NCERT Exemplar Class 12 Biology Solutions Chapter 2 Sexual Reproduction in Flowering Plants

Question:1

Among the terms listed below, those that are not technically correct names for a floral whorl are:
i. Androecium
ii. Carpel
iii. Corolla
iv. Sepal
(a) i and iv, (b) iii and iv (c) ii and iv (d) i and ii.

Answer:

The answer is option (c), (ii) and (iv)
Carpel and sepal are individual parts and make the gynoecium and calyx, respectively.

Question:2

The embryo sac is to an ovule as _______ is to an anther.
a. Stamen
b. Filament
c. Pollen grain
d. Androecium

Answer:

The answer is option (c), Pollen grains
The embryo sac is present in the ovule, while pollen grains are present in the anther.

Question:3

In a typically complete, bisexual and hypogynous flower, the arrangement of floral whorls on the thalamus from the outermost to the innermost is:
a. Calyx, corolla, androecium and gynoecium
b. Calyx, corolla, gynoecium and androecium
c. Gynoecium, androecium, corolla and calyx
d. Androecium, gynoecium, corolla and calyx

Answer:

Ans. The answer is option (a): Calyx, corolla, androecium and gynoecium

Question:4

A dicotyledonous plant bears flowers but never produces fruits and seeds. The most probable cause for the above situation is:
a. The plant is dioecious and bears only pistillate flowers
b. The plant is dioecious and bears both pistillate and staminate flowers
c. The plant is monoecious
d. The plant is dioecious and bears only staminate flowers.

Answer:

The answer is option (d) Plant is dioecious and bears only staminate flowers.
Option (a) is incorrect since a pistillate flower can be pollinated by pollen grains from another flower. A dioecious flower can show self-pollination or cross-pollination and hence can be transformed into fruit. So, option (d) is the correct answer.

Question:5

The outermost and innermost wall layers of microsporangium in an anther are respectively:
a. Endothecium and tapetum
b. Epidermis and endodermis
c. Epidermis and middle layer
d. Epidermis and tapetum

Answer:

Ans. The answer is option (d), Epidermis and tapetum

Question:6

During microsporogenesis, meiosis occurs in:
a. Endothecium
b. Microspore mother cells
c. Microspore tetrads
d. Pollen grains.

Answer:

The answer is option (b), Microspore mother cells
The microspore mother cell undergoes meiosis to produce haploid pollen grains.

Question:7

From among the sets of terms given below, identify those that are associated with the gynoecium.
a. Stigma, ovule, embryo sac, placenta
b. Thalamus, pistil, style, ovule
c. Ovule, ovary, embryo sac, tapetum
d. Ovule, stamen, ovary, embryo sac

Answer:

The answer is option (a): Stigma, ovule, embryo sac, placenta
Thalamus, tapetum and stamen are not associated with gynoecium.

Question:8

Starting from the innermost part, the correct sequence of parts in an ovule is,
a. egg, nucellus, embryo sac, integument
b. egg, embryo sac, nucellus, integument
c. embryo sac, nucellus, integument, egg
d. egg, integument, embryo sac, nucellus.

Answer:

The answer is option (b): egg, embryo sac, nucellus, integument

Question:9

From the statements given below, choose the option that is true for a typical female gametophyte of a flowering plant:
i. It is 8-nucleate and 7-celled at maturity
ii. It is free-nuclear during the development of
iii. It is situated inside the integument but outside the nucellus
iv. It has an egg apparatus situated at the chalazal end
(a) i and iv, (b) ii and iii, (c) i and ii, (d) ii and iv

Answer:

The answer is option (c) (i) & (ii)

Question:10

Autogamy can occur in a chasmogamous flower if:
a. Pollen matures before the maturity of the ovule
b. Ovules mature before the maturity of pollen
c. Both pollen and ovules mature simultaneously
d. Both anther and stigma are of equal length.

Answer:

The answer is option (c), both pollen and ovules mature simultaneously
Relative lengths of stigma and anther are not the only factors; time of maturity of pollens and ovules is also important in deciding the type of pollination. If pollens mature before ovules, they will become ineffective by the time the ovule matures. Hence, option (c) is the correct answer.

