Photosynthesis

Photosynthesis is how green plants use light energy to make their own food. In this reaction, carbon dioxide from the air and water from the soil react to form glucose (a sugar) and oxygen. This happens in the presence of chlorophyll and light.

What happens

Definition: Photosynthesis is the reaction between carbon dioxide and water to produce glucose and oxygen, using light energy and chlorophyll.

Equations to learn

Word equation: carbon dioxide + water → glucose + oxygen

Symbol equation:

$$6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$$

Glucose is $C_6H_{12}O_6$. The numbers balance atoms on both sides.

Where it happens

• In leaf cells, inside chloroplasts that contain green chlorophyll (the pigment that absorbs light).
• Carbon dioxide enters leaves through tiny pores called stomata.
• Water travels from roots up the stem to the leaves.
• Oxygen leaves the plant through stomata; glucose is used for energy, built into plant material, or stored as starch.

What it needs

• Light energy (from the Sun or lamps)
• Chlorophyll to absorb light
• Carbon dioxide and water
• A suitable temperature for enzymes in the leaf

Why it matters for air and climate

• Removes carbon dioxide from the air, helping reduce a greenhouse gas.
• Releases oxygen, supporting life and air quality.
• Plants and forests act as carbon stores, locking carbon into biomass.

Common misconceptions

• Chlorophyll is not used up; it captures light energy.
• Sunlight provides energy but does not appear in the equation as atoms.
• Plants also respire day and night, but during daylight they usually produce more oxygen than they use.