WBBSE Class 10 Life Science And Environment Model Question Paper 2023 Set 1

Model Question Paper Life Science And Environment Set 1 Group A

Answer to all questions is compulsory

1. Write the answer in complete sentences by choosing the correct answer for each question with the respective serial number.

Question 1. The tentacles on the leaves of an insectivorous plant, called sundew to bend to trap the insect as soon as they come in contact with the insect body. This is-

1. Seismonasty
2. Photonasty
3. Thermonasty
4. Chemonasty

Answer: 4. The tentacles on the leaves of an insectivorous plant, called sundew bend to trap the insect as soon as they come in contact with the insect body. This is chemonasty.

Question  2. In case of women, the Follicle Stimulating Hormone stimulates the Graafian Follicle of the ovary to secrete the hormone, is-

1. TSH
2. Oestrogen
3. ADH
4. ACTH

Answer: 2. In the case of women, the Follicle Stimulating Hormone stimulates the Graafian Follicle of the vary to secrete the hormone, is Oestrogen.

Question  3. Which one of the following is the correct reflex arc?

1. Receptor → Effector Efferent nerve → Nerve Centre → Afferent nerve
2. Nerve Centre → Receptor → Afferent nerve Effector → Efferent nerve
3. Efferent nerve →  Receptor → Afferent nerve → Nerve Centre → Effector
4. Receptor→ Afferent nerve → Nerve Centre → Efferent nerve Effector

Answer: The correct reflex arc is—Receptor → Afferent nerve → Nerve Centre → Efferent nerve Effector.

Question  4. In which stage of mitosis cell division, the nuclear membrane and nucleolus are seen to disappear?

1. Anaphase
2. Metaphase
3. Prophase
4. Telophase

Answer: 2. In the prophase stage of mitosis cell division, the nuclear membrane and nucleolus are seen to disappear.

Question  5. Which of the following is not a structural component of DNA?

1. Deoxyribose sugar
2. Thymine base
3. Uracil base
4. Phosphoric acid

Answer: 2. Uracil base is not a structural component of DNA.

Question  6. Which one of the following statements is correct regarding sexual reproduction?

1. Haploid gamete formation is essential in sexual reproduction
2. Sexual reproduction depends only on mitosis
3. In sexual reproduction, offspring could be produced from a single parental organism
4. The offsprings produced in sexual reproduction are genetically identical with the parental organism

Answer:  1. The correct statement regarding sexual reproduction is haploid gamete formation is essential in sexual reproduction.

Question  7. Which one of the following is the genotypic ratio at F₂ generation of Mendel’s monohybrid cross?

1. 1:2:1
2. 3:1
3. 9:3:3:1
4. 2:1:2

Answer: 1. The genotypic ratio at F₂ generation of Mendel’s monohybrid cross is 1:2:1.

Question  8. Which one of the following is not controlled by the autosomal gene of humans?

1. Roller tongue
2. Haemophilia
3. Thalassaemia
4. Attached ear lobe

Answer:  2. Haemophilia is not controlled by the autosomal gene of humans.

Question  9. What would be the phenotypic ratio in the F₂ generation of a monohybrid cross in case of incomplete dominance?

1. 3:1
2. 2:1:1
3. 9:3:3:1
4. 1:2:1

Answer: The phenotypic ratio in the F₂ generation of a monohybrid cross in case of incomplete dominance is 1:2:1.

Question  10. Which one of the following is the intraspecific struggle for the same food?

1. The struggle between Vulture and Hyaena
2. The struggle between Eagle and Kite
3. The struggle among the members of Rohu fish in a pond
4. Struggle between Egret and Kingfisher

Answer: The intraspecific struggle for the same ‘food is a struggle among the members of Rohu fish in a pond.

Question  11. Which of the following changes did not occur during the course of the evolution of the horse?

1. Lengthening of limbs
2. Increase in the length and thickness of all digits in limbs
3. Increase in the length and thickness of only the third digit in limbs
4. Increase in size of the whole body

Answer:  Increase in the length and thickness of all digits in limbs did not occur during the course of the evolution of the horse.

