells lack vacuoles to regulate cell division continuously.

1. The cell will die
2. Lysosomes will not be formed.

Question 33. Write the differences between Golgi bodies and the Endoplasmic reticulum.
Answer:

Differences between Golgi bodies and the Endoplasmic reticulum:

Points of differences	Golgi bodies	Endoplasmic reticulum
1. Location	Close to the nucleus.	Scattered throughout the cytoplasm.
2. Types	Only one type.	Two types-rough and smooth.
3. Function	Secretion.	Protein and lipid synthesis. Also, form a cellular skeletal framework.

 

WBBSE Class 8 Science Practice Questions on Living Organisms

Question 34. Write the differences between the Endoplasmic reticulum and the Nuclear reticulum.
Answer:

Differences between the Endoplasmic reticulum and the Nuclear reticulum:

Points of differences	Endoplasmic reticulum	Nuclear reticulum
1. Nature	Cell organelle.	Part of the nucleus.
2. Structure	Tubular.	Network like.
3. Composition	Membrane-bound.	Made up of DNA and protein.
4. Function	Form cellular framework.	Carry hereditary material.

 

Question 35. Write the differences between the Rough endoplasmic reticulum and Smooth endoplasmic reticulum.
Answer:

Differences between the Rough endoplasmic reticulum and Smooth endoplasmic reticulum

Points of differences	Rough ER	Smooth ER
1. Structure	Rough.	Smooth.
2. Ribosomal association	Ribosomes associated.	Ribosomes are not associated.
3. Function	Help in protein synthesis.	Help in the synthesis and storage of lipids.

 

WBBSE Class 8 Science Important Short Answers

Question 36. Write briefly about the structure of the centrosome. Mention its functions.
Answer:

Structure of the centrosome:

Centrosome consists of two parts: centrioles and centrosphere. Centrioles appear as two empty cylinders during cell division. They are situated at right angles to each other. Each cylinder is made up of fine microtubules arranged longitudinally.
The centrosphere is the clear homogeneous cytoplasm present around the centrioles. Functions:

1. Centrioles are necessary for spindle formation during cell division
2. The tail of spermatozoa is formed from one centriole.

 

 

Question 37. Write the differences between nuclei and Nucleolus.
Answer:

Differences between nuclei and Nucleolus:

Points of differences	Nucleus	Nucleolus
1. Location	Important cell organelle, present within the cytoplasm.	Part of the nucleus is present in the nucleoplasm.
2. Membrane association	Membrane-bound structure.	Not bound by a membrane.
3. Function	Control cellular activities and lodge genetic information.	Help in the synthesis of ribosomal RNA.

 

Question 38. Some of the adaptations in animals are given below:

1. White fur
2. Strong tail
3. a layer of fat under the skin
4. thick skin
5. Long beak.

Which of these adaptations are for polar regions? What do you mean by xerophytes?
Name the cells located in gills which can expel excess Na+ and Cl “from the body.
Answer:

Adaptations marked (1), (3) and (4). Plants growing in deserts or situations with a great dearth of water are called Xerophytes Example: Cactus Chloride cells (in gills).

WBBSE Chapter 6 The Structure Of Living Organisms VSAQs

Question 1. Name the structural and functional unit of a living body.
Answer:

The structural and functional unit of a living body is the cell.

Question 2. Who observed cells for the first time? Robert Hooke (1965) observed dead cork cells in honey-comb-shaped

Answer: cell walls for the first time.

Question 3. Who observed living cells for the first time? Leeuwenhoek (1673) observed living cells like
Answer:

bacteria, protozoa, spermatozoa, red blood cells, etc., for the first time.

Question 4. Who discovered the microscope?
Answer:

The first microscope was built by Janssen (1590). It was first modified by Galileo (1610) and then by Robert Hooke.

Question 5. What is cell theory?
Answer:

Cell theory:

Cell theory states that all organisms are made up of cells.

Read And Learn More WBBSE Solutions For Class 8 School Science Very Short Answer Type Questions

Question 6. Who proposed cell theory?
Answer:

Cell theory was proposed by Schleiden and Schwann (1839).

Question 7. What is the source of illumination of a light microscope?
Answer:

Visible light is the source of illumination of a light microscope.

Question 8. Why electron microscope is named so?
Answer:

In the case of the electron microscope, the source of illumination is a beam of electrons.

WBBSE Class 8 Very Short Answer Questions Living Organisms

Question 9. How many lenses are used in the simple light microscope?
Answer:

Only one ocular lens is used in the case of a simple light microscope.

Question 10. How many lenses are used in the compound light microscope?
Answer:

Three lenses are used in the compound light microscope.

Question 11. What types of lenses are used in light microscopes?
Answer:

Glass lenses are used.

WBBSE Solutions For Class 8 School Science Long Answer Type Questions	WBBSE Solutions For Class 8 School Science Short Answer Type Questions
WBBSE Solutions For Class 8 School Science Very Short Answer Type Questions	WBBSE Solutions For Class 8 School Science Review Questions
WBBSE Solutions For Class 8 School Science Solved Numerical Problems	WBBSE Solutions For Class 8 School Science Experiments Questions
WBBSE Solutions For Class 8 Maths	WBBSE Class 8 History Notes
WBBSE Class 8 History Multiple Choice Questions	WBBSE Solutions For Class 8 History
WBBSE Solutions For Class 8 Geography

 

Question 12. What types of lenses are used in an electron microscope?
Answer:

Electromagnetic lenses are used.

Question 13. What amount of magnification can be achieved in the light microscope?
Answer:

The magnification can be about 2000-4000 times.

Question 14. What amount of magnification can be achieved in an electron microscope?
Answer:

A magnification of about 50,000 to 300,000 times can be achieved.

Structure of Living Organisms Chapter 6 WBBSE Answers

Question 15. Name a unicellular organism.
Answer:

Amoeba is a unicellular organism.

Question 16. Name two multicellular organisms.
Answer:

Mosquitoes, humans etc., are multicellular organisms.

Question 17. Give two examples of hexagonal-shaped cells.
Answer:

Examples of hexagonal-shaped cells:

Liver cells and meristematic tissue cells are hexagonal.

Question 18. Name algae having a filamentous body.
Answer:

Spirogyra looks like a thread or filament.

Question 19. What are pseudopodia ?
Answer:

Pseudopodia:

Pseudopodia are temporary cellular outgrowths from the body of Amoeba, which help in locomotion.

Question 20. Write about the shape of our RBCs.
Answer:

Shape of our RBCs:

The cells are circular disc-like and flattened at the centre.

Question 21. Which cells can receive stimuli from the environment and conduct it?
Answer:

Nerve cells are capable of these functions.

Question 22. Where in the animal body, fat is stored?
Answer:

Most fat of the animal body is stored beneath the skin.

WBBSE Class 8 Science Very Short Answer Format

Question 23. Where do we find stone cells?
Answer:

Stone cells:

Stone cells are found in the seed coat and fruit coat of some plants.

Question 24. Which tissue cells are responsible for the movement of food through the alimentary canal?
Answer:

Muscle tissue cells are mostly responsible.

Question 25. What is the main difference between meristematic tissue and permanent tissue?
Answer:

Meristematic tissue is composed of meristematic cells which are in a state of cell division to produce new cells.
A permanent tissue is composed of mature cells that have lost the power of cell division and have attained a permanent form.

Question 26. Name the tissue that forms the horn in mammals.
Answer:

Epithelial tissue

Question 27. Give an example of two cells that aid in vision.
Answer:

Rod cells and cone cells of the retina.

Question 28. Name two organelles of a plant cell that contain their genetic material and ribosomes.
Answer:

Plastids and mitochondria.

Question 29. Name two cells that do not possess a nucleus.
Answer:

Prokaryotic cells like those of bacteria and cyanobacteria.

Question 30. Name the yellow and orange pigments of chromoplastids.
Answer:

Yellow ⇒carotene ⇒Orange Zanthophyll

Question 31. Which cell organelle participates in cell division of animal cells?
Answer:

Centrosome

WBBSE Class 8 Science Chapter 6 Quick Answers

Question 32. Name the principal types of plant tissue.
Answer:

Two principal types—meristematic and permanent.

