WBBSE Class 10 Life Science And Environment Model Question Paper 2023 Set 2

Model Question Paper Life Science And Environment Set 2 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. Select which of the following statement is correctly related to tropic movement-

  1. It is controlled by the intensity of the stimulus
  2. The overall change of place takes place by a plant or part of the plant
  3. This movement is observed in the algae called Volvox
  4. It is an induced movement of curvature controlled by the direction of the stimulus

Answer: 4. The correct statement related to tropic movement is—it is an induced movement of curvature controlled by the direction of the stimulus.

Question 2. Read the following sentences and identify the sentence which is not correct-

  1. AFSH, LH and Prolactin are different types of GTH
  2. Adrenaline decreases cardiac output
  3. Insulin facilitates the absorption of glucose into the cell through the cell membrane
  4. Progesterone helps in the formation of the placenta in the female body

Answer: 2. The statement which is not correct is— Adrenaline decreases cardiac output.

Question 3. Determine the number of Cranial nerves in human body-

  1. 10 Pairs
  2. 12 Pairs
  3. 31 Pairs
  4. 21 Pairs

Answer: 3. The number of cranial nerves in human body is 12 pairs.

Question 4. Identify the correct feature of Amitosis cell division-

  1. Occurs in germ mother cell of sexually reproducing organism
  2. It is called indirect cell division
  3. Chromosome and Spindle fibre are formed
  4. Chromosome and Spindle fibre are not formed

Answer: 4. The correct feature of amitosis cell division is—chromosome and spindle fibre are not formed.

Question 5. Determine which of the following statement is correct regarding the significance of meiosis-

  1. It results in overall growth and development of the body
  2. It results in the growth of reproductive organs and embryo of the organism
  3. It produces haploid gamete containing hereditary variations
  4. It regenerates the organ in the body of some animals if it is lost

Answer: 3. The correct statement regarding the significance of meiosis is—it produces a haploid gamete containing hereditary variations.

Question 6. Select the correct pair and write it-

  1. Multiple fission-Hydra
  2. Fragmentation-Spirogyra
  3. Regeneration-Fern
  4. Budding-Planaria

Answer: 2. The correct pair is—Fragmentation— Spirogyro.

Question 7. Identify which of the following is a dominant trait-

  1. Length of the stem-Dwarf
  2. The shape of the seed-Wrinkled
  3. Colour of the cotyledon-Yellow
  4. Colour of the flower-White

Answer: 3. The dominant trait is—the colour of the cotyledon—Yellow.

Question 8. Assess how many types of gametes are produced from the Pea plant having the genotype RRYY-

  1. One type
  2. Two types
  3. Four types
  4. Three types.

Answer: 1. The pea plant having the genotype RRyy will produce one type of gametes.

Question 9. Select which of the following two genotypes are responsible for the expression of the phenotype wrinkled yellow in Pea plants-

  1. ARRYY and rryy
  2. RRyy and Rryy
  3. BRRYY and RrYy
  4. rrYY and rrYy

Answer: 4. rrYY and rrYy are two genotypes responsible for the expression of the phenotype wrinkled yellow in the Pea plant.

Question 10. Identify which of the following indicates inter-specific struggle-

  1. The struggle among the members of guppy fish for feeding on mosquito larvae
  2. The struggle between snakes and owls for capturing rats for eating
  3. Struggle within a group of deer for feeding on grass at the same location
  4. The struggle between tigers in a jungle for preying on deer

Answer: 2. Struggle between snakes and owls for capturing rats for eating indicates inter¬specific struggle.

Question 11. Determine the term related to the theory of Lamarck-

  1. Struggle for existence
  2. Origin of variation
  3. Inheritance of acquired characters
  4. Natural selection

Answer: 3. The term related to the theory of Lamarck is—Inheritance of acquired characters.

Question 12. Identify the animal who communicates information with other members of its own group through specific dancing patterns regarding the sources of food-

  1. Chimpanzee
  2. Peacock
  3. Cockroach
  4. Honeybee

Answer: 4. Honey bee communicates information with other members of its own group through specific dancing patterns regarding the sources of food.

Question 13. Decide which of the following if remains for a long time in the environment, the probability of its biomagnification increases-

  1. Newspaper
  2. Faecal matters of animals
  3. Rotten leaves
  4. Chlorinated insecticide

Answer: 4. Chlorinated insecticide if remains for a long time in the environment, the probability of its biomagnification increases.

Question 14. Gorumara, Corbett, Kulik, and Nandadevi choose the correct sequence from the following which is correct for the above forests in sequence-

  1. Biosphere Reserve, Sanctuary, National Park, National Park
  2. National Park, National Park, Biosphere Reserve, Sanctuary
  3. National Park, National Park, Sanctuary, Biosphere Reserve
  4. Sanctuary, Biosphere Reserve, National Park, Sanctuary

Answer: 3. The correct sequence for Gorumara, Corbett, Kutik, and Nandadevi forests is— National Park, National Park, Sanctuary, Biosphere Reserve.

