11 min readConcept sheet1-mark MCQ and assertion-reason on cleistogamy and agencies, a 3-mark question comparing wind- and insect-pollinated flowers, and spotting in the practical; also a NEET favourite

Pollination: types, agencies and examples

Pollination moves pollen from anther to stigma. It may be autogamy, geitonogamy or xenogamy, and is carried by wind, water or animals.

AutogamyPollen goes from the anther to the stigma of the same flower

GeitonogamyPollen goes to another flower of the same plant; needs an agent but is genetically like autogamy

XenogamyPollen goes to a flower of a different plant; the only type that brings genetically different pollen

Cleistogamous flowersNever open; assured seed set without pollinators, but always autogamous (Viola, Oxalis, Commelina)

Three kinds of pollination

Kind	Pollen goes to	Agent needed?	Genetic result
Autogamy	Stigma of the same flower	Not always	Self-pollination; no new gene combinations
Geitonogamy	Another flower on the same plant	Yes	Functionally cross-pollination, but genetically the same as autogamy
Xenogamy	A flower on a different plant	Yes	Genetically different pollen reaches the stigma; brings variation

Chasmogamous vs cleistogamous flowers

ChasmogamousFlowers open, with exposed anthers and stigma, like most flowers. Autogamy happens only if pollen release and stigma receptivity coincide and the anther and stigma are close together.

CleistogamousFlowers never open. The anthers and stigma lie close, so pollen falls on the stigma. Seed set is assured even without pollinators, but there is no cross-pollination. Viola (common pansy), Oxalis and Commelina make both kinds of flower.

Agencies of pollination

Agency	Features of the flowers	Examples
Wind	Light, non-sticky pollen made in large amounts; well-exposed stamens; large, often feathery stigma; often one ovule per ovary and many flowers packed into an inflorescence	Grasses; maize, where the silky threads (silks) on the cob are the stigmas and styles
Water	Rare: about 30 genera, mostly monocots. In most species, a mucilage coat keeps the pollen from getting wet. Flowers not colourful and have no nectar	Vallisneria and Hydrilla (fresh water); Zostera (sea grass)
Insects	Large, colourful, fragrant flowers rich in nectar, or small flowers grouped into a showy inflorescence; sticky pollen. Fly- and beetle-pollinated flowers have a foul smell	Bees are the main pollinators; Salvia, sunflower; Amorphophallus; Yucca with its moth
Birds and bats	Large, brightly coloured flowers with plenty of nectar	Sunbirds and hummingbirds visit such flowers; in India, coral tree (Erythrina) and silk cotton (Bombax)

Water pollination and plant-animal partnerships

In Vallisneria, the female flower reaches the water surface on a long stalk. Male flowers or pollen float on the surface and drift with the current; some reach the female flowers.
In sea grasses such as Zostera, the female flowers stay under water. Long, ribbon-like pollen grains are released inside the water and drift to the stigma.
Not all water plants use water: water hyacinth and water lily flowers rise above the water and are pollinated by insects or wind.
Floral rewards are nectar and pollen. Some flowers also offer a safe place to lay eggs, as in Amorphophallus, whose flower is about 6 feet tall.
Yucca and its moth: the moth lays eggs in the ovary and pollinates the flower; the larvae hatch as the seeds develop. Neither can complete its life cycle without the other.
Pollen and nectar robbers take the rewards without pollinating. Lemurs, tree-dwelling rodents and lizards (gecko and garden lizard) are also reported as pollinators.

Activity: spotting flowers adapted to wind, insects and birds

1
Look at the specimen and note its size, colour, smell and nectar.
2
Check the stamens: long, hanging out, with plenty of dry, powdery pollen suggests wind.
3
Check the stigma: large and feathery and exposed suggests wind; sticky and inside a showy corolla suggests insects.
4
Identify, for example: maize or grass: wind-pollinated; Salvia or sunflower: insect-pollinated; coral tree or silk cotton: bird-pollinated.
5★
Write two adaptations for each spot. Examiners give marks for the identification and the reasons.

★ key step

In real life

Many of our fruits, vegetables and oilseeds depend on bees for pollination. Farmers who keep bee boxes near mustard and sunflower fields get both honey and a better seed yield.

Exam angle

3 marks: “Give three differences between wind-pollinated and insect-pollinated flowers, with one example of each.” Wind: light non-sticky pollen in large amounts, exposed stamens, large feathery stigma, dull flowers without nectar (maize, grasses). Insect: sticky pollen, colourful fragrant flowers with nectar, showy inflorescence (Salvia, sunflower).

2 marks: “Why do cleistogamous flowers always show autogamy? Give one advantage and one disadvantage of cleistogamy.” They never open and the anthers and stigma lie close, so only their own pollen reaches the stigma. Advantage: assured seed set without pollinators. Disadvantage: no cross-pollination, so no new gene combinations.

1 marks: “Name a water-pollinated plant whose female flowers stay under water.” Zostera, a sea grass.

Remember it

Auto = same flower; Geito = 'neighbour' flower on the same plant; Xeno = 'stranger' plant.