Pollination and Fertilization — ICSE Class 9 Biology Important Questions

Answer: (b) Pollination.

Pollination is the transfer of pollen grains from the anther to the stigma; fertilisation is the later fusion of gametes.

Answer: (c) Entomophily.

Entomophily is insect pollination; anemophily is by wind, hydrophily by water and ornithophily by birds.

Answer: (b) Seed.

After fertilisation the ovule becomes the seed, while the ovary as a whole develops into the fruit.

Answer: (c) Wind.

Feathery exposed stigmas to catch pollen, light dry pollen that blows easily, and the absence of scent, nectar and bright colour are typical adaptations of wind-pollinated (anemophilous) flowers.

Answer: (a) Cross-pollination brings together genes from two different plants, so the offspring show greater variation; this happens exactly because pollen goes to a genetically different plant of the same species, so R correctly explains A.

Self-pollination: The transfer of pollen grains from the anther to the stigma of the same flower, or to another flower on the same plant.

Cross-pollination: The transfer of pollen grains from the anther of a flower on one plant to the stigma of a flower on another plant of the same species.

Two adaptations of an insect-pollinated (entomophilous) flower are:

1. The flowers are large, brightly coloured and often scented to attract insects; they usually secrete nectar.

2. The pollen grains are sticky or spiny and the stigma is sticky, so that pollen adheres to the insect's body and to the stigma.

Wind-pollinated (anemophilous) flowers show the following adaptations:

1. The flowers are small, dull-coloured and produce no scent or nectar, since they need not attract insects.

2. They produce very large amounts of light, dry, smooth pollen that can be easily carried by the wind.

3. The anthers are versatile (loosely attached) and hang out of the flower, and the stigmas are large and feathery to catch floating pollen.

Examples: grasses, maize and wheat.

Fertilisation is the fusion of the male and female gametes. It occurs as follows:

1. After pollination, the pollen grain on the stigma absorbs moisture and nutrients and germinates, putting out a pollen tube.

2. The pollen tube grows down through the style towards the ovary, carrying two male gametes at its tip.

3. The pollen tube enters the ovule through a small opening called the micropyle.

4. The tip bursts and releases the male gametes; one male gamete fuses with the egg (female gamete) to form the zygote.

This fusion of gametes is fertilisation, and the zygote later develops into the embryo of the seed.

Pollination: It is the transfer of pollen grains from the anther to the stigma. It may be self-pollination (same plant) or cross-pollination (different plant of the same species), and cross-pollination is aided by agents like insects, wind, water and birds.

Fertilisation: After pollination the pollen grain germinates on the stigma and grows a pollen tube down the style. The tube enters the ovule through the micropyle and releases male gametes; one male gamete fuses with the egg to form the zygote. This fusion is fertilisation.

Post-fertilisation changes:

1. The zygote develops into the embryo.
2. The ovule develops into the seed.
3. The ovary develops into the fruit, which protects the seeds.
4. The calyx, corolla, stamens, stigma and style usually wither and fall off.

Thus a fertilised flower is gradually converted into a fruit containing seeds.

Self-pollination

Pollen is transferred within the same flower or plant.

Advantages:

1. Pollination is more certain and does not depend on external agents.
2. Less pollen is wasted and desirable parental characters are preserved.

Disadvantages:

1. It produces little variation, so the offspring may be weak.
2. New useful characters are not introduced and the species cannot adapt easily.

Cross-pollination

Pollen is transferred to a flower on a genetically different plant of the same species.

Advantages:

1. It produces greater variation, giving healthier and stronger offspring.
2. New characters may be introduced, helping the species adapt and improve.

Disadvantages:

1. It depends on external agents, so pollination is less certain.
2. Large amounts of pollen are wasted and the process is uneconomical.

(i) This is self-pollination, because the pollen from the anther falls on the stigma of the same flower.

(ii) The pollen tube grows down through the style, and it enters the ovule through a small opening called the micropyle.

(iii) The fusion of the male gamete with the female gamete (egg) is called fertilisation.

(iv) The ovule has developed into the seed, and the ovary has developed into the fruit (pea pod) enclosing the seeds.