Class 12 Biology Chapter 1 is “Sexual Reproduction in Flowering Plants”. This chapters includes sub-topics such as –
- 1.1 Flower – A Fascinating Organ of Angiosperms
- 1.2 Pre-fertilisation : Structures and Events
- 1.3 Double Fertilisation
- 1.4 Post-fertilisation: Structures and Events
- 1.5 Apomixis and Polyembryony
Important Topics for Chapter 1 “Sexual Reproduction in Flowering Plants”
Here’s a list of detailed topics for Class 12 Biology Chapter 1 “Sexual Reproduction in Flowering Plants. This topics are enough for complete preparation of chapter 1 for class 12 Biology exam. Also, Below you will get the NCERT Solutions for class 12 biology chapter 1. A download link for pdf format is also given below.
- Pre-fertilisation : Structures and Events
- Stamen, Microsporangium and Pollen Grain
- Structure of microsporangium
- The Pistil, Megasporangium (ovule) and Embryo sac
- Pollination – types of Pollination, factors affecting pollination, carriers of pollination
- Outbreeding Devices, Pollen-pistil Interaction and Artificial hybridisation
- Double Fertilization and Post fertilization
- Endosperm, Embryo and Seeds
- Dormancy, false and true fruits, Parthenocarpic fruits
- Apomixis and Polyembryony
NCERT Solutions for Class 12 Biology Chapter 1 “Sexual Reproduction in Flowering Plants”
1. Name the parts of an angiosperm flower in which the development of male and female gametophyte take place.
Ans: In an angiosperm, the male gametophyte take place within the anther. Whereas, the female gametophyte takes place within the ovules.
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.
Ans: The important differences between microsporogenesis and megasporogenesis are given below:
| Microsporogenesis | Megasporogenesis |
| It is the process in which a diploid microspore mother cell undergoes meiosis to form haploid microspores. | It is the process of formation of haploid megaspores from the diploid mother cell. |
| Occurs inside pollen sacs. | Occurs inside ovules. |
| The arrangement of microspores is tetrahedral. | The arrangement of megaspores is linear. |
| Pollens are produced by microsporogenesis. | Embryo sacs are produced by megasporogenesis. |
| All four microspores formed are functional. | Only one out of the four megaspores formed is functional. |
The type of cell division occurs during these events is Meiotic cell division and it leads to the production of haploid gametes.
The structures formed at the end of these events are:
- Microsporogenesis leads to the formation of Pollen grain
- Megasporogenesis leads to the formation of Embryo sac
3. Arrange the following terms in correct developmental sequence:
Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes
Ans: Sporogenous tissue → pollen mother cell → microspore tetrad → pollen grain → male gamete.
4. With a neat labelled diagram, describe the parts of a typical angiosperm ovule.
Ans: An angiosperm ovule is a female megasporangium where the formation of megaspores takes places.
Parts of an ovule are as follows:
- Funicle: It is a stalk-like structure which represents the point of attachment of the ovule to the placenta of the ovary.
- Hilum – It is the point, where ovary is attached to the funicle.
- Micropyle: It is the point where the pollen tube enters the ovule at the time of fertilization. It is formed by the projection of integuments.
- Integuments: It is the outer layers of the ovule that protects to the developing embryo.
- Nucellus: It is the mass of the parenchymatous tissue surrounded by the outer integuments.
- Chalazal: It is the swollen part of the nucellus from the integuments originates.
5. What is meant by monosporic development of female gametophyte?
Ans: Monosporic development of a female gametophyte is the development and maturation of the female reproductive structure (gametophyte) from single functional megaspore.
6. With a neat diagram, explain the 7-celled, 8-nucleate nature of female gametophyte.
Ans: The 7-celled, 8-nucleate nature of the female gametophyte is a characteristic feature in the reproductive structure of flowering plant (angiosperms). It is also known as the embryo sac and is a crucial for the process of sexual reproduction.
The process of formation of the 7-celled, 8-nucleate nature of female gametophyte is given below:
After the cell undergo the first mitotic division, two nuclei are formed.
- Then, these two nuclei move towards the micropylar end and the chalazal end.
- Again, they undergo mitotic division continuously, until they formed 8-nucleate cells.
- Now, the cell has four nuclei each on either end.
- At the micropylar end, three out of the four nuclei convert into an egg cell and synergids.
- Whereas, at the chalazal end, three out of the four nuclei convert into antipodal cells.
- Now, the remaining cells, each from either end move towards the centre. They are known as polar nuclei.
The 8-nucleate cells become 7-celled structure after maturation.
7. What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.
Ans: Chasmogamous flowers are flowers that exhibit an open or exposed petals to allow mode of cross-pollination. In these flowers, male reproductive organs, such as the stamens and female reproductive organs such as pistils are allowed to pollinators like insects, birds, or wind.
Cross-pollination is not allowed in cleistogamous flowers as they are small and have closed organs which allowed for cross-pollination. But self-pollination is allowed as stigma and anther are present near each other.