Question  12. According to the opinion of the scientists the prebiotic environment of the earth that led to the origin of life was like-

1. Hot dilute soup in the seawater
2. Cold dilute soup in the seawater
3. Cold dilute soup in the river water
4. Hot dilute soup in the groundwater

Answer: According to the opinion of the scientists the prebiotic environment of the earth that led to the origin of life was like hot dilute soup in the sea water.

Question  13. Which one of the following microbes takes part in nitrification?

1. Nitrosomonas
2. Azotobacter
3. Pseudomonas
4. Thiobacillus

Answer: Nitrosomonas takes part in ‘ nitrification.

Question  14. An example of Ex-situ conservation is-

1. Sunderban Tiger Reserve
2. Corbett National Park
3. Nilgiri Biosphere Reserve
4. Cryopreservation

Answer: An example of Ex-situ conservation is cryopreservation

Question  15. Which of the following effect is the result of water pollution?

1. Global warming
2. Eutrophication
3. Deafness
4. Bronchitis

Answer: Eutrophication is the result of water pollution

 

Model Question Paper Life Science And Environment Set 1 Group B

2. Answer any 21 questions out of 26 questions given below as instructed. Fill in the blanks with proper words in the following sentences (any five):

Question 1. Due to a deficiency of iodine, the synthesis of ________________ hormone is hampered.
Answer: Thyroxine /T₄/T₃

Question 2. During embryonic development and growth in vertebrates _______________ cell division takes place.
Answer: Mitosis

Question 3. The different _______________ of Pea Plant may show the same phenotype.
Answer: Genotype

Question 4. Homologous organs evolve due to _______________ evolution.
Answer: Divergent

Question 5. The name of one exotic species, that affects the local biodiversity, is _______________.
Answer: Water hyacinth/Parthenium/Tilapia fish.

Question 6. The fine droplets of smoke, ashes, dust, pollen grains etc., suspended in air collectively called _______________, which cause various lung diseases.
SPM or Suspended Particulate Matter.

Decide Whether The Following Statements Are True Or False Any Five:

Question 7. Hypothalamus helps to maintain body balance in humans.
Answer:  False

Question 8. In DNA, Adenine is linked with Guanine by 2.22 In the case of guineapig whether the phenotype hydrogen bonds.
Answer: False

Question 9. In his monohybrid cross experiment, Mendel obtained 75% pure tall Pea Plants in the first filial generation.
Answer: False

Question 10. In Lamarck’s opinion, organisms can acquire any particular inheritable physical trait according to their need.
Answer: True

Question 11. Acid rain is caused by SO₂ and NO₂ gases formed due to air pollution.
Answer: True

Question 12. Auxin helps the seed to germinate by breaking off dormancy.
Answer: False

Match the words in column-A with those which are most appropriate in column B and re-write the correct pair mentioning the serial no. of both columns (any five):

Answers: 13. F, 14. C, 15. E, 16. A, 17. B, 18. G

Answer In A Single Word Or In A Single Sentence Any Six:

Question 19. Choose the odd one and write it: Dwarfism, Goiter, Thalassaemia, Diabetes Mellitus.
Answer: Thalassaemia

Question 20. Mention one function of the lens of the human eyeball.
Answer: The lens creates an image on the retina by the refraction of incident rays of light entering into the eye.

Question 21. A pair of related terms is given below. On the basis of the relationship in the first pair write the suitable word in the gap of the second pair. Mitosis: Radicle::____________: Spore Mother cell.
Answer: Meiosis

Question 22. In the case of guineapig whether the phenotype of the two genotypes bbRR and bbRr is same?
Answer: Yes, the phenotype of the two genotypes bbRR and bbRr will be the same in the case of guineapig.

Question 23. Write the phenotypic ratio obtained in the F₂ generation of Mendel’s Dihybrid cross experiment.
Answer: 9 : 3 : 3: 1

Question 24. Mention one adaptation of the Sundari plant for salt tolerance.
Answer: Salt glands present on the leaves of the Sundari plant help in removing excess salt from the plant body.