Question 15. If the amount of pollen grains, fungal spores and dust particles increase suddenly in the air, decide which of the following problems may increase-

  1. Tuberculosis
  2. Malaria
  3. Asthma
  4. Dengue

Answer: 2. If the amount of pollen grains, fungal spores and dust particles increase suddenly in the air, problem of asthma will increase.


Model Question Paper Life Science And Environment Set 2 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. By the influence of _______ was the aggregate of some large colloidal molecules during the early phase of the origin of life. hairs on the skin get erected an emergency situation.
Answer: Adrenaline

Question 2. A chromosome is the condensed coiled structure of _______ molecule.
Answer: DNA

Question 3. The sexual reproduction that occurs among two genotypically different organisms belonging to the same species, is called _______.
Answer: Hybridization

Question 4. _______ was the aggregate of some large colloidal molecules during the early phase of the origin of life.
Answer: Coacervate

Question 5. _______is derived from the root of the Sarpagandha plant which is used as medicine for lowering high blood pressure
Answer: Reserpine

Question 6. The ex-situ conservation by keeping sample seeds in liquid nitrogen at a temperature of -196°C is called _______.
Answer: Cryopreservation

Decide whether the following statements are true or false (any five):

Question 7. Dilute urine is profusely eliminated by a person affected with Diabetes Insipidus.
Answer: True

Question 8. The Carpel of flowering plants collects pollen grains with the help of a hairy and sticky style.
Answer: False

Question 9.A pair of sex-determining sex chromosomes are present in the ovum of humans.
Answer: False

Question 10. According to Darwin organisms reproduce at geometric ratios.
Answer: True

Question 11. One-horned rhinoceros is conserved at Manas National Park of West Bengal.
Answer: True

Question 12. Acetylcholine and adrenaline are neurotransmitters.
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):

WBBSE Model Question Paper 2019 Life Science And Environment Set 2 Match The Columns

Answer: 13. C, 14. F, 15. A, 16. B, 17. D, 18. E,

Answer in a single word or in a single sentence (any six):

Question 19. Choose the odd one and write it: Glossopharyngeal, Oculomotor, Trigeminal, Oxytocin
Answer: Oxytocin

Question 20. What is the function of the fluid present in the intermediate chamber between the lens and retina of the eyeball?
Answer: Vitreous humor is the fluid present in the intermediate chamber between the lens and retina of the eyeball i.e. vitreous chamber, which helps to form images by refracting the light rays and also maintains the shape of the eyeball.

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. Grafting: Mango:: _________ : China Rose
Answer: Stem cutting

Question 22. What is the cause of expression of haemophilia disease only at homozygous conditions?
Answer: Haemophilia is an X-linked recessive disease so it is expressed in females in the homozygous condition (XhXh) and in males in the hemizygous condition (XhY). The female in heterozygous condition (XhXh+) is a carrier for the disease and phenotypically normal, so the disease is not expressed in her body.

Question 23. Write the genotypic ratio obtained at 2nd filial generation in the monohybrid experiment done by Mendel.
Answer: Pure tall: hybrid tall: dwarf =1:2: 1.

Question 24. Which type of evolution is indicated by homologous organs?
Answer: Divergent evolution

Question 25. Among the following four terms, one includes the other three. Find it out and write it: Pesticides used in Agriculture, Typhoid, Water Pollution, liquid wastes from factories.
Answer: Water pollution

Question26. In which type of in-situ conservation practice, the diversity, culture and lifestyle of humans is preserved along with microorganisms, wild animals and wild plants?
Answer: Biosphere Reserve


Model Question Paper Life Science And Environment Set 2 Group C

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

Question 1. Illustrate with the help of a word diagram the nervous pathway of the way you will open the door by hearing the door bell.


When someone rings the bell at the door, we listen to the bell with our ears and open die door. In this case, the receptors present in our ear receive the stimulus and send it to the central nervous system (CNS).

CNS processes that stimulus and sends motor signals to our body parts (muscles of hands and legs) and as a result, we open the door.


WBBSE Solutions For Class 10 Life Science And Environment Chapter 1 Response And Physical Co-Ordination In Animals Nervous Nervous pathway


Question 2. State the locations of Meninges and CSF.



Meninges is located just outside the brain and spinal cord as a membranous outer covering.


The functions of meninges are as follows

  1. Meninges protects the central nervous system from injury and infection.
  2. Capillaries of the meninges supply blood to the skull and cerebral cortex.

The functions of CSF or cerebrospinal fluid are as follows

  1. CSF supplies nutrients and oxygen to the neural cells of the central nervous system.
  2. It also acts as a cushion to protect the brain and spinal cord against external shocks and pressure.

Question 3. What influences gibberellin hormone exerts on the seeds and internode of plants? Explain.


Types of gibberellins:

The chemical name of gibberellin is gibberellic acid (GA). There are about 40 different types of gibberellins isolated from different plants. Some of the common types are GA3, GA7, GAp, etc.

Role of gibberellin in plants:

Gibberellins play different roles in the plant bodies, which are mentioned below.


WBBSE Solutions For Class 10 Life Science And Environment Chapter 1 Response And Chemical Co Ordination In Plants Hormones Role of gibberellin in internodal growth


1. Breaking dormancy of seed and bud:

For a certain period, the sign of life is not visible in seeds. This phase is called dormancy of seed. During the dormant stage, the seed contains less gibberellin.

