Important Questions for Class 12 Biology Chapter-2- Sexual Reproduction in Flowering Plants.

Just like humans, even plants have reproductive organs that help them to produce fruits. Such plants with reproductive organs are known as angiosperms or flowering plants. Sexual reproduction in flowering plants involves an important phenomenon called pollination. The pollen grains from the male flower are transferred to the stigma of the female flower. These pollens then travel through the pollen tube into the female reproductive tract and release the pollens, thereby, proceeding the reproduction process.

Mentioned below are the important questions on sexual reproduction in flowering plants for Class 12. The answers are also provided for reference.

Very Short Answer Type Questions

Q.1. What are the component cells of the egg apparatus in an embryo sac?
A.1. An egg apparatus consists of:

• One egg cell
• Two synergids

Q.2. Which part of gynoecium determines the compatible nature of pollen grain?
A.2. Stigma

Q.3. What is common in the function performed by nucellus and cotyledon?
A.3. The cotyledons and nucellus both store reserve food material and does the work of providing nourishment- nucellus (embryo sac), cotyledons (embryo).

Q.4. Fill in the missing words:
Pollen mother cell → Pollen tetrad → Pollen grain → Vegetative cell, ___?____
A.4. Generative cell

Q.5. In the following events, indicate the stages where mitosis and meiosis occur (1,2,3).
Megaspore mother cell →(1)→Megaspores→(2)→Embryo sacs→(3)→Egg

A.5. 1- Meiosis 2- Mitosis 3- Meiosis

Q.6. Show the direction of the pollen tube from the pollen on the stigma in the embryo sac in the given diagram.

A.6.

Q.7. Which regions of pistil form fruits and seeds?
A.7. The ovary develops into a fruit. The ovule develops into the seed.

Q.8. During polyembryony, if one embryo is formed from synergids and the other from nucellus, state the one that is haploid and the one that is diploid.
A.8. Embryo developed from the synergid- haploid Embryo developed from the nucellus- diploid.

Q.9. Is it possible that an unfertilized apomictic embryo sac gives rise to a diploid embryo? Give a reason in support of your answer.
A.9. Yes, an unfertilized apomictic embryo sac can give rise to a diploid embryo. If the megaspore develops into an embryo sac without mitotic division, it will give rise to a diploid embryo.

Q.10. When a pollen grain is shed at the 3-celled stage, which three cells are found?
A.10. The following three cells are found at the three-celled stage:

• One vegetative cell
• Two male gametes

Q.11. Define self-incompatibility. How do self-incompatible plants pollinate?
A.11. Self-incompatibility is a genetic mechanism in which the growth of the pollen tube in the pistil is inhibited which prevents self pollens from fertilizing the ovules. The self-incompatible plants pollinate by cross-pollination.

Q.12. Which is a triploid tissue? How is the condition achieved in a fertilized ovule?
A.12. The endosperm is a triploid tissue in a fertilized ovule. Triple fusion, leading to the fusion of one male gamete and two haploid polar nuclei form the triploid tissue.

Q.13. Does apomixis require fertilization and pollination? Give reasons in support of your answer.
A.13. No, apomixis does not require pollination and fertilization. This is because apomixis is a form of asexual reproduction in which the female reproductive apparatus is used. The embryos can develop directly from the nucellus or synergids.

Q.14. Mention the kind of carpel in the diagram given below.

A.14.

• (a) Multicarpellary, the syncarpous pistil of Papaver
• (b) Multicarpellary, apocarpous gynoecium of Michelia

Q.15. How do aquatic plants undergo pollination?
A.15. A few aquatic plants have their flowers growing in the air. They are pollinated by the insects. Other plants that have their flowers submerged in water release their pollen in the water that drifts in the water and are caught by the feathery stigma of female flowers.

Q.16. Each pollen grain in the flowering plants produces male gametes. State the function of the male gametes.
A.16. One male gamete fuses with the nucleus of the egg cell, while the other male gamete moves towards the two polar nuclei present in the central cell and fuses with it to form a triploid primary endosperm nucleus.

Q.17. List out the agents of pollination.

A.17. The pollinating agents are involved in transferring pollen grains from the male to the female part of the flower. Animals, birds, insects, wind and other biotic and abiotic agents are all examples of pollinating agents.

Q.18. What is pollination?

A.18.Pollination is a process of transferring pollen grains from the male anther of a flower to the flower’s female part called the stigma. Pollination is the sexual mode of reproducing, which is carried out by all flowering plants of a plant kingdom.

Q.19.What are the stages of post-fertilization in plants?

