Photosynthesis

Photosynthesis is an endothermic reaction in which energy from sunlight is transferred to the chloroplasts in green plants
- Green plants use this energy to make the carbohydrate glucose from the raw materials carbon dioxide and water
- At the same time, oxygen is made and released as a waste product
Photosynthesis can be defined as the process by which plants manufacture carbohydrates from raw materials using energy from light
Plants are
- Autotrophs – they can make complex molecules (glucose) from simple molecules (carbon dioxide and water)
- Producers – they can make their own food and so are the first organism at the start of all food chains
  - E.g. Plants and algae
Photosynthesis can be summarised in a word equation as shown below:

Word equation for photosynthesis

Where do the reactants come from and where do the products go?

This equation can also be shown as a balanced chemical equation
- Six carbon dioxide molecules combine with six water molecules to make one glucose molecule and six oxygen molecules

The balanced chemical equation for photosynthesis

Plants use the glucose they make as a source of energy in respiration
They can also use it to
- Produce starch for storage
- Synthesise lipids for an energy source in seeds
- To form cellulose to make cell walls
- Produce amino acids (used to make proteins) when combined with nitrogen and other mineral ions absorbed by roots

The fate of glucose molecules produced in photosynthesis

If asked for the raw materials required for photosynthesis, the answer is carbon dioxide and water.

Although required for the reaction to take place, light energy is not a substance and therefore cannot be a raw material.