NCERT Exemplar Solutions for Class 12 Biology Chapter 1: Reproduction in Organisms

Subject specialists of Infinity Learn have created NCERT Exemplar Solutions for Class 12 Biology Chapter 1: Reproduction in Organisms, which includes thorough solutions for reference. All of the unsolved questions from the textbook’s exercises are answered here. The NCERT Exemplar Solutions for Class 12 provide useful solutions for improving conceptual knowledge and help in entrance examinations like JEE mains and NEET.

The solutions are carefully solved using student-friendly terms while still adhering to the norms that must be followed when solving NCERT Exemplar Solutions for Class 12. Practising these answers can be incredibly advantageous not only in terms of exams but also in terms of helping Class 12 pupils perform well in upcoming competitive exams.

The approaches for answering have been given special consideration to stay on target while not deviating from the intended answer. Because time is so important in exams, excellent time management when answering questions is essential for getting the best results.

Class12_Biology_Chapter1(DE-81)

Exercise:

Question 1: A few statements describing certain features of reproduction are given below:

1. Gametic fusion takes place
2. Transfer of genetic material takes place

iii. Reduction division takes place

1. Progeny have some resemblance with parents

Select the options that are true for both asexual and sexual reproduction from the options given below:

1. i and ii
2. ii and iii
3. ii and iv
4. i and iii

Answer: Correct Option C

Transfer of genetic material takes place and progeny have some resemblance with parents are the two features from the given option that are true for both asexual and sexual reproduction. Reproduction is a biological process in which the genetic material of the parents has to be passed on to the offspring, whatever the mode of reproduction. So passing of genetic material from parents to offspring occurs in both modes of reproduction due to which progeny have some resemblance with their parents.

 

Question 2: The term ‘clone’ cannot be applied to offspring formed by sexual reproduction because:

1. Offspring do not possess exact copies of parental DNA
2. DNA of only one parent is copied and passed on to the offspring
3. Offspring are formed at different times
4. DNA of parents and offspring are completely different.

Answer: Correct Option A

Clones are an exact copy of their parents because they carry the same genetic material as their parents carry. In the case of sexual reproduction, offspring do not possess exact copies of their parental DNA. Offspring produced as a result of sexual reproduction carries half genetic material from the mother and half genetic material from the father, hence we can not use the term clone for the offspring produced from the sexual reproduction.

 

Question 3: Asexual method of reproduction by binary fission is common to which of the following?

1. Some eukaryotes
2. All eukaryotes

iii. Some prokaryotes

1. All prokaryotes

Choose the correct option from the following:

1. i and ii
2. ii and iii
3. i and iii
4. iii and iv

Answer: Correct Option C

There are many types of reproduction, out of which asexual reproduction is found in some prokaryotic masses and some in eukaryotic. Binary fishing and boarding are also forms of asexual reproduction.

 

Question 4: A few statements with regard to sexual reproduction are given below:

1. Sexual reproduction does not always require two individuals
2. Sexual reproduction generally involves gametic fusion

iii. Meiosis never occurs during sexual reproduction

1. External fertilisation is a rule during sexual reproduction

Choose the correct statements from the options below:

1. i and iv
2. i and ii
3. ii and iii
4. i and iv

Answer: Correct Option B

In some cases, both sexes are present in an individual, and in some of those cases, both the gametes of the same individual have been involved in fertilization, e.g. We can observe self-pollination in many flowering plants and hermaphrodite organisms both sexes are present in individual so for sexual reproduction in hermaphrodite animals there is no need for two individual. Fusion of gametesis an important process in sexual reproduction.

 

Question 5: A multicellular, filamentous alga exhibits a type of sexual life cycle in which the meiotic division occurs after the formation of zygote. The adult filament of this alga has

1. Haploid vegetative cells and diploid gametangia
2. Diploid vegetative cells and diploid gametangia
3. Diploid vegetative cells and haploid gametangia
4. Haploid vegetative cells and haploid gametangia.