A.19.In all flowering plants, the post-fertilization is a critical stage which occurs after the double fertilization and includes the series of steps:

1. Endosperm development.
2. Embryo improvement.
3. Development of ovule into a seed.
4. Development of ovary into a fruit.

Q.20.What are the male and female reproductive parts of a flower?

A.20.A flower plays a vital role in the reproduction process of a plant. Therefore, it is called the reproductive organ of plants. 

The male reproductive parts of the flower include the stamen the filament and the anther, which are collectively termed the androecium. 

The female reproductive parts of the flower include carpels, pistils, stigma, style and an ovary, which are collectively termed the gynoecium.

Q.21.What is cross-pollination?

A.21.Cross-Pollination is the complex type of pollination during which the pollen grains are transferred from the anther of one flower into the stigma of another flower. This type of pollination makes use of both biotic and abiotic agents like wind, water, insects, birds, animals, and other agents as pollinators.

Q.22.Define double fertilization.

A.22.In plants, double fertilization refers to the fusion of one female gametophyte with two male gametophytes. It is a complex process in all flowering plants.

Q.23.What are the main layers of a flower?

A.23. There are different types of flowers in a plant kingdom. A few among them vary in colour, structure, shape, etc. However, all flowers have unique layers. The four main layers of a flower:

1. Calyx 
2. Corolla
3. Androecium
4. Gynoecium

Q.24. Define Morphogenesis.

A.24.Morphogenesis is defined as a biological process which controls the growth, development in size, shape and structure and distribution of cells during the embryonic development of an organism.

Q.25. State the role of endothecium.

A.25. The endothecium protects the microsporangium and helps in the dehiscence of anther for the release of pollen grains.

Short Answer Type Questions

Q.1. How does a chasmogamous bisexual flower prevent self-pollination?
A.1. A chasmogamous bisexual flower prevents self-pollination in the following ways:

1. Dichogamy: In this strategy, the release of pollens and the receptivity of stigma are not synchronized. For eg., in sunflower, the stigma becomes receptive long after the pollen release.
2. Herkogamy: In this, the male and female flowers are present at different locations. In this, the pollen of the flower cannot come in contact with the stigma of the same flower. For eg., Hibiscus gloriosa
3. Self-sterility: It is a mechanism in which the growth of the pollen tube in the pistil or the germination of pollen grains is inhibited. This prevents the fertilization of the ovules from the pollen of the same flower. For eg., Abolition.

Q.2. Arrange them sequentially according to how they appear in the artificial hybridization programme.

1. Rebagging
2. Selection of parents
3. Bagging
4. Dusting the pollen on the stigma
5. Emasculation
6. Collection of pollen

A.2. a) Selection of parents b) Emasculation c) Bagging d) Collection of pollen e) Dusting of pollen on the stigma f) Rebagging

Q.3. How do self-incompatibility restrict autogamy? How does pollination occur in such plants?
A.3. Self-incompatibility restricts autogamy by a mechanism known as self-sterility. This is a genetic mechanism in which the germination of pollen grains or the pollen tube growth in the pistil is inhibited which prevents the pollen from fertilizing the ovules. Such plants pollinate by the process of cross-pollination.

Q.4. Label the following diagram.

A.4.

Q.5. Explain the term polyembryony. How is it exploited commercially?
A.5. When more than one embryo occurs in a seed, it is referred to as polyembryony. This can be seen in a few citrus fruits and mango varieties. Polyembryony plays a significant part in plant breeding and horticulture. These embryos give rise to virus-free plantlets and are healthy. Hybrid varieties of such plants and vegetables are being grown extensively. These varieties thus obtained are highly productive.

Q.6. Is there any difference between apomixis and parthenocarpy? Explain the benefits of each.
A.6. Yes, parthenocarpy is different from apomixis. In parthenocarpy, the fruit is produced without the fertilization of the female gamete. It is used for the production of fruits without seeds such as banana and grapes for commercial purposes. Apomixis is the process in which the seeds are produced without fertilization but the process occurs in the female reproductive tract of the plant. In this, the megaspore mother cell does not undergo meiosis. It is used for the commercial production of hybrid varieties and in the production of virus-free varieties.

Q.7. The zygote divides only after the division of the primary endosperm cell. Give reasons in support of the statement.
A.7. Zygote requires nourishment for its growth and division. This nourishment is provided by the primary endosperm cell. That is why the zygote divides only after the growth, food storage and division of the primary endosperm cell.

Q.8. Why is it that the generative cell of 2-celled pollen divides in a pollen tube and not of 3-celled pollen?
A.8. The generative cell divides to form two male gametes. In three-celled pollen, the generative cell divides into two gametes, therefore, no further division takes place in the pollen tube. However, in two-celled pollen, the generative cell moves down the pollen tube and divides to form two male gametes.