Question 25. Among the following four terms one includes the other three. Find out that term and write it: Overall knowledge regarding local biological resources, PBR, Traditional belief regarding local biological resources, Sustainable use of local biological resources.
Answer: PBR

Question 26. Name one endangered animal conserved at Singalila National Park.
Answer: Red panda/Clouded leopard

 

Model Question Paper Life Science And Environment Set 1 Group C

3. Answer any 12 questions in 2-3 sentences out of 17 questions given below.

Question 1. Reflex actions occur when the following incidents happen in the everyday life of humans. Write the importance of these two reflex actions:

1. When food particles enter into the trachea
2. When foreign particles enter inside the nasal cavity
   

Answer:

1. When food particles enter into the trachea, coughing occurs. Through coughing, the food particles are expelled out of the trachea along with pulmonary air.
2. When foreign particles enter inside the nasal cavity, sneezing occurs. Sneezing helps to expel the foreign particle from th6 nasal cavity.

Question  2. For correction of which defects in the vision of the eye, spectacles of convex and concave lenses are used?
Answer:

Spectacles of convex lenses are used in hyperopia and spectacles of concave lenses are in myopia.

Question  3. List the names of the hormones related to the following functions:

1. Regulation of sugar level in blood
2. Stimulation for the secretion of hormones from the Thyroid gland
3. Causing the growth of the Corpus Luteum and stimulating the secretion of Progesterone hormone in the female body
4. Increasing blood pressure due to anxiety

Answer:

1. Insulin and glucagon.
2. TSH or Thyroid Stimulating Hormone.
3. LH or Luteinizing Hormone.
4. Adrenaline or Epinephrine.

Question  4. A resting animal attempts to move. Mention four probable reasons behind it.

Answer:

Driving forces of locomotion;

The driving forces of locomotion are mentioned below.

1. Search of food:

Unlike plants, animals are not capable of synthesising their own food. Therefore animals have to roam around in search of food resources.

2. Escaping predation:

Among animals, prey-predator interaction continues all the time. Here the aggressor is called the predator and the victims are called the prey.

To avoid predation’ prey have to flee from the predator. Therefore, locomotion is essential for prey to escape predation.

3. Migration:

Due to environmental changes, various species move from one place to another this is called migration. To avoid natural calamities, epidemics and other adversities, animals migrate to favourable places. This is a driving force of locomotion.

For example: during rain ants upward in search of a dry habitat.

4. Searching for favourable habitat:

Animals always look out for places with adequate food, water, ambient temperature, light, etc. This is also a purpose of animal locomotion.

5. Searching for a mating partner and favourable mating place:

Animals and a few plants perform locomotion in search of favourable places for reproduction. Animals roam around in searc 1 o suitable mating partners for successful reproduction.

Question 5. Distinguish between autosome and sex chromosome of humans based on the following features:

1. Nature
2. Number

Answer:

Differences between autosome and allosome are—

Question  6. What are the processes of asexual reproduction in Spirogyra and Planaria?

Answer:

Spirogyra mediates their reproduction by fragmentation, whereas planaria make it by regeneration.

Question  7. Mention two changes related to vision and bones at late adulthood or the senescence phase of human development.

Answer:

During adulthood or the senescence phase of human development, some noticeable changes are-

1. Vision: Due to the weakening of eyesight, symptoms of presbyopia can be seen.
2. Bones: Due to the decaying of bones and joints, symptoms of osteoarthritis and osteoporosis can be noticed.

Question  8. With the help of a cross show how the sex of offspring of humans is determined.
Answer:

Differentiate between autosome and allosome.

Question  9. One day students read an article in the newspaper on Thalassemia and were very scared to know the fate of a thalassemic patient. Write what kind of measures they can take to eradicate this disease from the population.

