WBBSE Solutions For Class 8 School Science Chapter 7 The Microbial World Short Answer Type Questions

Chapter 7 The Microbial World Short Answer Type Questions


Question 1. What are 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?


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?


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?


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 on the basis of their unicellularity and were assigned to the kingdom Protista. Protozoa are eukaryotic organisms which exist as structurally and functionally independent individual cells.

Question 5. What are 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.

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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 contain cellulose, unlike the cell walls of bacteria What are algae?

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.

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.

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

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?

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 have no effect on viruses, but antiviral drugs have been developed to treat life-threatening infections. Vaccines that produce lifelong immunity can prevent some viral infections.

Question 10. Write two characteristics of bacteria.

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.

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.

Harmful Bacteria:

There are many types of harmful bacteria, some of which are absolutely 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 causes some harmful plant diseases like the soft rot of potatoes, angular leaf spot of cotton, plant tumors, etc.

Question 13. State two characteristics of protozoa.

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 which are employed in

  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.

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.

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.

Question 17. State two characteristics of fungus.

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.

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.

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.

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?

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.

Question 22. Write briefly about useful algae.

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?


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

Question 24. What is 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?


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?


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?


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

Question 28. What are 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?


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?


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?


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?

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?

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?

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.

Question 35. What is 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?


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?


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?

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


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?


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.

Question 41. What is 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?


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?

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?


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?

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?


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

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.


Question 48. Write the differences between fungi and bacteria.

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.

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.

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.

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.


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