Question 33. Name the principal types of animal tissues.
Answer:

Four principal types—epithelial, connective, muscular, and nervous.

Question 34. Give two examples of connective tissue.
Answer:

Examples of connective tissue:

Blood and bones are connective tissue.

Question 35. Name two organelles that are formed from the cell membranes.
Answer:

Endoplasmic reticulum and Golgi bodies are formed from the plasma membrane.

Question 36. Name the part of protoplasm present inside the nucleus.
Answer:

Nucleoplasm is present inside the nucleus.

Question 37. What is the chemical name of a gene?
Answer:

Chemical name of a gene:

Deoxyribonucleic acid (DNA).

Question 38. State the function of the nucleolus.
Answer:

Function of the nucleolus:

It helps in the formation of ribosomes by forming ribosomal RNA.

Very Short Answer Questions for Class 8 Organisms

Question 39. What are cristae? Where it is found?
Answer:

Cristae:

These are finger-like projections of the inner mitochondrial membrane towards the matrix.

Question 40. From which cell organelles, enzymes, and hormones are synthesized?
Answer:

Golgi bodies.

Question 41. Which cell organelles are associated with the destruction of pathogens?
Answer:

Lysosomes are responsible for the destruction of some pathogens.

Question 42. What are rough endoplasmic reticulums?
Answer:

Rough endoplasmic reticulums:

The endoplasmic reticulums provided with ribosomes on their outer surface are called rough endoplasmic reticulums.

Question 43. What is histology?
Answer:

Histology:

The microscopic study of cells and tissues is known as histology.

Question 44. What is cytology?
Answer:

Cytology:

The study of cells is known as cytology.

WBBSE Class 8 Science Important Very Short Answers

Question 45. What is a histological stain?
Answer:

Histological stain:

These are chemical substances (generally colored and known as dyes) that help to differentiate different parts of a cell under a microscope.

Question 46. Write the characteristics of a desert region.
Answer:

Characteristics of a desert region:

The environment is very dry and hot, as is the minimum rainfall.

Question 47. What is a high-altitude environment?
Answer:

High-altitude environment:

The environment above the height of 15000 feet or more from ground level.

Question 48. What is antifreeze protein?
Answer:

Antifreeze protein:

These are protein molecules that prevent ice formation inside the cell.

Question 49. In which animals do we find antifreeze proteins?
Answer:

In animals which live in very dry and cold environments.

WBBSE Class 8 Very Short Answer Resources

Question 50. What is aerenchyma?
Answer:

Aerenchyma:

Aerenchyma is a modified parenchyma cell of plants, filled with enough air bubbles to help them float in water.

Question 51. What are chloride cells?
Answer:

Chloride cells:

These are some specialized cells found in animals living in salt water, which help to eliminate excess salt from the body.

Question 52. What are mesosomes?
Answer:

Mesosomes:

These are the structures found in bacterial cells, which compensate for the absence of mitochondria and help in respiration.

Question 53. Which animals can tolerate high acidity?
Answer:

Animals living in environments rich in decaying compounds.

Question 54. Why wing muscles of insects contain more mitochondria?
Answer:

Flapping of wings requires more energy.

Question 55. Where do you find myoglobin?
Answer:

Myoglobin:

Myoglobin is a protein found in muscle cells.

Question 56. Name one similarity between the nucleus and mitochondria.
Answer:

Both nucleus and mitochondria are double membrane-bound organelles.

Living Organisms WBBSE Study Guide for Short Answers

Question 57. What do you mean by polymorphism of Lysosomes?
Answer:

Polymorphism of Lysosomes:

Lysosomes are polymorphic, i.e. these have four main types based on morphology. These are primary lysosome, secondary lysosome, residual body and autophagic vacuole.

Question 58. Which cell organelle remains attached to the nuclear membrane?
Answer:

RER

Question 59. Identify the following cells—
Answer:

1. spindle-shaped with both ends tapering helps in contraction and relaxation
2. of isodiametric cells located in the stem or root tip, leaf bud etc.
3. kidney-shaped, controls the opening and closing of stomata.
4. a cell devoid of organelles like mitochondria, ER, Golgi bodies etc.
5. Muscle cells
6. meristematic cells
7. guard cells
8. Prokaryotic bacterial cell

Question 60. Bacteria do not have chloroplast but some bacteria are photoautotrophic in nature. Which part of bacterial cell performs photosynthesis?
Answer:

Bacteria do not have chloroplast but some bacteria are photoautotrophic in nature:

The photosynthetic pigments or thylakoids are present in the cytoplasm of bacterial cells that carry out photosynthesis.

Chapter 6 The Structure Of Living Organisms Review Questions MCQs

Question 1. Which one of the following is non-living

1. Mimosa plant
2. House fly
3. Wooden log
4. Bacteria

Answer: 3. Wooden log

Question 2. Though non-living, it is produced from a living organism

1. Stone,
2. Wooden chair
3. Coal
4. Brick

Answer: 1. Stone,

Question 3. As a ‘brick is to a house/ similar is

1. Cell to a living body
2. Stomach to intestine
3. Eye to brain
4. Organ to tissue

Answer: 1. Cell to a living body

Question 4. The structural unit of our body is

1. Brick
2. Cell
3. Lung
4. Organ

Answer: 2. Organ

Read And Learn More WBBSE Solutions For Class 8 School Science Review Questions

Question 5. Lysosome arises from

1. Endoplasmic reticulum
2. Nucleus
3. Mitochondria
4. Golgi apparatus

Answer: 4. Golgi apparatus

Question 6. The term cell was coined by

1. Robert Hooke
2. Darwin
3. Franklin
4. C. Golgi

Answer: 1. Robert Hooke

Question 7. Which one is not a light microscope?

1. Simple microscope,
2. Compound microscope,
3. Electron microscope
4. None of these

Answer: 3. Electron microscope

WBBSE Solutions For Class 8 School Science Long Answer Type Questions	WBBSE Solutions For Class 8 School Science Short Answer Type Questions
WBBSE Solutions For Class 8 School Science Very Short Answer Type Questions	WBBSE Solutions For Class 8 School Science Review Questions
WBBSE Solutions For Class 8 School Science Solved Numerical Problems	WBBSE Solutions For Class 8 School Science Experiments Questions
WBBSE Solutions For Class 8 Maths	WBBSE Class 8 History Notes
WBBSE Class 8 History Multiple Choice Questions	WBBSE Solutions For Class 8 History
WBBSE Solutions For Class 8 Geography

 