Answer:

The measure they can take to eradicate this disease from the population are-

1. Genetic counselling before marriage and not to conduct marriage between carrier male and female or affected and normal individual.
2. If genetic counselling is not done before marriage then it must be done before conceiving a child and not to conceive in sensitive cases.

Question  10. What are all probable gametes to be produced from the hybrid plant YyRr produced at F₁ generation in a dihybrid cross experiment?

Answer :

The probable gametes to be produced from the hybrid plant YyRr at F₁, generation in a dihybrid cross experiment are four types which are YR, Yr, YR, yr.

Question  11. What are the two adaptive significances of air-sacs of a pigeon?

Answer:

The roles of air sacs in volant adaptation of it needs more supply of oxygen to generate extra pigeons are

1. Pigeon is a volant animals; hence energy during its flight. The air sacs, attached to its lungs, supply extra oxygen and therefore this process enhances the ability of the lungs.
2. These air sacs hold air to reduce the specific gravity of the body during flight.

Question  12. Write the names of one each vestigial organ present in the vertebral column and alimentary canal in the human body.

Answer:

In the human body, the vestigial organ present in the vertebral column is the coccyx and that present in the alimentary canal is the appendix.

Question 13. Write in chronological sequence the names of four main fossil ancestors during the course of the evolution of the horse.

Answer:

Four important features modified in the evolution of horse are-

1. Gradual increase in height,
2. Decrease in the number of digits in both forelimbs and hindlimbs and formation of the hoof,
3. Increase in the size of crown of molar and pre-molar teeth,
4. Increase in volume of the cerebral hemisphere.

Question 14. “Nitrogen cycle is affected due to human activities”-state two phenomena to justify it.

Answer:

Human actions affecting nitrogen cycle:

The human actions affecting the nitrogen cycle are discussed below.

1. Application of nitrogen-rich fertilisers:

Nowadays, farmers apply excess amounts of nitrogen-rich fertilisers in crop fields to increase productivity. Due to this practice, the content of N₂O and NO₂ is rising alarmingly in the atmosphere.

2. Cultivation of nitrogen-fixing plants:

Leguminous plants like gram, peas, lentils, soya beans, etc. are important sources of plant protein. To fulfil the need of protein, different pulses are being cultivated more and more. These plants efficiently absorb nitrogen from the atmosphere and trap it in the soil.

3. Burning of fossil fuel:

Excessive burning of fossil fuels such as mineral oils, coal, etc. increases nitric oxide (NO), nitrous oxide (NO) and nitrogen dioxide (NO₂) in air. It increases the supply of nitrogen in the environment.

Question  15. What would be the environmental consequences as a result of recurrent destruction of wetlands and depletion of a number of agricultural lands?

Answer:

Wetlands are full of biodiversity. These help in removing pollutants from water and also control the local Due environment. overpopulation, civilisation and industrialisation these wetlands are getting destroyed.

As a result, water pollution is increasing and local bio-diversity is decreasing. Due to urbanisation, the quantity of urban land is being depleted.

As a result, worldwide food Due to urbanisation, the quantity of urban land is production is decreasing compared to the increasing human population.

Question 16. What are the harmful impacts sound pollution can exert on the ears and heart in the human body?

Answer:

Adverse effects of noise pollution on man:

The adverse effects of noise pollution on humans are mentioned below.

1. Effect on the ear:

Hearing a high-frequency sound for a prolonged period causes the sound-sensory cells of the organ of Corti inactive. In this case, the person may gradually become deaf. Drivers of metro rail face a similar problem.

A sudden sound of more than 150 dB may rupture the eardrums and may damage the cochlea to cause permanent deafness. Survivors of bomb blasts often face similar consequences.

2. Effect on heart:

1. Hearing high-intensity noise causes excitement which in turn increases heartbeat.
2. Continuous hearing a noise above 90 dB increases systolic pressure.
3. Prolonged listening to a sound above 60 dB may cause myocardial infarction to the listener.
4. Hearing high intensity sound for some time increases the chance of heart attack.

