Pollination
Pollination is part of sexual reproduction in plants. It describes the pollen grains getting to the female parts of a plant. Pollen grains, which contain the male gametes (sperm), need to get to where the female gamete(s) are.
What happens is basically the same as sexual reproduction in animals. Each pollen grain is haploid: it has half of the DNA (genetic information) that is needed to make a new plant. During fertilization this combines with the DNA that is in the egg of the female part and a zygote is formed. In seed plants a seed is started.
[change] Ways of pollinating
In flowering plants, pollen has to get from one flower to another. There are two main ways that this can happen: by non-living things like wind or water, or by living things such as insects or birds.
- Maize and the wind
Maize (called corn in some parts of the world) is pollinated by wind. The male anthers let go of their pollen and it blows over to a nearby female flower on another corn plant. Most of the flowers are either male or female on a corn plant (monoecious), rather than both sexes in one flower (hermaphrodite).
Maize flowers have evolved (changed over time) to use wind for pollination. They do not need pretty petals. The pollen is light so it can blow around, and the ends of the female parts (stigma) are fluffy to catch all the tiny pollen grains.
- Tomatoes and bees
Tomato plants need bees to move the pollen from the male parts of one flower (anthers), to the female parts of another flower (stigma). The bee moves between flowers, not because it is feeling helpful, but because it needs to collect the sweet nectar that the flowers have on offer. The bees take the nectar home to their hive to make honey and the tomato plants get to reproduce (make new tomato plants).
Because the tomato flowers have evolved to attract bees, they have spread-out petals and are white to human eyes (bees, like most insects, can see into the ultraviolet range as well as our visual range of wavelengths). The pollen is often stuck together in clumps called pollinia, which in turn get stuck to the bee. Bees are extremely hairy, and carry tiny electric charges which attract the pollen onto their bodies. Honey bees have special pollen baskets, usually on their rear legs; they groom the pollen off their bodies into these pockets.
Much of the pollen gets taken back to the nest or hive, where it is used as a source of protein, most needed by the larvae. Some gets rubbed off on the next flower, where the female stigma is sticky. A pollen tube grows down to permit the male gamete to fertilize an egg and make a seed.
80% of plants are pollinated by living things, and only 20% use abiotic (non-living) pollination. Of these abiotic pollinations, 98% is done by wind and just 2% by water.
