Photosynthetic Reactions

ninja icon


•  Oxygen is produced in photosynthesis from the photolysis of water

•  Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide

Photosynthesis is a two step process:

  • The light dependent reactions convert light energy from the Sun into chemical energy (ATP)
  • The light independent reactions use the chemical energy to synthesise organic compounds (e.g. carbohydrates)

Step 1:  Light Dependent Reactions

  • Light is absorbed by chlorophyll, which results in the production of ATP (chemical energy)
  • Light is also absorbed by water, which is split (photolysis) to produce oxygen and hydrogen
  • The hydrogen and ATP are used in the light independent reactions, the oxygen is released from stomata as a waste product

Step 2:  Light Independent Reactions

  • ATP and hydrogen (carried by NADPH) are transferred to the site of the light independent reactions
  • The hydrogen is combined with carbon dioxide to form complex organic compounds (e.g. carbohydrates, amino acids, etc.)
  • The ATP provides the required energy to power these anabolic reactions and fix the carbon molecules together

Summary of the Overall Process of Photosynthesis

photosynthesis reactions