Just before germination, the gibberellin level elevates in it. This phytohormone increases the activity of enzymes in the seed and helps in breaking its dormancy and facilitates germination.

2. Promoting the growth of internodes:

Gibberellin increases the rate of cell division in the intercalary meristem. Due to this, the internodes of the stem increase in length, and thus, the overall height of the plant increases.

3. Increasing the size of the fruit:

Gibberellin quickens the growth of fruits and thus, increases their size. A synthetic form of gibberellin also helps in the formation of seedless or parthenocarpic fruits. Seedless tomatoes, apples, pears, grapes, etc. can be produced by gibberellin treatment.

4. Increasing the size of leaves and flowers:

Gibberellin enhances cell division to increase the size of leaves and flowers.

Question 4. Write the names of the different refractive mediums of eyeballs in proper sequence.


The refractive mediums of the eyeball from outside to inside are—cornea → aqueous humour→lens→vitreous humour.

Question 5. During the meiosis cell division, a reduction in the number of chromosomes and exchange of segments between chromatids take place- Analyse what are the significance of these two phenomena.


During meiotic division, the number of chromosomes gets reduced from 2n to n for gamete formation. Because during fertilization two cells get fused with each other and form Zygote (2n).

So if these cells have contain 2n chromosomes then the zygote will possess 4n number of chromosome, that is not impossible for the existence of an organism. For that reason, the gamete should contain only half the number of chromosomes (n).

This reduction in chromosome number is only possible because of meiotic division. Another important phenomenon is an exchange of segments between two chromatids.

This exchange can play an important role in genetic recombination, that will give rise to variation in the new progeny. This variation is most important for the newly formed progeny because it helps them tp with the changed environment and to survive. this has an ultimate effect on evolution.

Question 6. Distinguish between asexual and sexual reproduction on the basis of the following features:

  1. Number of Parents
  2. Nature of offspring


Principle of micropropagation:

Certain plant cells have a unique ability to grow into a full plant body by means of cell division. This unique ability of plant cells is known as totipotency. Micropropagation is a tissue culture technique, which depends upon totipotency.

The word ‘micro’ means ‘very small. In micropropagation, very small portions are collected from vegetative parts of a plant and are cultured in a proper culture medium inside the laboratory to produce saplings.

Differences between asexual and sexual reproduction

WBBSE Solutions For Class 10 Life Science And Environment Chapter 2 Reproduction Differences between Asexual and Sexual reproduction

Question 7. Identify the stages of Karyokinesis of mitotic cell division depending on the following features:

  1. Alignment of chromosomes along the equator of the cell and their arrangement in a definite pattern
  2. The disintegration of spindle fibres
  3. The disappearance of nuclear membrane and nucleolus
  4. Movement of daughter chromosomes to the opposite poles of the cell


  1. Alignment of chromosomes along the equator of the cell and their arrangement in a definite pattern-Metaphase
  2. The disintegration of spindle fibre-Telophase
  3. The disappearance of nuclear membrane and nucleolus-Prophase
  4. Movement of daughter chromosomes to the opposite poles of cell-Anaphase

Question 8. To establish the law of segregation in the case of the Pea plant, you are asked to select characters. Write two such characters having opposite traits.

Answer :

WBBSE Solutions For Class 10 Life Science And Environment Chapter 3 Mendel's Laws And Their Deviation Characters having oppisite traits


Question 9. A daughter is born to a woman carrier for the colour-blind disease who married a colour-blind man. What would be the probability of expression of colour blindness in that girl child? Analyse your answer.



WBBSE Solutions For Class 10 Life Science And Environment Chapter 3 Some Genetic Diseases Carrier colour blind woman and man


Checker board

WBBSE Solutions For Class 10 Life Science And Environment Chapter 3 Some Genetic Diseases Checker board.


Colour blind girl =  ½ x 100 = 50%

There will be a 50% chance of the daughter being colour-blind. This is because the X chromosome that she will obtain from her father will definitely bear an allele for colour blindness.

However, the X chromosome that she will obtain from her mother may either bear the allele for colour blindness or that for normal vision. So, she has a 50% chance of being colour-blind.

Question 10. Write the name of two genetic diseases which are expressed in human populations.

Two genetic diseases expressed in the human population are-

  1. Thalassemia and
  2. Haemophilia.

Question 11. Tigers are extinct but there are many deer in the jungle. A few tigers are brought from another sanctuary and released in such a jungle. Imagine and write the names of different kinds of struggles for existence those tigers have to be involved in.


The tigers, brought from another sanctuary, have to face mainly two types of struggle for existence.

These are-

Inter-specific struggle:

They have to get involved in an inter-specific struggle with deer for food.

The struggle against nature:

Firstly, the tigers will face difficulty in adjusting with the new environment and secondly, as the number of deer is high in that jungle, the jungle will be devoid of bushes which generally provide hiding space to tigers during hunting sessions.

Question 12. Describe any two adaptations in the Sundari Plant for tolerance of salt.

