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

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Question 13:

Draw the diagram of a mature embryo sac and show its 8-nucleate, 7-celled nature. Show the following parts: antipodals, synergids, egg, central cell, polar nuclei.

Answer:

Image of Mature Embryo sac and 8-nucleate, 7-celled nature.

Image of Mature Embryo Sac and 8-Nucleate, 7-Celled Nature.

Image of Mature Embryo sac and 8-nucleate, 7-celled nature.

The antipodal is 3-celled with 3 nucleus.

Polar nuclei and Central cell constitute 2 nucleus and it is 1-celled.

Egg apparatus is 3-celled with 3 nucleus.

So in total there are 7-celled and 8-nucleate.

Question 14:

Which is the triploid tissue in a fertilised ovule? How is the triploid condition achieved?

Answer:

The triploid tissue in a fertilised ovule is endosperm which is developed from Primary Endosperm nucleus.

This triploid condition is achieved by fusion of three haploid nuclei called triple fusion. The three haploid nuclei are one male gamete and two haploid polar nuclei.

Question 15:

Are pollination and fertilisation necessary in apomixis? Give reasons.

Answer:

Apomixis is a form of asexual reproduction that mimics sexual reproduction.

i. Apomixis is development of a seeds without prior fertilization. Apomixis avoids the processes of meiosis and fertilization, leading to embryo development.

ii. The diploid egg cell in many species is formed without reduction division and develops into the embryo without fertilization.

Hence pollination and fertilisation are not necessary in apomixes.

Question 16:

Identify the type of carpel with the help of diagrams given below:

Chapter-2- Question - 16-Image of the Carpel

Chapter-2- Question - 16-Image of the Carpel

Chapter-2- Question - 16-Image of the Carpel

Answer:

Carpel can be of two types Monocarpellary (single pistil) or Multi carpellary (more than one pistil).

In multi carpellary the pistils may be fused called Syncarpous or pistils may be free called Apocarps.

So the diagram (a) is Syncarpous multi carpellary (i.e., have more than one pistil fused together).

The diagram (b) is Apocarps multi carpellary (i.e., have more than one pistil but free).

Question 17:

How is pollination carried out in water plants?

Answer:

Pollination carried in water plants are in following ways:

i. Pollination above the surface of water: In few species, female flower reach the surface of water by the long stalk and pollen grains from male flowers are released on to the surface of water. These pollen grains are carried by water currents. And out of these some of them reach the female flowers and the stigma. For example in Vallisnaria

ii. Pollination below the surface of water: In few species, female flowers remain submerged in water and the pollen grains are released inside the water. Pollen grains in such species are long, ribbon like and they are carried passively inside the water; some of them reach the stigma and achieve pollination. Example Sea grasses.

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