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

NCERT Solutions for Class 12 Biology Chapter 2 Sexual Reproduction in Flowering Plants is the essential study material needed to perfect Sexual Reproduction in Flowering Plants topics.

NCERT Class 12 Biology solutions provided here have correct answers to NCERT textbook questions. Solutions curated in a comprehensive manner will help students to understand the subtopics in this chapter in a better way.

IMPORTANT SUB-TOPICS MENTIONED IN THE NCERT CLASS 12 BIOLOGY CHAPTER 2 SEXUAL REPRODUCTION IN FLOWERING PLANTS:

NCERT Solutions for Class 12 Biology Chapter 2 Sexual reproduction in flowering plants has the following sub-topics as given below:

Sr. no	Topics
1	Flower- A Fascinating Organ of Angiosperms
2	Pre-fertilisation- Structures and Events
3	Double Fertilisation
4	Post-fertilisation- Structures and Events
5	Apomixis and Polyembryony

NCERT SOLUTIONS CLASS 12 BIOLOGY CHAPTER 2 SEXUAL REPRODUCTION IN FLOWERING PLANTS:

1. Name the parts of an angiosperm flower in which the development of male and female gametophytes takes place.

Answer – In an angiosperm flower in which development of male and female gametophytes takes place in anther and ovules, respectively.

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.

Answer – Differences between microsporogenesis and megasporogenesis are as follows:

MICROSPOROGENESIS	MEGASPOROGENESIS
The process of formation of microspores from a pollen mother cell (PMC) through meiosis is called microsporogenesis.	The process of formation of megaspores from the megaspore mother cell is called megasporogenesis.
Pollen grains are produced.	Embryo sac is produced.
It occurs inside the pollen sacs.	It occurs inside the ovules.
The arrangement of microspores is tetrahedral.	The arrangement of megaspores is linear.
All four microspores are fuctional.	One out of four megaspores is functional.

Miotic division takes place during microsporogenesis and megasporogenesis. This is also called reduction division to produce haploid gametes.

The structure formed at the end of these two events:

• Microsporogenesis- Pollen Grain
• Megasporogenesis- Embryo sac

3. Arrange the following terms in the correct developmental sequence: Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, and male gametes.

Answer – The correct developmental sequence for the formation of male gametes-
Sporogenous tissue→ Pollen mother cell→ Microspore tetrad→ Pollen grain → Male gametes

4. With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.

Answer –

An ovule is a small structure which is formed inside the ovary and is also called female megasporangium where the formation of megaspores takes place. The various parts of an ovule are as follows:

• Funicle- The stalk with which the ovule is attached to the placenta of the ovary.
• Hilum- The point in the body of ovule where the funicle is attached.
• Integuments- The outer layer of the ovule that provides protection to the developing embryo.
• Micropyle- Integuments encircle the nucellus except at the tip where a small opening called the micropyle is organized. It is the point where the pollen tube enters the ovule at the time of fertilisation.
• Nucellus- It is the mass of parenchymatous tissues that surrounds the embryo sac and gives nutrition to the developing embryo sac.
• Chalazal- It is the swollen part of the nucellus from where the integuments originate.

5. What is meant by monosporic development of female gametophyte?

Answer – In a majority of flowering plants, one of the megaspores out of the four is functional while the other three degenerate. Only the functional megaspore develops into the female gametophyte (embryo sac). This method of embryo sac formation from a single megaspore is termed monosporic development.

6. With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.

Answer –

Only the functional megaspore develops into the female gametophyte (embryo sac). The process of formation of the 7-celled, 8-nucleate nature of the female gametophyte is mentioned below-

• The nucleus of the functional megaspore divides mitotically to form two nuclei which move to the opposite poles, i.e. micropylar and chalazal end respectively, forming the 2-nucleate embryo sac.
• Two more sequential mitotic nuclear divisions result in the formation of the 4-nucleate and later the 8-nucleate stages of the embryo sac. These mitotic divisions are strictly nuclear.
• At the micropylar end, three nuclei differentiate into an egg cell and two synergids. The egg cell and three synergids together make the egg apparatus.
• At the chalazal end, the three nuclei differentiate into three antipodal cells.
• Remaining two nuclei make polar nuclei and move towards the centre making a central cell.
• Therefore, this makes a 7-celled 8-nucleate structure.

7. What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.

Answer –

• Chasmogamous flowers which are similar to flowers of other species with exposed anthers and stigma and allow cross-pollination. Examples- Viola (common pansy), Oxalis, and Commelina.
• Cleistogamous flowers do not open at all. There anther and stigma are close to each other, therefore when anthers dehisce in the flower buds, pollen grains come in contact with the stigma to affect pollination. They are invariably autogamous and cannot undergo cross-pollination.

8. Mention two strategies evolved to prevent self-pollination in flowers.

Answer – The strategies involved in preventing self-pollination in flowers are-

• Self-incompatibility- Self-incompatibility refers to a genetically controlled mechanism that prevents self-pollination and promotes cross-pollination. In this, pollen grains of a flower are unable to grow pollen tubes on the stigma of the same flower.
• Dichogamy- It refers to the production of the male and female reproductive organs at different times in order to prevent self-pollination.

