Photosynthesis (Edexcel GCSE Biology: Combined Science)

• 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

The products of 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