Exams K12 Pollination: Definition, Type and Significance

Written By Sagarika Swamy
Last Modified 24-01-2023

Pollination: Definition, Type and Significance

Why are the flowers so colourful? Why are bees attracted to them? Flowers help plants to reproduce. Pollination is the process of transferring pollen grains from a flower’s male anther to its female stigma.

The ovules of flowering plants are stored in a hollow body called the pistil, and pollen is deposited on the stigma’s surface. In simple words, pollination is the reproduction process in plants. Let us understand the process of pollination with some examples in this article.

What is Pollination?

Pollination is defined as the transfer of pollen grains from the anther to the stigma. Pollination may involve:

A single flower.
Two different flowers on the same plant.
Flowers on two different plants.

Pollination Process

The pollination process begins when the pollen grains from the different flowers of the same species land on the stigma and form a pollen tube with the style length, which connects both the stigma and ovary. The pollen tube contains the male gametes, eventually fusing with the egg cell inside the embryo sac. Fusion of the male gamete and egg is termed fertilization, which forms a zygote and eventually a seed. Seeds develop into new plants.

Diagram

Types of Pollination

Pollination is basically of two types:

(i) Self Pollination or Autogamy
(ii) Cross-Pollination or Allogamy

Self Pollination is the transfer of pollen grains from the anthers of a flower to the stigma of the same flower or of another flower born by the same plant.

Self-pollination generally occurs in bisexual flowers. Since the male and female gametes that take part in fertilization are formed in the same flower, their genetic make-up is identical. As a result, the new individual formed resembles the parent plant.

Advantages and Disadvantages

Advantages	Disadvantages
1. Genetic make-up remains identical. 2. More economical, as no agent is needed. 3. Wastage of pollen grains is comparatively less.	1. Gradually there is a decline in vigour of the hybrid. 2. Genetic defects can not be rectified. 3. This does not support the evolution of new species.

Cross-Pollination or Allogamy is the transference of pollen grains from the anther of a flower of one plant to the stigma of a flower of another plant of the same species.

Cross-pollination occurs both in unisexual and bisexual flowers and results in intermixing of genetic characters of the two parent plants. It brings about variations in offspring.

Advantages and Disadvantages of Cross-Pollination

Advantages	Disadvantages
1. Offspring is always healthier. 2. New genetic combinations are developed. 3. This supports evolution.	1. Agent dependency is always there. 2. Huge amount of pollen is wasted. 3. Flowers need to spend energy in producing nectar and colour to attract pollinators.

Adaptations (Contrivances) for Pollination

Contrivances for Self Pollination

Contrivances for Cross Pollination

1. Homogamy or the maturation of male and female reproductive organs at the same time. This is found in wheat, rice and
Mirabilis.
2. Some bisexual flowers never open. They are called cleistogamous flowers. Since they never open, they are always self-pollinated. Commelina benghalensis shows cleistogamy.

1. Some plants produce only unisexual flowers and are always cross-pollinated.
The unisexual flowers (male or female) may be borne on the same plant (as in maize, castor, cucumber) or two separate plants (as in palm, mulberry, papaya).
2. The flowers are bisexual, but stamens and carpels mature differently.
This condition is known as dichogamy which stands as a barrier to self-pollination.
3. Some flowers show self-sterility. The pollen grains of flowers does not germinate on the stigma of the same flower but germinate on the stigma of a flower born by another plat of the same species, thus ensuring cross-pollination.

Agents of Cross-Pollination

Angiosperm pollens cannot move on their own and need external agents to get transferred to the stigma. There are two main groups of agents:

(i) Biotic agents which include animals of different types such as insects, birds, bats and snails and
(ii) Abiotic agents like wind and water.

Agents of Pollination	Types of Pollination	Example
Biotic: Animals (Zoophily)	Insects – Entomophily Birds – Ornithophily Bats – Chiropterophiy Snails – Malacophily Ants – Myrmecophily	1. Lotus, sunflowers are insect-pollinated. 2. Bottle-brush is bird pollinated. 3. Baobab is bat pollinated. 4. Volvulopsis nummularium is snail pollinated. 5. Certain orchids are ant pollinated.
Abiotic: Non-living agents	Wind – Anemophily Water – Hydrophily	6. Grasses are wind-pollinated. 7. Vallisneria and Zostera are water pollinated.

Pollination and Fertilization

Pollination eventually facilitates fertilization. Fertilization is the fusion of the nuclei of two dissimilar sexual reproductive units called the male and female gametes. Fertilization results in the formation of a diploid zygote.

After the pollen grains are deposited on the stigma, the pollen grains absorb water and sugar from the surface of the stigma and swell up. From one of the germ pores, the pollen tube is generated. This tube produces enzymes at the tip and dissolves the tissue of the style as it grows.

Eventually, it travels down the whole length of the style into an ovary. In the meantime, inside the pollen tube, the generative nucleus is divided into two male gametes. The pollen tube carrying the two male gametes enters the embryo sac through the micropyle, and its tip dissolves. The two male gametes are liberated inside the embryo sac. One male gamete fuses with the egg to form a zygote that grows into an embryo and a new plant. The other male gamete fuses with the secondary nucleus to form the triploid endosperm, nourishing the growing embryo.

The fusion of the male gamete with the female gamete is called fertilization.

Significance of Pollination

The major significance of pollination are:

Since the male and female gametes of flowering plants are non-motile, pollination brings them closer together so that syngamy or fertilization can take place.
Cross-pollination helps in the evolution of species, as it brings new combinations of genes.

Summary

The male and female gametes must come together for plants to produce seeds. The male gamete is produced by the androecium within the pollen grain, while the gynoecium produces the female gamete within the ovule. Pollination is the process that helps in bringing male and female gametes together. Self-pollination and cross-pollination are two major ways. Flowering plants are adapted to use vivid agents, like biotic and abiotic.

FAQs

Q.1. What is cross-pollination?
Ans: The transference of pollen grains from the anther of a flower of one plant to the stigma of a flower of another plant of the same species is called cross-pollination.

Q.2. What is self-pollination?
Ans: Self-pollination is the transference of pollen grains from the anthers of a flower to the stigma of the same flower or of another flower born by the same plant.

Q.3. How is the process of pollination different from fertilization?
Ans:

Pollination	Fertilization
Pollination is the transfer of pollen grains from an anther to a stigma.	The fusion of male and female gametes is called fertilization.
Pollen can be transferred by an animal or by the wind.	Fertilization occurs once the pollen grain reaches the stigma, it produces a pollen tube, which grows down through the style to the ovary.

Q.4. Why is pollination important?
Ans: A pollination is an important event in the sexual reproduction of plants. This is needed for fertilization and zygote formation as it helps in the transfer of gametes for fusion.

Q.5. What is pollination?
Ans: Pollination is the process of transfer of pollen from the anther to the stigma of a flower.

Q.6. What is the significance of pollination?
Ans:
1. Pollination is an important process that brings the two types of gametes closer to fertilization which results in zygote formation.
2. Pollination helps in genetic recombination between plants.

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