Pollination in plants and agents of pollination

CONTENT

• Definition
• Pollination in plants
• Features of self and cross pollinated flowers
• Agents of pollination

DEFINITION

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

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

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 involve two parent plants i.e. unisexual flowers or dioecious plants.  Cross pollination depends on external agents like wind, insect etc.

ADVANTAGES OF SELF POLLINATION

1. It ensures effective pollination in bisexual flowers
2. It avoids 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.

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 insect 
2. It leads to wastage of pollen grain especially in wind pollination.

EVALUATION

1. What is pollination?
2. Differentiate between self and cross pollination

FEATURES OF SELF POLLINATED FLOWERS

Features favouringself pollination include

1. Homogamy: This is the ripening of anther and stigma of  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.

FEATURES OF CROSS POLLINATED FLOWERS

1. Dioecious flowers: When male and female flowers occur on separate plant e.g. pawpaw
2. Dichogamy: When male and female parts mature at different times. Dichogamy can be
3. protandry : when anther matures or ripens before the stigma e.g. sunflowe, okro and cotton
4. protogyny when stigma matures before anther e.g. palms and figs.

3. Possession of brightly coloured petals to attract insect e.g. hibiscus.
4. Possession of sweet smell for attracting insects e.g. rose flower.
5. Unisexual flowers
6. Self incompatibility
7. Position of anthers and stigmas

EVALUATION

1. What are the features of cross-pollinated flowers?
2. Define the terms (a)homogamy (b)cleistogamy (c)dichogamy.

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. This pollinator include: insects, birds, snails, bats and man and also physical factors like wind and water.

The two major agents of pollination are:

• insects
• 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.

Entomophilous flowers include hibiscus, crotolaria, pride of barbadous, etc.

CHARACTERISTICS OF WIND POLLINATED FLOWER (ANAEMOPHILOUS FLOWER)

1. Small inconspicuous petals and sepals
   1. Dull coloured flowers
   1. Absence of scent
   1. Absence of nectars
   1. Large quantity of pollen grains
   1. Pollen grains are small, lightened sticky
   1. Elongated sticky stigma with large surface area.

Examples include cereals like maize, guinea corn and rice 

GENERAL EVALUATION

1. What is pollination
2. Explain what you understand by self and cross pollination.
3. What are the features of self and cross pollination?
4. State five characteristics of entomophilous and anaemophilous flowers.
5. What are the agents of pollination?

READING ASSIGNMENT

College Biology, chapter 16, page 333 – 348

WEEKEND ASSIGNMENT

SECTION A

1. Which of these is not condition for cross pollination A. protandry B. protogyny C. homogamy D. self incompatibility
2. The following are entomophilous flowers except A. hibiscus B. crotolaria C. maize flower D. pride of Barbados
3. Courtship behaviours in animals include the following except A. display B. migration C. pairing D. adaptation
4. Which of these is not a type of courtship display in animals A. croaking in toad B. colour change in chameleon C. bright colour feather in peacock D. singing in human being
5. The following are advantages of cross pollination except A. wastage of pollen grains B. production of viable seeds C. leads to varieties of offspring D. offspring are more adapted to the environment

SECTION B

1. Differentiate between entomophilous and anaemophilous flower
2. Outline four features that favours cross pollination