The mechanisms used by the Sundari plant to excrete the excess salt from its body are-

  1. Presence of a salt gland in the leaf to excrete excess salt along with water,
  2. Deposition of excess salt in specialized cells of bark and root; later, by means of bark exfoliation and other specific mechanisms, the salt are eliminated from the plant body,
  3. Deposition of salt in mature leaves, in larger amounts, so that it can be eliminated easily by leaf exfoliation,
  4. Deposition of excess salt in the cell sap of vacuoles and eliminate it when needed.

Question 13. Explain how do the chimpanzees hunt termites for food.

Importance of behaviour in evolution:

Organisms show neurally controlled reactions in response to any visual, auditory or olfactory signals or any stimulus, like light, sound, smell or any action by other organisms. These responses are called behaviour.

The favourable behaviours which help an organism to survive and propagate on earth, are selected by nature. The effect of these behaviours is so far-reaching that it may help in the course of evolution.

WBBSE Solutions For Class 10 Life Science and Environment Chapter 4 Adaptation Eating of leaves by Chimpanzee

Adaptive behaviours of chimpanzees:

  1. Chimpanzees break branches of trees and then eat up the leaves to prepare a stick. With the stick, they make a hole in a termite mound. Then, they insert the thin stick into the mound to tease the termite colony inside it. As soon as the termites grab the probing stick, chimpanzees pull it out and lick them up. Few termites, which come out through the hole are eaten up by other chimpanzees. This particular behavioural adaptation of chimpanzees is known as termite fishing.
  2. When a chimpanzee is attacked by parasites, it starts eating medicinal plants. Scientists revealed that chimpanzees can recognise and consume 19 different medicinal plants including Aspilia rudis, when attacked by parasites.
  3. To crack hard nutshell, wild chimpanzees use a piece of rock as an anvil and a strong branch of the tree as a hammer. They keep hard-shelled nuts on the rock and then hammer it with the woody branch to crack it. Finally, they remove the shell and eat the nut inside.

WBBSE Solutions For Class 10 Life Science and Environment Chapter 4 Adaptation Termite fishing by Chimpanzee

Question 14. List the harmful effects of the following pollutants:

  1. Greenhouse gas
  2. SPM
  3. Chemical fertilizers used in agriculture
  4. Non-biodegradable chemical insecticide


The harmful effects of some pollutants are as follows-

WBBSE Solutions For Class 10 Life Science And Environment Chapter 5 Topic 2 Environmental Pollution Harmful effects of some pollutants

Question 15. Give one example of exotic species causing damage of local biodiversities in each of terrestrial and aquatic ecosystem.

In aquatic ecosystems, the exotic species that damage the local biodiversity is-water hyacinth. In terrestrial ecosystems, the exotic species that damage the local biodiversity is American. cockroach.

Question 16. Write the in-situ conservation measures taken for one endangered reptile species and name one site of such conservation in West Bengal.

One endangered reptile is a crocodile. Measures taken for the in-situ conservation of crocodiles are-

  1. Protect the remaining population of crocodilians in their natural habitat by creating sanctuaries.
  2. Promote captive breeding.
  3. Prevent poaching of crocodiles and as well as their eggs.

The name of such conservation in West Bengal is the Bhagabatpur crocodile project, Sundarban.

Question 17. “Poaching is one of the fundamental causes of endangeredness of animal diversity in India”-Assess four causes for which animals are poached in India.

Four causes of poaching are-

  1. Some animals are mainly killed for their skins and bones, for example, elephants are killed for ivory, and tigers are killed for their bones and skins.
  2. Some animals like deer, pigs, bulls are poached for meet the needs of meat.
  3. The body parts of some animals are also used for medicinal purposes and for home. decor.
  4. Illegally traded items fetch lucrative prices, that encourage poachers to look out for more money.


Model Question Paper Life Science And Environment Set 2 Group D

4. Answer 6 questions or their alternatives given below.

Question 1. Draw a neat diagram of the neurone and label the following parts:

  1. Dendron
  2. Node of Ranvier
  3. Myelin sheath
  4. Schwann cell


Structure of a typical neurone:

A typical neurone has two structural components—

  1. Cell body or cyton and
  2. Projections.

1. Cell body or cyton:

The structural features of the cell body of a neurone is as follows—

  1. The largest, round or star-shaped portion of the neurone is called the cell body.
  2. The cell body contains thick protoplasm, called neuroplasm, surrounded by a cell membrane.
  3. This cell bears a distinct nucleus within it
  4. Neuroplasm contains different cell organelles like mitochondria, Golgi bodies, etc. Other than these, numerous typical nucleoprotein granules, called Nissl granules are present in the neoplasm.
  5. Fine thread-like neurofibrils remain scattered within the neoplasm.
  6. The centrosome is present in an inactive state, therefore, neurones cannot undergo mitosis.


WBBSE Solutions For Class 10 Life Science And Environment Chapter 1 Response And Physical Co-Ordination In Animals Nervous Structure of neurone


2. Projections:

The projections of a neurone are of two types

  1. Axon and
  2. Dendron.

The structural features of these two projections are given below.


