Biology Class 12 NCERT Solutions: Chapter 1 Reproduction in Organisms Part 5

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Q.15 Describe the post-fertilization changes in a flower.

Answer:

  • Fertilization is the process of the fusion of the male and the female gamete to form a diploid zygote. After fertilization, the zygote divides several times to form an embryo.

  • The fertilized ovule forms a seed. The seed contains an embryo, enclosed in a protective covering, called the seed coat.

  • As the seed grows further, other floral parts wither and fall off. This leads to the growth of the ovary, which enlarges and ripens to become a fruit with a thick wall called the pericarp.

  • In flowering plants, zygote is formed inside the ovule. After fertilization, sepals, petals and stamens of the flower wither and fall off.

  • The pistil remains attached to the flower. Zygote forms the embryo and ovule having embryo forms the seed. Ovary wall develop into fruit wall (pericarp). Ovary develops into fruit

Image of Post-Fertilization Changes

Image of Post-Fertilization Changes

Q.16 What is a bisexual flower? Collect five bisexual flowers from your neighbourhood and with the help of your teacher find out their common and scientific names.

Answer:

  • A flower that contains both the male and female reproductive structure (stamen and pistil) is called a bisexual flower.

  • Examples of plants bearing bisexual flowers are:

  • Water lily ( Nymphaea odorata)

  • Rose (Rosa multiflora )

  • Hibiscus (Hibiscus Rosa-sinensis )

  • Mustard ( Brassica nigra)

  • Petunia (Petunia hybrida)

Q.17 Examine a few flowers of any cucurbit plant and try to identify the staminate and pistillate flowers. Do you know any other plant that bears unisexual flowers?

Answer:

Image of Cucurbit Plant

Image of Cucurbit Plant

  • Cucurbit plant bears unisexual flowers as these flowers have either the stamen or the pistil. The staminate flowers bear bright, yellow coloured petals along with stamens that represent the male reproductive structure.

  • On the other hand, the pistillate flowers bear only the pistil that represents the female reproductive structure.

  • Other examples of plants that bear unisexual flowers are corn, papaya, cucumber, etc.

Q.18 Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?

Answer:

  • Oviparous animals lay eggs outside their body. As a result, the eggs of these animals are under continuous threat from various environmental factors.

  • On the other hand, in viviparous animals, the development of the egg takes place inside the body of the female.

  • Hence, the offspring of an egg-laying or oviparous animal is at greater risk as compared to the offspring of a viviparous animal, which gives birth to its young ones.

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