Reproduction: How Life Continues · Lesson 4 of 12
How Pollination Occurs in Flowers
“Bees, birds, wind and water all moonlight as pollen delivery services.”
• Distinguish self-pollination and cross-pollination. • Explain how wind, water, insects and birds transfer pollen. • Relate flower characteristics to pollinating agents. • Compare pollen production and seed formation data. • Connect pollination with plant breeding and crop production.
Pollen has no ability to walk from anther to stigma. A flower must either position its parts so pollen reaches a suitable stigma nearby or use wind, water or animals as carriers. Each strategy solves the same problem in a different way.
Pollination may occur within the same flower, between flowers on the same plant or between plants of the same type. The destination must be a suitable stigma because pollen transfer begins the sequence leading towards fertilisation, fruit and seed formation.
Self-pollination is the transfer of pollen to the stigma of the same flower or another flower on the same plant.
Cross-pollination is the transfer of pollen from a flower on one plant to a flower on another plant of the same type.
Problem
Pollen from one maize variety reaches the stigma of another maize plant of the same type. Which process is involved?
- 1.The pollen leaves a flower on one plant.
- 2.It reaches a flower on another plant.
- 3.The plants are of the same type.
- 4.Therefore, the transfer is cross-pollination.
Pollination strategies and reproductive success
Wind-pollinated plants such as wheat, maize and rice produce small, lightweight pollen grains in very large numbers. Wind movement is not precisely directed, so much pollen fails to reach a suitable flower. A long, feathery stigma increases the chance of trapping airborne grains.
In aquatic plants such as Vallisneria and Hydrilla, water currents carry pollen from one flower to another. The strategy depends on the plant’s habitat and the movement of surrounding water.
Sunflower, hibiscus and marigold may be pollinated by insects such as bees and butterflies. Bright colours, fragrance and nectar attract visitors. Pollen is often large, sticky or spiny so it attaches to the insect’s body, while a sticky stigma helps receive it. Coral-tree and hibiscus flowers may also be visited by birds such as the Indian white-eye and sunbirds.
| Agent | Example plants | Helpful features |
|---|---|---|
| Wind | Wheat, maize and rice | Small light pollen in large numbers; long feathery stigma |
| Water | Vallisneria and Hydrilla | Pollen carried by water currents |
| Insects | Sunflower, hibiscus and marigold | Colour, fragrance, nectar and sticky or spiny pollen |
| Birds | Coral tree and hibiscus | Flowers that attract visiting birds and position pollen for transfer |
Problem
A flower is brightly coloured, fragrant, nectar-producing and has sticky pollen. Which agent is strongly suggested?
- 1.Colour and fragrance help an animal locate the flower.
- 2.Nectar rewards a visitor.
- 3.Sticky pollen can attach to the visitor’s body.
- 4.These features strongly support insect pollination rather than undirected wind transfer.
Activity: Let us find out
The chapter compares approximate pollen production and seed formation. Wind-pollinated grasses release about 5,00,000-10,00,000 pollen grains per flower and form roughly 50-200 seeds. Insect-pollinated plants may release about 20,000-40,000 pollen grains and form approximately 800-1,000 seeds.
Problem
Using 5,00,000 pollen grains and 100 seeds for a wind-pollinated flower, what is the approximate pollen-to-seed ratio?
- 1.Write pollen grains : seeds = 5,00,000 : 100.
- 2.Divide both quantities by 100.
- 3.The simplified ratio is approximately 5,000 : 1.
- 4.This means many pollen grains are produced for each seed formed.
- 5.The large wastage is balanced by producing and releasing enormous quantities.
Problem
Using 30,000 pollen grains and 1,000 seeds for an insect-pollinated flower, find the approximate ratio.
- 1.Write 30,000 : 1,000.
- 2.Divide both values by 1,000.
- 3.The ratio is approximately 30 : 1.
- 4.Compared with the wind example, pollen transfer is more directed and fewer grains are needed per seed.
A lower pollen-to-seed ratio suggests greater transfer efficiency, but both strategies can succeed. Wind is widely available and can carry large numbers over an area. Animals provide more directed transport but depend on suitable visitors and attractive flower features.
Bridging Science and Society
Pollination has applied importance in plant breeding. Selective breeding uses plants with desirable characteristics. Artificial hybridisation removes stamens before pollen release, covers the flower to prevent unwanted pollen and manually adds selected pollen. Declining natural pollinators can reduce fruit setting, while beekeeping near orchards may improve pollination and also produce honey.
Quiz
Which description best matches Self-pollination?
Which description best matches Cross-pollination?
Which term matches this description: Self-pollination is the transfer of pollen to the stigma of the same flower or another flower on the same plant.
Which term matches this description: Cross-pollination is the transfer of pollen from a flower on one plant to a flower on another plant of the same type.
Which statement is a key takeaway from this lesson?
Practice Problems
- Distinguish self-pollination from cross-pollination.
- Why do wind-pollinated flowers produce so much pollen?
- Relate a feathery stigma to its function.
- Which features help insect-pollinated flowers attract and use insects?
- Calculate the pollen-to-seed ratio for 8,00,000 pollen grains and 200 seeds.
- Why is bagging used during artificial hybridisation?
- Predict one consequence of a severe decline in pollinator populations.
Key Takeaways
• Pollination transfers pollen from anther to stigma. • Self-pollination occurs within one plant; cross-pollination occurs between plants of the same type. • Wind, water, insects and birds act as pollinating agents. • Flower features match the method of transfer. • Pollination efficiency affects seed and fruit production.