Question:11

Choose the correct statement from the following:
a. Cleistogamous flowers always exhibit autogamy
b. Chasmogamous flowers always exhibit geitonogamy
c. Cleistogamous flowers exhibit both autogamy and geitonogamy
d. Chasmogamous flowers never exhibit autogamy

Answer:

The answer is option (a), Cleistogamous flowers always exhibit autogamy
Cleistogamous flowers do not open at all, and thus entry of pollens from another flower is not possible. Hence, cleistogamous flowers exhibit autogamy.

Question:12

A particular species of the plant produces light, non-sticky pollen in large numbers, and its stigmas are long and feathery. These modifications facilitate pollination by:
a. Insects
b. Water
c. Wind
d. Animals

Answer:

The answer is option (c) Wind
Light and non-sticky pollens are ideal to be blown away by the wind. Feathery stamens can sway with the wind, which helps in the release of pollens into the air.

Question:13

From among the situations given below, choose the one that prevents both autogamy and geitonogamy.
a. A monoecious plant bearing unisexual flowers
b. A dioecious plant bearing only male or female flowers
c. Monoecious plant with bisexual flowers
d. Dioecious plant with bisexual flowers

Answer:

The answer is option (a) Monoecious plant bearing unisexual flowers
Autogamy can happen in the case of bisexual flowers. Geitonogamy can happen in the case of dioecious plants bearing only male or female flowers. Hence, option (a) is correct.

Question:14

In a fertilised embryo sac, the haploid, diploid and triploid structures are:
a. Synergid, zygote and primary endosperm nucleus
b. Synergid, antipodal and polar nuclei
c. Antipodal, synergid and primary endosperm nucleus
d. Synergid, polar nuclei and zygote.

Answer:

The answer is option (a): Synergid, zygote and primary endosperm nucleus

Question:15

In an embryo sac, the cells that degenerate after fertilisation are:
a. Synergids and primary endosperm cell
b. Synergids and antipodals
c. Antipodals and primary endosperm cell
d. Egg and antipodals.

Answer:

The answer is option (b), Synergids and antipodals
PEN provides food for the growing embryo, while the egg develops into the embryo. Hence, option (b) is the correct answer.

Question:16

While planning for an artificial hybridisation programme involving dioecious plants, which of the following steps would not be relevant:
a. Bagging of female flower
b. A dusting of pollen on stigma
c. Emasculation
d. Collection of pollen

Answer:

The answer is option (c), Emasculation
In the case of a dioecious plant, male and female flowers are not usually on a single plant. Hence, emasculation may not be necessary in certain cases.

Question:17

In the embryos of a typical dicot and a grass, true homologous structures are:
a. Coleorhiza and coleoptile
b. Coleoptile and scutellum
c. Cotyledons and scutellum
d. Hypocotyl and radicle

Answer:

The answer is option (c), Cotyledons and scutellum
In monocots, the cotyledon is called the scutellum

Question:18

The phenomenon observed in some plants wherein parts of the sexual apparatus is used for forming embryos without fertilisation is called:

a. Parthenocarpy
b. Apomixis
c. Vegetative propagation
d. Sexual reproduction

Answer:

The answer is option (b) Apomixis
When seeds are produced without fertilisation, this phenomenon is called apomixis. In parthenocarpy, seeds are not produced, which means embryos are not produced. Hence, option (b) is the correct answer

Question:19

In a flower, if the megaspore mother cell forms megaspores without undergoing meiosis and if one of the megaspores develops into an embryo sac, its nuclei would be:
a. Haploid
b. Diploid
c. A few haploid and a few diploid
d. With varying ploidy.

Answer:

The answer is option (b), Diploid
Since no meiosis takes place, no change in ploidy will take place.

Question:20

The phenomenon wherein the ovary develops into a fruit without fertilisation is called:
a. Parthenocarpy
b. Apomixis
c. Asexual reproduction
d. Sexual reproduction

Answer:

The answer is option (a) Parthenocarpy

Get Answers to Class 12 Science Chapter 2 Sexual Reproduction in Flowering Plants NCERT Exemplar (Very Short Answer Questions)

The detailed answers to the very short answer questions are given below:

Question:1

Name the component cells of the ‘egg apparatus’ in an embryo sac.