The structural features of the axon is as follows—

  1. The longer and unbranched protoplasmic projection of a neurone is called an axon.
  2. Axon emerges from a conical portion of the cell body, called the axon hillock.
  3. The semi-liquid cytoplasm present in the axon is called axoplasm, which is externally lined by a cell membrane called axolemma.
  4. Axoplasm does not contain Nissl granules.
  5. In several neurones, the axon has an extra lipid-rich insulating coat outside the axolemma, called myelin sheath.
  6. The myelin sheath has a number of periodic gaps, which are called nodes of Ranvier.
  7. A few tiny nucleated cells remain associated with myelin sheath, these are known as Schwann cells.
  8. The neurones with myelin sheath are called medullated nerve fibres whereas the axons having no myelin sheath are called non-medullated nerve fibres.
  9. Axon terminally gives off a few fine branches, this portion is called the end brush. The end of each branch swells to form a synaptic knob or end button.


The structural features of dendron is as follows—

  1. The shorter and branched protoplasmic projection of a neurone is known as a dendron. Branches of dendrons are known as dendrites.
  2. The base of each dendrone is wide but it gets terminally finer and branched.
  3. Neuroplasm, neurofibrils and Nissl granules are present in the dendron, but it does not have any myelin sheath.

Draw a neat diagram of anaphase of mitosis of an animal cell and label the following parts:

  1. Polar region
  2. Spindle fibre
  3. Chromatid
  4. Centromere.


Anaphase of mitosis in plant and animal cells:

The third phase of karyokinesis, in which the daughter chromosomes move from the equatorial plate towards the two opposite poles of the dividing cell, is called anaphase. The events which occur during this phase, in both plant and animal cells, are discussed below.

1. Anaphase in plant cells:

The events occurring during anaphase, in plant cells, are as follows-

  1. The Centromere of each chromosome splits longitudinally, as a result, two sister chromatids separate from each other with their own share of centromere and emerge as two daughter chromosomes.
  2. The Centromere of each daughter chromosome remains attached to the chromosomal spindle fibre.
  3. Inter-polar or Chromosomal continuous spindle fibres connect the two poles of the -spindle fibre spindle.
  4. Gradually, the chromosomal fibres contract. -Chromatid to pull half of the daughter chromosomes towards one separation Inter-zonal pole and the remaining half to the opposite pole. This is a spindle fibre called anaphasic movement.
  5. During anaphasic, movement, metacentric, sub-metacentric, acrocentric and telocentric chromosomes appear like the English letters ‘V’ ‘L’, ‘J’ and ‘I’ respectively, based on the position of centromere on the chromosome.


WBBSE Solutions For Class 10 Life Science And Environment Chapter 2 Mitotic And Meiotic Cell Division Anaphase in plant cell


2. Anaphase in animal cells:

The above-mentioned events also occur during anaphase in animal cells. Here, inter-zonal spindle fibres cluster in between separating chromosomes to form columnar stem bodies, which help in anaphasic movement.


WBBSE Solutions For Class 10 Life Science And Environment Chapter 2 Mitotic And Meiotic Cell Division Anaphase in animal cell


Question 2. Why reproduction is important for an organism? “Meiosis is characteristically different from Mitosis”-how would you justify the statement”?


Common features of reproduction:

Different phases of reproduction involve mitosis, meiosis or both the processes of cell division. From gametogenesis to the embryonic development of a progeny, cell division is required in every phase.

  1. The molecular basis of reproduction is DNA replication.
  2. An offspring is formed through the union of gametes, germination of spores or division of vegetative cells.

Significance of reproduction:

The significance of reproduction are as follows.

1. Increasing population size:

By means of reproduction, new individuals are born. As a result, the number of individuals in a population increases and the race of a species is maintained.

2. Maintaining the flow of genes:

By reproduction, the genes of a species flow from one generation to the next maintaining the hereditary characteristics.

3. Maintaining ecological balance:

Natural or unnatural death of individuals reduces the population size of a species. By reproduction, this loss is replenished in nature. This process keeps the ratio of different species in an ecosystem constant and thus maintains the ecological balance.

4. Variation:

By sexual reproduction, different genetic variations come into existence. These variations assist any species to adapt in its surroundings and finally help in the evolution of new species.

Meiosis is called as reduction division:

In meiosis, the chromosome number of a diploid mother cell reduces to its half to give rise to a haploid number of chromosome-bearing daughter cells. Thus, meiosis is called reduction division.

Differences between mitosis and meiosis:

WBBSE Solutions For Class 10 Life Science And Environment Chapter 2 Mitotic And Meiotic Differences between mitosis and meiosis

Describe five processes of asexual reproduction with one suitable example for each.


Processes of asexual reproduction:

The following types of asexual reproduction can be seen in organisms-

1. Fission:

In most of unicellular organisms, two or more offspring are produced through mitosis or amitosis. This process is called fission. Some examples are given below.

1. Amoeba:

Binary fission:

In favourable conditions, the nucleus of Amoeba undergoes amitotic division and gives of two nuclei. Its cytoplasm divides longitudinally creating a furrow and forms two offsprings.

Multiple fission:

In unfavourable conditions, the pseudopodia of Amoeba are destroyed and the body gets encapsulated by a cyst wall. Inside the cyst, numerous small spores are formed through multiple fission of the nucleus and cytoplasm.

