Photosynthesis

The Basic Facts

• It is the conversion of light energy into chemical potential energy.

• The energy is stored in organic molecules (e.g. ATP and glucose)

• Carbon dioxide is reduced to produce carbohydrate

• So, it needs a supply of electrons hydrogens and energy!

Chloroplast Structure

1. outer membrane2. intermembrane space3. inner membrane (1+2+3:

envelope)4. stroma (aqueous fluid)

5. thylakoid lumen (inside of thylakoid)

6. thylakoid membrane7. granum (stack of

thylakoids)

8. thylakoid (lamella)9. starch10. ribosome11. plastidial DNA12. plastoglobule (drop of lipids)

Light dependent stage

(on thylakoid membranes)

• The aim is to produce a supply of ATP (energy) and electrons that can be used to reduce carbon dioxide.

• The electrons are carried by NADP (called reduced NADP or NADPH when it is carrying electrons).

• Oxygen is released as a waste product.

Or put a different way…

light dependent

reaction

ADP + P ATP

NADPNADPH

water oxygen

This is a blank slide for Mr King to do his own drawing on

Photolysis

• Using light energy to split water into electrons, hydrogen ions and water.

• H2O H+ + e- + O2

• Replacing the electrons and hydrogen ions now carried by NADPH

summary• Chlorophyll absorbs light energy

and its electrons are ‘excited’• ‘excited’ electrons pass through a

series of carriers releasing energy to generate ATP from ADP and P (photophosphorylation)

• Electrons are picked up by NADP• Light energy splits water and the

electrons are used to replace missing electrons in chlorophyll

• This all happens on membranes.

Light Independent stage

• Energy from ATP, hydrogens and electrons from reduced NADP are used to reduce carbon dioxide to produce carbohydrate.

• This happens in the stroma.

Light independent stage

light independent

reaction

Reduced NADP

NADP

Carbon dioxide

ATP ADP + Pi

glucose

Ribulose Biphosphate

2X Glycerate-3-Phosphate

2X Triose Phosphate

Glucose

(1C)

(5C)

(3C)

(3C)

(6C)

NADPH

ATP

ATP

CO2

What happens without light?

• Which stages can still continue when the light is turned off?

• Which molecules will build up when the light is turned off?