Answer:

The egg apparatus consists of two synergids and one egg cell.

Question:2

Name the part of the gynoecium that determines the compatibility of pollen grains.

Answer:

The pistil can recognize compatible pollen grains.

Question:3

Name the common function that cotyledons and nucellus perform.

Answer:

Cotyledons and nucellus contain abundant food that is utilized by the developing cells.

Question:4

Complete the following flow chart
Pollen mother cell → Pollen tetrad → Pollen grain (a) = vegetative cell (b) =?

Answer:

Generative cell

Question:5

Indicate the stages where meiosis and mitosis occur (1, 2 or 3) in the flow chart.
Megaspore mother cell →Megaspores → Embryo sac →Egg

Answer:

1. Meiosis 2. Mitosis 3. Mitosis

Question:6

In the diagram given below, show the path of a pollen tube from the pollen on the stigma into the embryo sac. Name the components of the egg apparatus.

Answer:

Longitudinal section of a flower showing growth of pollen tube.
Synergids and egg cells are the components of the egg apparatus.

Question:7

Name the parts of the pistil which develop into fruit and seeds.

Answer:

The ovary develops into fruits, and ovules develop into seeds.

Question:8

In the case of polyembryony, if an embryo develops from the synergid and another from the nucellus, which is haploid, and which is diploid?

Answer:

The embryo developing from the synergid will be haploid, and the embryo developing from the nucellus will be diploid.

Question:9

Can an unfertilized, apomictic embryo sac give rise to a diploid embryo? If yes, then how?

Answer:

We know that when seeds develop without fertilization, it is known as apomixis. In this, the embryo can develop from the nucellus, which is diploid. Thus, an apomictic embryo sac can give rise to a diploid embryo.

Question:10

Which are the three cells found in a pollen grain when it is shed at the three-celled stages?

Answer:

When a pollen grain is shed at the three-celled stage, it contains 2 male gametes and a vegetative cell. The generative cell divides into two male gametes.

Question:11

What is self-incompatibility?

Answer:

When pollen from the same plant is incompatible for fertilization, this condition is called self-incompatibility.

Question:12

Name the type of pollination in self-incompatible plants.

Answer:

In the case of self-incompatible plants, cross-pollination takes place.

Question:13

Draw the diagram of a mature embryo sac and show its 8-nucleate, 7-celled nature. Show the following parts: antipodals, synergids, egg, central cell, polar nuclei.

Answer:

Question:14

Which is the triploid tissue in a fertilized ovule? How is the triploid condition achieved?

Answer:

PEN or Primary Endosperm Nucleus shows triploid conditions. When one of the male gametes fuses with the polar nuclei, it results in the formation of triploid PEN.

Question:15

Are pollination and fertilization necessary in apomixes? Give reasons.

Answer:

Pollination and fertilization are not necessary for apomixis. Apomixis is a condition in which an embryo develops without fertilization.

Question:16

Identify the type of carpel with the help of the diagrams given below:

Answer:

Figure “a” shows the multicarpellary syncarpous condition, and figure “b” shows the multicarpellary apocarpous condition.

Question:17

How is pollination carried out in water plants?

Answer:

Water-mediated pollination takes place in a selected number of plants. For example, in Vallisneria, the female flower reaches the surface of the water. Pollen grains are sprinkled on the water surface, and they are passively transported to the female flower for pollination.
Another example is that of seagrasses, the female flower remains submerged in water, and pollen grains are released below the water surface. In the case of pollination by water, pollen grains have a mucilaginous covering which prevents the pollen from becoming wet.

Question:18

What is the function of the two male gametes produced by each pollen grain in angiosperms?

Answer:

The male gametes fuse with the female gametes and form the embryo. The embryo subsequently develops into a new plant. Another male gamete fuses with polar nuclei and eventually forms endosperm. The endosperm supplies food to the developing embryo.

Access Answers to the Chapter 2 Sexual Reproduction in Flowering Plants NCERT Exemplar for Class 12 Science (Short Answer Questions)

The detailed answers to the Short answer questions are given below:

Question:1

List three strategies that a bisexual chasmogamous flower can evolve to prevent self-pollination (autogamy).

