Factors Affecting Photosynthesis

Question 1

Describe and explain the optimum conditions for photosynthesis

Answer 1

1) High light intensity of a certain wavelength
Light is needed to provide energy for the light-dependent reaction - the higher the light intensity, the more energy it provides, so ATPP and NADPH are produced at a higher rate.
Only certain wavelengths of light are used for photosynthesis. The photosynthetic pigments chlorophyll a, chlorophyll b, and carotene only absorb the red and blue light in sunlight whereas green light is reflected
(As light intensity increases, ATP and reduced NADP are produced at a higher rate)
2) Temperature around 25°C
Photosynthesis involve enzymes (e.g. ATP synthase and RuBisCO).
If temperature is too low, enzymes become inactive, but if temperature is too high they may start to denature.
Also at high temperatures:
- stomata close to avoid losing too much water, causes photosynthesis to slow down as less CO2 enters leaf
- thylakoids membranes may get damaged
- chlorophyll could be damaged. This would reduce the amount of pigment that can absorb light energy, therefore reducing the rate of reaction

3) Carbon dioxide concentration
(0.4%)
If all the other conditions are met, increasing the carbon dioxide concentration increases the rate of carbon fixation in the Calvin cycle, and therefore increases the rate of TP production

Question 2

List the limiting factors of photosynthesis

Answer 2

• light intensity
• temperature
• carbon dioxide concentration

Question 3

Why is water not considered as a limiting factor of photosynthesis?

Answer 3

For water potential to have become low enough to limit the rate of photosynthesis the plan will have already closed its stomata and ceased photosynthesis.
Even though photosynthesis requires water, only a small amount is needed

Water stress can affect photosynthesis. When plants dont have enough water, their stomata will close to preserve water, leading to less CO2 entering the leaf for the Calvin cycle, slowing the rate of TP production

Question 4

Describe and explain the effect of light intensity on the Calvin cycle

Answer 4

Reducing light intensity will reduce the rate of the light-dependent reaction of photosynthesis. This will reduce the quantity of ATP and NADPH produced.
ATP and NADPH are needed to converted GP into TP. The concentration of GP will therefore increase and the conc of TP will decrease.
As there is less TP to regenerate RuBP, the conc of RuBP will also decrease.

The reverse will happen if light intensity increases

Question 5

The effect of temperature on the Calvin cycle

Answer 5

All reactions making up the Calvin cycle are catalysed by enzymes, e.g. RuBisCO in carbon fixation.
At low temps all reactions will be slower as the enzymes work more slowly, this means levels of RuBP, TP and GP will fall

The same effect will be seen at high temps as the enzymes start to denature

Question 6

The effect of carbon dioxide concentration on the Calvin cycle

Answer 6

At low CO2 conc, conversion of RuBP into GP will be slow as theres less CO2 to be combines with RuBP.
the conc of RuBP will increase as it is still being formed from TP but not being used to fix carbon dioxide
Conc of GP and TP will be reduced