Class 12 Biology Chapter 1 Sexual Reproduction in Flowering Plants Solutions. Master Class 12 Biology Chapter 1 Sexual Reproduction in Flowering Plants with NCERT solutions, important questions, and easy-to-understand answers for exam preparation.

Class 12 Biology Chapter 1 Sexual Reproduction in Flowering Plants Solutions

A. Very Short-Answer Questions (1 mark each)

1. What is a stamen?

Ans: A stamen is one of the long, slender, hair-like structures that make up the androecium of a flower.

2. What is a pollen grain?

Ans: The anther of a flower contains numerous fine, powder-like particles. These particles are called pollen grains.

3. What does sterility mean?

Ans: Sterility means the inability to reproduce.

4. Name two plants that have sterile pollen grains.

Ans: Pineapple and Sonaru.

5. What is sporopollenin?

Ans: Sporopollenin is a special substance present in the outer wall of a pollen grain. It protects the pollen grain from heat, acids, enzymes and other environmental stresses.

6. What structures are formed when the cells of a flower bud differentiate?

Ans: Sepals, petals, stamens and carpels are formed.

7. Which cells form the tapetum?

Ans: The source states that sporogenous cells form the tapetum.

8. How many sporangia can develop in an anther?

Ans: Four.

9. What is the main function of the tapetum?

Ans: Its main function is to provide nourishment to the developing pollen grains.

10. What is the outer wall of a pollen grain made of?

Ans: It is made of a substance called sporopollenin.

11. What is sporogenesis?

Ans: Sporogenesis is the developmental process that begins in the anther and continues until spores are produced in the pollen sacs.

12. Which cell produces the embryo sac?

Ans: The megaspore mother cell gives rise to the female gametophyte/embryo-sac lineage.

13. Which cells are present in the egg apparatus of the embryo sac?

Ans: Two synergids and one egg cell.

14. What is an embryo sac?

Ans: The embryo sac is the structure formed when a functional megaspore undergoes three mitotic divisions to produce an eight-nucleate structure. It contains the female reproductive cell for embryo formation and the nuclei involved in endosperm formation.

15. What is meant by seed development?

Ans: Seed development involves the development of the zygote into an embryo and the development of the primary endosperm nucleus into the endosperm.

16. What is pollination?

Ans: Pollination is the transfer of pollen grains from the anther to the stigma of a flower.

17. What are the two cells of a mature pollen grain?

Ans: The vegetative cell and the generative cell.

18. What is a carpel or pistil?

Ans: A carpel is a unit of the gynoecium, the female reproductive whorl of a flower.

19. Which parts of the carpel develop into the fruit and seed?

Ans: The ovary develops into the fruit, and the ovule develops into the seed.

20. How many haploid cells or nuclei are present in the female gametophyte of a flowering plant?

Ans: Eight nuclei are present in the typical mature embryo sac.

21. What is an ovule?

Ans: An ovule is a small structure attached to the placenta inside the ovary.

22. What do ovules develop into?

Ans: Ovules develop into seeds.

23. What structures are present in an ovule?

Ans: The ovule contains the funicle, hilum, integuments, micropyle, chalaza and embryo sac.

24. What is the pollen–pistil interaction?

Ans: Pollen–pistil interaction is the series of events that occurs after a pollen grain lands on the stigma and continues until the male gametes are formed and delivered.

25. Which cell of the embryo is called the hypophysis?

Ans: The cell at the base of the embryo, towards the micropylar end, is called the hypophysis.

26. Into which parts is the embryo axis divided?

Ans: It is divided into the epicotyl, hypocotyl and cotyledon(s).

27. What is the main difference between monocot and dicot embryos?

Ans: A monocot embryo has one cotyledon, generally terminal in position, while a dicot embryo has two cotyledons, generally lateral in position.

28. From where does an embryo obtain food for its growth and development?

Ans: From the endosperm.

29. What is parthenocarpy?

Ans: Parthenocarpy is fruit development from the ovary without fertilisation. Such fruits are generally seedless.

30. What is agamospermy?

Ans: Agamospermy is the formation of seeds and embryos without fertilisation.

31. Which hormone promotes the initial growth of the ovary?

Ans: Auxin.

32. Name the growth-promoting hormones involved in seed development.

Ans: Auxins, cytokinins and gibberellins.

