Last Updated on August 28, 2020 by Sagar Aryal
Pollination is the process of transfer of male gametes (pollen grains) in plants from the male reproductive part (anther) to the female reproductive part (stigma).
- Pollination is the prerequisite of fertilization in plants as it ensures the movement of gametes in otherwise immobile plants.
- The act of pollination is brought about by various pollinating agents like wind, water, insects, and even animals.
- Sometimes, plants themselves might result in pollination by a process termed self-pollination. It occurs mostly in closed flowers.
- The transfer of gametes takes place often within the same species; however, if the transfer occurs between different species, a hybrid will be formed.
- In non-flowering plants like cycads, the pollen is caught in the fluid secreted by the ovule as the ovules are exposed. In flowering plants, however, ovules are enclosed within a structure termed pistil and thus require pollination by external agents.
- Pollen grains undergo dehydration to reduce their mass so that they can be easily moved from one flower to another.
- The hydration and activation of pollen grains occur once they land on the stigma before the formation of the pollen tube.
- As discussed, pollination is brought about by both biotic and abiotic agents. Abiotic agents include wind, water, and rain, whereas biotic agents include insects, birds, and animals.
- Some plants might have varying pollination methods with a combination of biotic and abiotic methods.
- Pollination occurs by one of the two methods; self-pollination and cross-pollination
- Self-pollination is the transfer of pollen grains from the anther of one flower to the stigma of another flower of the same plant. Plants undergoing self-pollination usually have stamens and carpels of the same length developing at the same stage.
- Cross-pollination is the transfer of pollen grains from the anther of one flower to the stigma of the flower of another plant of the same species. Plants undergoing cross-pollination have mechanisms to prevent self-pollination with the reproductive organ developing at different stages of the lifecycle.
- The color of the flower and nectar produced are important agents that facilitate pollination in plants by attracting insects and animals.
- Similarly, other modifications like reduction in weight and water-resistant spores are other modifications assisting in pollination.
- Examples of pollination are seen in the pollination of Yucca plant by moths and self-pollination in wheat and barley.
Fertilization is the process of fusion of haploid male and female gametes to form a diploid zygote, resulting in the initiation of the development of a new individual.
- Fertilization is a part of sexual reproduction that follows copulation in animals and pollination in plants.
- In plants, fertilization follows pollination and begins with the hydration and activation of pollen grains and the formation of the pollen tube.
- The process of rehydration also prevents the premature germination of pollen in the anther.
- During hydration, the plasma membrane of pollen regains its structure and activation involves the development of actin filaments that eventually lead to the formation of the pollen tube.
- Because the male gamete in plants is non-motile, it depends on the pollen tube for its transfer from the stigma to the ovary.
- The pollen tube penetrates the stigma and elongates along with the extracellular matrix of style, finally reaching the ovary.
- It then penetrates the ovule through the micropyle and the pollen tube bursts in the embryo sac, releasing the sperm.
- In gymnosperms, however, the formation of the pollen tube doesn’t occur as the ovules are not enclosed with the ovary.
- Angiosperms, in turn, undergo double fertilization where two sperms from each pollen tube fertilize two cells present in the ovary.
- The first sperm fertilizes the haploid egg cell resulting in a diploid zygote whereas the other sperm fuses with a central cell with two haploid polar nuclei, resulting in a triploid cell.
- The triploid develops to form endosperm that nourishes the zygote inside the ovary.
- Like pollination, fertilization in plants also might either be self-fertilization or cross-fertilization.
- Mostly, self-pollination results in self-fertilization, and cross-fertilization results in cross-fertilization.
- Fertilization, in animals, however, can occur via internal or external mechanisms.
- In internal fertilization, the sperm enters the body of the female via copulation and fuses with the egg cell.
- In external fertilization, eggs are deposited on a surface by the female and then are fertilized by sperm cells released by the male over the egg cell externally.
- Thus, fertilization is an internal process taking place inside the parts of the organisms in both animals and plants. Because it is an internal process, it doesn’t require external factors for its completion.
- Fertilization in plants also takes place in all types of plants ranging from flowering to non-flowering to primitive plants like bryophytes and thallophytes.
Key Differences (Pollination vs Fertilization)
Basis for Comparison
|Definition||Pollination is the process of transfer of male gametes (pollen grains) in plants from the male reproductive part (anther) to the female reproductive part (stigma).||Fertilization is the process of fusion of haploid male and female gametes to form a diploid zygote to initiate the development of a new individual.|
|Nature of the process||Pollination is a physical process.||Fertilization is a genetic and biochemical process.|
|Type of process||Pollination is an external process taking place outside the body of the plants.||Fertilization is an internal process occurring inside the parts of the plants.|
|Occurs in||Pollination occurs only in plants with flowers or differentiated male and female reproductive parts.||Fertilization occurs in all types of plants and animals reproducing by sexual mode of reproduction.|
|Time||Pollination is a prerequisite of fertilization in plants and thus occurs before fertilization.||Fertilization occurs after pollination.|
|External factors||Pollination is dependent on external biotic and abiotic factors.||Fertilization is independent of external factors.|
|Involves||Pollination only involves the movement of pollen grains or the male gametes.||Fertilization involves both male and female gametes.|
|Pollen tube||No pollen tube is formed during pollination.||Fertilization in plants occurs via the formation of the pollen tube.|
|Types||Pollination occurs via two types of mechanisms; self-pollination and cross-pollination.||Fertilization in plants is of three types; Chalazogamy, Porogamy, and Mesogamy|
|Mechanism||Pollination occurs with the help of pollination agents like water, air, insects, and animals.||Fertilization occurs by the process of hydration, activation, and pollen tube formation.|
|Pollen grains||Pollen grains undergo dehydration to reduce their masses to ease the process of pollination.||Pollen grains undergo rehydration after reaching the stigma to initiate the process of pollen tube formation.|
|Flowers involved||Pollination might occur between two different flowers.||Fertilization always occurs within a single flower.|
References and Sources
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- 1% – https://en.wikipedia.org/wiki/Pollination
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