3. Other effects:

1. Noise pollution leads to mental depression.
2. High-intensity sound causes a lack of concentration.
3. It may lead to insomnia.
4. Noise curtails physical ability and enhances fatigue.
5. A person may become ill-tempered with the effect of noise pollution.

Adverse effects of noise pollution on animals

The adverse effects of noise pollution on animals are mentioned below.

1. Deafness:

A high-intensity sound may cause deafness in animals.

2. Hampered reproduction:

The noise changes the reproductive behaviour of many animals. The population of birds and several other animals has shrunk significantly due to noise pollution.

3. Effect on foetal growth:

It is experimentally proved that high-intensity sound restricts foetal development in rats. Speculate the probable causes of each of the following phenomena

Question  17. Mention the roles of biodiversity in the following two aspects in the progress of human civilization:

1. Production of foods
2. Manufacturing of medicines

Answer:

Production of food:

We all depend on nature for food. Nature can give us a wide range of various organisms that meet the need of food. Different food items provide different essential nutrients like-Vitamin, and minerals along with energy.

Other than that a wide range of animal protein are also acquired from poultry and fishery. All these animals and plants are the gift of the biodiversity of nature.

Manufacturing of medicine:

In the early decade. We mainly depended on plants for medicine. A variety of plant species are provided by biodiversity, mainly used for medicinal purposes. Not only plants, many fungi and body parts of animals are also used as medicine.

For example, we get quinine from the cinchona plant; a vital drug for malaria reserpine from the roots of rauwolfia; maintain blood pressure level to normal, daturine from datura prevents hyperventilation etc.

Along with that, holy basil, and margosa plants are also exert their medical value. Fungi like Penicillium notatum is essential for producing penicillin, an antibiotic that fights against a wide range of bacteria. So biodiversity helps to progress overall human welfare and civilization.

 

Model Question Paper Life Science And Environment Set 1 Group D

4. Write the 6 questions or their alternatives given below.

Question  1. Draw a diagram of a reflex arc and label the following parts:

1. Receptor
   Sensory nerve
   Nerve centre
   Motor nerve
   Or,
   Draw the morphology of an ideal eukaryotic chromosome and label the following parts:

Chromatid
Centromere
Nucleolar Organizer
Telomere

Answer:

Functional activities of a simple reflex arc:

If a thorn pricks our sole, we withdraw the foot at once. This is an example of a reflex action. The process of this reflex action occurs in the following way—

1. As the thorn pricks, the receptors in the skin below our soul sense the stimulus.
2. The receptors at once, generate a sensory impulse and sensory or afferent neurone (afferent nerve) carries it to the spinal cord (nerve centre).
3. Immediately, the sensory impulse is modified into a motor impulse and sensory or afferent neurone (afferent nerve) carries it to the spinal cord (nerve centre).
4. Immediately, the sensory impulse is modified into a motor impulse and it is conveyed to the motor or efferent neurone (efferent nerve) by an inter-neurone within the spinal cord.
5. The efferent neurone instantly carries the motor impulse to the leg muscles (effector).
6. The muscles of the leg act at once to lift the foot promptly to avert a deeper prick.

 

or

Answer:

 

 

Question  2. What types of chemical components are synthesized in different stages of Interphase in a cell cycle? What might happen if normal control at different points of a cell cycle is lost?
Or,
Depict the alternation of generation in a fern with the help of a flowchart. “In case of Prophase and Telophase changes of opposite nature happens”-Write two such changes.

Answer:

Different phases of the cell cycle:

The systematic cycle of events, which continuously occurs from the end of a cell division to the end of the next cell division, is called the cell cycle. A cell cycle has two main phases-

1. Interphase:

The longer phase of a cell cycle in which a new daughter cell grows by synthesis of DNA, proteins, RNA etc. and gets all necessary cellular components to become a fully matured cell, ready for division, is called interphase.

This phase is divided into three sub-phases-G₁ or growth-1 phase, S or synthesis phase and G₂ or growth-2 phase.

