During photosynthesis, light energy is trapped and used to synthesise organic compounds from CO2 and water; the chloroplast is the organelle involved in photosynthesis.
The rate of photosynthesis is affected by a number of factors including light intensity, carbon dioxide concentration and temperature; the rate is determined by the limiting factor.
The absorption spectrum is a graph that shows how much light a particular pigment absorbs at each wavelength. Different pigments absorb light of different wavelengths.
The action spectrum is a graph that shows the rate of photosynthesis that takes place at different wavelengths.
Stages of Photosynthesis
- Different chlorophyll and carotenoid molecules (clustered at photosystems on the lamellae) absorb light maximally at different wavelengths.
- This allows photosynthesis to take place over a range of wavelengths
- As pigment molecules are energised, energy passes by resonance to a primary pigment that emits high-energy electrons
- Electrons pass from PS II to PS I through an electron transport system within the lamellae that synthesises ATP (photophosphorylation).
- PS II regains electrons from the photolysis of water; oxygen is released.
- Energised electrons from PS I reduce NADP+ to NADPH
- Occurs in the stroma, CO2 is fixed by RuBP forming glycerate phosphate.
- Using energy from ATP, this is reduced by NADPH to triose phosphate.