9. What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?

Answer – Self-incompatibility refers to a genetically controlled mechanism that prevents self-pollination and promotes cross-pollination. Self-pollination cannot lead to the formation of seeds in the self-incompatible species. This is because the pollens are not able to fertilise the ovules of the same plant, therefore, preventing the formation of seeds.

10. What is the bagging technique? How is it useful in a plant breeding programme?

Answer –

• Emasculated flowers are covered with a bag of suitable size, generally made up of butter paper, to prevent contamination of its stigma with unwanted pollen. This process is called bagging.
• Plant breeders use this technique to prevent the contamination of stigmas with unwanted pollen during artificial hybridisation.

11. What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.

Answer –

• The other male gamete moves towards the two polar nuclei located in the central cell and fuses with them to produce a triploid primary endosperm nucleus (PEN). As this involves the fusion of three haploid nuclei it is termed triple fusion.
• This process takes place in the embryo sac.
• The following events take place during triple fusion:
  • The pollen grains on the stigma germinate a pollen tube which enters the ovule and reaches the micropylar end of the embryo sac.
  • The pollen tube passes into one of the synergids and releases two male gametes.
  • One male gamete fuses with the egg nucleus to form a zygote.
  • The other male gamete fuses with two polar nuclei located in the central cell to form triploid PEN.
• Nuclei involved in the triple fusion are;
  • A male gamete nucleus
  • Two polar nuclei from the central cell.

12. Why do you think the zygote is dormant for some time in a fertilised ovule?

Answer – The zygote remains dormant until the formation of the endosperm, the product of triple fusion. The endosperm provides assured nutrition to the developing embryo.

13. Differentiate between

• (a) hypocotyl and epicotyl;
• (b) coleoptile and coleorhiza;
• (c) integument and testa;
• (d) perisperm and pericarp

Answer –

(a) hypocotyl and epicotyl

HYPOCOTYL	EPICOTYL
The part of embryo above the cotyledon.	The part of the embryo below the cotyledon.
It terminates at the plumule.	It terminates at the cotyledonary node.
Develops into the upper part of the stem.	Develops into the part of the stem that develops into the root.
Elongates in epigeal germination.	Elongates in Hypogeal germination.

(b) coleoptile and coleorhiza

COLEOPTILE	COLEORRHIZA
It is a protective sheath.	It is an undifferentiated sheath
It protects young shoot tips in cereals and grass.	It protects the roots of germinating grass and cereals.
Covers the plumule.	Covers the radical.
It comes out of the soil.	It remains inside the soil.

(c) integument and testa;

INTEGUMENT	TESTA
It is the covering of the ovule.	It is the covering of seeds.
The cells of integuments are living.	The cells of the testa are dead.
It is pre fertilised structure.	It is post fertilised structure.
It is one or two-layered.	It is one-layered.
Sclereids are absent.	Cells are rich in sclereids.
It arises from the Chazal end of the ovule.	It is derived from the outer integument of the ovule after fertilisation.

(d) perisperm and pericarp

PERISPERM	PERICARP
It is a part of a seed, i.e, an unused part of the nucellus of the seed.	It is part of a fruit, i.e., the outermost covering of the fruit wall developed from the ovary wall.
It is usually dry.	It is dry or fleshy.
It is often non-functional for seed.	It is a protective covering and also helps in dispersal and nutrition.
It is present in a few seeds.	It is present in all fruits.

14. Why is apple called a false fruit? Which part(s) of the flower forms the fruit?

Answer – A false fruit is a fruit derives from any other secondary part and not the ovary. Apple fruit is formed 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?

Answer –

• If the female parent bears bisexual flowers, the removal of anthers from the flower bud before the anther dehisces using a pair of forceps is called emasculation.
• The technique of emasculation is employed in artificial hybridisation when the breeder wants to perform controlled pollination with the pollens of desired traits.

16. If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?

Answer – Parthenocarpy is the development of fruits without fertilisation. As parthenocarpic fruits are seedless, bananas, grapes, oranges, pineapples, guava, watermelon, and lemon because their seedless units are of economic importance. Fruits with seeds as edible parts are not selected for parthenocarpy.

17. Explain the role of tapetum in the formation of pollen-grain wall.

Answer –

• Tapetum is the innermost layer of the microsporangium and plays a part in the formation of pollen grains.
• Cells of the tapetum possess dense cytoplasm and generally has more than one nucleus. It provides nourishment to the maturing pollen grains.
• It also forms the exine layer in the pollen grains.

18. What is apomixis and what is its importance?

Answer –

• Apomixis is a form of asexual reproduction that mimics sexual reproduction. In some flowering species of Asteraceae and grasses, the plant produces seeds without fertilisation.
• Hybrid seeds are extensively cultivated to increase yield. But the seeds of the hybrids are to be produced each year which is not an economic method for farmers.
• This can be prevented by introducing apomixis in hybrid seed technology.

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