Class 12 biology chapter 2 questions and answers

Class 12 biology chapter 2 notes

NCERT class 12 biology chapter 2 ” Sexual Reproduction in flowering plants ”

Reproduction:

It is a biological process that produces new individuals of the same species, allowing the continuation of a species. It ensures the survival of a species by producing new individuals that can carry on the traits of the species and adapt to changing environmental conditions.

Sexual reproduction:

It is a type of reproduction that involves the fusion of male and female gametes to form a zygote. The offspring produced through sexual reproduction have a combination of traits from both parents, leading to genetic diversity and a better chance of survival in changing environments.

Flower:

Flowers are the reproductive organs of flowering plants, and they play a crucial role in sexual reproduction. Flowers can vary greatly in size, shape, and color, but they typically have four main parts: sepals, petals, stamens, and pistils. The sepals are usually the outermost parts of the flower and protect the flower bud. The petals, which are usually brightly colored, are often the most noticeable part of the flower and serve to attract pollinators. The stamens contain the anthers, which produce and release pollen, and the pistils contain the stigma, style, and ovary, which produce the egg cells. Flowers also produce nectar, a sugary solution, which attracts pollinators and provides a food source for them.

Stamen: The stamen is the male reproductive structure in a flower and consists of the anther and filament. The anther produces and contains male gametes (pollen grains), which are transferred to the pistil through pollination.

Pistil: The pistil is the female reproductive structure in a flower and consists of the stigma, style, and ovary. The stigma is the part of the pistil that receives the pollen grains, the style supports the stigma, and the ovary contains the female gametes (ovules).

Pre-fertilization:

Before fertilization can occur, the male and female reproductive structures in the flower must mature. The stamens produce and release pollen, while the pistils develop the ovules. Pollination, the transfer of pollen from the anthers of one flower to the stigma of another, is the first step in fertilization. The pollen grains germinate and grow a pollen tube towards the ovules, where they fertilize the egg cells.

Fertilization:

Fertilization is the fusion of male and female gametes to form a zygote. The zygote develops into an embryo, which later grows into a mature plant.

Pollination:

Pollination is the transfer of pollen grains from the anther to the stigma of a flower or to the stigma of another flower of the same or different plant. This is an essential step in sexual reproduction as it leads to the formation of a zygote through fertilization.

Self-pollination: Self-pollination is the transfer of pollen grains from the anther of a flower to its own stigma. This type of pollination results in offspring that are genetically similar to the parent plant.

Cross-pollination: Cross-pollination is the transfer of pollen grains from the anther of one flower to the stigma of another flower on the same or different plant. This type of pollination results in offspring that have a combination of traits from both parents, leading to genetic diversity.

Embryo sac:

The embryo sac is the female gametophyte in flowering plants and contains the female gametes. It forms within the ovule after pollination and serves as a site for fertilization.

Endosperm:

Endosperm is a triploid tissue in flowering plants that provides nourishment to the developing embryo. It forms as a result of double fertilization, where one sperm nucleus fertilizes the egg and the other sperm nucleus fertilizes the central cell of the embryo sac.

Seed: The seed is the fertilized ovule, consisting of the embryo and endosperm surrounded by a protective covering. The seed serves as a means of dispersal, enabling the establishment of new individuals.

Fruit: The fruit is the mature ovary of a flowering plant, containing seeds. Fruits serve as a means of dispersal and protect and provide nourishment to the developing seeds.

Dispersal: Dispersal is the spreading of seeds from one place to another, enabling the establishment of new individuals. This helps to ensure the survival of a species by spreading it to new habitats, avoiding overcrowding, and reducing competition for resources.

Germination: Germination is the process by which a seed begins to grow and develop into a mature plant. It starts with the uptake of water by the seed, which leads to the activation of metabolic processes and the growth of the embryo.

Vegetative reproduction: Vegetative reproduction is a type of reproduction that involves the production of new individuals from vegetative structures such as roots, stems, and leaves. This type of reproduction does not involve the formation of seeds and does not result in genetic diversity.