Q.9. Label the following parts in the diagram given below:
Male gametes, egg cell, polar nuclei, synergid, pollen tube.

A.9.

Q.10.Explain the events which occur after the process of fertilization in plants.

A.10.Fertilization is a vital process, which takes place in all sexually reproducing organisms. In all flowering plants, fertilization occurs after pollination and germination. After the process of fertilization, the following events occur:

1. The ovary becomes the fruit 
2. The ovules become the seeds. 
3. The other structures including the corolla, calyx, and other remaining parts of the androecium and gynoecium degenerate or fall off.

Long Answer Type Questions

Q.1. Explain the pollination occurring in the chasmogamous flowers.
A.1. The chasmogamous flowers are open with their anther and stigma exposed for pollination. In these flowers two types of pollinations take place:
Self-Pollination: Self-pollination occurs when both the anther and the stigma mature simultaneously and come in contact with each other.
Cross-Pollination: This type of pollination occurs in self-incompatible plants. In this, the anther and the stigma mature at different times so cannot come in contact with each other. Cross-pollination is of two types:

• Geitonogamy– When the pollen grains from the anther transfer to the stigma of a different flower in the same plant, it is known as geitonogamy.
• Xenogamy– When the pollen grains from the anther of a flower get transferred to the stigma of a flower in some other plant, it is known as xenogamy. This process carries genetically different pollen to the stigma.

Q.2. Describe the structure of the embryo sac of a mature angiosperm. Explain the role of synergids in it.
A.2.

• The cell walls of the 8 nucleate stage are organized in the form of a female gametophyte or embryo sac.
• Six out of the eight nuclei are surrounded by cell walls.
• The egg apparatus comprises two synergids and one egg cell.
• Three cells called the antipodals are present at the chalazal end.
• The central cell is formed by the fusion of two polar nuclei.
• On maturity, the embryo sac of the angiosperms consists of 8 nuclei and 7 cells.
• A single megaspore gives rise to the embryo sac, hence called monosporic embryo sac.

Role of Synergids
The synergids are responsible for the reproduction in an angiosperm. During fertilization, a pollen tube grows into one of the synergids. The tube ceases growth, ruptures and releases two sperm cells.

Q.3. How is it that the embryo sacs of some apomictic species look normal but contain diploid cells?
A.3. The offsprings produced by apomixis are genetically identical to the parent. In flowering plants apomixis is used to reproduce asexually through seeds. In a few species, the diploid egg cell does not undergo reduction division and forms an embryo without fertilization. In a few citrus species, the nucellar cells surrounding the embryo sac divide and give rise to an embryo. This takes place in the megaspore mother cell. It only undergoes mitosis and hence produces diploid cells in the embryo sac.

Q.4. What are the characteristics of wind, water and insect-pollinated flowers?

A.4. Characteristics of wind-pollinated flowers:

• These flowers are not brightly coloured.
• They possess no special odours or nectar.
• They are small and have no petals.
• Their stigma and stamens are exposed to air currents.
• The pollen is smooth, light can be blown easily by wind and are in large numbers.
• The stigma is feathery and can catch pollen from the wind.

Characteristics of water-pollinated flowers:

• They possess small male flowers that are not clearly visible.
• A large number of pollens are released in water that is caught by large, feathery stigma of female flowers.
• This pollen keeps floating on the water surface until they are caught by female flowers.

Characteristics of insect-pollinated flowers:

• They are large with bright-coloured petals to attract insects.
• The flowers have nectar and a pleasant fragrance.
• The pollen grains are sticky and can easily stick to the insect’s body.

Q.5. Explain the structure of the pollen.

A.5. Pollen grains are microscopic structures that carry the male reproductive cells of a plant. It is a double-walled structure with a thin inner wall known as endospore composed of cellulose and a thick outer wall known as exospore, composed of sporopollenin.

The exospore protects the male genetic material during transportation from an anther to stigma. The waxes and proteins present on the pollen surface repel moisture and interact with the stigma.

Q.6.What are the functions of a flower?

A.6.The flowers are the reproductive organs of plants and are mainly involved in the reproduction process. The essential functions of flowers are mentioned below:

1. It provides the beauty of the plant.
2. Gametophytes developed in the flowers.
3. Helps in the development of fruit with a seed.
4. Involved in the union of male and female gametes.
5. It accommodates the sex organs of the plant.
6. Flowers provide nectar to certain birds and insects.
7. It protects the reproductive organs of a plant.
8. The flowers can produce diaspores without fertilization.
9. Flowers also promote the union of sperm and eggs from the same flower or different flowers.
10. It helps in pollination by attracting insects and other animals prior to transfer pollen grains.

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