Answer: Correct Option A

A multicellular, filamentous alga exhibits a type of sexual life cycle in which the meiotic division occurs after the formation of zygote. The adult filament of this alga has haploid vegetative cells and diploid gametangia. This type of alga produces different types of progeny which are similar to their parents and may look different from them.

Question 6: The male gametes of rice plants have 12 chromosomes in their nucleus.

The chromosome number in the female gamete, zygote and the cells of the seedling will be, respectively,

1. 12, 24, 12
2. 24, 12, 12
3. 12, 24, 24
4. 24, 12, 24.

Answer: Correct Option C

The chromosome number in the female gamete in

Female gamete:12

Zygote: 24

Cells of the seedling:24

The number of chromosomes in the male gamete of the rice plant is n=12, so the number of chromosomes in the female gamete will also be 12. The zygote is diploid as it is the product of fertilization and the seeding cells will be meiocytes and other diploid cells. Hence, the number of chromosomes in both zygote and seed cells are 24.

 

Question 7: Given below are a few statements related to external fertilization. Choose the correct statements.

1. The male and female gametes are formed and released simultaneously
2. Only a few gametes are released into the medium

iii. Water is the medium in a majority of organisms exhibiting external fertilization

1. Offspring formed as a result of external fertilization have better chance of survival than those formed inside an organism
2. iii and iv
3. i and iii
4. ii and iv
5. i and iv

Answer: Correct option B

Fertilization that takes place outside the female body is known as external fertilization. In external fertilisation, the male and female gametes are formed and released simultaneously in large amounts. Most organisms that perform external fertilization release their gametes in water, so water is the medium in a majority of organisms exhibiting external fertilization. Offspring formed as a result of internal fertilization have a better chance of survival than those formed outside an organism

 

Question 8: The statements given below describe certain features that are observed in the pistil of flowers.

1. Pistil may produce more than one seed
2. Each carpel may have more than one ovule

iii. Each carpel has only one ovule

1. Pistil has only one carpel

Choose the statements that are true from the options below:

1. i and ii
2. i and iii
3. ii and iv
4. iii and iv

Answer: Correct Option A

The gynoecium is that female part of the flower, a unit of which is called a pistil. A pistil may have one or more carpels (monocarpellary, carpellary, etc.). Each carpel may contain more than one egg.

 

Question 9: Which of the following situations correctly describe the similarity between an angiosperm egg and a human egg?

1. Eggs of both are formed only once in a lifetime
2. Both the angiosperm egg and human egg are stationary

iii. Both the angiosperm egg and human egg are mobile

1. Syngamy in both results in the formation of zygote

Choose the correct answer from the options given below:

1. ii and iv
2. iv only
3. iii and iv
4. i and iv

Answer: Correct Option B

The feature that is similar in human egg and angiosperm egg is the formation of the zygote due to syngamy. Human eggs are always reproductively active and angiosperm eggs are mostly active during their reproductive phase, so they produce eggs more than once not. During ovulation, human eggs are transferred to the uterus, so they are not immobile but angiosperms eggs always stay in the ovule.

 

Question 10: Appearance of vegetative propagules from the nodes of plants such as sugarcane and ginger is mainly because:

1. Nodes are shorter than internodes
2. Nodes have meristematic cells
3. Nodes are located near the soil
4. Nodes have non-photosynthetic cells

Answer: Correct Option B

Asexual reproduction takes place in different plants in this way and different types of progeny are formed in it. Each road produces more than one saint. Thus we can say that the second option of this question is correct.

So, the correct answer is ‘Nodes have meristematic cells’.

Question 11: Which of the following statements, support the view that elaborate sexual

The reproductive process appeared much later in organic evolution.

