Pollination — NEET/JEE Quick Notes

1. Definition

Pollination = Transfer of pollen grains from the anther to the stigma of a pistil.

Since male and female gametes are non-motile, pollination brings them together for fertilisation.

2. Agents of Pollination

External agents include:

• 🌬️ Wind — Anemophily
• 🐝 Insects — Entomophily
• 🐦 Birds — Ornithophily
• 🦇 Bats — Chiropterophily
• 💧 Water — Hydrophily

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3. Types of Pollination

Type	Transfer of pollen	Genetic nature
Autogamy	Anther → stigma of the same flower	Similar to self-pollination
Geitonogamy	Anther of one flower → stigma of another flower on the same plant	Genetically similar to autogamy
Xenogamy	Anther of one plant → stigma of a different plant	Genetically different

Autogamy

• Occurs within the same flower.
• Requires:
  • Synchrony between pollen release and stigma receptivity
  • Anther and stigma should be close together
• Complete autogamy is relatively rare in normal open flowers.

Cleistogamy

Cleistogamous flowers do not open.

Examples:

• Viola
• Oxalis
• Commelina

Because anthers and stigma are very close, pollen reaches the stigma within the unopened flower.

Key point:

Cleistogamous flowers are invariably autogamous and provide assured seed set even without pollinators.

Advantage: Reproduction is assured even when pollinators are absent.
Disadvantage: It does not promote genetic variation because cross-pollination is prevented.

Geitonogamy

Pollen transfer occurs between two different flowers of the same plant.

• Functionally → cross-pollination, because a pollinating agent is generally required.
• Genetically → similar to autogamy, because pollen and ovule originate from the same plant.

Xenogamy

Pollen is transferred from one plant to the stigma of a different plant of the same species.

Most important: Xenogamy is the only type that brings genetically different pollen grains to the stigma.

🔥 NEET One-Liners

• Same flower → Autogamy
• Different flowers, same plant → Geitonogamy
• Different plants → Xenogamy
• Cleistogamous flowers → Always autogamous
• Genetically different pollen → Xenogamy
• Assured seed set without pollinators → Cleistogamy