Answer:

The following are 3 strategies that a bisexual chasmogamous flower can evolve to prevent self-pollination or autogamy:

1. Pollen release and stigma receptivity are not synchronised in many flowers. Either the pollen is released much before the maturity of the stigma, or the stigma matures much before the release of pollen.

2. In some flowers, the anthers and stigma are placed in different places so that pollen grains from the same flower cannot reach the stigma.

3. Self-incompatibility between pollen and stigma is seen in some flowers. This is a genetically mediated process that prevents autogamy in these flowers.

Question:2

Given below are the events that are observed in an artificial hybridisation programme. Arrange them in the correct sequential order in which they are followed in the hybridisation programme.
(a) Re-bagging (b) Selection of parents (c) Bagging (d) Dusting the pollen on stigma (e) Emasculation (f) Collection of pollen from male parent.

Answer:

The correct sequence of steps being followed in hybridisation is:
Selection of parents-> Emasculation -> Bagging -> Collection of pollen from male parent -> Re-bagging.

Question:3

Vivipary automatically limits the number of offspring’s in a litter. How?

Answer:

Viviparity is present in both animals and plants. In the case of animals, it means an animal gives birth to young ones. In the case of plants, viviparity means germination of the embryo on the plant itself, without the normal sequence of development of the seed. Viviparity involves too much drain of resources on the mother.
In the case of animals, a female has to constantly supply the nutrients and oxygen to the growing foetus, if the foetus is developing in the womb. Enough resources are not available to support a large litter, and hence viviparity automatically limits the number of offspring in a litter. This is true in the case of plants also because a germinating embryo on the plant would require resources from the mother plant.

Question:4

Does self-incompatibility impose any restrictions on autogamy? Give reasons and suggest the method of pollination in such plants.

Answer:

Self- incompatibility is the condition in which pollen from the same plant cannot pollinate the flower. Thus, self-incompatibility imposes complete restriction on autogamy.
This evolution might have occurred to prevent too much inbreeding because continuous inbreeding prevents variations. In such plants, cross pollination is the norm and pollen from a plant pollinates the flower on another plant. This ensures the accumulation of gene pools from 2 different plants.

Question:5

In the given diagram, write the names of the parts shown with lines.

Answer:

Question:7

Are parthenocarpy and apomixis different phenomena? Discuss their benefits.

Hint: Yes, parthenocarpy, and different apomixis phenomena. Parthenocarpy leads to the development of seedless fruits. Apomixis leads to embryo development.

Answer:

Parthenocarpy is the condition in which fruits develop without seeds, while apomixis is a condition in which seeds develop without fertilization. Fertilization is absent in both cases, but seeds are present in apomixis only. Benefits of parthenocarpy: Seedless fruits are easier to consume, especially those fruits that naturally contain too many seeds, e.g., papaya, watermelon, and banana.
Benefits of Apomixis include the fact that it can be used to produce apomicts hybrid seeds every year. This will help in drastically cutting the cost for farmers.

Question:6

What is polyembryony, and how can it be commercially exploited?

Answer:

In some varieties of citrus and mango, the nucellar cells start dividing and protrude into the embryo sac. They eventually produce multiple embryos. This condition is called polyembryony. Embryos develop without fertilization in this apomictic condition.
Polyembryony can be commercially exploited by producing seeds of hybrid varieties at a lower cost. In the case of hybrid plants, a farmer needs to buy seeds every year because plants from hybrid seeds fail to produce hybrid seeds due to the law of inheritance.
Buying fresh seeds every season is very costly. If hybrid seeds are produced with a polyembryonic condition, then it would be possible for the farmers to utilize those seeds for the next year and the subsequent years. This is still at the research stage, but there are bright prospects for the future.

Question:8

Why does the zygote begin to divide only after the division of the Primary endosperm cell (PEC)?

Answer:

The endosperm plays an important role in supplying food to the developing embryo. Once the division of PEC or Primary Endosperm Cell is complete, there is sufficient availability of food for the embryo.
In the absence of food, the zygote won’t be able to get the necessary raw materials for making new cells. Hence, the division of zygote beings only occurs after the division of the Primary Endosperm Cell (PEC).

