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Pollination
INTRODUCTION
- Pollination is the transfer of pollen to the female reproductive organs of a plant, facilitating fertilization.
- Seed plants aim to pass genetic information to the next generation, with pollination being vital in seed production.
- Pollen grains from the anther (male part) must be transferred to the stigma (female part) of the same species for successful pollination.
- Angiosperms (flowering plants) differ from gymnosperms in their pollination process.
- In angiosperms, pollen creates a pollen tube that grows down the style to the ovary, where fertilization occurs, resulting in seed formation.
PROCESS OF POLLINATION
- Pollen germination has three stages: hydration, activation, and pollen tube emergence.
- The dehydrated pollen grain rehydrates upon landing on a stigma, enabling germination.
- The pollen tube grows toward the ovule, allowing sperm cells to fertilize the egg cell and form seeds.
- In gymnosperms, pollen is drawn into the ovule through a pollination drop, where it waits before germinating and delivering sperm to the egg.
TYPES OF POLLINATION
A. On the Basis of Pollen Source
- Self-Pollination:
- Pollen is transferred from the anther to the stigma of the same flower (Autogamy) or different flowers on the same plant (Geitonogamy).
- Cross-Pollination (Xenogamy):
- Pollen is transferred from the anther of one plant to the stigma of a different plant.
B. On the Basis of Pollinating Agent
- Abiotic Pollination:
- Pollination occurs without the involvement of organisms, most commonly via wind (Anemophily) or water (Hydrophily).
- Biotic Pollination:
- Pollination is facilitated by living organisms, such as insects, birds, or mammals.
MECHANISM OF POLLINATION
Modes of Cross-Pollination
- 1. Anemophily (Wind Pollination):
- Wind transfers pollen. Plants like grasses produce vast amounts of lightweight pollen to increase the chance of pollination.
- 2. Hydrophily (Water Pollination):
- Pollination occurs in water. For example, in Vallisneria, male flowers float to the water surface to meet female flowers for pollination.
- 3. Entomophily (Insect Pollination):
- Bees, wasps, flies, and beetles pollinate flowers by collecting nectar, transferring pollen as they move between flowers.
- 4. Ornithophily (Bird Pollination):
- Birds like hummingbirds pollinate flowers by feeding on nectar. These flowers often have bright colors and copious nectar.
- 5. Chiropteriphily (Bat Pollination):
- Bats pollinate night-blooming flowers that emit strong scents, such as Bauhinia.
- 6. Malcophily:
- Some plants are pollinated by snails or slugs, typically in damp environments.
Mechanism of Self-Pollination
- Self-Pollination occurs when a flower’s own pollen fertilizes it. It’s common in plants where pollinators are unreliable, ensuring reproduction even in isolation.
- Cleistogamy refers to self-pollination before the flower opens, allowing fertilization without external pollinators.
POLLEN VECTORS
- Biotic pollen vectors include animals like insects, birds, mammals, and even reptiles, which transport pollen while feeding or seeking shelter.
- Insects like bees and butterflies carry pollen between plants, increasing pollination efficiency through flower constancy—their tendency to visit the same type of flower repeatedly.
- Some flowers have evolved mechanisms to trap or attract specific pollinators, such as releasing intoxicating odors.
CONCLUSIONS
- Pollination management in agriculture seeks to enhance pollinator activity, often by introducing managed pollinators such as honey bees and bumblebees to commercial crops.
- The world’s largest managed pollination event occurs in California’s almond orchards, utilizing nearly half of the US’s honeybee population.
- Native pollinators significantly enhance crop yields, offering both ecological and economic benefits.
BIBLIOGRAPHY
- Biological Science (Third Edition) by N.P.O. Green, G.W. Stout, D.J. Taylor
- Exploring Biology by Ella Thea Smith
- NCERT Textbook
- Tell Me Why
- Encyclopedia Britannica
- Wikipedia
