Pollination In Plants SS2 Biology Lesson Note

This is the transfer of mature pollen grains from the anther of one flower to the mature stigma of the same or another flower of the same plant or another plant of closely related species. Pollination usually precedes fertilization. There are two types of pollination namely; self-pollination and cross-pollination.

1. Self Pollination

This is the transfer of mature pollen grain from the anther of a flower to the stigma of the same flower or to that of another flower of the same plant e.g. tomato and pear. Therefore, self-pollination involves only one parent plant i.e. bisexual flowers or monoecious plants

Advantages of Pollination

1. It ensures effective pollination in bisexual flowers.
2. It avoids the wastage of pollen grains.

Disadvantages Of Self Pollination

1. Production of weak offspring due to continuous self-pollination.
2. The offspring are less adaptive to the environment.

Features Of Self Pollinated Flowers

Features favouring self-pollination include:

1. Homogamy: This is the ripening of the anther and stigma of a bisexual flower at the same time
2. Cleistogamy: This is when ripe pollen grains are deposited on the stigma which then becomes ripened at the same time.

2. Cross-Pollination

This is the transfer of mature pollen grains from the anther of a flower to the stigma of a flower on another plant of the same or closely related species e.g. hibiscus, pawpaw. Therefore cross pollination involves two parent plants i.e. unisexual flowers or dioecious plants.  Cross-pollination depends on external agents like wind, insects etc

Advantages Of Cross-Pollination

1. Production of healthier offspring.
2. Production of viable seeds
3. The offspring are more adapted to the environment.
4. Formation of new varieties with good characteristics 

Disadvantages Of Cross-Pollination

1. It depends on external agents e.g. wind and insects.
2. It leads to wastage of pollen grain especially in wind pollination.

Features Of Cross Pollinated Flowers

i. Dioecious flowers: When male and female flowers occur on separate plants e.g. pawpaw

ii. Dichogamy: When male and female parts mature at different times. Dichogamy can be

protandry: when another matures or ripens before the stigma e.g. sunflower, okra and cotton

protogyny when the stigma matures before another e.g. palms and figs.

iii. Possession of brightly coloured petals to attract insects e.g. hibiscus.

iv. Possession of a sweet smell for attracting insects e.g. rose flower.

v. Unisexual flowers

vi. Self-incompatibility

vii. Position of anthers and stigmas

AGENTS OF POLLINATION

Agents of pollination (pollinators) are the organisms which help in the transfer of pollen grains from the anther to the stigma of flowers. These pollinators include insects, birds, snails, bats and man and also physical factors like wind and water.

The two major agents of pollination are:

1. insects
2. wind 

Flowers pollinated by them are marked with certain features that will be stated below:

Characteristics Of Insect Pollinated Flowers (Entomophilous) 

1. Large conspicuous petals and sepals.
2. Bright colouration.
3. Possession of scent.
4. Presence of nectars.
5. Presence of rough, sticky and relatively few pollen grains.
6. Flat, sticky stigma to receive pollen grains.
7.  Entomophilous flowers include hibiscus, crotalaria, pride of barbadous, etc.

Characteristics of Wind Pollinated Flower (Anaemophilous Flower)

1. Small inconspicuous petals and sepals.
2. Dull coloured flowers.
3. Absence of scent.
4. Absence of nectars.
5. Large quantity of pollen grains
6. Pollen grains are small, lightened and sticky.
7.  Elongated sticky stigma with large surface area.
8. Examples include cereals like maize, guinea corn and rice.