Question 8. Unicellular organism is

1. Amoeba
2. Leucocyte
3. Mosquito
4. Hydra

Answer: 1. Amoeba

Question 9. Muscle cells of our body are

1. Round shaped
2. Star-shaped
3. Spindle-shaped
4. Spiral shaped

Answer: 3. Spindle-shaped

Question 10. Nerve cells can

1. Carry oxygen
2. Receive environmental stimulation
3. Contract and relax
4. Undergo cell division

Answer: 2. Receive environmental stimulation

Question 11. Cells are generally measured by unit

1. Nanometre
2. Metre
3. Millimetre
4. None of these

Answer: 1. Nanometre

Chapter 6 Living Organisms WBBSE Solutions

Question 12. Chlorophyll is present in

1. Stroma
2. Cristae
3. Quantosome
4. Grana

Answer: 4. Grana

Question 13. In plants, new organs are formed from

1. Connective tissue
2. Permanent tissue
3. Meristematic tissue
4. None of these

Answer: 3. Meristematic tissue

Question 14. An outer protective layer of our body contains

1. Epithelial tissue
2. Muscular tissue
3. Connective tissue
4. Skeletal tissue

Answer: 1. Epithelial tissue

Question 15. Centrosomes are present in

1. Prokaryotes
2. Animal cells
3. Plant cells
4. Viruses

Answer: 2. Animal cells

Question 16. Animal cells do not contain

1. Plastids
2. Mitochondria
3. Nucleus
4. Vacuoles

Answer: 1. Plastids

Question 17. Generally, the largest vacuoles are found in

1. Animal cells
2. Nerve cells
3. Plant cells
4. None of these

Answer: 3. Plant cells

Question 18. Nucleic acids are not found within

1. Cell membrane
2. Mitochondria
3. Plastids
4. All of these

Answer: 1. Cell membrane

Analysis of Living Organisms WBBSE Resources

Question 19. Double membrane-bound cell organelles are

1. Mitochondria
2. Golgi bodies
3. Ribosomes
4. Lysosomes

Answer: 1. Mitochondria

Question 20. Membraneless cell organelles are

1. Golgi bodies
2. Ribosomes
3. Plastids
4. Nucleus

Answer: 2. Ribosomes

Question 21. Cell organelles associated with secretion are

1. Mitochondria
2. Vacuoles
3. Golgi bodies
4. Cell wall

Answer: 3. Golgi bodies

Question 22. A dry and hot environment is found in

1. Desert region
2. Polar region
3. Aquatic region
4. Marshy region

Answer: 1. Desert region

Question 23. Animals living in very dry and cold environments have

1. Antifreeze protein
2. Vacuoles
3. Mesosomes
4. Streamlined body

Answer: 1. Antifreeze protein

WBBSE Class 8 Science Practice Questions

Question 24. The number of RBCs increases in

1. High altitude
2. Low altitude
3. Desert environment
4. Forest environment

Answer: 1. High altitude

Question 25. The part of protoplasm inside the nucleus is known as

1. Endoplasm
2. Nucleoplasm,
3. Cytoplasm
4. Ectoplasm

Answer: 1. Endoplasm

Question 26. The parenchyma cells filled with air vacuoles are known as

1. Sclerenchyma,
2. Collenchyma
3. Aerenchyma
4. Mesenchyma

Answer: 3. Aerenchyma

Question 27. Two autonomous cell organelles are

1. Mitochondria and chloroplastid
2. Mitochondria and golgi bodies
3. Plastid and centriole
4. Cell membrane and cell wall

Answer: 1. Mitochondria and chloroplastid

Question 28. Which type of microscope is used for observing two sections of root, stem and leaf?

1. Simple light microscope
2. Compound light microscope
3. Electron microscope
4. All of these

Answer: 2. Compound light microscope

Question 29. Rod-like cells are found in our

1. Retina of eye
2. Cornea of eye
3. Lung
4. Brain

Answer: 1. Retina of the eye

Question 30. The longest cell in our body is

1. White blood corpuscles
2. Ovum
3. Nerve cell
4. Liver cells

Answer: 3. Nerve cell

Question 31. The cell organelle which directly helps in protein synthesis is

1. Ribosome
2. Nucleus
3. Endoplasmic reticulum
4. Mesosome

Answer: 1. Ribosome

Question 32. The brain of a cell is

1. Nucleus
2. Mitochondria
3. Lysosome
4. Vacuoles

Answer: 1. Nucleus

Question 33. Which organelle may be considered a suicide bag?

1. Ribosome
2. Mitochondria
3. Golgi bodies
4. Lysosome

Answer: 4. Lysosome

Question 34. The powerhouse of the cell is

1. Nucleus
2. Mitochondria
3. Vacuole
4. Ribosome

Answer: 2. Mitochondria

Review Questions for Class 8 Structure of Living Organisms

Question 35. An electron microscope uses

1. Magnetic ocular lens
2. Objective lens
3. Photographic film
4. Simple lens

Answer: 1. Magnetic ocular lens

Question 36. Hereditary characteristics are stored in

1. Nucleic acid
2. Protein
3. Atp
4. Cytosol

Answer: 1. Nucleic acid

Question 37. Grana is found within

1. Chloroplastid
2. Ribosomes
3. Nucleus
4. Centrosome

Answer: 1. Chloroplastid

Question 38. Bacterial cells perform respiration by

1. Plastid
2. Mitochondria
3. Mesosome
4. None of these

Answer: 3. Mesosome

Question 39. Cactuses are adapted for

1. Aquatic environment
2. Desert
3. Hills
4. Saline rich marshes

Answer: 2. Desert

Question 40. Coloured petals contain

1. Chloroplastid,
2. Chromoplastid
3. Leucoplastid
4. All of these

Answer: 2. Chromoplastid

Question 41. Increase of activity of which of the following cell organelle leads to cancer?

1. Mitochondria
2. Golgi body
3. Ribosome
4. Lysosome

Answer: 4. Lysosome

Question 42. The undefined nuclear region of prokaryotes is also known as

1. Nucleus
2. Nucleolus
3. Nucleic acid
4. Nucleoid

Answer: 4. Nucleoid

Question 43. Which of the following is not a function of the vacuole?

1. Storage
2. Providing turgidity and rigidity to the cell
3. Locomotion
4. Waste excretion

Answer: 3. Locomotion

Question 44. Antifreeze proteins are found in

1. Kangaroo
2. Piranha
3. Polar fish
4. Deer

Answer: 3. Polar fish

Chapter 6 The Structure Of Living Organisms Fill In The Blanks

 

Question 1. Bacteria are __________ cells.
Answer: Prokaryotic

Question 2. Protoplasm is made up of nucleoplasm and __________
Answer: Cytoplasm

Question 3. __________ causes the colour of a flower.
Answer: Chromoplastid

Question 4. The cell membrane is __________ but the cell wall is
Answer: Living, dead

Question 5. The nucleus of bacteria is known as __________.
Answer: Nucleoid

Question 6. Plastids are present only in __________ cells.
Answer: Plant

Question 7. Cristae are found within __________.
Answer: Mitochondria

Question 8. __________ is a cell organelle without a membrane.
Answer: Ribosome

Question 9. The plastids present in the root are __________.
Answer: Leucoplastic

Question 10. The dense round dots within the nucleus are known as __________.
Answer: Nucleolus

Living Organisms WBBSE Class 8 Study Guide

Question 11. __________ contain chlorophyll pigment.
Answer: Chloroplastid

Question 12. Autolysis of a cell is performed by __________.
Answer: Lysosome

Question 13. The secretory activity of a cell is performed by __________
Answer: Golgi bodies

Question 14. __________ are considered units of a living body.
Answer: Cells

Question 15. Blood is a liquid __________ tissue.
Answer: Connective

Question 16. Root tips contain __________ tissue.
Answer: Meristematic

Question 17. Adipose tissue cells store __________
Answer: Fat

Question 18. The network-like structure within the nucleus is known as nuclear.
Answer: Reticulum

Question 19. Sulphur bacteria can survive in temperature.
Answer: High

Question 20. Haemoglobin is present within our blood corpuscles.
Answer: Red

Question 21. Huge calcium is found in the cells of.
Answer: Bones

Question 22. Salt-storing cells are found in plants growing in water.
Answer: Saline

Question 23. proteins prevent ice formation within the cytoplasm.
Answer: Antifreeze

Question 24. substitute mitochondria in bacteria.
Answer: Masosome

Question 25. An environment with high pressure is found in the sea.
Answer: Deep

Question 26. Primordial utricle is found in cell.
Answer: Plant

Question 27. Four types of animal tissues are epithelial, nervous and connective.
Answer: Muscular

Question 28. The majority of cells are 5 to 10 in size.
Answer: micron

Question 29. The kidney helps in the elimination of waste.
Answer: Metabolic

Question 30. Cells can be observed under
Answer: Microscope

Chapter 6 The Structure Of Living Organisms Identify As ‘True’ Or ‘False’

Question 1. The lung is associated with blood circulation.
Answer: False

Question 2. The heart is a blood circulation organ.
Answer: True

Question 3. A cell is the unit of a living body.
Answer: True

Question 4. Leeuwenhoek observed dead cork cells.
Answer: False

Question 5. Simple light microscopes have magnifications of about 2000X.
Answer: False

Question 6. In the electron microscope, visible light is the source of illumination.
Answer: False

Question 7. Elephants and Amoeba are multicellular organisms.
Answer: False

Question 8. Fat is stored beneath our skin.
Answer: True

Question 9. Leucocytes can change their shape.
Answer: True

Question 10. Muscle cells are generally star-shaped.
Answer: False

Question 11. The nerve cell is the longest cell in the human body.
Answer: True

Question 12. A small single visible dot may contain hundreds of cells.
Answer: True

Question 13. Permanent tissue provides mechanical strength to plants.
Answer: True

WBBSE Class 8 Science Important Review Questions

Question 14. Cells can be stained by fountain pen ink.
Answer: False

Question 15. Centrosomes lack membranes.
Answer: True

Question 16. DNA is found inside Golgi bodies.
Answer: False

Question 17. All endoplasmic reticulums are smooth in outline.
Answer: False

Question 18. – Ribosomes are covered by a double membrane.
Answer: False

Question 19. The cell wall is porous.
Answer: True

Question 20. A saline environment is found in estuaries.
Answer: True

Question 21. Cacti can grow in the desert
Answer: True

Question 22. At high altitudes, the number of RBCs in the blood decreases.
Answer: False

Question 23. Microbes are visible under the naked eye.
Answer: True

Question 24. Stages of body organization are: cell tissue -> organ -» system
Answer: True

Question 25. Mitochondria is absent in bacteria.
Answer: True

Chapter 6 The Structure Of Living Organisms Match The Columns

 

1.

