Light is a form of energy. In a leaf some of the energy in light is turned into stored energy. The substance which traps light and stores it is green. It is called chlorophyll.

Leaves need more than energy to make food. They need raw materials. They get two raw materials from the soil. These are water and minerals. They get another raw material from the air. This is carbon dioxide.

When sunlight shines on a leaf the water and carbon dioxide are broken up to make new substances. One of the substances is starch. This is a food which is rich in stored energy. This energy comes from the sunlight. The other substance is oxygen, which is released to the air.

The plant uses the energy in the food it has made for growth and making flowers, fruits and seeds. It may also store some of the food in roots stems and leaves for use later. Other processes take place in the plant which allow a mineral called nitrogen to join with the food the plant has made. This makes a food substance called protein. The plant uses this as a building material to make new parts of the root and shoot.

The food and energy stored in a plant are also used by herbivores. These are animals that feed on plants. They cannot survive without plants so if photosynthesis did not occur not only would there not be any plants there would also not be any herbivores. Some animals, called carnivores, do not feed on plants. They feed on other animals such as herbivores. If photosynthesis did not occur there would not be any carnivores as their source of food would not exist. This link between plants and animals through feeding explains why photosynthesis is essential not only for plant life but for animal life too.

Photosynthesis links plants and animals together in another way. Most of the carbon dioxide in the air is produced by animals when they breathe out. The plants take this in and use it to make food. The oxygen in the air is produced when plants make food through photosynthesis and animals need this to stay alive. So photosynthesis links plants and animals close together. Animals provide a raw material for plants and plants provide food and oxygen for animals.