Increase in light intensity:
Alters the rate of the light-dependent reaction.
- The electrons take part in photophosphorylation, so increasing light intensity means more ATP and reduced NADP will be produced.
- ATP and reduced NADP are both used in the light-independent stage to reduce glycerate-3-phosphate to triose phosphate.
- ATP is also used to help 5 out of every 6 TP regenerate RuBP.
Decrease in light intensity:
The light-dependent stage will stop.
- This will also stop the light-independent as this stage uses products from the light-dependent stage.
- GP cannot be converted to TP as there wil be no ATP or reduced NADP availlable.
- This will reduce the amount of RuBP, whih reduces the fixation of carbon dioxide and the formation of more GP.
Carbon dioxide concentration
Increase in carbon dioxide concentration:
Leads to an increase in carbon dioxide fixation in the Calvin Cycle.
- More carbon fixation leads to more molecules of GP and so more being converted into TP. Also more regeneration of RuBP.
- However, the number of stomata open to allow gaseous exchange leads to more transpiration and wilting. This will lead to a stress response and the stomata will close.
- This will reduce the uptake of carbon dioxide and reduce the rate of photosynthesis.
Decrease in carbon dioxide concentration:
- If carbon dioxide concentration is reduced below 0.01% then RuBP, the carbon dioxide acceptor will accumulate.
- As a result, levels of GP and therefore TP will fall.
Increasing the temperature:
Have little effect on the light-dependent reaction, because it is not dependent on enzymes.
- Will affect the rate of the light-independent stage as this is a series of biochemical steps catalysed by a specific enzyme.
- Increasing temperature will at first increase the rate of photosynthesis.
Temperature above 25 degrees:
- Photorespiration exceeds photosynthesis.
- As a result, ATP and reduced NADP from the light-dependent reaction are wasted.
- Very high temperatures also damage proteins involved in photosynthesis.
- Increased temperatures cause an increase in water loss from leaves by transpiration.
- This may lead to closure of stomata and a reduction in the rate of photosynthesis.