8. Mention two strategies evolved to prevent self-pollination in flowers.
Ans: The two strategies involved in preventing self-pollination in flowers are:
- Dichogamy – It is the process where male reproductive organs (stamens) mature and release pollen before the female reproductive organs (pistils) become receptive. Thus, prevents self-pollination.
- Self-incompatibility – It is a genetically controlled mechanism in which pollen grains of a flower are unable to grow completely on the stigma of the same flower.
9. What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
Ans: Self-incompatibility refers to a genetically controlled mechanism that prevents self-pollination and promotes cross-pollination in flowers. Self-pollination cannot lead to the formation of seeds in a self-incompatible species. This happens because the pollens are unable to fertilize the ovules that would develop into an embryo and hence form seeds.
10. What is bagging technique? How is it helpful in a plant breeding programme?
Ans: The bagging technique helps prevent fertilization of the stigma by any undesired pollen by covering the emasculated flower (flower whose anther is removed) with a polybag or butter paper. The bagging technique is beneficial in the plant breeding programme. In this, only desired pollens are made to fertilize the stigma in order to produce plants with desired characteristics.
11. What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
Ans: Triple fusion occurs when a male gamete fuses with two polar nuclei within the embryo sac of flowering plants. The following events take place in triple fusion:
- The pollen grains get dusted on the stigma and germinate, giving rise to a pollen tube that enters the ovule.
- The pollen tube passes into one of the synergids and releases two male gametes.
- One out of the two gametes’ fuses with the egg nucleus and forms a zygote.
- The other gamete fuses with the two polar nuclei located in the central cell and forms a triploid endosperm nucleus.
The nuclei involved in triple fusion are:
- A male gamete nucleus
- Two polar nuclei
12. Why do you think a zygote is dormant for some time in a fertilized ovule?
Ans: The zygote remains inactive until the endosperm is formed as a result of triple fusion. The endosperm provides nutrition to the developing embryo and is formed from the primary endosperm cell that results from triple fusion.
13. Differentiate between:
- Epicotyl and hypocotyl
- Coleoptile and coleorrhiza
- Integument and testa
- Perisperm and pericarp
Ans: Differences between are as follow:
- Epicotyl and hypocotyl
| Epicotyl | Hypocotyl |
| Region of embryo above the cotyledon. | Region of the embryo below the cotyledon. |
| Terminates at the plumule. | Terminates at the cotyledonary node. |
| Starts from the cotyledonary node. | Starts from the radicle. |
| Develops into the upper part of the stem. | Develops into that part of the stem that develops into roots. |
| Elongates in epigeal germination. | Elongates in hypogeal germination. |
- Coleoptile and coleorrhiza
| Coleoptile | Coleorrhiza |
| It is a protective sheath. | It is an undifferentiated sheath. |
| Protects young shoot tip in cereals and grass. | Protects the roots of a germinating grass or cereal. |
| Comes out of the soil. | Remains inside the soil. |
| Covers the plumule. | Covers the root cap and radical. |
| Breaks the seed coat and grows. | Breaks the seed coat and stops growth. |
- Integument and testa
| Integument | Testa |
| Covers the ovule. | Outer covering of seed. |
| The cells are living. | The cells are dead. |
| Pre-fertilized structure. | Post-fertilized structure. |
| Sclereids are absent. | Sclereids are present. |
| One or two layered. | One layered. |
- Perisperm and pericarp
| Perisperm | Pericarp |
| Part of a seed. | Part of a fruit. |
| Usually, dry. | Dry or fleshy. |
| Present in only a few seeds. | Found in all fruits. |
| Non-functional in seed. | Protects the fruit and helps in nutrition and dispersal. |
14. Why is apple called a false fruit? Which part of the flower forms the fruit?
Ans: A false fruit is derived from some secondary parts and not from the ovary. Apple is derived from the thalamus and is hence called a false fruit.
15. What is meant by emasculation? When and why does a plant breeder employ this technique?
Ans: Emasculation refers to the removal of stamens from bisexual flowers before the maturation of the anther in order to avoid self-pollination in the flowers. This technique is employed when the breeder wants plants of desired characteristics. The flowers are bagged even before the anther matures. When the anther matures, the pollen grains are shed on the covered stigma and are allowed to pollinate with the flowers of the desired characteristics.
16. If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?
Ans: Parthenocarpy refers to the development of fruits without fertilization. Fruits devoid of seeds, such as watermelon and muskmelon, are in great demand. Therefore, these varieties will be developed by parthenocarpy.
17. Explain the role of tapetum in the formation of pollen grain walls.
Ans: Tapetum is the internal layer of microsporangium and plays an important role in the formation of pollen grain walls. It provides nutrition to the maturing pollen grains. Various amino acids, enzymes, and hormones are produced by tapetum cells that are essential for the maturation of pollen grains. Tapetum also forms the exine layer of pollen grains.
18. What is apomixis and what is its importance?
Ans: Apomixis is the process of seed formation without the occurrence of fertilization (the process of meiosis and syngamy, to be precise). It plays a vital role in the production of hybrid seeds. Apomixis inhibits the loss of desired characters in a hybrid. Also, the process of production of hybrid seeds through cultivation is expensive. Therefore, apomixis is used for the production of hybrid seeds.