4.7.6Additional lessons
Pollination — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 60 of 101
Part 1 of 5Types of Pollination
Self-pollination
- Pollen lands on a stigma of the same flower or plant, producing offspring with less variation.
Cross-pollination
- Pollen is carried to a flower on a different plant of the same species, increasing genetic variation.
Inbreeding risk
- Repeated self-pollination reduces variation and can lead to weaker offspring.
Avoiding self-pollination
- Anthers and stigmas may ripen at different times, or plants may be self-incompatible so the pollen tube fails to grow.
Part 2 of 5Insect-Pollinated Flowers
Petals
- Large, brightly coloured or scented petals attract insects, and ultraviolet patterns guide them to the nectar.
Nectar
- A sugary reward that encourages insects to visit and carry pollen on their bodies.
Pollen
- Often sticky or spiky, so it attaches to the insect, and produced in smaller amounts.
Stigma
- Sticky and positioned where an insect will brush against it.
| Feature | Insect-pollinated | Wind-pollinated |
|---|---|---|
| Petals | Large, colourful | Small or absent |
| Pollen | Sticky, few grains | Light, smooth, many grains |
| Stigma | Sticky, inside flower | Feathery, outside flower |
| Anthers | Inside the flower | Dangle outside |
Part 3 of 5Wind-Pollinated Flowers
Anthers
- Hang outside on long filaments so that wind blows the pollen away easily.
Pollen quantity
- Huge amounts are produced, because most pollen does not land on a stigma.
Stigma
- Large and feathery, forming a net-like surface to catch passing pollen.
No nectar
- Energy is not wasted on petals and nectar, since the flower does not need to attract animals.
Part 4 of 5Mutualism
Benefit to plant
- Pollinators transfer pollen over distance, leading to cross-pollination.
Benefit to animal
- Pollinators gain food such as nectar and pollen.
Co-evolution
- Flower shape and pollinator mouthparts often match closely in specialised partnerships.
Part 5 of 5Exam Checklist & Tips
4.7.6 – Key Points for the Exam
- Self-pollination Pollen transfer to a stigma of the same plant.
- Cross-pollination Pollen transfer to a stigma of a different plant of the same species.
- Nectar A sugar solution secreted by flowers to attract pollinators.
- Self-incompatibility A mechanism preventing fertilisation by pollen from the same plant.
Common Mistakes
- Describing wind-pollinated flowers as brightly coloured.
- Saying pollination and seed dispersal are the same.
- Claiming that cross-pollination happens only in insect-pollinated plants.
- Thinking pollen is the female gamete.
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