NCERT Class 12 Biology: Chapter – 2 Sexual Reproduction in Flowering Plants Part 4 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 6:

In the diagram given below, show the path of a pollen tube from the pollen on the stigma into the embryo sac. Name the components of egg apparatus.

Chapter-2- Question - 6-Pollen Tube

Answer:

Pollen tube, Antipodal, Polar Nuclei, Egg cell, Synergids

Explanation: the path of a pollen tube from the pollen on the stigma into the embryo sac is as listed below (as shown in figure) :

i. After the pistil selects the compatible pollen grain pollination takes place by pollen grain getting germinated on the stigma to produce a pollen tube. The pollen tube is generated from any of the germ pores.

ii. The contents of the pollen grain now move into the pollen tube.

iii. Now the pollen tube grows through the tissue of the style and reaches the ovary.

iv. Now it enters the ovule through Micropyle and enters the embryo sac through one of the two synergids. And the synergid is degenerated.

Question 7:

Name the parts of pistil which develop into fruit and seeds.

Answer:

The ovary develops into fruits and ovules develop into seeds.

Question 8:

In case of polyembryony, if an embryo develops from the synergid and another from the nucellus which is haploid and which is diploid?

Answer:

The embryo developing from synergid will be haploid and the embryo developing from nucellus will be diploid.

Question 9:

Can an unfertilised, apomictic embryo sac give rise to a diploid embryo? If yes, then how?

Answer:

Yes, an unfertilised, apomictic embryo sac can give rise to a diploid embryo.

When megaspore develops into embryo sac without metiotic division, the egg developed will be diploid.

This diploid egg develops into embryo by mitotic division.

Question 10:

Which are the three cells found in a pollen grain when it is shed at the three celled stage?

Answer:

One vegetative cell and two male gametes

Explanation: In over of angiosperms, pollen grains are shed at this 2-celled stage namely vegetative cell and generative cell.

In the remaining species, the generative cell divides mitotically to give rise to the two male gametes before pollen grains are shed. This is 3-celled stage i.e.. , one vegetative cell and two male gametes.

Question 11:

What is self-incompatibility?

Answer:

Self-incompatibility is a genetic mechanism that prevents self-pollination (i.e.. , pollination from same flower or other flowers of same plant) from fertilizing the ovules by inhibiting pollen germination or pollen tube growth in the pistil.

Question 12:

Name the type of pollination in self-incompatible plants.

Answer:

Xenogamy

Explanation: In Self-incompatible plants self-pollination (i.e.. , pollination from same flower or other flowers of same plant) doesn՚t occur. So in such case cross-pollination particularly xenogamy takes place.

That is transfer of pollen grains from anther to the stigma of a different plant.