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)
  

Light Dependent Reactions

In plants, the light dependent reactions occur within the membranous discs called thylakoids (which are arranged into stacks called grana)

• Light is absorbed by photosynthetic pigments (such as chlorophyll), resulting in the production of ATP (chemical energy)
  

• Light is also absorbed by water, which is split (photolysis) to produce oxygen and hydrogen (carried by NADPH)
  

• The hydrogen and ATP are used in the light independent reactions, the oxygen is released from stomata as a waste product