Bulbs: Bulbs are modified underground stems that store food and serve as a means of vegetative reproduction. They produce new individuals through the growth of offsets or bulblets, which are clones of the parent plant.

Runners: Runners are horizontal stems that grow along the ground and produce new individuals at the tips. This type of vegetative reproduction is common in plants such as strawberries.

Rhizome: A rhizome is a horizontal underground stem that serves as a means of vegetative reproduction. It produces new individuals through the growth of shoots and roots, which develop into new plants.

Layering: Layering is a type of vegetative reproduction that involves rooting of a stem while it is still attached to the parent plant. Once rooted, the stem detaches and forms a new individual.

Cuttings: Cuttings are pieces of stems, leaves, or roots that are used for vegetative reproduction. They are planted in soil and produce new individuals through the growth of roots and shoots.

Grafting: Grafting is a horticultural technique used for vegetative reproduction. It involves the joining of two plant parts, a scion and a rootstock, to produce a single plant. The scion provides the desired traits, while the rootstock provides the root system and resistance to diseases and pests.

Double Fertilization:

Double fertilization is a unique feature of angiosperms, and it refers to the fertilization of two cells in the ovule. The first fertilization involves the fusion of the sperm and egg to form the zygote, which will develop into the embryo of the seed. The second fertilization involves the fertilization of the central cell to form the endosperm, a food source for the developing embryo. The endosperm will nourish the embryo until it is able to produce its own food through photosynthesis.

Post-fertilization:

After fertilization, the fertilized egg develops into an embryo, and the ovules develop into seeds. The seeds are usually surrounded by a protective structure, called the fruit, which can help with seed dispersal. The fruit can also provide nourishment to animals that eat it, helping to spread the seeds to new locations. The mature fruit can then be dispersed from the parent plant by wind, water, animals, or other means.

Apomixis and Polyembryony:

Apomixis is a form of asexual reproduction in plants where seeds are produced without fertilization. In other words, the seeds develop without the fusion of sperm and egg. As a result, the offspring produced through apomixis are genetically identical to the parent plant. Polyembryony refers to the formation of multiple embryos from a single fertilized egg. This can result in the development of multiple seedlings from a single seed. Polyembryony is more common in certain species of plants, such as citrus, and it can be a way for plants to increase their chances of survival.

Class 12 biology chapter 2 NCERT questions and answers

QUESTIONS:

1. Name the parts of an angiosperm flower in which development of male and female gametophyte take place.
2. Differentiate between microsporogenesis and megasporogenesis. Which type of cell division occurs during these events? Name the structures formed at the end of these two events.
3. Arrange the following terms in the correct developmental sequence:
Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.
4. With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.
5. What is meant by monosporic development of female gametophyte?
6. With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.
7. What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.
8. Mention two strategies evolved to prevent self-pollination in flowers.
9. What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
10. What is bagging technique? How is it useful in a plant breeding programme?
11. What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
12. Why do you think the zygote is dormant for sometime in a fertilised ovule?
13. Differentiate between:
(a) hypocotyl and epicotyl;
(b) coleoptile and coleorrhiza; (c) integument and testa;
(d) perisperm and pericarp.
14. Why is apple called a false fruit? Which part(s) of the flower forms the fruit?
15. What is meant by emasculation? When and why does a plant breeder employ this technique?
16. If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?
17. Explain the role of tapetum in the formation of pollen-grain wall.
18. What is apomixis and what is its importance

