Brent Cornell

    
Photosynthesis is the process by which cells synthesise organic molecules (e.g. glucose) from inorganic molecules (CO₂ and H₂O) in the presence of sunlight

This process requires a photosynthetic pigment (chlorophyll) and can only occur in certain organisms (plants, some bacteria)

• In plants, photosynthesis occurs within a specialised organelle called the chloroplast

Photosynthesis Equation

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 releases energised electrons that are used to produce ATP (chemical energy)
• The electrons are donated to carrier molecules (NADP⁺), which is used (along with ATP) in the light independent reactions 
• The electrons lost from the chlorophyll are replaced by water, which is split (photolysis) to produce oxygen and hydrogen
• The light dependent reactions occur in the intermembrane space of membranous discs called thylakoids

Step 2:  Light Independent Reactions

• ATP and hydrogen / electrons (carried by NADPH) are transferred to the site of the light independent reactions
• The hydrogen / electrons are combined with carbon dioxide to form complex organic compounds (e.g. carbohydrates)
• The ATP provides the required energy to power these anabolic reactions and fix the carbon molecules together
• The light independent reactions occur within the fluid-filled interior of the chloroplast called the stroma

Overview of the Two Stages of Photosynthesis