An acorn develops from the female flower on an oak tree. Oaks produce male and female flowers on the same tree. The male flowers develop in a large group called a catkin. They hang down from twigs and release their pollen into the air. The female flowers are found in groups of two or three.

After pollination, the base of the flower forms a woody cup, and the flower forms a woody fruit called a nut – an acorn.

When the acorn first forms it is green, but it turns brown as it ripens. The spike at its tip is the remains of the pollinating tube (stigma) of the flower.

Inside an acorn is a tiny plant, and two leaves. The rest of the acorn contains the young plant's food store. The acorn contains substances which give it a bitter taste, and this helps stop some of them from being eaten. Despite this, animals such as pigeons, woodpeckers, badgers, squirrels and woodmice love to eat them.

When the acorn germinates, a root grows downwards. Finally the shoot bursts through the soil, and the oak seedling uses the food in the acorn to grow its first pair of new leaves.

So an acorn it not just a vital part of a tree, allowing it to produce new plants, but it is also part of a food chain for many animals. The oak tree produces so many acorns that some survive, even after many have been eaten. Squirrels even bury acorns, and forget where some were buried. In this way, acorns rely on animals to survive, too.