33. What is a true fruit? Give examples.

Ans: A fruit that develops from the ovary is called a true fruit. Examples include mango, orange and brinjal.

34. What is a false fruit? Give examples.

Ans: A fruit that develops from parts other than the ovary, in addition to or instead of the ovary, is called a false fruit. Examples include apple, cashew apple and strawberry. (The final example in the source is unclear.)

35. Why is an apple called a false fruit?

Ans: An apple develops largely from the thalamus rather than from the ovary alone; therefore, it is called a false fruit.

36. Into what is the starch in a fruit converted during ripening?

Ans: It is converted into sugars.

37. Which chemicals make unripe fruits bitter or astringent?

Ans: Substances such as anthocyanins and tannins are mentioned in the source; the first term is unclear in the supplied text.

38. Name two hormones necessary for fruit development.

Ans: Auxin and gibberellin.

39. What is apomixis? What type of reproduction is it?

Ans: Apomixis is seed formation without fertilisation. It is a form of asexual reproduction.

40. Flowers pollinated by wind are generally …….. in nature.

Ans: Unisexual.

41. The outer wall of pollen grains can withstand extreme heat and dryness because it is made of ……..

Ans: Sporopollenin.

42. The chromosome number of the secondary nucleus in the centre of the embryo sac is ……..

Ans: Diploid (2n).

43. The first cell of the embryo sac is ……..

Ans: The functional megaspore.

44. The antipodal cells and synergids are formed in the embryo sac.

Ans: The source wording is unclear; the expected terms appear to be antipodal cells and synergids.

45. The water of a tender coconut is ……..

Ans: Free-nuclear endosperm.

46. In flowering plants, the role of double fertilisation is to produce ……..

Ans: Endosperm. (The source gives this as the only product, but double fertilisation also produces a zygote.)

47. The point where an ovule is attached to the placenta is called the ……..

Ans: Hilum.

48. The …….. of the carpel develops into the fruit, and the …….. develops into the seed.

Ans: Ovary; ovule.

49. Flowers pollinated by …….. are small and produce pollen grains in large quantities.

Ans: Wind.

B. Short-Answer Questions (Sexual Reproduction in Flowering Plants Solutions)

50. Draw a longitudinal section of a flower and label its parts. (HS ‘24)

Ans: A labelled diagram is required. The source does not contain the diagram.

51. Describe the structure of a pollen grain.

Ans: A pollen grain is generally oval or spherical. It has a thick, often spiny outer wall and a thin inner wall made of cellulose-like material. The outer wall, called the exine, is composed of sporopollenin. It has germ pores through which the pollen tube emerges during germination. A pollen grain typically contains a vegetative cell and a generative cell. The generative cell divides to form two male gametes.

52. Describe the development of the female gametophyte.

Ans: Before the female gametophyte develops, one cell in the middle of the nucellus of the ovule becomes distinct from the surrounding cells. It has dense cytoplasm and a large nucleus. This cell divides transversely into two cells: one towards the outside and the other towards the inside. The outer cell divides repeatedly to form the outer tissue. The inner cell has a diploid nucleus. Meiosis in the megaspore mother cell produces four haploid cells. The three cells at one end degenerate, while the remaining functional megaspore develops into the female gametophyte.

53. What is the bagging technique? Why is it important in plant breeding?

Ans: The bagging technique is used in artificial hybridisation. In a bisexual flower, the anthers are removed without damaging the female reproductive organs, and the flower is covered with a bag to prevent unwanted pollination. This ensures that only pollen from the selected parent is used to pollinate the stigma, helping breeders obtain the desired hybrid.

54. What are self-pollination and cross-pollination? (HS ‘24)

Ans: Self-pollination is the transfer of pollen grains to the stigma of the same flower or another flower on the same plant. Cross-pollination is the transfer of pollen grains from a flower on one plant to the stigma of a flower on another plant of the same species.

55. Explain the statement: “Angiosperms undergo double fertilisation.”

Ans: In angiosperms, two fertilisation events occur. One male gamete fuses with the egg cell to form the zygote, while the other male gamete fuses with the secondary nucleus (formed by the polar nuclei) to form the primary endosperm nucleus. Therefore, this process is called double fertilisation.