1. Lower groups of organisms have a simpler body design
2. Asexual reproduction is common in lower groups

iii. Asexual reproduction is common in higher groups of organisms

1. The high incidence of sexual reproduction in angiosperms and vertebrates

Choose the correct answer from the options given below:

1. i, ii and iii
2. i, iii and iv
3. i, ii and iv
4. ii, iii and iv

Answer: Correct Option C

Very simple body design found in primitive types of animals i.e. in older animals. Asexual reproduction occurs mainly in creeper primitive organisms because they do not have the production of ho in the age for sexual reproduction. Again, sexual reproduction is found in some plants and animals and this is the main reason for the present.

So, the correct answer is (i), (ii) and (iv).

 

Question 12: Offspring formed by sexual reproduction exhibit more variation than those formed by Asexual reproduction because:

1. Sexual reproduction is a lengthy process
2. Gametes of parents have a qualitatively different genetic composition
3. Genetic material comes from parents of two different species
4. Greater amount of DNA is involved in sexual reproduction.

Answer: Correct Option B

Asexual reproduction is also a type of reproduction in which different types of institutions are formed, but due to the lack of sexual reproduction, the pair is not formed due to which fertilization did not take place. Recommendations are formed without fertilization.

So, the correct option is ‘the gametes of the parents have qualitatively different genetic structures’.

 

Question 13: Choose the correct statement from amongst the following:

1. Dioecious (hermaphrodite) organisms are seen only in animals
2. Dioecious organisms are seen only in plants
3. Dioecious organisms are seen in both plants and animals
4. Dioecious organisms are seen only in vertebrates

Answer: Correct Option C

Dioecious organisms are found in both males and females and in plants and animals. Thus we can say that the third option of this question is correct.

So, the correct answer is Dioecious organisms are seen in both plants and animals

 

Question 14: There is no natural death in single celled organisms like Amoeba and bacteria because:

1. They cannot reproduce sexually
2. They reproduce by binary fission
3. Parental body is distributed among the offspring
4. They are microscopic

Answer: Correct Option C

There is no natural death in single-celled organisms such as amoeba and bacteria. This is because, due to asexual reproduction, the body of the parent cell divides into daughter cells. So, there is no practical death in amoeba and bacteria.

 

Question 15: There are various types of reproduction. The type of reproduction adopted by an organism depends on:

1. The habitat and morphology of the organism
2. Morphology of the organism
3. Morphology and physiology of the organism
4. The organism’s habitat, physiology and genetic makeup

Answer: Correct Option D

The type of reproduction adopted by an organism depends on the habitat, physiology and genetic structure of the organisms. Habitat determines the type of reproduction such that if the organism lives in a habitat that supports mating or promotes cross-fertilization or cross-pollination it undergoes sexual reproduction, whereas if the habitat is self-pollinated Supports and restricts mating so asexual reproduction occurs.

Physiology is also governing factor for sexual or asexual reproduction. For example, if male or female sex organs mature at different times, unfertilized gametes develop into an individual by parthenocarpy which is a form of asexual reproduction. Sexual reproduction occurs if the male or female genitals mature at the same time.

 

Question 16: Identify the incorrect statement.

1. In asexual reproduction, the offspring produced are morphologically and genetically identical to the parent
2. Zoospores are sexual reproductive structures
3. In asexual reproduction, a single parent produces offspring with or without the formation of gametes
4. Conidia are asexual structures in Penicillium

Answer: Correct Option B

A zoospore is a motile asexual spore that uses the flagellum for locomotion. Also called a swarm spore, these spores are produced by some protists, bacteria, and fungi to propagate themselves.

So, the correct option is ‘zoospores are sexual reproductive structures.

 

Question 17: Which of the following is a post-fertilisation event in flowering plants?

1. Transfer of pollen grains
2. Embryo development
3. Formation of flower
4. Formation of pollen grains

Answer: Correct Option B

The events of sexual reproduction after fertilization are called post-fertilization events. After fertilization, all sexually reproducing organisms form a diploid zygote. The process of development of the embryo from zygote is called embryogenesis.

