Limiting Factors (calvin cycle)

Question 0

What happens to the Calvin cycle in bright light?

Answer 0

• more excitation of electrons so more photophosphorylation
• lots of ATP + NADPH from light dependent reaction so lots of TP as a as GP is converted to TP quickly
• low levels of GP as it is quickly converted to TP
• because there is lots of TP there will be lots converted to RuBP, increasing the conc of RuBP

Question 1

What happens to the Calvin cycle in dim light?

Answer 1

• very small amounts of ATP + NADPH from light dependent reaction
• not much conversion of GP to TP so the conc of GP increases and the conc of TP decreases
• because there is a low conc of TP there is a low conc of RuBP

Question 2

What happens to the Calvin cycle in high CO2 concentration?

Answer 2

• high conc of GP as RuBP is quickly converted to GP so the conc of TP is also high
• conc of RuBP is low as all available RuBP IS quickly converted to GP

However open stomata may lead to increased transpiration

- so the plant may wilt if the water loos exceed water uptake 
- this leads to a stress repos she and following the release of abscisic acid the stomata close reducing the Co2 uptake and therefore the rate of photosynthesis

Question 3

What happens to the Calvin cycle in low CO2 concentration?

Answer 3

• because CO2 is limiting, conc of GP is low
• because there is a low conc of GP, conc of TP is also low as not much GP is converted to TP
• there is a high conc of RuBP as not much is converted to TP so it builds up