Photosynthesis

Plants use energy from light to make carbohydrates from carbon dioxide and water. This process is called photosynthesis. Glucose is a carbohydrate produced by photosynthesis; oxygen is also produced.

The word equation for photosynthesis is:

Photosynthesis takes place in structures in plant cells called chloroplasts. Chloroplasts contain chlorophyll, a green pigment that absorbs light.

Chlorophyll transfers energy from light into chemical energy. The plant uses this energy to synthesise carbohydrates from carbon dioxide and water.

Chemical formulae in photosynthesis

Photosynthesis uses carbon dioxide and water to make glucose and oxygen. Carbon dioxide and water are the reactants: the substances used in the reaction. Glucose and oxygen are the products: the substances made.

• Reactants: carbon dioxide, $$\ce{CO2}$$, and water, $$\ce{H2O}$$.
• Products: glucose, $$\ce{C6H12O6}$$, and oxygen, $$\ce{O2}$$.

Reading the formulae

In these formulae, $$\ce{C}$$ represents carbon, $$\ce{H}$$ represents hydrogen and $$\ce{O}$$ represents oxygen. A subscript gives the number of atoms of the element immediately before it in one molecule. If there is no subscript, there is one atom of that element.

For example, one molecule of carbon dioxide, $$\ce{CO2}$$, contains one carbon atom and two oxygen atoms. One molecule of oxygen, $$\ce{O2}$$, contains two oxygen atoms.

One molecule of water, $$\ce{H2O}$$, contains two hydrogen atoms and one oxygen atom. One molecule of glucose, $$\ce{C6H12O6}$$, contains six carbon atoms, twelve hydrogen atoms and six oxygen atoms.