Plants, unlike animals, can make their own food. They do this using a process called photosynthesis.

During photosynthesis, plants produce glucose from simple inorganic molecules – carbon dioxide and water – using light energy.

The word and symbol equations for photosynthesis are:

Diagram illustrating the word and symbol equations for photosynthesis
Be careful not to confuse this photosynthesis equation with respiration which is the reverse of this.

Photosynthesis requires energy in the form of light to drive the chemical reaction. Photosynthesis is an endothermic reaction.

The light energy required is absorbed by a green pigment called chlorophyll in the leaves. Chlorophyll is located in chloroplasts in plant cells, particularly the palisade and spongy mesophyll cells. Revise plant cells and their part in photosythesis here.

Plant leaves are the main photosynthetic organ, but any part of the plant exposed to the light will develop chlorophyll and photosynthesise.

The carbon dioxide required for photosynthesis comes from the air. It enters leaves through the stomata. Water enters the plant through the roots, and is transported to the leaves in the xylem.

Oxygen is formed as the waste product. Some is used for the plant's respiration, and also released which makes it available for respiration to animals and many microorganisms. During the day, provided the rate of photosynthesis is sufficiently high, plant leaves, and water plants, give out oxygen.


Some of the glucose produced by photosynthesis is used for respiration.

Glucose is the starting point for the biosynthesis of materials that plants need to live.

The glucose not used for respiration is used in the following ways:

An image showing the cycle of gluecose.