ANSWERS

1. The male gametophyte development takes place in the anther (located in the stamen), and the female gametophyte development occurs in the ovule (located in the ovary).
2. Microsporogenesis is the development of microspores from microsporocytes through meiosis. Megasporogenesis is the development of megaspores from megasporocytes through meiosis. During microsporogenesis, meiotic cell division occurs, and during megasporogenesis, mitotic cell division takes place. The end products of microsporogenesis are microspores, which give rise to pollen grains. The end product of megasporogenesis is the megaspore, which develops into the female gametophyte.
3. Pollen mother cell, microspore tetrad, microspores, pollen grain, male gametes
4. A diagram of the parts of a typical angiosperm ovule would include the nucellus, integuments, micropyle, and funicle.
5. Monosporic development of female gametophyte refers to the development of the female gametophyte from a single megaspore, which undergoes three mitotic divisions.
6. The female gametophyte of angiosperms is 7-celled and 8-nucleate due to the three mitotic divisions of the megaspore, resulting in the formation of seven cells and eight nuclei. A diagram explaining this structure would include labels for the three antipodal cells, two synergid cells, and two polar nuclei in addition to the egg cell.
7. Chasmogamous flowers are those in which the flower opens widely, allowing cross-pollination to occur. Cleistogamous flowers, on the other hand, do not open, and cross-pollination cannot occur.
8. Two strategies evolved to prevent self-pollination in flowers are self-incompatibility and dioecism.
9. Self-incompatibility is a mechanism by which a flower prevents self-pollination and promotes cross-pollination. This is achieved through specific biochemical or molecular recognition systems that recognize and reject self-pollen. When self-pollination occurs in self-incompatible species, it does not lead to seed formation because the self-pollen is rejected.
10. The bagging technique involves covering the flowers of a plant with a bag to prevent cross-pollination and ensure that self-pollination occurs. This technique is useful in plant breeding programs because it allows the plant breeder to control the pollination process and produce offspring with desired characteristics.
11. Triple fusion refers to the fusion of the two polar nuclei, the male gamete, and the egg cell in the fertilized ovule. It takes place in the female gametophyte and results in the formation of a triploid endosperm tissue.
12. The zygote is dormant for some time in a fertilized ovule because it allows the embryo to develop to a certain stage before germination. This ensures that the embryo has sufficient resources for survival and growth.

13. (a) Hypocotyl is the lower part of the stem in a seedling that connects the radicle to the cotyledons. Epicotyl is the upper part of the stem in a seedling above the cotyledons. (b) Coleoptile is a sheath-like structure covering the shoot tip of monocot seedlings that protects the emerging shoot and helps to guide it towards the light. Coleorrhiza is a protective sheath surrounding the radicle in monocot seedlings. (c) Integument is a protective layer surrounding the ovule in flowering plants. Testa is the seed coat that covers the embryo and the endosperm. (d) Perisperm is a tissue formed from the nucellus of an ovule in flowering plants. Pericarp is the outermost layer of a fruit that surrounds the seeds and comes from the ovary wall of a flower.
14. An apple is called a “false fruit” because the fleshy part that is usually considered the fruit is actually derived from the receptacle (the enlarged base of the flower stalk) and the true fruits are the small seeds enclosed in the ovary. The fleshy part that we eat is a modified stem tissue, while the core of the apple containing the seeds is the actual ovary of the flower.
15. Emasculation refers to the removal of anthers (male reproductive organs) from a flower to prevent self-fertilization. Plant breeders employ this technique to ensure cross-fertilization and control the genetic traits of offspring.
16. Fruits that have a high demand in the market and are prone to spoilage can be selected to induce parthenocarpy through the application of growth substances. Examples include banana, pineapple, and seedless grapes. This technique can be useful in increasing the yield and improving the quality of the fruit.
17. The tapetum is a layer of cells surrounding the microsporangium in the anthers of flowering plants. It plays a crucial role in the formation of the pollen grain wall by providing nutrients to the developing microspores. It also helps in the formation of the exine (outer layer) of the pollen grain, which is important for the proper functioning and dispersal of the pollen.
18. Apomixis is a form of asexual reproduction in plants where seeds are produced without fertilization. This process results in offspring that are genetically identical to the parent plant. The importance of apomixis lies in its ability to preserve desirable traits in plants and to reduce the time and costs associated with traditional breeding techniques. It also has potential applications in agriculture, horticulture, and conservation biology.

Class 12 biology chapter 2 Extra question answers:

2.1 Flower:

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