So, the correct answer is ‘Embryo development.

 

Question 18: The number of chromosomes in the shoot tip cells of a maize plant is 20.

The number of chromosomes in the microspore mother cells of the same plant shall be:

1. 20
2. 10
3. 40
4. 15

Answer: Correct Option A

In maize plants, microspore mother cells and shoot tip cells are both diploid.

The number of chromosomes in the shoot tip cell is

 

Very Short Answer Type Questions

Question 1: Mention two inherent characteristics of Amoeba and Yeast that enable them to reproduce asexually.

Answer: Two inherent characteristics of Amoeba and Yeast that enables them to reproduce asexually is:

• It is a unicellular organism
• They have simple organization thus reproduce rapidly

 

Question 2: Why do we refer offspring formed by asexual method of reproduction as clones?

Answer:

A clone is a group of genetically and morphologically similar individuals. As asexual reproduction involves only one parent and there’s no fusion of male and female gamete, So the offspring produced are genetically and morphologically similar to each other and to the parent. Hence they are referred to as clones.

 

Question 3: Although potato tuber is an underground part, it is considered as a stem. Give reasons.

Answer:

Potato tuber is an underground part, but it is considered as stem because:-

• The tuber has nodes as well as internodes
• Scaly leaves are present in the nodes

 

Question 4: Between an annual and a perennial plant, which one has a shorter juvenile phase? Give one reason.

Answer:

Juvenile phase is the growth phase of an organism that lies between after the birth and before it reaches reproductive maturity. The entire life of an annual plant is shorter and has to be completed in one growing season, but that of a perennial plant grows throughout the year. Hence the juvenile phase of the annual plant is shorter.

 

Question 5: Rearrange the following events of sexual reproduction in the sequence in which they occur in a flowering plant:

Embryogenesis, Fertilization, Gametogenesis, Pollination.

Answer:

The events of sexual reproduction in sequence in which they occur are as:-

• Gametogenesis, Pollination, Fertilization, Embryogenesis

The gametogenesis is the phase where the gametes are formed in their respective flowers. Then by the medium of wind or insect or water, the male gamete moves in the air and falls on the stigma, this is termed as Pollination. If the pollen or male gamete is compatible then it penetrates the stigma wall forming a pollen tube and then fertilizes the ovule, and then an embryo is formed which is known as Embryogenesis.

 

Question 6: The probability of fruit set in a self-pollinated bisexual flower of a plant is far greater than a dioecious plant. Explain.

Answer:

A self-pollinated plant doesn’t depend on any kind of pollinating agent from different plants. It can fertilize using its own gamete. On the other hand, a dioecious plant depends only on pollinating agents for Fertilization to happen, which leads to fruit set. But sometimes the pollinating agents are not available due to different factors such as: – excessive use of pesticides leading to a decrease in the number of insects. As a result of which fruit set is unable to form. So the probability of fruit set is greater in a bisexual plant than in a dioecious plant.

 

Question 7: Is the presence of a large number of chromosomes in an organism a hindrance to sexual reproduction? Justify your answer by giving suitable reasons.

Answer:

The presence of a huge number of chromosomes in a living organism is not a hindrance to sexual reproduction. The chromosome number has no effect on the mode of reproduction.

For example:-there are 380 chromosomes in the somatic cell of a butterfly and 8 chromosomes in the somatic cell of a fruit fly and both of them reproduce sexually. Another example is Ophioglossum, a fern that has 1260 chromosomes and reproduces sexually.

 

Question 8: Is there any relationship between the size of an organism and its lifespan? Give two examples to support your answer.

Answer:

There is no relationship between the size of an organism and its life span. For example- the mango tree and Peepal tree are both similar in size but the mango tree has a shorter duration as compared to peepal.

Another example is parrot and crow. Both have the same size but a parrot lives for more than 100 years and that of a crow is 10-15 years. So it is very clear that there is no relationship between the size of an organism and its life span.

