BIOLOGY [3 marks Question Answer]

In angiosperms, during fertilization, one male gamete fuses with the egg cell and forms diploid zygote in a process called syngamy. The other male gamete fuses with the two polar nuclei to form a triploid nucleus called the primary endosperm nucleus. This process is called triple fusion. Since fertilization takes place twice here, so this process is called double fertilization.

Significance - Due to double fertilization, the triploid nucleus develops into endosperm which serves as nutrition for embryo.

Adaptations required by self-pollinated plants are:
(i) Bisexuality - Self-pollination occurs only in bisexual flowers.
(ii) Homogamy - Both anther and stigma need to mature at the same time.
(iii) Cleistogamy - Flowers which are bisexual and never open are called cleistogamous flowers. They are small, colourless, odourless and without nectar. The pollen grains fall on the stigma inside the closed flower. Example - Arachis

Advantages of cross-pollination:

1. The offspring are healthier.
2. The seeds produced are abundant and viable.
3. New varieties may be produced by cross-pollinating two different varieties of the same species.

Disadvantages of cross-pollination:

1. Pollination is not always certain.
2. The pollen has to be produced in large quantities.
3. The process is uneconomical for the plant because the flowers have to be large, colored, scented and have to produce nectar for attracting pollinating agents.

Advantages of self-pollination:

(i) Puri ty of race is maintained.
(ii) Wastage of pollen grains is avoided.
(iii) Less chances of failure of pollination.
(iv) Flowers need not produce scent, nectar or be coloured.

Disadvantages of self-pollination:
(i) Continued self-pollination leads to weakening of the progeny.
(ii ) Poor quality of seeds are produced.
(iii ) Defective or weaker characters cannot be eliminated.

The two modes of pollination are:

(i) Self-pollination - It is the transfer of pollens produced within the anther of a flower to the stigma of the same flower or to the stigma of another flower of the same plant. In such flowers, pollination is ensured since the flowers bear similar genetic characters. Self-pollination can occur in bisexual or monoecious flowers. Examples of plants showing self-pollination are Mirabilis, Arachis, etc.

(ii) Cross-pollination - It is the transfer of pollen grains from the anthers of a flower of one plant to the stigma of a flower of another plant. Cross-pollination occurs in unisexual or dioecious flowers such as papaya, maize, jasmine, rose etc.

Pollination is the transfer of pollen grains from the anther to the stigma of the same or another flower.
The male gametes are produced inside pollen grains located in the anthers of androecium whereas the female gametes are produced in the ovules located in the ovary of gynoecium. For forming a zygote, the male gametes need to be transferred to the gynoecium for fusing with the female gametes. This is achieved through pollination. Pollination occurs through insects, wind, or other agents.

There are two types of pollination - Self-pollination, and cross-pollination.