56. Describe how cross-pollination occurs through insects or wind.

Ans: Insect pollination: Insects visit flowers in search of nectar or other food. Pollen grains stick to their bodies. When the insects visit another flower of the same species, some pollen grains are deposited on its stigma, resulting in cross-pollination.

Wind pollination: Pollen grains are very light and can be carried by the wind over long distances. They may land on the stigma of another flower of the same species, resulting in cross-pollination.

57. How does pollination occur in Vallisneria?

Ans: Vallisneria is an aquatic plant. The male and female flowers are borne on separate plants. When the male flowers mature, they detach and float on the water surface. At the same time, the stalk of the female flower elongates and brings the flower to the surface. Contact with the floating male flowers allows pollination to occur. After pollination, the stalk of the female flower coils and draws the flower underwater.

58. State the advantages and disadvantages of self-pollination.

Advantages: In bisexual flowers, the stamens and carpels are present in the same flower, so pollination can occur easily. Because they are close to each other, pollen wastage is reduced.

Disadvantage: Self-pollination produces little genetic variation and may not produce improved offspring.

59. Describe the advantages and disadvantages of cross-pollination.

Ans: Advantages: Cross-pollination can produce vigorous seeds and offspring with improved traits and better adaptability to environmental conditions. It may give rise to plants with desirable varieties.

Disadvantages: It depends on external agents. Flowers may need adaptations to attract insects, and pollen grains may need special features to attach to insects or be carried by wind. A considerable amount of pollen may be wasted.

60. Describe the process of double fertilisation.

Ans: After the pollen tube enters a synergid, the two male gametes are released into its cytoplasm. One male gamete moves towards the egg cell and fuses with it to form a diploid zygote. The other male gamete moves towards the two polar nuclei in the central cell and fuses with them to form the primary endosperm nucleus, which is usually triploid. The fusion of one male gamete with the egg and the other with the central cell is called double fertilisation.

C. Descriptive Questions (Sexual Reproduction in Flowering Plants Solutions)

61. Describe the mechanisms of self-pollination.

Ans: The mechanisms include:

Cleistogamy: Some bisexual flowers never open. Therefore, reproduction takes place through self-pollination. Examples given in the source include balsam and Portulaca; one plant name is unclear.

Homogamy: In some flowers, the anthers and stigma mature at the same time, so self-pollination usually occurs. In some flowers, mature stamens bend towards the stigma, allowing pollen to reach it. The source gives the evening glory as an example.

Self-pollination may also occur in flowers that usually undergo cross-pollination if cross-pollination fails. When the stigma grows past already mature stamens, pollen attached to the stamens or petals may reach the stigma. The source gives periwinkle as an example.

62. What is self-incompatibility? Why do such flowers fail to produce seeds through self-pollination?

Ans: In some flowers, pollen grains cannot fertilise the egg cells of the same flower because the pollen and the female reproductive tissue are genetically incompatible. Consequently, self-pollination usually does not result in fertilisation or seed formation. Such flowers need pollen from another flower for fertilisation.

63. Discuss the mechanisms that promote cross-pollination.

Ans: The mechanisms include:

Unisexuality: In unisexual flowers, cross-pollination is the only possible means of pollination. Examples include pumpkin, maize and papaya.

Self-incompatibility: In some bisexual flowers, self-pollination may occur, but fertilisation does not take place. Fertilisation occurs only when compatible pollen from another flower reaches the stigma. Examples given in the source include tea and a climbing plant whose name is unclear.

Dichogamy: In many bisexual flowers, the androecium and gynoecium do not mature at the same time, promoting cross-pollination. Examples in the source are unclear.

Herkogamy/heterostyly: In some bisexual flowers, the stamens and styles occur at different heights. In one flower, the stamens are short and the style is long; in another, the stamens are long and the style is short. This arrangement promotes pollen transfer between flowers. Primrose is given as an example.

64. How are artificial hybrids produced? Explain.

Ans: Hybridisation combines desirable characteristics of two plants to produce a new plant. It has been used to develop improved varieties of rice, wheat, maize, sugarcane and other crops. The parent plants may be different varieties of the same species or, in some cases, different species. Crosses between varieties of the same species are generally easier. For example, one rice variety may produce many seeds but be susceptible to disease, while another may produce fewer seeds but have greater disease resistance. Crossing them may produce hybrids that combine desirable traits from both parents.

