Pollen

Pollen is a powder made of pollen grains. They produce sperm cells (male cells used for reproduction) of seed plants. The pollen grains are actually haploid male gametophytes. This is to do with alternation of generations. All plants go through a cycle with a haploid gametophyte alternating with a diploid sporophyte. In the case of flowering plants the gametophyte stage is very small and brief.

Cross section of a male cone of a pine tree. The scales of the cone support microsporangia, which produce a large number of pollen grains

Flowering plants

Development of pollen grains

The anther contains microsporangia. Each microsporangium contains pollen mother cells. These undergo meiosis, and produce pollen grains, which produce the male gametes (sperm).

The pollen is released by the opening of the anther. The pollen is carried by some agent (wind, or some animal) to the surface of the carpel of the same or another flower. This process is known as pollination. After successful pollination, the pollen grain (which is an immature microgametophyte) completes its development by growing a pollen tube and undergoing mitosis to produce two male gametes.

Pollination

See the main article: Pollination

There are two main kinds of pollination. One kind happens when pollen from a stamen sticks to the pistil of the same plant. That is self-pollination.

Bees help plants. They spread pollen from flower to flower. Other animals that spread pollen are butterflies, birds, and bats.

The other kind of pollination takes place when pollen from one plant travels to the pistil of another plant. Most plants use this kind of pollination. Plants need help for this kind of pollination, because they cannot move. So, they need another way to move pollen from one plant to another plant.

Wind moves pollen between plants. The pollen of some plants is very light. Wind blows it from the flowers on one plant to the flowers on another plant. The wind can move pollen a long way before the pollen hits the sticky top of a pistil.

Animals also help move pollen between plants. Many flowers are colourful and their scent attracts some animals. These flowers also make a sweet juice called nectar. Sometimes an animal, such as a bee, sees or smells a flower. Then, it lands on the flower to get nectar. As the bee drinks the nectar, the stamens brush pollen onto its body. Then, the bee flies to another flower that has a pistil. The pollen on the bee's body brushes onto the sticky top of the flower's pistil. The pollen is used as protein for the bee larvae.

The plants help feed the animal. In return, the animal helps the plants by moving pollen from flower to flower. The relationship has evolved together; it is a kind of co-evolution called mutualism or symbiosis.

Explosive dehiscence

This is the term for when a rapid plant movement flings seeds away from the plant. In the genus Impatiens, explosive dehiscence is triggered by being touched.