(2) Types of pollen and the process of pollination

Types of pollen

For insect-pollinated flowers, the pollen grains produced are larger in size, sticky and spiny, which helps the insect to carry the pollen grains i.e. more likely to stick to the insects legs and body.

For wind-pollinated flowers, the pollen grains produced are smaller and lighter in weight, which can be carried by the wind easily.

Types of pollination

Pollination involves getting the male pollen from the stamen to the female parts of the flower.

The pollen transfer is specifically from the 'male' anther to the 'female' stigma.

After that, the male and female sex cells (gametes) must somehow fuse in the fertilisation process.

There are various types of pollination and plants display various evolutionary adaptations to aid the pollination process.

Apart from wind blow pollination, there is a wide variety of animal pollinators. These include birds, bats, butterflies, bees, moths, flies, beetles, wasps, small mammals. Many insects visit flowers to drink nectar or feed off of pollen and transport pollen grains as they move from plant to plant.

Self-pollination

Self-pollination is when the pollen grains are transferred from the anther of a flower to the stigma of the same flower (or a different flower on the same plant).

Cross-pollination

Cross-pollination is when pollen is transferred from the anther of one flower of a plant to the stigma of a flower of different plant by some means or other - details below.

Two typical ways in which cross-pollination takes place and evolutionary flower adaptations

Insect pollination

Many plants depend on insects to pollinate them and without the intervention of bees, moths and butterflies, many species of plants would struggle to reproduce. This has implications for the food chains from which we derive our own food, if pollination is disrupted, so is our food supply, so the more bees, moths and butterflies we have, the better for our ecosystems including our food supply.

Nectaries are specialised glands of the flower near the base of the carpel that produce a sugary liquid which functions as an attractant (a “reward”) to promote animal pollination, usually by flying insects.

When an insect like a bee alights on the flower seeking food, some of the pollen sticks on to the insect from the stamen and carried away with the insect. When the same insect visits another flower, some of the male pollen brushes off onto the female stigma of another flower, potentially allowing fertilisation to take place.

Flowering plant adaptation features for insect pollination include:

(i) brightly coloured petals,

(ii) scented flowers,

(iii) nectaries to supply the insect with food (see above).

(iv) A sticky surface on the stigma to increase the chance of pollen grains sticking to it.

I've recently learned that nighttime moths are just as effective pollinators as daytime bees and butterflies. Don't swat the moths, they are good for us all, and in the UK there are far more species of moths than are butterflies!

Wind pollination

Pollen grains are usually tiny and very 'light' in weight, and so easily carried away by wind. So the natural movement of air carries away pollen from the stamen of one plant to the stigma of another plant.

Flowering plant adaptation features for wind pollination include:

(i) usually small dull in colour (attracting insects is not a priority),

(ii) no scent or nectaries (attracting insects is not a priority),

(iii) long filament hang the anthers outside of the flower so pollen is more easily blown away by wind,

(iv) stigmas are feathery in structure, more like a 'net' system, to capture the pollen grains floating by in the air.

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