Column – A	Column – B
A. Stomach	1. Circulation
B. Lung	2. Excretion
C. Heart	3. Digestion
D. Kidney	4. Respiration

Answer: A-3, B-4,C-1,D-2

2.

Column – A	Column – B
A. Epithelial tissue	1. Mechanical strength and framework
B. Connective tissue	2. Conduction of impulse
C. Muscular tissue	3. Outer covering
D. Nervous tissue	4. Contraction-

Answer: A-3, B-1,C-4,D-2

3.

Column – A	Column – B
A. Mitochondria	1. Protein synthesis
B. Golgi Body	2. Secretion
C. Lysosome	3. Energy production
D. Ribosome	4. Cellular destruction

Answer: A-3, B-2,C-4,D-1

4.

Column – A	Column – B
A. Dry and very hot	1. Polar region
B. Dry and very cold	2. Pond, River
C. Aquatic	3. Ocean, Estuaries
D. Saline	4. Desert region

Answer: A-4, B-1,C-2,D-3

5.

Column – A	Column – B
A. Antifreeze protein	1. Floating
B. Aerenchyma	2. Prevent ice formation
C. Mesosome	3. Sulphur bacteria
D. High temperature	4. Respiration

Answer: A-2, B-1,C-4,D-3

Chapter 6 The Structure of Living Organisms

Introduction

We are surrounded by living and non-living things. All animals and plants are living things and biology is the study of these living things.

A cat, playing with a ball, is living. A pigeon flying from tree to tree is also a living thing.

There are seven characteristics of living things: feeding, movement, breathing or respiration, excretion, growth, sensitivity and reproduction.

Some non-living things may show one or two of these characteristics but living things show all seven characteristics.

Non-living things can be divided into two groups, those which were once part of a living thing (Organic) and those which were never part of a living thing (Inorganic).

Some non-living things show one or two of the seven characteristics of living things. Machines, such as washing machines, can create movements of their parts.

The car needs to be fed with petrol to move. Sand, wood and glass are all non-living things. None of them shows any of the characteristics listed above.

They were never part of a living thing. The second group is those who were once part of living things. Coal is a good example. It was formed when trees died and sank into the soft ground.

This happened many millions of years ago when the Earth was covered with forests. Paper is non-living but it is also made from trees. Jam is also non-living but it was made from the fruit of a plant.

 

 

Read And Learn More WBBSE Notes For Class 8 School Science

The Seven Characteristics of Living Things 

1. Feeding: All living organisms need to take substances from their environment to obtain energy, grow and stay healthy.

2. Movement: All living organisms show the movement of one kind or another. All living organisms have internal movement, which means that they can move substances from one part of their body to another.

Some living organisms show external movement as well—they can move from place to place by walking, flying or swimming.

3. Breathing or Respiration: All living things exchange gases with their environment. Animals take in oxygen and breathe out carbon dioxide.

4. Excretion: Excretion is the removal of waste from the body. If this waste is allowed to remain in the body it could be poisonous.

Humans produce liquid waste called urine. We also excrete waste when we breathe out. All living things need to remove waste from their bodies.

Growth: When living things feed they gain energy. Some of this energy is used for growth. Living things become larger and more complicated as they grow.

Sensitivity: Living things react to changes around them. We react to touch, light, heat, cold and sound, as do other living things.

Reproduction: All living things produce young. Humans make babies, cats produce kittens and pigeons lay eggs. Plants also reproduce. Many make seeds which can germinate and grow into new plants.

WBBSE Class 8 Structure of Living Organisms notes

Differences Among Living And Non-Living

An attempt should now be made to distinguish living things from lifeless nonliving or inanimate objects. There is no difficulty in recognising a coconut palm or guinea pig as living objects and rocks in the field or the sand grains in the seashore as non-living bodies.

It may be mentioned here that viruses are an intermediate stage between living and nonliving forms of matter.
The principal points of difference between living and nonliving objects are described in tabular form below:

	Living		Non-living
1	Each kind of plant and animal has a definite form and size, which may vary within very narrow limits in different individuals of the same kind.	1	Non-living objects, such as masses of clouds or collections of stones have neither a definite size nor any precise form
2	A living body is organized of cells, tissues and organs with the division of labour.	2	No such organisation exists
3	Life is an external manifestation of metabolic activities like nutrition, respiration, secretion, circulation, excretion etc.	3	None of the metabolic activities is detected in nonliving objects.
4	The living body increases in bulk by wedging in new particles in between already existing cellular matter.	4	Growth may occur occasionally by deposition of particles only on the outer surface of the body
5	A living body can reproduce its own kind and thus perpetuate its race.	5	There is no power to reproduce its own kind
6	A living body has a definite life cycle.	6	No life cycle is observed. The period of duration is infinite and there is no death.

 

Cell-The Unit of an Organism

Your body, as a whole, is one organism. However, many, many parts make up that whole. First, you notice the entire body. Next, you see that the entire body is made up of parts and organs, and each of those organs is made up of a variety of tissues.

And if, as a pathologist does, you examine a magnified sample of one of the human body’s tissues under a microscope, millions of cells become visible.

Yet you can turn up the magnification for an even closer look, Cells contain molecules that are made up of even smaller components called atoms.

Atoms, molecules, cells, tissues, organs, and organ systems are the body’s building blocks. ‘Schleiden and Schwann together proposed the cell theory in 1839.

Cell theory states that “all plants and animals are composed of cells and cellular products.” Thus, the cell is the basic unit of life.

1. Salient points of cell theory:
2. All living things are composed of cells and their products.
3. All cells arise from pre-existing cells.
4. AII cells are basically alike in chemical composition and metabolic activities.
5. The function of an organism as a whole is the outcome of the activities and interaction of the constituent cells of which the organism is built.

Therefore, all living beings are made up of cells which are the smallest structural and functional unit of the body. Some of them are made up of only one cell and others have many cells.

All living organisms are made up of individual and identifiable cells, whose number, together with their size and type, ultimately defines the structure and functions of an organism.

While the total cell number of lower organisms is often known, it has not yet been defined in higher organisms. In particular, the reported total cell number of a human being is about 37 trillion (one trillion =1,000,000,000,000).

 

 

How a Cell can be seen?

Cells got their name from an Englishman named Robert Hooke in the year 1665. He first saw and named “cells” while he was experimenting with a new instrument we now call a “microscope.

“For his experiment, he cut very thin slices from cork. He looked at these slices under a microscope.

He saw tiny box-like shapes. These tiny boxes reminded him of the plain small rooms that monks lived in called “cells”. The smallest objects that the unaided human eye can see are about 0.1 mm long.

A magnifying glass can help you to see them more clearly, but they will still look tiny. Cells are not visible under ordinary magnifying glasses.

 

Smaller cells are easily visible under a light microscope. Light microscopes use a system of lenses to magnify an image.

The power of a light microscope is limited by the wavelength of visible light, which is about 500 nm. The most powerful light microscopes can resolve bacteria but not viruses.

Light microscopes (optical microscopes) that are commonly used in schools are of two types – compound microscopes and simple or stereo microscopes (also known as dissecting or binocular microscopes).

Left: Stereo microscope; Center: Compound microscope with a binocular head; Right: Compound microscope with a monocular head is greater resolving power than light microscopes, so we can use them to see even more detail than is visible under a light microscope.

