All living things will die; and if the species is to continue, and is to have any future, then it needs to reproduce. Reproduction produces new offspring of their kind - plant or animal. As the old die off, the young take their place. A species that is good at reproduction will survive.

Green plants reproduce by flowering. The flowers contain the cells that will combine to produce the seeds and then the new plant. Ideally, cells from two different plants will combine; but if all else fails, a plant can fertilise itself to produce seeds.

The flower produces female egg cells in its ovary. The ovary has a sticky stigma on a long style to catch the male pollen cells. The pollen cells are produced in the stamens. These tiny specks are carried to the stigma of another plant by the wind, or on an insect. The insect gets sticky, sugary nectar from one plant and gives it to another plant - like a postal service.

When the egg cell is fertilised, it develops into a seed. The ovary may develop too, into a fruit. Because now the challenge is to move the seed - away from its parent plant to somewhere where it will grow. The wind may blow it, or water may carry it; it may stick to a passing animal, or be swallowed by one, only to emerge in the animal's droppings and grow. The new plant will flower in turn.

This is all a risky business - and so lots of pollen and seeds are produced to help ensure that new plants will grow. The whole process - from flower to flower - is called the flower's life cycle.