This type of multiple fission is called sporulation. When the condition becomes favourable, spores come out rupturing the cyst wall and giving rise to new Amoeba offspring.

2. Plasmodium:

In the case of Plasmodium, multiple fission takes place in two stages-Schizont and sporont. In the stomach of female Anopheles mosquito, numerous Plasmodium offsprings are born by the multiple fission called schizogony and sporogony is the schizont and sporont stages respectively.

The Plasmodium offsprings born through schizogony and sporogony are called merozoite and sporozoite respectively.

2. Budding:

Budding is a type of asexual reproduction in which a new organism develops from an outgrowth or bud of the parent body due to cell division at one particular site. Some examples of budding are given below.


Due to the unequal division of the yeast parent cell, a small outgrowth or bud is formed which contains the parent’s nucleus. Later on the bud separates from the parental body and develops into new yeast.

In special cases, the bud of yeast divides many times in the torula stage through the Formulation process and forms mycelium.


In the case of Hydra, the bud is formed outside the parent body (exogenous bud). After the formation of the oral aperture, tentacles, etc. when the offspring matures, it gets detached from the parent body.

3. Fragmentation:

The type of asexual reproduction where the parent body is fragmented into two or more pieces and each fragment turns into new offspring, is called fragmentation.


The filamentous body of Spirogyra, an alga gets fragmented due to water currents or external damage. Each fragment undergoes mitotic cell division and gives rise to new offspring.

4. Regeneration:

The type of asexual reproduction where a mere body part of a parent organism creates a new offspring, is called regeneration. It is also called morphallaxis.


If any body part of Planaria, a flatworm gets detached, it forms a new offspring. This process also can be seen in Hydra.

5. Sporulation:

Sporulation is a type of asexual reproduction in which unicellular spores are produced in moss, fern and fungi, they are dispersed and give birth to new offspring. Examples of sporulation are given below.


In fungi, spores with different structures and with or without motility can be seen. These spores germinate in favourable conditions and new fungi are born. Different types of spores are motile zoospores, non-motile aplanospores, thick-walled chlamydospores, oidia, and conidia formed from fragments of filaments, sporangiospores formed in sporangium.

Moss and Fern:

Spores are formed from the sporophytic tissue of the sporophytic plant body of moss. In the sporangium of the sporophytic plant body of fern, spores with similar or different shapes are formed.

Question 3. Show the result of hybridization till F2 generation between a pure black (BB) coarse-haired (RR) guinea pig and a pure white (bb) smooth-haired (rr) guinea pig by a checkerboard. State the conclusion one can reach from this hybridization experiment.

Answer :

Dihybrid cross in Guineapig


WBBSE Solutions For Class 10 Life Science And Environment Chapter 3 Mendel's Laws And Their Deviation Pure black and white coare haired guinea pig

F1………… Hybrid black and coarse-haired guinea pig.


WBBSE Solutions For Class 10 Life Science And Environment Chapter 3 Mendel's Laws And Their Deviation Hybrid black and coarse haried guiena pig


Checker board of F2 generation

WBBSE Solutions For Class 10 Life Science And Environment Chapter 3 Mendel's Laws And Their Deviation Checker board of F2 generation


Phenotype and genotype of F2 generation

WBBSE Solutions For Class 10 Life Science And Environment Chapter 3 Mendel's Laws And Their Deviation Phenotype and genotype of F2 generation


In a cross between pure black and coarse-haired guinea pig and pure white and smooth-haired guinea pig all the F1 individuals will be black and coarse-haired guinea pig because these are dominant traits.

Each of the F1 individuals can produce four types of gametes and their cross produce four types of individuals in a ratio of 9:3:3:1.


The conclusion that can be reached from this hybridisation experiment i.e. —when two organisms with two or more characters with their opposite phenotypes are crossed then the characters not only get separated but remain expressed in all possible combinations independent to each other.

What symptoms are expressed in a child affected with Thalassaemia? What suggestions are given at the time of genetic counselling in such cases?


Symptoms of thalassemia affected child:

  1. Continuous fatigue or weakness,
  2. Shortness of breath,
  3. Yellowing of skin and eyes,
  4. Slow growth and abdominal swelling,
  5. Facial bone deformities and anaemia,
  6. Dark colouration of urine

The suggestions are given at the time of genetic counselling

  1. Not to conduct marriage between carrier male and female.
  2. Not to conduct marriage between thalamic male and normal or carrier female or vice-versa.
  3. Must rest for genetic diseases before marriage or child planning

Question 4. Describe the brief outline of the chemical origin of life mentioning Miller and Urey’s experiment.


The experiment of Miller and Urey:

Based on the concept of chemosynthesis of life, proposed by Oparin and Haldane, Stanley Miller and Harold Urey performed an experiment in 1953 in the laboratory of Chicago University.

1. Procedure:

They prepared a highly heat-resistant instrument with two inter-connected chambers of unequal diameters. The larger chamber was fitted with two electrodes and was filled with a mixture of hydrogen, methane and ammonia gases.