 

Question 9: In the figure given below the plant bears two different types of flowers marked ‘A’ and ‘B’. Identify the types of flowers and state the type of pollination that will occur in them.

Answer:

‘A’ is a dioecious flower while ‘B’ is a cleistogamous flower. A bisexual flower that opens normally is called a chasmogamous flower. Cleistogamous flowers do not open at all.

Cleistogamous flowers are always autogamous because there is no possibility of cross-pollination landing on the stigma.

In a normal flower that opens and exposes anthers and stigmas, complete self-marriage is rare. Chasmogamous flowers may show autogamy, geitonogamy or xenogamy.

Question 10: Give reasons as to why cell division cannot be a type of reproduction in multicellular organisms.

Answer:

Most multicellular organisms have complex organizations. Especially those animals that show the tissue level and the level of organization of the organ system. It is not possible for a single cell to form different tissues by mitosis alone. Therefore, cell division cannot be a type of reproduction in multicellular organisms.

Question 11: In the figure given below, mark the ovule and pericarp.

Answer:

1. After fertilization, the zygote develops to form an embryo. The ovule develops into the seed.
2. Pericarp develops from the wall of the ovary. It protects the seed.

Question 12: Why do gametes produced in large numbers in organisms exhibit external fertilisation?

Answer:

In the case of external fertilization the gametes are completely at the mercy of the environment. Gametes can be blown away by the wind, washed away by water, or eaten by predators. So, most of the gametes are destroyed before fertilization. To ensure the survival of the species, it is necessary to produce as many gametes as possible so that at least some of them can undergo fertilization. Therefore, organisms that exhibit external fertilization produce a large number of gametes.

 

Question 13: Which of the following are monoecious and dioecious?

1. Earthworm
2. Chara
3. Marchantia
4. Cockroach

Answer: Correct Answer: a. Earthworm – Monoecious, b. Chara – Monoecious, c. Marchantia – Dioecious, d. Cockroach – Dioecious.

Terms such as homothallic and monoecious are used to represent the bisexual conditions in male and female reproductive structures in the same plant, whereas the terms like heterothallic and dioecious are used to indicate unisexual conditions in male and female reproductive structures on separate plants, but not in animals. Individuals which are either male or female are usually known as unisexual and the individual which possesses both the male and female reproductive organs are known as bisexual.

Question 14. Match the following given in Column ‘A’ with the vegetative propagules given in column ‘B’.

Col. A Col. B

1. Bryophyllum a) offset
2. Agave b) eyes
3. Potato c) leaf buds
4. Water hyacinth d) bulbils

Answer: Correct Answer:

Column A	Column B
Bryophyllum	leaf buds
Agave	bulbils
Potato	eyes
Water hyacinth	offset

Bryophyllum buds are known as epiphyllous buds. The leaves of this plant are utilized for vegetative propagation in a natural way. In the case of agave, the flower buds are modified into bulbils and, when it is shed from the mother plant, develop into new plants. In the case of potatoes, the tuber is the swelling tip of an underground branch and each tuber has many notches on the surface known as ‘eyes’. Water Hyacinth propagation by offsets. An offset is a short thick runner like the branch which develops into a new plant at its tip.

Question 15: What do the following parts of a flower develop into after fertilization?

• Ovary

• Ovules

Answer:

(a) Ovary develops into Fruit

(b) Ovules develop into Seeds

The zygote develops into the embryo after fertilization, while the ovules develop into a seed. The ovary develops into the fruit, which has a thick, protective wall known as the pericarp. The event of fertilization takes place when one of the sperm cells fuses with the egg inside an ovule. Each ovule develops into a seed after fertilisation. Each seed contains an embryo, which is a tiny, undeveloped plant. The ovary that surrounds the ovules develops into a fruit with one or more seeds.

