There is an lump in each cell. It is egg shaped and called the nucleus. The nucleus is like the brain of the cell and controls all its activities. Many plant cells contain green specks These are made from a substance called chlorophyll which traps energy in sunlight. Cells, like those in the root, which are not in the light do not have chlorophyll and are not green.

The leaf is made of layers of cells. The upper and lower surfaces are covered with flat thin cells which are arranged like flags in a pavement. They do not have chlorophyll and from a transparent coating over the other layers of cells. There is a thin layer of wax above these leaf cells. The wax stops water entering or escaping from the leaf so the leaf can control the amount of water it contains.

Below the upper surface of flat transparent cells are like rectangular boxes standing on their ends. These cells are packed tightly together and contain large amounts of chlorophyll because this is the main sunlight catching layer of the leaf.

Below the layer of rectangular box cells is a thicker layer of cells. Here the cells are more rounded and do not packed tightly together. They have spaces between them and make a material that looks like a sponge. If you peel the top of some kinds of leaves you can expose this layer and see its spongy texture. The purpose of the cells in the spongy layer is to allow water to evaporate from their surfaces. They also trap sunlight to make food.

The amount of water leaving a leaf is controlled by holes called pores on the lower surface of the leaf. Each pore is made from two long cells. These cells can change shape. When they are sausage shaped they lie together and the pore is closed. When they are banana shaped they push away from each other and the pore is open.

The leaf is a busy place. The green cells make food. The cells in the spongy layer let water evaporate into the air spaces between them and the evaporated water forms vapour inside the leaf. The cells in the pores open in the day to let the water vapour out and close at night to keep the water vapour in.