 

 

To see anything smaller than 500 nm, you will need an electron microscope Electron microscopes shoot a high-voltage beam of electrons onto or through an object, which deflects and absorbs some of the electrons.

Resolution is still limited by the wavelength of the electron beam, but this wavelength is much smaller than that of visible light. The most powerful electron microscopes can resolve molecules and even individual atoms.

Some of the specialized types of electron microscopes are – Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), Reflection Electron Microscope (REM), and Scanning Transmission Electron Microscope (STEM).

Cell Diversity

Living organisms include unicellular organisms living as only one cell, and multicellular organisms whose bodies are made of many cells. Unicellular organisms exist, from bacteria such as the 1-2 pm long Escherichia coli (E. coli) to protists such as the 200 pm long paramoecia.

Multicellular organisms, e.g., humans, are made of a great variety of cells. Cells have various shapes, including flat cells (e.g., skin epithelial cells), disc-shaped cells (e.g., red blood cells),

And long, narrow, extended cells (e.g., nerve cells). Cell sizes vary from a diameter of about 7 pm in red blood cells to a dendrite of length up to 1m in nerve cells.

Plant cells also have a variety of shapes and sizes, including rectangular compartmentalized cells (e.g., cork cells), cells resembling jigsaw puzzle pieces (e.g., spongy cells), and cells elongated from a few millimetres to several dozen centimetres in length (e.g., pollen tube cells).

1. Several different types of cells.
2. The protist Giardia lamblia,
3. a plant cell,
4. a budding yeast cell,
5. a red blood cell,
6. a fibroblast cell, a eukaryotic nerve cell, and

A retinal rod cell In the human body, the heart and the brain are made of different types of cells having different functions. Different organs are made of more than one type of cell for proper body functions.

 

Types of cell

There are two distinct types of cells: prokaryotic and eukaryotic. Prokaryotic cells are much simpler than eukaryotic cells. Prokaryotic cells do not possess membrane-bound organelles.

The primitive nucleus (nucleoid) lies freely in the cytoplasm. Bacteria and cyanobacteria (Blue-green algae) are prokaryotes.
A cell which possesses membrane-bound organelles like the nucleus, mitochondria, chloroplasts etc is called a eukaryotic cell. The eukaryotic cells further show diversities in plant cells and animal cells.

Cells and their sizes

Prokaryotic cells are the smallest cells, typically example, an Escherichia coli (often referred to as E. coli) bacterium is typically a few PMs long.

 

Understanding living organisms for Class 8

Mammalian red blood cells are among the smallest eukaryotic cells. They are typically about 8 pm in diameter and have a distinctive bi-concave shape in humans.

It is interesting to note that the shape can be very different. For example, the red blood cells of sheep are nearly spherical and those of camels are elliptical.

The Amoeba is a relatively large single-celled organism, typically 10 to 100 pm across. Technically, the yolk of an ostrich egg is one cell though it is rather specially adapted.

All the nucleotide material is contained in a small volume at the edge of the yolk. The bulk is a supply of ‘raw material’ that the cells of the growing embryo use to assemble the cells of the ostrich chick.

Single giraffe nerve cells can be the length of the giraffe, from head to toe, several metres! Of course, these cells are still extremely narrow and the diagram shown here is very schematic.

Sclerenchyma fibre cells (1m long) are the longest plant cells and Acetabularia (10 cm) is the single largest plant cell.

Specialised Cells

The table below shows examples of some specialised animal and plant cells, with their functions and special features.

 

Levels of organisation:

The Organisation of Cells, Tissues, Organs, Systems and the Organism

From the least complex to the most complex, the organisms are made up of—

1. Atom – The smallest piece of matter that still has physical and chemical properties of matter.
2. Molecule – The smallest piece of a compound that still has the physical and chemical properties of that substance (e.g., water). The molecule is composed of atoms.
3. Cell – The smallest piece of life (some arguments remain about viruses). It is the basic unit of all living beings.
4. Tissue – Collection of cells that work together.
5. Organ – Collection of tissues that work together.
6. Organ System – Collection of organs that work together.
7. Organism – Collection of organ systems that makes up a single life form.

Two or more kinds of tissues together form each of our organs, like the heart or lungs. Many organs together form an organ system, like the digestive or respiratory system.

All the organ systems together form an organism, such as a person, dog or blue whale. The body’s organisation goes from cells to tissues to organs to organ systems to a whole working organism. In unicellular (single-celled) organisms, the single cell performs all life functions.

It functions independently. However, multicellular (many-celled) organisms have various levels of organization within them. Individual cells may perform specific functions and also work together for the good of the entire organism.

The cells become dependent on one another. Multicellular organisms have the following 5 levels of organization ranging from simplest to most complex:

WBBSE Chapter 6 summary on structure of organisms

Level-1 Cells

Are the basic unit of structure and function in living things. May serve a specific function within the organism.
Examples – are blood cells, nerve cells, bone cells, etc.

 

 

Level-2 Tissues

Made up of cells that are similar in structure and function and which work together to perform a specific activity.
Examples – are blood, nervous, bone, etc. Humans have 4 basic tissues: connective, epithelial, muscle, and nervous.

 

 

Level-3 Organs

Made up of tissues that work together to perform a specific activity. Examples – heart, brain, skin, etc.

 

 

Level-4 Organ Systems

Groups of two or more tissues that work together to perform a specific function for the organism.
The Human body has 11 organ systems – circulatory, digestive, endocrine, excretory (urinary), immune (lymphatic), integumentary, muscular, nervous, reproductive, respiratory, and skeletal.

 

Components of living organisms for Class 8

Level -5 Organisms

Entire living things can carry out all basic life processes. Meaning they can take in materials, release energy from food, release wastes, grow, respond to the environment, and reproduce.

Usually made up of organ systems, but an organism may be made up of only one cell such as bacteria or protists.
Examples – are bacteria, Amoeba, mushrooms, sunflowers, and humans.

 

 

The levels of organization in the correct order are:
cells ⇒ tissues⇒  organs ⇒ organ systems ⇒ organisms

Levels of the body from smallest to largest: Atoms, molecules, cells, tissues, organs, and organ systems.

 

 

What Are Tissues

A group of cells having a common origin, similar structure and performing a definite function is called a tissue. Tissues are found in plants and animals.

Plants and animals are made up of many different kinds of tissues. For example, groups of bone cells form bone tissues and muscle cells form muscle tissue.

Different types of tissues have distinctive architectures best suited for what they do. We will see that plant tissues are different from animal tissues in many ways.

Every organism, whether its body is unicellular or multicellular, is capable of performing all vital functions such as respiration, ingestion, excretion and reproduction.

In multicellular organisms, because of the increase in body size, it is difficult for each cell to efficiently cope with the vast variety of physiological needs of the organism. So cells group together to perform definite functions.

Plant Tissues

Plant tissues can be grouped into two basic types: meristematic and permanent tissues.

Meristematic tissue: This tissue is in a state of cell division and produces new cells. It is found in various growing organs of plant-like roots, shoots, leaves buds and flowers.

Permanent tissue: This tissue is composed of mature cells that have lost the power of division and have definite form and shape. These tissues are responsible for photosynthesis, storage of food, secretion and mechanical functions. Permanent cells always derive their origin from the meristematic cells.

Types of cells in living organisms for Class 8

Structure and function of cells Class 8

Animal Tissues

The smallest units of the body-the cells-are are individually too small to be seen by the naked eye. Yet when many like cells are together, they form a tissue. Tissues are groups of cells with a common structure and function.

There are four main tissues in the body – epithelium, muscle tissue, connective tissue and nervous tissue.

Epithelium (or epithelial tissue) is found all over the body with several functions. In the skin, it protects us from the outside world, in the stomach and intestines it absorbs. In the kidney, it filters and in the glands it secretes.

Muscle tissue is responsible for body movement, moves blood, food, and waste through the body’s organs, and is responsible for mechanical digestion.

Connective tissue wraps around, supports, cushions and protects organs. It stores nutrients and gives the skin strength. As tendons and ligaments, it protects joints and attaches muscles to bone and each other. It includes some specialized tissues including cartilage, bone and blood.

