Biology Class 12 NCERT Solutions: Chapter 2 Sexual Reproduction in Flowering Plants Part 5

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Q.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 process of developing fruits without involving the process of fertilization or seed formation.

  • Therefore, the seedless varieties of economically important fruits such as orange, lemon, water melon etc. are produced using this technique.

  • This technique involves inducing fruit formation by the application of plant growth hormones such as auxins.

  • Parthenocarpic fruits are seedless. Because seedless fruits in plants like banana, grapes and guava are in great demand, the process is of practical value

Image of Process of Fertilization or Seed Formation

Image of Process of Fertilization or Seed Formation

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

Answer:

  • Tapetum is the innermost layer of the microsporangium. It provides nourishment to the developing pollen grains.

  • During microsporogenesis, the cells of tapetum produce various enzymes, hormones, amino acids, and other nutritious material required for the development of pollen grains.

  • It also produces the exine layer of the pollen grains, which is composed of the sporopollenin.

Image of Developing Pollen Grains

Image of Developing Pollen Grains

Q.18 What is apomixes and what is its importance?

Answer:

  • Apomixes is the mechanism of seed production without involving the process of meiosis and syngamy. It plays an important role in hybrid seed production.

  • The method of producing hybrid seeds by cultivation is very expensive for farmers.

  • Also, by sowing hybrid seeds, it is difficult to maintain hybrid characters as characters segregate during meiosis.

  • Apomixes prevents the loss of specific characters in the hybrid. Also, it is a cost-effective method for producing seeds.

  • In apomixis seeds are formed without fertilization. It has been reported particularly in grasses

  • Apomixis has advantages in horticulture and agriculture. Apomixis term was coined by Winkier (1906).

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