Photosynthesis

Photosynthesis is a process which light energy is used in the synthesis

of organic molecules.

What is the equation for photosynthesis?

Water + carbon dioxide +light energy

=

Oxygen + glucose

The role of chloroplasts in Photosynthesis.

• Chloroplast is an organelle in the leaf of a plant that contain the thylakoid cells and the stroma. These are shown on the following diagram.

• Here 2 important reactions take place. The light dependant reactions take place in the thylakoid cells and the light independent in the stroma.

Chloroplasts

What happens in the light dependent reactions.

• Electrons in the chloroplast gain energy from sunlight , this energy is used to add a phosphate group to ADP making ATP.

• The energy is used also used in the photolysis of water to split it into oxygen and hydrogen molecules

• The electrons, protons and energy for the light dependent reactions are used to make NaDPH2.

• The ATP/NADPH2 from the Light Dependent reactions enter the light independent reactions.

What happens in the light independent reactions.

The light independent reactions occur at night for only a few seconds due to limited amounts of ATP and

supply of NADPH2.

Role of NADPH2 and ATP

Energy from ATP and electrons from NADPH2 are used to reduce carbon

dioxide and build it to sugars

The following cycle is called the Calvin cycle.

• This is called Fixing the carbon dioxide. The carbohydrates(sugars) are in a form of RuBP.

• The following cycle is called the Calvin cycle.

• What happens in the Calvin cycle?

• RuBP with the addition of carbon dioxide splits into 2 moles of GP. For GP to be turned to Carbohydrates it requires ATP and NADPH2. The NADPH2 give up its electrons which enter the GP molecules making GALP.

GALP

GALP is converted to a whole series of mostly sugars, some lipids and

some Proteins.

• Also some GALP is regenerated back to RUBP if sufficient amounts of NADPH2 and ATP are provided.