Nervous tissue conducts impulses to and from body organs via neurons. It makes up the brain, spinal cord and nerves.

 

Difference between Animal and Plant Tissues

 

Animal Tissue	Plant Tissue
Since animals are mobile so they require more energy, hence more living tissues are required.	Since plants are stationary so they do not require much energy. Hence more living tissues are not required.
Animals move from one place to another in search of food, shelter etc., hence they need more energy and there more tissues are living.	In plants, most tissues provide structural strength. Most of these tissues are dead, can provide mechanical strength as easily as the living ones and need less maintenance.
Cell growth is uniformly distributed.	Growth is limited to certain regions.
The structural organisation of organs and organ systems is more specialised and complex.	The structural organisation of organs is comparatively less complex.

 

Structure and Function of a typical cell

Cell organelles and their structure and function

An organelle is any specialized structure based on the analogy that cells have their cell, especially one for which a specific organelle is just as complex as a multicellular function can be assigned.

As we mentioned organisms have their livers, kidneys, and stomachs earlier, the name means “little organ” and in other organs.

The Three Main Components of any Plant or Animal Cell:

1. Plasma Membrane / Cell Membrane

Structure – It is a bilipid membraneous layer containing proteins and lipids. There are two outer layers of protein and a middle layer of phospholipid. It is called a unit membrane and is semifluid and dynamic in nature.

Function – The cell membrane separates the cell from its external environment, and is selectively permeable (controls what gets in and out). It protects the cell and provides stability.

Proteins are found embedded within the plasma membrane, with some extending all the way through in order to transport materials.
Carbohydrates are attached to proteins and lipids on the outer lipid layer.

2. Cytoplasm

Structure – It is a colourless, semisolid and jelly-like substance composed of main water and found between the cell membrane and nucleus.

The cytoplasm makes up most of the “body” of a cell and is constantly streaming. The transparent fluid part of the cytoplasm is called cytosol.

Function – Organelles are found here and substances like salts may be dissolved in the cytoplasm. It helps in the exchange of materials between cell organelles and is the active site for metabolic processes like sugar, protein and fatty acid synthesis.

3. Nucleus

Structure – The largest organelle in the cell. It is dark and round and is surrounded by a double membrane called the nuclear envelope/ membrane.

In spots, the nuclear envelope fuses to form pores which are selectively permeable. The nucleus contains genetic information (DNA) on special strands called chromosomes.

The colourless dense sap present inside the nucleus is called the nucleoplasm. One or more round bodies present in the nucleoplasm are called nucleoli. A network of dark-staining fibre in the nucleus is called chromatin.

Function – The nucleus is the “control centre” of the cell, for cell metabolism and reproduction. It regulates the cell cycle and is the storehouse of genes.

2. The Organelles found in both Plant and Animal cells:

1. “ER” or Endoplasmic Reticulum

The Endoplasmic Reticulum is a network of membranous canals filled with fluid. They carry materials throughout the cell. The ER is the “transport system” of the cell.

There are two types of ER: rough ER (RER) and smooth ER. (SER)Rough Endoplasmic Reticulum is lined with ribosomes and is rough in appearance and smooth endoplasmic reticulum contains no ribosomes and is smooth in appearance.

ER gives support to the cytoplasm. It forms an intracellular transport system. SER plays a crucial role in detoxifying many poisons and drugs. It also helps in the formation of proteins and lipids.

2. Ribosomes

Ribosomes are small particles which are found individually in the cytoplasm and also line the membranes of the rough endoplasmic reticulum. Ribosomes produce protein. They could be thought of as “factories” in the cell.

3. Golgi Body / Apparatus

Golgi bodies are stacks of flattened membranous sacs, (they look like pancakes). The Golgi Body temporarily stores protein which can then leave the cell via vesicles pinching off from the Golgi.

In plants, the Golgi apparatus is scattered in the cytoplasm and found in the diffused form. These are known as Dictyosomes.
Secretion is the main function of the Golgi complex. It mainly performs the function of packaging.

The material synthesized near the ER is packaged and dispatched to various targets inside and outside the cell through the Golgi apparatus. It is directly involved in the formation of lysosomes.

Characteristics of living organisms Class 8

4. Lysosomes

Lysosomes are small sac-like structures surrounded by a single membrane and containing strong digestive enzymes which when released can break down worn-out organelles or food.

The lysosome is also known as a suicide sac. This help to keep the cell clean by digesting any foreign material and worn-out cell organelles.

5. Mitochondria (Singular = Mitochondrion)

The mitochondria are round “tube-like” organelles that are surrounded by a double membrane, with the inner membrane being highly folded.

The mitochondria are often referred to as the “powerhouse” of the cell. The mitochondria release food energy from food molecules to be used by the cell.

This process is called respiration. Some cells ( muscle cells) require more energy than other cells and so would have many more mitochondria.

6. Vacuoles

Vacuoles are fluid-filled organelles enclosed by a membrane. They can store materials such as food, water, sugar, minerals and waste products.

3. Animal Cell Organelles not found in Plant Cells

1. Cilia and Flagella

Both cilia and flagella are hair-like organelles which extend from the surface of many animal cells. The structure is identical in both, except that flagella are longer and whip-like and cilia are shorter.

There are usually only a few flagella on a cell, while cilia may cover the entire surface of a cell. The function of cilia and flagella include locomotion for one-celled organisms and moving substances over cell surfaces in multi-celled organisms.

4. Organelles and other features found only in Plant Cells

1. Cell Wall

The cell wall is a rigid organelle composed of cellulose lying just outside the cell membrane. The cell wall gives the plant cell its box-like shape. It also protects the cell. The cell wall contains pores which allow materials to pass to and from the cell membrane.

2. Plastids

Plastids are double membrane bound organelles. It is in plastids that plants make and store food. Plastids are found in the cytoplasm and there are two main types:

Leucoplasts – Colourless organelles which store starch or other plant nutrients, (for example – starch stored in a potato).

Chromoplasts – Contain different coloured pigments. The most important type of chromoplast is the chloroplast, which contains the green pigment chlorophyll. This is important in the process of photosynthesis.

3. Central Vacuole

The central vacuole is a large fluid-filled vacuole found in plants.

Components of animal and plant cells

 

 

Differences between plant and animal cells:

Point	Plant cell	Animal cell
Cell wall Plastids	Present	Absent
Centrosome	Present	Absent
Vacuoles	Absent	Present
Size	Large, central and permanent large	Small, many and temporary Smaller

 

Types of Habitat

1. Habitat: Habitat is the immediate surroundings of an organism. It is the place that is natural for the life and growth of an organism. Animals and plants adapt themselves to their different habitats.

2. Terrestrial habitat: All the deserts, mountains and forests and grasslands are included under terrestrial habitat.

3. Desert: Camels show different adaptations to live in deserts. They possess long legs, long eyelashes, covered nostrils, special fat cells, and modified cells in the stomach as adaptations. Snakes and rats live in burrows and come out only during the night when it is cool.

Desert plants are called xerophytes and they exhibit some typical adaptations to live in desert conditions. Leaves are reduced to spines.

Stems are green and fleshy to carry out photosynthesis and store water. Roots grow deep into the soil to absorb water. The reduced leaf and the thick waxy layer of the stem minimise the rate of transpiration.

4. Cold region: Most of the trees in cold mountains are cone-shaped. The leaves are very thin and needle-shaped to slide off the snow and rainwater immediately.

Most deciduous plants shed their leaves and remain dormant during the intense cold. Plants may hold on to layers of dead leaves for thermal insulation.

Animals in cold areas have long thick skin and fur to protect themselves from cold climates. They possess strong hooves to run easily and large furry feet to distribute the load uniformly as well as to increase the grip on ice.

They have a small body surface area to volume ratio to minimise heat loss. Certain vertebrates in cold regions produce antifreeze proteins (AFPs), a class of polypeptides that bind to small ice crystals to inhibit the growth and recrystallization of ice. This permits survival in subzero temperatures.

RBC count increases abruptly in animals living in high altitudes and cold climates. There is a substantial increase in the number of mitochondria and myoglobin content in muscle cells.