G₁, or growth-1 phase: It is the primary phase of interphase, where rRNA, mRNA, tRNA, ribosomes and the materials necessary for DNA synthesis are produced. Doubling of various cell organelles occurs in this phase.

S or synthesis phase: This is the intermediate phase between G₁, and G₂ phases. During this phase, the synthesis or replication of DNA and the synthesis of histone proteins occur. Here, the DNA content of a chromosome becomes double.

G₂ or growth-2 phase: It is the last phase of the interphase. In this phase, the proteins, necessary for upcoming cell division, are synthesised.

2. Mitotic phase:

It is the shortest phase of a cell cycle. This phase is divided into two sub-phases-

Karyokinesis, where the nucleus of a cell divides through prophase, metaphase, anaphase and telophase.

Cytokinesis, in which cytoplasm divides to give rise to two daughter cells.

A human needs 20-24 hours to complete a cell cycle, of which 19-23 hours goes for interphase only and 1 hour for the mitotic phase.

Result of the uncontrolled cell cycle:

If for certain reasons, the checkpoints of cell cycle lost its function, then any diseased or torn-out cells can easily proceed towards cell division in an uncontrolled way and thereby give rise to cancer.

or

Answer:

Alternation of generations:

The cyclic alternation between haploid gametophytic and diploid sporophytic generations in the life cycle of any sexually reproducing organism is called the alternation of generation.

Example:

In plants like moss, fern etc. and protists like Paramoecium, Monocystis etc. distinct alternation of generation is seen.

Importance of mitosis in the alternation of generations:

During the alternation of generation, the cyclic rotation continues between haploid (n) and diploid (2n) generations. Diploid spore mother cells divide by meiosis to give rise to haploid spores.

These spores germinate to grow as haploid (n) gametophytes. The gametophytes carry separate gametangia to produce haploid male and female gametes. These gametes fertilise to form diploid zygotes to initiate the sporophytic generation. That is why meiosis is important for the alternation of generations.

Question 3. Colour of seed and shape of seed of a pea plant-taking these two characters Mendel performed a dihybrid cross. Write the genotypes of pea plants having yellow and round seeds produced in the F₂ generation of this experiment. State the law of Independent Assortment of Mendel.
Or,
State the opposite traits for each of the characters of flowers of the pea plant chosen by Mendel for his experiment. “For developing the scientific ideas on heredity the experiments performed by Mendel on peas, and plants are epoch-making.”-Mention three reasons behind his success in performing these experiments.

Answer :

The genotypes of yellow and round seeds of F₂ generation are—

1. YYRR
2. YYRr
3. YyRR
4. YyRr.

Law of independent assortment

Mendel derived this law from the results of his dihybrid cross-experiment. It states that—each pair of alleles segregates independently of other pair of alleles during gamete formation.

In other words, the allele a gamete receives for one gene does not influence the allele received for another gene.

or

Answer :

Opposite traits for the characters of flowers of pea plant chosen by Mendel

 

Question  4. How the special feature of RBC in camels is related to their ability to withstand the extreme loss of water? Give examples of the ways Chimpanzees solve their problems intelligently for procuring food and preventing disease.
Or,
Explain the process of Natural Selection as proposed by Darwin with the help of a suitable example. What are the roles of the swim bladder in the aquatic adaptation of rohu fish?

Answer:

The physiological adaptations of camel:

Camel is one of the best-adapted animals in desert environments. The adaptive features of a camel with respect to the conservation of water and modification of RBC are mentioned below.

1. Adaptive features helping in the conservation of water:

1. The hump on the back of the camel reserves fat, which is oxidised to produce water and energy during their long walk through the desert.
2. Camels discharge highly concentrated urine to conserve water.
3. A camel can drink up to 36 litres of water at a time, which is stored in the water reservoir cells of its stomach.
4. The mucous membrane of the nasal passage absorbs moisture from the air that the camel exhales.
5. Body temperature of the camel changes in accordance with the external temperature, which reduces perspiratory water loss, even at a high temperature of 49° Celsius.