65. Explain the statement: “Sterility is a natural barrier to the fusion of gametes.”

Ans: Sterility may arise for different reasons. Sometimes the male or female gametes are non-functional. In other cases, even when pollen reaches the stigma of the same flower, it fails to germinate, preventing inbreeding. Cross-pollination can produce healthier seeds and fruits and offspring with improved traits. It also contributes to species evolution. Plants therefore use several mechanisms to promote cross-pollination. Self-incompatibility in bisexual flowers is an important mechanism: it prevents self-pollination from resulting in fertilisation and favours cross-pollination.

66. Discuss the steps involved in producing hybrids.

Ans: The steps are as follows:

1. Select the male and female parent plants of the desired varieties for the breeding experiment. They should flower at approximately the same time.
2. If the female parent has bisexual flowers, remove the anthers from the selected flowers. If there are many flowers, select only some and remove the others.
3. Cover each selected female flower with a clean polythene bag to prevent pollen from other plants from reaching the stigma.
4. When the stigma of the female flower and the anthers of the male flower are mature, collect pollen from the mature anthers with a clean brush and place it on the stigma. Immediately cover the flower again. Remove the bag after fertilisation is evident and the ovary begins to develop.
5. Collect the seeds carefully after they mature, for study and for testing in the next generation.
6. Explain the different types of polyembryony and their causes.

Ans: Polyembryony is the development of more than one embryo in a single ovule or seed. The types described in the source are:

Simple polyembryony: More than one embryo is present, associated with the fertilisation of more than one egg. Mustard is given as an example in the source.

Mixed polyembryony: More than one pollen tube enters an embryo sac, and an additional male gamete fuses with a synergid. Examples given include Allium, Plantago and Poa.

Cleavage polyembryony: One embryo splits to form two or more embryos. Lemon is given as an example.

D. Additional Questions and Answers (Sexual Reproduction in Flowering Plants Solutions)

1. Name the four layers of the anther wall.

Ans: The epidermis, endothecium, middle layers and tapetum.

2. What is monosporic development?

Ans: It is the development of the female gametophyte from a single functional megaspore.

3. What is the function of the tapetum?

Ans: It provides nourishment to developing pollen grains.

4. What is pollen recognition or pollen compatibility?

Ans: It is the ability of the stigma and style to distinguish compatible pollen from incompatible pollen.

5. What are the stages of artificial reproduction by hybridisation?

Ans: They include emasculation of the bisexual flower on the female parent, bagging the female flower, collecting pollen from the male parent, transferring the pollen to the stigma, and bagging the flower again so that the fruit can develop.

6. Which fruits are seedless?

Ans: Fruits that develop without fertilisation are called seedless fruits. Banana is an example.

7. What changes result in fruit formation?

Ans: The ovule develops into a seed, and the ovary develops into a fruit.

8. How can pollen grains be preserved?

Ans: Pollen grains can be preserved in liquid nitrogen for long periods.

9. How can parthenocarpy be induced?

Ans: Parthenocarpy can be induced by applying growth hormones.

10. What are the advantages of vegetative propagation?

Ans: Its advantages include:

(i) preserving the desirable characteristics of the parent plant;

(ii) allowing plants with low sexual reproductive capacity to be propagated easily;

(iii) enabling propagation of plants whose seeds are weak or difficult to develop;

(iv) helping eliminate certain systemic diseases when healthy propagation material is used; and

(v) producing economically important plants within a short period.

11. Distinguish between syngamy and triple fusion.

Ans: In angiosperms, one male gamete from the pollen tube fuses with the egg cell to form a zygote. This fusion is called syngamy.

The second male gamete fuses with the two polar nuclei in the central cell, forming a triploid primary endosperm nucleus. This is called triple fusion.

12. What is hydrophily?

Ans: Hydrophily is pollination in which water transfers pollen grains from the anther of one flower to the stigma of another flower. It occurs in only some aquatic plants, such as Vallisneria and Zostera.

13. What is apomixis? Explain its importance.

Ans: Apomixis is seed formation without meiosis and syngamy. It is useful in agriculture because producing hybrid seeds can be expensive. Apomixis can reduce the cost of producing hybrid seed and preserve desirable characteristics across generations.

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