The outlet pipe of the larger chamber was fitted with a cooling device and a tap which was used to tap down the contents from it. The smaller chamber was used as a boiler and a connecting pipe was fitted with it to supply vapour to the larger chamber.

Powerful electric sparks were generated in the larger chamber to mimic the lightning-like situation (that prevailed in the primitive atmosphere). The water of the smaller chamber was boiled by heating it externally, thus the newly formed water vapour is pushed into the larger chamber.

The machine was run continuously for one week and the product from the larger chamber was tapped down after condensation.


WBBSE solutions For Class 10 Life Science And Environment Evolution Concepts Of Evolution Experimental set up of Miller and Urey


2. Observation:

After analysing the product, scientists found a number of amino acids, viz. glycine, alanine, glutamic acid, aspartic acid, etc. in it.

3. Conclusion:

From the result, Miller and Urey concluded that in the primitive, free oxygen-lacking, reducing atmosphere, different inorganic matter reacted with each other to synthesize organic substances.

In this reaction, heat, lightning, ultraviolet ray and other cosmic rays provided the energy that was needed. The organic matter, thus synthesized, acted as the building blocks of cells and finally helped in the origin of life.

Significance of Miller and Urey’s experiment:

Miller and Urey’s experiment supports the abiogenetic theory of the origin of life. According to this theory, life was originated from abiotic or inorganic substances around 3.7 billion years ago.

Describe two major tenets of Lamarck’s evolutionary theory. How the comparative anatomy of hearts act as a proof in favour of evolutionary theory?


Lamarckian concept of evolution:

In 1809, Lamarck proposed the concept of organic evolution in his famous book, titled ‘Philosophie Zoologique. This concept is popularly known as Lamarckism.

Lamarckism is based on the following basic propositions.


WBBSE Solutions For Class 10 Life Science And Environment Chapter 4 Evolution Theories Of Organic Evolution Lengthening of giraffe's neck


1. Internal vital force:

An internal vital force or energy in all life forms helps in the development of the body and organs.

2. Development of new organs according to need:

With the change in environment, a need develops among the organisms for morphological and behavioural change. Newly developed organs help the organisms to adapt in the changing environment.

3. Law of use and disuse:

Any organ, which is used more, grows in size and strength, whereas, that which is used less, reduces in size, becomes weak and finally becomes extinct.

Example of use of organ:

Ancestors of giraffes had short necks. To collect the leaves of taller plants, they stretched their necks continuously. This conscious effort made their necks long and eventually, giraffes with longer necks evolved.

Example of disuse of organ:

The ancestors of snakes had limbs. While adapting to the fossorial habitat, their limbs were left unused. Finally, limbs. of snakes were lost during the course of evolution.

4. Inheritance of acquired characters:

Any change in the characteristics of an organism, which an organism achieves by conscious effort, is inherited by its offspring.

5. Formation of new species:

The characters acquired during the lifetime are passed onto the progeny and after a number of generations, new species is produced.

To get leaves from tall trees, ancestors of giraffes stretched their necks. By this process, one might have lengthened it a little, which was inherited directly by its offspring.

This process continued for several thousand generations and finally completely different-looking long-necked giraffes emerged as a new species from their ancestors.

Comparative anatomical evidence in support of organic evolution:

A comparative study on related groups of organisms, clearly reveals the basic structural similarity among few of their organs. It also indicates the evolutionary trend of those organisms.

Here, comparative studies on some organs of different groups of vertebrates are mentioned below.

1. Heart of vertebrates:

The basic structure of the hearts of fishes, amphibians, reptiles, birds and mammals is similar. All of them have an auricle as the blood-receiving chamber and a ventricle as the chamber that expels blood from the heart. However, in the course of evolution, the hearts of different vertebrates encountered some changes.

The heart of fish has one auricle and one ventricle and thus carries only deoxygenated blood along a single circuit. Amphibians have two auricles and one ventricle in their heart. Here, oxygenated and deoxygenated blood get mixed in the ventricle.

Apart from two auricles, the reptilian heart has a partially divided ventricle, in which partial mixing of oxygenated and deoxygenated blood occurs (exception-crocodile has a four-chambered, double-circuit heart).

Hearts of birds and mammals have two auricles and two ventricles. Therefore oxygenated and deoxygenated blood flow through separate circuits.


WBBSE Solutions For Class 10 Life Science And Environment Chapter 4 Evolution Evidence For The Theory Of Evolution Structure of heart of vertibrates



The above-mentioned evidence proves that advanced and complex forms of animals have evolved from primitive and simple forms. The gradual development of the heart and circulatory system of different vertebrates point towards the evolutionary trend as mentioned below.

Fishes → Amphibians → Reptiles → Birds and mammals

2. Forelimbs of different vertebrates:

The basic skeletal structures of the forelimbs of whales, bats, birds, horses and men are all alike. All possess humerus, radius-ulna, carpals, metacarpals and phalanges.

However, these animals use their forelimbs in different ways to adapt in different environments. As whale uses its forelimbs for swimming, birds and bats use them for flying. The horse runs with the help of their forelimbs and man use them for grasping.


This evidence strongly indicates that all vertebrates have evolved from a single ancestor but diverged from each other to adapt in separate environments.