2. Adaptive modifications of RBC:

The RBCs of camel are very small and oval in shape. This modification facilitates the movement of these blood cells through finer blood capillaries even at very low water content in plasma.

When plasma contains adequate water, the RBCs of camels can expand up to about 240 times of its normal size, by absorbing water by endosmosis. These cells can withstand a high osmotic pressure and do not rupture even after the intake of a huge quantity of water at a time.

or

Answer:

Natural selection:

Natural selection means the selection of a suitable organism in an environment by nature itself. According to Darwin, organisms acquire either favourable or unfavourable variations during their struggle for existence.

Those with favourable variations are selected by the nature. They can adapt perfectly with its environment and come out victorious in the struggle for life. They thrive successfully and propagate quickly.

On the other hand, the organisms, which have unfavourable variation, do not get the favour of natural selection and cannot adapt themselves in their environment. The population of these forms reduces gradually and finally, becomes extinct.

For example, in an ecosystem, some giraffes have long necks and others have short necks. If a situation arises, where there is scarcity of low-lying shrubs, the giraffes with short necks would not get enough food. After a few generations, all the giraffes would have long necks.

Drawbacks of Darwinism:

1. Darwin mentioned the role of variation in evolution but could not explain the sources of it.
2. Darwin emphasised on small variations but in reality, small variations play no role in the origin of species.
3. Darwin supported the concept of survival of the fittest, however, he could not explain the cause of the emergence of the fittest.
4. According to Darwin, excessive development of any organ facilitates evolution but it is seen that over-specialisation often pushes a species towards extinction.
5. Darwin did not differentiate between somatic and reproductive variations.
6. During natural calamities, even the fittest organisms also die, where natural selection does not operate.

Question  5. ‘A lot of indiscriminate activities of humans pollute environment-Support the statement by giving three examples in favour of it. Give examples of a national park and a biosphere reserve situated in West Bengal.
Or,
Show the steps of the Nitrogen Cycle with the help of a flowchart.

Answer:

Three examples in favour of the statement:

A lot of indiscriminate activities of human beings pollute the environment in large scale. These are-

1. Combustion of fossil fuels causes an excessive increase in the level of greenhouse gases which in turn result global warming.
2. Excessive use of chemical fertilisers and pesticides causes soil pollution.
3. Industrial sewage, oil spill, etc. create water pollution. These examples justify the statement correctly.

Different types of pollution:

Based on the nature of the environmental resources, pollution can be classified into four types. These are-

1. Air pollution,
2. Water pollution,
3. Soil pollution and
4. Noise pollution.

or,

Answer:

Nitrogen cycle:

The nitrogen cycle is a bio-geochemical process which involves different phases, which are-nitrogen fixation in soil, entry of nitrogen from soil into living organisms, return of nitrogen from organisms to soil, and liberation of nitrogen in the atmosphere. The phases are explained in the next section.

1. Nitrogen fixation:

By this process, atmospheric nitrogen is trapped in the soil. This occurs by three different processes, which are-

Natural N₂ fixation:

During lightning, a huge amount of heat is generated in the atmosphere, when nitrogen and oxygen react gradually to produce nitric oxide (NO) and nitrogen dioxide (NO₂).

When rainwater mixes with atmospheric nitrogen dioxide two acids, namely nitrous acid (HNO₂) and nitric acid (HNO₃) are produced. The reactions are given below-

N₂+O₂ → 2NO,  2NO+O₂ → 2NO₂, 2NO₂ + H₂O → HNO₂ + HNO₃

These two acids then react with the minerals present in soil and form nitrates (potassium nitrate, calcium nitrate, etc.).

Biological fixation:

Biological nitrogen fixation is done in the following ways-

1. Soil-dwelling nitrifying bacteria like Azotobacter sp., Clostridium sp., etc. absorb atmospheric nitrogen and trap it in their cells. When these bacteria die, the nitrogenous compounds mix in the soil.
2. Cyanobacteria like Anabaena sp. and Nostoc sp. absorb nitrogen from the atmosphere and add it to the soil.
3. Rhizobium sp. present in root nodules of leguminous plants traps atmospheric nitrogen and converts it into nitrogenous compounds. With the death of the host plants, these compounds mix in the soil to increase its nitrogen content.