 

Short Answer Type Questions

Question 1: In haploid organisms that undergo sexual reproduction, name the stage in their life cycle when meiosis occurs. Give reasons for your answer.

Answer:

In the haploid organisms undergoing sexual reproduction, meiosis occurs in their zygote stage because:-

• Zygote, after fertilisation, has a 2n number of chromosomes in which meiosis is possible.
• In haploid organisms, n number of chromosomes is necessary for their normal life cycle, therefore the zygote needs to reduce its chromosome number.

Question 2: The number of taxa exhibiting asexual reproduction is drastically reduced in higher plants(angiosperms) and higher animals(vertebrates) as compared with lower groups of plants and animals. Analyse the possible reasons for this situation.

Answer: The number of taxa exhibiting asexual reproduction is drastically reduced in higher plants(angiosperms) and higher animals(vertebrates) as compared with lower groups of plants and animals because:-

• As we move to the higher and advanced forms of plants and animals, their bodies become complex and sexual dimorphism occurs. Hence, the males and females undergo mutual attraction and perform sexual reproduction.
• The process of evolution requires variation in the hierarchy of classification which is fulfilled by sexual reproduction.

Question 3: Honeybees produce their young only by sexual reproduction. In Spite of this, in a colony of bees we find both haploid and diploid individuals. Name the haploid and diploid individuals in the colony and analyse the reasons behind their formation.

Answer:

Haploid individuals are male as drones. Diploid individuals are sterile females as workers and one female as queen.

Reason: Both haploid and individuals are the result of both sexual reproduction and parthenogenesis. Fertilized eggs (Zvgote) give rise to females (Both workers and queens) by the process of sexual reproduction and unfertilized eggs give rise to male individuals (Drones) by the process of parthenogenesis.

 

Question 4: With which type of reproduction do we associate the reduction division? Analyse the reasons for it.

Answer:

Meiosis is associated with sexual reproduction. In sexual reproduction, fertilization involves the fusion of two gametes. To ensure continuity of characters in a species. It is necessary to develop some mechanism by which the number of chromosomes can be haploid in gametes so that zvgote could be diploid. Hence, gametogenesis involves reduction division so that the gametes have a haploid number of chromosomes.

Question 5: Is it possible to consider vegetative propagation observed in certain plants like Bryophyllum, water hyacinth, ginger etc., as a type of asexual reproduction? Give two/three reasons.

Answer:

Yes, Vegetative propagation in certain plants (like Bryophyllum, Eichhornia crassipes, Ginger etc.) is contemplated as asexual reproduction, because

1. Offspring get the set of DNA from a single parent i.e., reproduction is uni-parental.
2. Meiosis (reduction division) doesn’t happen throughout any stage of division.
3. Production of new individuals does not involve the formation and fusion of gametes.
4. Offspring is genetically and morphologically similar to its parent.

Yes, Vegetative propagation in certain plants (like Bryophyllum, Eichhornia crassipes,

Ginger etc.) is contemplated as asexual reproduction.

Reasons:

1. Offspring get the set of DNA from a single parent i.e., reproduction is uni-parental.

2. Meiosis (reduction division) doesn’t happen throughout any stage of division.
3. Production of new individuals does not involve the formation and fusion of gametes.
4. Offspring is genetically and morphologically similar to its parent.

 

Question 6: ‘Fertilisation is not an obligatory event for fruit production in certain plants’. Explain the statement.

Answer:

There are some other methods from which fruit can be developed without fertilization. Some fruits are developed from infertile ovaries known as Parthenocarpic fruits. These are seedless fruits Eg. Pomegranate Banana Grapes etc. Flowers are sprayed with some hormones to become fruits however the ovules of such fruits fail to develop seeds. Hence, Fertilization isn’t an obligatory event for fruit production in certain plants.

 

Question 7: In a developing embryo, analyse the consequences if cell divisions are not followed by cell differentiation.