Question 5. Analyse the role of bacteria at any three steps of nitrogen cycle. “Luxurious and comfortable lifestyle is one of the major reasons of air pollution”-Support the statement with arguments.


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.

WBBSE Solutions For Class 10 Life Science And Environment Chapter 5 Nitrogen Cycle Industrial fixation

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-


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.


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


WBBSE Solutions For Class 10 Life Science And Environment Chapter 5 Nitrogen Cycle Nitrogen in to the atmosphere or denitrification

Explanation to support the statement:

‘Luxurious and comfortable lifestyle is one of the major reasons of air pollution-this statement can be well supported and explained by the facts, like-

  1. CFC used in refrigerators and air conditioners caused global warming, destroys the ozone layer and renders the harmful effects of UV rays on the environment to increase.
  2. Methane gas produced during natural gas extraction causes global warming.
  3. Different oxides of sulphur, nitrogen and smoke from agricultural and industrial field enhances the chances of acid rain and causes different respiratory disorder.

Reason of the increase of methane in the atmosphere:

Methane is produced due to the partial combustion of certain organic matters, putrefaction of dead plants and animals in wetlands and emission from coal mines. These processes increase the percentage of methane in the atmosphere.

Give two examples of animal biodiversity endangered by the pollution of the river Ganga. Explain any three incidences which are occurring as a result of disruption of the nitrogen cycle.


Two examples of animal biodiversity endangered by the pollution of river Ganga are-

  1. Gangetic dolphin and
  2. Gharial.

Human actions affecting the nitrogen cycle:

The human actions affecting the nitrogen cycle are discussed below.

1. Application of nitrogen-rich fertilizers:

Nowadays, farmers apply an excess amount of nitrogen-rich fertilizers 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 (N2O), and nitrogen dioxide (NO2) in the air. It increases the supply of nitrogen in the environment.


WBBSE Solutions For Class 10 Life Science And Environment Chapter 5 Nitrogen Cycle Root nodules of pea plant


Adverse effects of excess nitrogen in the atmosphere due to human activity:

The adverse effects of excess nitrogen in the atmosphere, due to human activity, are mentioned below.

1. Global warming:

Nitrous oxide (N2O) is a potent greenhouse gas. Accumulation of this gas in air arrests more heat in the atmosphere and causes global warming.

2. Acid rain:

Oxides of nitrogen present in the atmosphere mix with rainwater to produce nitrous and nitric acids. These acids come down on earth as acid rain, which acidifies soil and water bodies to cause serious environmental pollution.

3. Photochemical smog:

Nitric oxide (NO), released as automobile exhaust, reacts with atmospheric hydrocarbons in the presence of sunlight. This reaction produces a polluting gas, named PAN (Peroxy-acetyl nitrate).

It mixes with smoke and creates a very harmful photochemical smog. This reduces visibility through air, and causes inflammation of the respiratory tract and various other respiratory diseases.

Question 6. “Change of climate and global warming is a problem resulting from the increasing human population”-Summarise what impacts it might exert on the environment. “Children and adults both suffer with different respiratory problems during the winter”-Write two names of such problems and state one symptom of each of them.


Effect of change of climate and global warming on the environment:

Change of climate and global warming is a problem resulting from the increasing human population. Their effects on the environment are as follows-

  1. Due to the increased level of greenhouse gases in the environment, the number of atmospheric components are being changed. These gases increase global temperature, as a result, polar ice is melting. Polar bears, polar foxes, etc. are becoming endangered as they are losing their habitats.
  2. Due to global warming, sea water level is increasing, as a result, land areas near the sea are getting submerged.
  3. The ecosystem is being destroyed due to global warming, biodiversity is also being decreased. The example-Great barrier reef of Australia is depleting gradually.
  4. Climate change is causing harm to agriculture which in turn causing scarcity of food.
  5. In altered temperatures, harmful germs are getting more active and causing diseases.

Two respiratory problems during winter were found in children and adults

WBBSE Solutions For Class 10 Life Science And Environment Chapter 5 Environment And Human Population respiratory problems during winter

You have identified three environmental problems while on research in Sunderbans-

  1. Disbalance in prey-predator number
  2. Destruction of mangrove plants due to urbanization
  3. Submergence of islands due to rising sea level. Analyse what impacts they might exert on biodiversity. Write the location of the Sundaland hotspot and one important species of its biodiversity.


Problems of Sundarban:

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

1. Loss of mangrove forest due to urbanization:

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


WBBSE Solutions For Class 10 Life Science And Environment Chapter 5 Importance Of Biodiversity Destruction of mangrove foreset in Sundaraban


2. Agricultural problem:

Due to soil erosion and siltation, the depth of rivers becomes shallow. During high tide saline water spills over, and 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 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 into an increase in sea water level. As a result, the delta of Sundarban is going under seawater.

One of the most important biodiversity hotspots Sundaland is located in Southeastern Asia, and comprises of the landmass of Malay, Java, Sumatra, Peninsula, Bali, Borneo, Andaman, and Nicobar islands.

The important species of Sundaland is-Sundari plant (plant) or Orangutan (animal).

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