Industrial fixation:

In fertilizer industries, different nitrogen-rich fertilizers are produced. By the Haber-Bosch method, N₂ and H₂ are made to react at 300-400°C under 35-100 MPa (Mega Pascal) pressure to produce NH₃.

This NH₃ and other nitrogen-rich fertilisers when added to soil increases the nitrogen content.

2. Entry of nitrogen from soil into living organisms:

Plants absorb soluble nitrogenous salts from the soil through their roots. This nitrogen takes part in synthesizing plant proteins. Animals get nitrogen either directly or indirectly by consuming plants.

Finally, plant proteins are transformed into animal proteins and remain in the animal bodies.

3. Return of nitrogen from organisms to soil:

Nitrogen returns from the body of organisms to the soil through two different steps. These are-

Ammonification:

The ammonifying bacteria (Bacillus mycoides, Micrococcus sp., etc.) act upon dead animal and plant bodies and the excretory materials to convert the nitrogenous compounds in it into ammonia. This is called ammonification.

Nitrification:

Certain nitrifying bacteria convert ammonia into nitrates through two steps of reaction.

1. Nitritation-In the first step, Nitrosomonas sp. converts ammonia and ammonium ions into nitrites.
2. Nitratation-In the next step, soil-dwelling Nitrobacter sp. transforms nitrites into nitrates.

2NH₄⁺+3O₂ → 2NO₂^–+ 4H⁺ + 2H₂O,   2NO₂^–+O₂ → 2NO₃

4. Liberation of nitrogen into the atmosphere or denitrification:

In this phase, several bacteria act upon nitrites and nitrates in the soil and liberate free nitrogen into the atmosphere. This biochemical process is called denitrification. Pseudomonas sp., Thiobacillus sp., etc. are a few bacterial species, which help in denitrification.

2NO₃^–  → 2NO₂^–, → NO + N₂O → N₂

 

 

Question  6. What environmental factors may cause cancer in humans? If the water level in the sea increases enormously due to global warming, what problems the humans and the biodiversity of Sunderban may face?
Or,
Mention the in-situ measures adopted for the conservation of lions in Gir National Park of India. What environmental problems may arise in a locality due to the ever-increasing human population?

Answer:

Problems of Sundarban:

In recent days Sundarban is facing many environmental problems. These are mentioned below.

1. Loss of mangrove forest due to urbanisation:

Population pressure has initiated urbanisation. Due to this, many areas along the periphery of Sundarban are deforested.

2. Agricultural problem:

Due to soil erosion and siltation, the depth of rivers becomes shallow. During high tide saline water spills over, floods the agricultural fields to make the soil salty and infertile.

3. Scarcity of fresh water:

The estuarine water is salty. Frequent flood makes inland water bodies like ponds and wells saline. Therefore, sweet water is becoming scarce in the Sundarban area.

4. Destruction of natural habitat:

Deforestation is reducing the natural habitats of large to small animals. As a result, the biodiversity of Sundarban is gradually getting destroyed.

5. Pollution:

The most provocative problem for Sundarban is increasing pollution. All rivers are disposing of gallons of pollutants in the water. Several pollutants are percolating in the soil of the Sundarban area making the soil infertile and toxic.

The oil and grease, spilling from fishing and tourist vessels are polluting the aquatic environment of this area. This pollution is affecting the propagation of fish, prawns and other aquatic animals.

6. Imbalance in the prey-predator ratio:

Due to overpopulation and pollution, the number of many animal species has declined. This has resulted in to an imbalance in the prey-predator ratio. The scarcity of natural food compels tigers to enter into human localities in search of food.

7. Rise in water level:

Due to global warming, the glaciers of the polar region are melting. This results in to an increase in sea water level. As a result, the delta of Sundarban is going under seawater.