Haemoglobin amount also increases with a proportionate increase in RBC count to combat the less oxygenated environment.

5. Grasslands: Lions living in the forests possess skin colour so as to match their environment. They hide in grasslands to catch their prey. They possess strong claws and teeth to tear food. They have sharp eyesight.

Deer possess long ears to have sharp hearing sense. Deers possess eyes on the side of its head which makes them look in all directions. They have long legs to run fast.

Aquatic Habitat: All the fresh water and marine water bodies are included under aquatic habitat. Fish possess streamlined bodies, which reduce friction and allow them to move freely in the water.

Sea animals like the octopus and squid do not possess a streamlined bodies as they stay deep inside the ocean. They have the ability to make their body streamlined when they move in the water.

The cells of these animals have a large number of mitochondria. The level of calcium is relatively high in cells of the endoskeleton to give additional energy and strength.

Aquatic animals possess gills that help them to absorb the dissolved oxygen from water. Dolphins and whales possess blowholes to breathe in air from the atmosphere directly.

Aquatic plants have much smaller roots which are mostly free-floating. Stems are long and light. Leaves in submerged plants possess ribbon—like leaves which allow the plants to bend themselves in the direction of the flowing water. Plants have aerenchyma tissue that helps in floatation.

Frogs are amphibious in nature, i.e., a frog can live both in water and on land. Frogs have strong hind legs to hop on land and webbed feet to swim in the water.

Frogs also have a protective membrane called the nictitating membrane on their eyes.

6. Harsh environment: Bacterial cells are adapted to anaerobic respiration using mesosomes in a less oxygenated environment.
They can carry out chemosynthesis at high temperatures and high sulphur-containing environments.

The thermophile bacteria can survive very high temperatures even as high as 235°C. Acidophilic bacteria can tolerate high levels of acidity (pH 5.5 or below). The organisms growing in an environment rich in decaying organic compounds usually can tolerate high levels of acidity.

 

 

Chapter 5 Analysis Of Natural Phenomena Long Answer Type Questions

Question 1. Describe in short how lightning occurs during a thunderstorm.
Answer:

Thunderstorm 

A thunderstorm is a type of storm characterized by the presence of lightning and thunder accompanied by strong winds and heavy rain.

Thunderstorms result from the rapid upward movement of warm moist air. As the warm, moist air moves upward (called updraft of air), it cools, condenses, and forms cumulonimbus clouds that can gain heights of 12 km or more.

The upward movement of air in a storm cloud has been measured as more than 80 kilometres per hour. ‘ As the moist air reaches its dew point at the upper atmosphere, it converts to water droplets and tiny ice particles.

These particles begin to fall a long way through clouds and collide with other particles and thus become larger. Downdrafts of air are created by the falling water droplets because they don’t just drag other droplets down with them as they fall, they drag cooler air with them as well. The combined warm updraft and cool downdraft create a storm cell.

Read And Learn More WBBSE Solutions For Class 8 School Science Long Answer Type Questions

Question 2. Write about the characteristics of epidemic diseases.
Answer:

Characteristics Of Epidemic Diseases

1. All epidemics have the following common characteristics:
2. An unexpected number of cases of a particular disease occur at a particular point in time affecting a large segment of the population.
3. Generally confined to a definite population or geographical area.
4. Usually have a common source of infection,
5. Epidemics generally tend to follow a pattern and repeat periodically when the conditions are favourable again.

Types Of Epidemic Diseases

Epidemics generally follow a pattern depending on the geographical and environmental conditions, the distribution and characteristics of the host population, and their cultural behaviour.

If there is no intervention or change in these conditions, those epidemics tend to repeat themselves. Therefore, knowledge about various types of epidemics and the conditions under which they occur can help in managing them.

WBBSE Class 8 Analysis of Natural Phenomena Long Answers

Question 3. Write briefly about cholera.
Answer:

Cholera

Cholera is an acute intestinal infection caused by the

ingestion of food or water contaminated with the bacterium Vibrio cholera.

It has a short incubation period and produces an enterotoxin that causes a copious, painless, watery diarrhoea that can quickly lead to severe dehydration and death if treatment is not promptly given.

Vomiting also occurs in most patients. Most persons infected with V. cholerae do not become ill, although the bacterium is present in their faeces for 7-14 days.

When illness does occur, about 80-90% of episodes are of mild or moderate severity and are difficult to distinguish clinically from other types of acute diarrhoea.

Less than 20% of ill persons develop typical cholera with signs of moderate or severe dehydration.

Question 4. Write the cause and symptoms of kala-azar.
Answer:

Kala-azar

Kala-azar is the second largest parasitic killer in the world – only Malaria is more deadly. It is also known as Dumdum fever.
Kala-azar is caused by bites from sandflies – which carry the Leishmania donovani parasite, a type of protozoa, responsible for the disease.

If blood containing Leishmania donovani parasites is drawn from an animal or human, the next person to receive a bite will then become infected.

Initially, Leishmania parasites cause skin sores or ulcers at the site of sand fly bites. If the disease progresses, it attacks the immune system.

Kala-azar presents after two to eight months, with more generalised symptoms including prolonged fever and weakness. Indian scientist Upendranath Brahmachari invented the medicine of Kala-azar.

Chapter 5 Natural Phenomena Detailed Questions WBBSE

Question 5. Write about an epidemic due to a non-infectious disease.
Answer:

Epidemic due to a non-infectious disease

Epidemics of non-infectious disease are often caused by exposure to industrial products, intermediates or byproducts, either in the workplace or as a result of the contamination of a wider environment.

The Global Status Report on Non-communicable Diseases 2010 is the first report on the worldwide epidemic of cardiovascular diseases, cancer, diabetes and chronic respiratory diseases, along with their risk factors and determinants.

Non-communicable diseases killed tens of millions of people in 2008, and a large proportion of these deaths occurred before the age of 60, so during the most productive period of life. The magnitude of these diseases continues to rise, especially in low- and middle-income countries.

Question 6. How can a common disease turn into an epidemic? What do you mean by zoonotic disease?
Answer:
The epidemic is due to the sudden rise of cases usually resulting from a new infectious agent or a change in an existing agent,

For example:

1. An agent moving between host populations, for example, moving from animals to humans (zoonotic disease).
2. A genetic change or mutation occurs in the infectious agent, eg. bacteria, viruses, fungi etc.
3. Introduction of the new pathogen to a host population
4. Initially, scattered or isolated incidences of small clusters of the disease occur in humans
5. In the next step human to human transmission occurs at a rate that causes outbreaks in communities.

Zoonotic diseases are caused by germs that spread between animals and people. Examples include Covid-19, Plague, Rabies, Zoonotic influenza etc. Zoonotic diseases are caused by germs that spread between animals and people. Examples include Covid-19, Plague, Rabies, Zoonotic influenza etc.

WBBSE Class 8 Science Long Answer Format

Question 7. Name the causative agents of cholera and tuberculosis.
Answer:

Some Common Infectious Diseases Induced Epidemics

WBBSE Solutions For Class 8 School Science Long Answer Type Questions	WBBSE Solutions For Class 8 School Science Short Answer Type Questions
WBBSE Solutions For Class 8 School Science Very Short Answer Type Questions	WBBSE Solutions For Class 8 School Science Review Questions
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WBBSE Solutions For Class 8 Maths	WBBSE Class 8 History Notes
WBBSE Class 8 History Multiple Choice Questions	WBBSE Solutions For Class 8 History
WBBSE Solutions For Class 8 Geography

 

1. Cholera

Cholera is an acute intestinal infection caused by the

ingestion of food or water contaminated with the bacterium Vibrio cholera.

It has a short incubation period and produces an enterotoxin that causes a copious, painless, watery diarrhoea that can quickly lead to severe dehydration and death if treatment is not promptly given.

Vomiting also occurs in most patients. Most persons infected with V. cholerae do not become ill, although the bacterium is present in their faeces for 7-14 days.

When illness does occur, about 80-90% of episodes are of mild or moderate severity and are difficult to distinguish clinically from other types of acute diarrhoea.

Less than 20% of ill persons develop typical cholera with signs of moderate or severe dehydration.