Question:9

The generative cell of two-celled pollen divides into the pollen tube but not in three-celled pollen. Give reasons.

Answer:

In three-celled pollen, one of the cells is a vegetative cell that has no role to play in fertilization. The remaining two cells are the male gametes, and they are the actual participants in fertilization. Rather than the vegetative cells, the generative cells divide inside the pollen tube.
In 60% of the cases, the generative cell divides inside the pollen tube. In the remaining case, the generative cell divides much before pollination.

Question:10

In the figure given below, label the following parts: male gametes, egg cell, polar nuclei, synergid, and pollen tube.

Answer:

Know Answers to Sexual Reproduction in Flowering Plants NCERT Exemplar for Class 12 Science Chapter 2 (Long Answer Questions)

The detailed answers to the Long answer questions are given below:

Question:1

Starting with the zygote, draw the diagrams of the different stages of embryo development in a dicot.

Answer:

Question:2

What are the possible types of pollinations in chasmogamous flowers? Give reasons.

Answer:

Chasmogamous flowers are open flowers in which stigma and anthers are exposed, and the flowers are similar to other species. Possible types of pollinations in chasmogamous flowers are as follows:

1. Geitonogamy: The situation in which pollen grains from the same plant but different flower reaches the stigma is called geitonogamy. This is similar to autogamy because the zygote gets the gene pool from the same plant.

2. Xenogamy: The situation in which the pollen grains from a different plant reaches the stigma is called xenogamy. This can be termed as the true cross-pollination because the zygote gets the gene pool from 2 different plants.

Most of the plants produce hermaphrodite flowers, and thus, self-pollination is a clear-cut eventuality. However, continuous self-pollination can result in inbreeding depression. The variation will not be possible in the case of self-pollination. Hence, plants have evolved in various ways and means to facilitate cross-pollination even in dioecious flowers. One of the strategies followed by plants is a loss of synchronization between pollen release and stigma maturity. Another strategy is self-incompatibility between pollens and the stigma of the same flower.
A third strategy is a positional difference between anthers and stigma so that pollens from the same flower are unable to reach the stigma.

Question:3

With a neat, labeled diagram, describe the parts of a mature angiosperm embryo sac. Mention the role of synergids.

Answer:

Structure of a mature Embryo Sac: A mature embryo sac is a 7-celled structure and has 8 nuclei. The end near the micropyle is called the micropylar end, while the opposite end is called the chalazal end. The following are the main parts of the embryo sac:

• Egg Apparatus: The egg apparatus is composed of two synergids and an egg. There are special thickenings at the micropylar end of synergids. These thickenings are known as the filiform apparatus.

• The function of Synergids: The synergids provide a channel for the pollen tube to enter through the filiform apparatus.

• Polar Nuclei: The two nuclei enclosed in the central cell are called polar nuclei.

• Antipodals: The three cells at the chalazal end are called antipodals.

Question:4

Draw the diagram of a microsporangium and label its wall layers. Write briefly on the role of the endothelium.

Answer:

Role of Endothecium: Endothecium, along with the epidermis and the middle layer, protects the pollens during development. Once pollen grains are mature, the three layers (including endothecium) rupture and thus facilitate the dehiscence of pollens.

Question:5

Embryo sacs of some apomictic species appear normal but contain diploid cells. Suggest a suitable explanation for the condition.

Answer:

The condition in which seeds are produced without fertilization is called apomixis. It is a kind of asexual reproduction, but it mimics sexual reproduction. There are several mechanisms for apomixis. One of them is seen in citrus and mango fruits. In this case, the nucellus begins to divide and intrude into the embryo sac. It eventually develops into a seed. Since the nucellus is composed of diploid cells, the embryo sac in such a case has diploid cells.
It is also important to recall that fertilization cannot happen in the cells which were not formed after meiosis. Moreover, haploid cells are never involved in apomixes. It is the diploid cells which bring about apomixes. Hence, embryo sacs apomictic species appear normal but contain diploid cells.