Answer:

During embryogenesis or the stage of developing the embryo, the embryo undergoes the process of mitosis. Cell division can start at any stage of the embryogenesis after which if the differentiation of the cell does not occur then the cells which are remained as cell mass are not grouped into different tissues or organs.

 

Question 8: List the changes observed in an angiosperm flower subsequent to pollination and fertilisation.

Answer:

Following are the changes which take place in an Angiosperm flower after the process of pollination and fertilization:

• The primary endosperm cell gives rise to endosperm.
• The sepals, petals and stamens wither and ultimately fall off
• Zygote develops into the embryo and ovule develops into the seed
• Integuments develop into seed coats.
• Ovary develops into fruit
• Fruit develops a thick outer covering; called pericarp.

 

Question 9: Suggest a possible explanation why the seeds in a pea pod are arranged in a row, whereas those in tomato are scattered in the juicy pulp.

Answer:

Placentation is responsible for arranging the seeds in a fruit. A pea flower shows marginal placentation, the placenta in marginal placentation’s makes a ridge across through the ventral suture of the ovary, ovules are attached on the ridge to form two rows. The tomato shows axile placentation. In axile placentation, the placenta is on a central axis and ovules are attached to it. Therefore, due to the difference in placentation in pea pods, seeds are arranged in a row while, in tomatoes, they are scattered within the juicy pulp.

 

Question 10. Draw the sketches of a zoospore and a conidium. Mention two dissimilarities between them and at least one feature common to both structures.

Answer:

Dissimilarities:

Zoospores	Conidia
These are motile spores	These are non-motile spores
They are produced within the sporangium	They are produced at the tip of conidiophores, exogenously

The common feature between both structures is that they are involved in asexual reproduction.

 

Question 11: Justify the statement ‘Vegetative reproduction is also a type of asexual reproduction’.

Answer: The above-mentioned statement is that vegetative reproduction is also a type of asexual reproduction is true because

1. A new plant is produced only from the somatic cells of the parent plant.
2. In vegetative reproduction, only a single parent is involved and there is no gamete formation.
3. The process of reduction division does not occur in this.
4. Offspring produced are clones of their parents.
5. The chromosome number remains constant.
6. No genetic variations in the progeny are observed.

 

Long Answer Type Questions

Question 1. Enumerate the differences between asexual and sexual reproduction. Describe the types of asexual reproduction exhibited by unicellular organisms.

Answer:

Asexual Reproduction	Sexual Reproduction
a) Zygote formation is absent.	a) Zygote formation is present (fusion of gametes)
b) Single parent is involved (uniparental).	b) Two parents are involved (biparental)
c) Somatic cells helps in asexual reproduction.	c) Germ cells are involved in this reproduction.
d) Only mitotic division of cells occurs.	d) Meiosis is observed during gamete formation.
e) Offspring is a clone of the parent.	e) The offspring show variation.

Asexual reproduction by unicellular organisms:

Asexual reproduction is a process in which a single-celled organism is involved and offsprings are produced by cell division.

• Binary fission is a mode of asexual reproduction in which the cell divides into two cells and each one rapidly grows into an adult. This mode is seen in Paramecium and Amoeba.
• Budding is another mode of asexual reproduction that is observed in yeast. Small buds are attached to the parent body and as it matures, it detaches itself and grows into another adult organism.

Question 2: Do all the gametes formed from a parent organism have the same genetic composition (identical DNA copies of the parental genome)? Analyse the situation with the background of gametogenesis and provide or give a suitable explanation.

Answer: The gametes formed from a parent do not have the same genetic composition. In meiosis I, during the pachytene stage in prophase I, the crossing-over of genes occurs. The non-sister chromatids of homologous chromosomes interchange genetic material for recombination. Also, during anaphase, I of prophase I, the maternal and paternal chromosomes go through an independent assortment.

Therefore, this genetic recombination is a result of the genetic reshuffling that in turn reproduces an offspring with the combination of different traits.