2. Malaria

Malaria is caused by a protozoan parasite called Plasmodium, which is transmitted via the bites of infected female Anopheles mosquitoes.

In the human body, the parasites multiply in the liver and then infect red blood cells. Symptoms of malaria include fever, headache, and vomiting, and usually appear between 10 and 15 days after the mosquito bite.

1. If not treated, malaria can quickly become life-threatening by disrupting the blood supply to vital organs.
2. Key interventions to control malaria include:
3. prompt and effective treatment with artemisinin-based combination therapies,
4. use of insecticidal nets and
5. indoor spraying with insecticide.

3. Dengue

Dengue is transmitted by the bite of a mosquito. A type of mosquito called Aedes Egypt carries the germ of this disease. It is a febrile illness that affects infants, young children and adults with symptoms appearing 3-14 days after the infective bite.

Dengue is not transmitted directly from person to person and symptoms range from mild fever to incapacitating high fever, with severe headache, pain behind the eyes, muscle and joint pain, rash and lowering of platelet count to an alarming level.

It causes the oozing of blood in the skin due to the lowering of WBC. There is no vaccine or any specific medicine to treat dengue. People who have dengue fever should take rest, drink plenty of fluids and reduce the fever using paracetamol or see a doctor. It reduces the immunity power.

4. Plague

Plague is a bacterial disease, caused by Yersinia pestis, which primarily affects wild rodents such as rats. It is spread from one rodent to another by fleas (a type of insect).

Humans bitten by an infected flea usually develop a bubonic form of plague, which is characterized by a bubo, i.e. a swelling of the lymph node draining the flea bite site.

A type of fly called Xenopsylla cheopis carries the bacteria from the body of a rat afflicted with plague. If the bacteria reach the lungs, the patient develops pneumonia (pneumonic plague), which is then transmissible from person to person through infected droplets spread by coughing.

Initial symptoms of bubonic plague appear 7-10 days after infection. In 1987, Waldemar Haffkine invented the vaccine for the plague in Mumbai.

5. Smallpox

Smallpox is a disease caused by the Variola major virus. Some experts say that over the centuries it has killed more people than all other infectious diseases combined. Worldwide immunization stopped the spread of smallpox three decades ago The last case was reported in 1977.

Smallpox spreads very easily from person to person. Symptoms are flu-like. They include high fever, fatigue, headache, backache, and a rash with flat red sores.

There is no treatment. Fluids and medicines for pain or fever can help control symptoms. Most people recover, but some can die. Those who do recover may have severe scars. Edward Jenner, in 1976 used the cow-Pox virus in the human body to develop resistance against smallpox.

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6. Kala-azar

Kala-azar is the second largest parasitic killer in the world – only Malaria is more deadly. It is also known as Dumdum fever.
Kala-azar is caused by bites from sandflies – which carry the Leishmania donovani parasite, a type of protozoa, responsible for the disease.

If blood containing Leishmania donovani parasites is drawn from an animal or human, the next person to receive a bite will then become infected.

Initially, Leishmania parasites cause skin sores or ulcers at the site of sand fly bites. If the disease progresses, it attacks the immune system.

Kala-azar presents after two to eight months, with more generalised symptoms including prolonged fever and weakness. Indian scientist Upendranath Brahmachari invented the medicine of Kala-azar.

7. Diarrhoea

Diarrhoea is the passage of loose or liquid stools 3 or more times per day, or more frequently than is normal for the individual.

Diarrhoea means ‘to flow/ It is usually a symptom of gastrointestinal infection, which can be caused by a variety of bacterial, viral and parasitic organisms.

Infection is spread through contaminated food or drinking water, or from person to person as a result of poor hygiene.

Severe diarrhoea leads to fluid loss, and may be life-threatening, particularly in young children and people who are malnourished or have impaired immunity. A quick intake of ORS (Oral Rehydration Solution) is an effective remedy for diarrhoea.

8. Tuberculosis

Tuberculosis, or TB, is an infectious bacterial disease caused by Mycobacterium tuberculosis, which most commonly affects the lungs.

It is transmitted from person to person via droplets from the throat and lungs of people with active respiratory disease.
In healthy people, infection with Mycobacterium tuberculosis often causes no symptoms, since the person’s immune system acts to “wall off” the bacteria.

The symptoms of active TB of the lung are coughing, sometimes with sputum or blood, chest pains, weakness, weight loss, fever and night sweats. It is possible to control the disease by proper treatment through DOTS or Directly Observed Treatment, a short course.

9. Hepatitis

Hepatitis is an inflammation of the liver, most commonly caused by a viral infection. There are five main hepatitis viruses, referred to as types A, B, C, D and E.

These five types are of greatest concern because of the burden of illness and death they cause and the potential for outbreaks and epidemic spread.

In particular, types B and C lead to chronic disease in hundreds of millions of people and together, are the most common cause of liver cirrhosis and cancer.

Hepatitis A and E are typically caused by the ingestion of contaminated food or water. Hepatitis B, C and D usually occur as a result of contact with infected body fluids.

Common modes of transmission for these viruses include receipt of contaminated blood or blood products, invasive medical procedures using contaminated equipment and hepatitis B transmission from mother to baby at birth, from family member to child, and also by sexual contact.

Acute infection may occur with limited or no symptoms or may include symptoms such as jaundice (yellowing of the skin and eyes), dark urine, extreme fatigue, nausea, vomiting and abdominal pain.

10. Influenza/Flu

Influenza is a viral infection that affects mainly the nose, throat, bronchi and occasionally, lungs. Infection usually lasts for about a week and is characterized by sudden onset of high fever, aching muscles, headache and severe malaise, non-productive cough, sore throat and rhinitis.

The virus is transmitted easily from person to person via droplets and small particles produced when infected people cough or sneeze.

Influenza tends to spread rapidly in seasonal epidemics. Most infected people recover within one to two weeks without requiring medical treatment.

However, in the very young, the elderly and those with other serious medical conditions, the infection can lead to severe complications of the underlying condition, pneumonia and death.

11. AIDS

The Human Immunodeficiency Virus (HIV) is a retrovirus that infects cells of the immune system, destroying or impairing their function.

As the infection progresses, the immune system becomes weaker, and the person becomes more susceptible to infections. The most advanced stage of HIV infection is Acquired Immuno Deficiency 9/ndrome (AIDS).

It can take 10-15 years for an HIV-infected person to develop AIDS; antiretroviral drugs can slow down the process even further.
HIV is transmitted through unprotected sexual relations, transfusion of contaminated blood, sharing of contaminated needles and between a mother and her infant during pregnancy, childbirth and breastfeeding.

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12. COVID-2019

Coronaviruses are a large family of viruses that cause illnesses ranging from the common cold to Middle East Respiratory Syndrome (MERS-CoV) and Severe Acute Respiratory Syndrome (SARS- CoV).

A novel coronavirus (nCoV) is a new strain that has not been previously identified in humans. Coronaviruses are zoonotic. SARS-CoV was transmitted from civet cats to humans and MERS- CoV from dromedary camels to humans with infected body fluids.

Common modes of transmission for these viruses include receipt of contaminated blood or blood products, invasive medical procedures using contaminated equipment and hepatitis B transmission from mother to baby at birth, from family member to child, and also by sexual contact.

Acute infection may occur with limited or no Common signs of infections including respiratory symptoms, fever, cough, shortness of breath and breathing difficulties.

In severe cases, the infection can cause pneumonia, severe acute respiratory syndromes, kidney failure and death. Standard recommendations to prevent infection spread include regular hand washing, covering mouth and nose when coughing and sneezing, avoiding close contact with people or social gatherings etc.

Epidemic due to a non-infectious disease

Epidemics of non-infectious disease are often caused by exposure to industrial products, intermediates or byproducts, either in the workplace or as a result of the contamination of a wider environment.

The Global Status Report on Non-communicable Diseases 2010 is the first report on the worldwide epidemic of cardiovascular diseases, cancer, diabetes and chronic respiratory diseases, along with their risk factors and determinants.

Non-communicable diseases killed tens of millions of people in 2008, and a large proportion of these deaths occurred before the age of 60, so during the most productive period of life. The magnitude of these diseases continues to rise, especially in low- and middle-income countries.