B2.3 Photosynthesis

All green plants and algae use light energy to make their own food. All green plants and algae obtain the raw materials they need to make this food from the air and the soil. The conditions in which plants are grown can be changed to promote growth.

Photosynthesis is summarised by the equation:
carbon dioxide + water -- light energy/chlorophyll  --> glucose + oxygen

During photosynthesis:

• light energy is absorbed by a green substance called chlorophyll, which is found in chloroplasts in some plant cells and algae
• this energy is used by converting carbon dioxide (from the air) and water (from the soil) into sugar (glucose)
• oxygen is released as a by-product. 
• photosynthesis takes place in the leaves of all green plants and is the main function of leaves.

Know that the rate of photosynthesis may be limited by:

• shortage of light (usually sunlight) slows photosynthesis
• low temperature, slows down the rate of photosynthesis
• shortage of carbon dioxide will also slow down the rate of photosynthesis,

The glucose produced in photosynthesis may be converted into insoluble starch for storage. Plant cells use some of the glucose produced during photosynthesis for respiration.

Some glucose in plants and algae is used:

• to produce fat or oil for storage
• to produce cellulose, which strengthens the cell wall
• to produce proteins.

To produce proteins, plants also use nitrate ions that are absorbed from the soil.