 

Question 3: Although sexual reproduction is a long drawn, energy-intensive complex form of reproduction, many groups of organisms in Kingdom Animalia and Plantae prefer this mode of reproduction. Give atleast three reasons for this.

Answer: The reasons for this are as follows:

1. Genetic recombination is a product of sexual reproduction that ensures variation in the species.
2. Sexual reproduction involves both mother and father parent by which the offspring have combined traits.
3. Due to variation, a new offspring has to face the changing environment and in the run of survival of the fittest.
4. An organism has better chances of survival in this transforming environment so that they adapt to it.

 

Question 4. Differentiate between (a) oestrus and menstrual cycles; (b) ovipary and vivipary. Cite an example for each type.

Answer:

(a) Oestrus and Menstrual cycles

Oestrus Cycle	Menstrual Cycle
It is a cyclical change during reproduction that is only seasonal.	This cyclical change is throughout the year during their reproductive phase.
The endometrium is reabsorbed during the process.	Endometrium flows out of the uterus during menstruation.
The female allows copulation during their oestrus period.	The female does not allow copulation during this period.
The unfertilised egg flows out of the body with the blood.	No blood loss is observed.
It is generally observed in non-primates such as cows, sheep, rats, deer, etc.	It comprises primates such as monkeys, apes, humans.

1. b) Ovipary and vivipary

Ovipary	Vivipary
The formation of a zygote occurs outside the female body.	The formation of a zygote occurs inside the female body.
They lay fertilised or unfertilised eggs.	The fertilisation occurs inside the body that gives birth to offspring.
Fertilised eggs remain in a hard calcareous shell, laid in safe surroundings that hatch after a significant period.	The young one develops inside of the mother and after it attains a certain growth, the young one is delivered out of the female body.
The chances of survival are less because of the open environment.	The chances of survival are high because of the closed environment.
Birds and reptiles are examples of oviparous organisms.	Mammals such as humans, cows, elephants, giraffes etc., are viviparous.

Question 5: Rose plants produce large, attractive bisexual flowers but they seldom produce fruits. On the other hand a tomato plant produces plenty of fruits though they have small flowers. Analyse the reasons for failure of fruit formation in roses.

Both these plants – rose and tomato – both selected by human beings for different characteristics, the rose for its flower and tomato for its fruit. Roses, being vegetatively propagated, do not need to produce seeds.

Answer:

There could be many reasons that a rose cannot produce fruits:

• They cannot self-pollinate.
• Entomophily pollination is also difficult because of the multi-layered petals. The ovary is well-protected, enclosed in the corollae.
• The ovary of a rose flower may not have functional eggs that hinder
• If the rose has a sterile stigma, the flower cannot be fertilised.
• There could be an internal barrier for the pollen tube to reach the ovary to carry out fertilisation.
• Roses are vegetatively propagated and not self-pollinated so there are high chances that they are sterile.
• Roses are asexually propagated for ornamental and fragrance use that makes the seeds and fruits non-essential.

Introduction of Chapter:

The topic covers both sexual and asexual reproduction in both plants and animals. Asexual reproduction includes a single parent and the fusing of male and female gametes, whereas sexual reproduction involves the fusion of male and female gametes. The generation of gametes in plants and animals is discussed in a step-by-step manner. NCERT Exemplar Solutions for Class 12 Biology gives students a thorough understanding of all pre-fertilization and post-fertilization phenomena in plants and animals.

In essence, biology is the narrative of life on Earth. Many other topics in Biology are built on the foundation of this chapter. Living things have a set of basic traits that distinguish them from non-living things. All living things have one of the most basic characteristics: reproduction. Students will be able to easily answer all of the questions on the exam relevant to this unit once they have a thorough understanding of this chapter and grasp the basic phenomena.

 

Benefits of NCERT Exemplar Solutions Class 12 Biology: Chapter 1 Reproduction in Organisms

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• The most useful content for preparing for CBSE board exams.

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