Photosynthesis has two stages: (1) the light-dependent stage where chloroplasts use light energy to produce ATP and NADPH, and (2) the light-independent stage where carbon dioxide is fixed into carbohydrates using ATP and NADPH. During the light-dependent stage, light is absorbed by chlorophyll, electrons are transferred through an electron transport chain to produce ATP, and water is split to provide electrons that reduce NADP to NADPH. The light-independent stage can continue in the dark using ATP and NADPH to reduce carbon dioxide into carbohydrates like glucose.

2. 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!

3. Chloroplast Structure
1. outer membrane 5. thylakoid lumen (inside of 9. starch
2. intermembrane space thylakoid) 10. ribosome
3. inner membrane (1+2+3: 6. thylakoid membrane 11. plastidial DNA
envelope) 7. granum (stack of thylakoids) 12. plastoglobule (drop of lipids)
4. stroma (aqueous fluid) 8. thylakoid (lamella)

4. 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.

5. Or put a different way…
NADPH
NADP
light
water dependent oxygen
reaction
ADP + P ATP

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

7. 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

8. 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.

9. 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.

10. Light independent stage
Reduced NADP
NADP
Carbon light
dioxide independent glucose
reaction
ATP ADP + Pi

11. (5C)
Ribulose Biphosphate
CO2
(1C)
ATP
2X Glycerate-3-Phosphate(3C)
NADPH ATP
(3C) 2X Triose Phosphate
Glucose (6C)

12. 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?