EDEXCEL International A level Biology, Topic 5, Photosynthesis

1. The
biochemistry of
photosynthesis
Chapter 5A

2. Learning objectives

3. General introduction

6. The light dependent stage
• The light reactions (in the thylakoids):
o Split H2O
o Release O2
o Reduce NADP+ to NADPH
o Generate ATP from ADP by photophosphorylation

7. Photolysis
• It is a breaking down of water molecule by the light.
• It is a photochemical reaction.

8. Cyclic photophosphorylation
• Involves only PS I and drives the production of ATP.

9. Non-cyclic photophosphorylation
• During non-cyclic photophosphorylation water molecules
are broken down, providing hydrogen ions to reduce
NADP. Also produces ATP.
• Involves PS I and PS II.

11. NADP
• Nicotinamide adenine dinucleotide
phosphate.
• Collects electrons from PS I and
hydrogen ions, and becomes reduced
NADP or NADPH.

14. Light independent stage
• Also known as Calvin cycle, occurs in the stroma.

15. Calvin cycle

17. Using the products of photosynthesis
• Main product is GALP.
• Some of the GALP is used in cellular respiration directly.
• Some of the GALP will change to glucose by
gluconeogenesis.
• It is also a part of amino acid, fatty acid, nucleotide
production.

19. Limiting factors in photosynthesis
• The factor needed for a reaction to progress that is
closest to its minimum value
• Limiting factors are:
• 1. Light (light intensity and wavelength of the light )
• 2. Carbon dioxide (concentration of carbon dioxide)
• 3. Temperature

20. CO2
• In natural environments carbon
dioxide concentration is the most
common limiting factor of
photosynthesis in plants.

21. Temperature