1. Limiting factors in Photosynthesis Discuss the limiting factors in photosynthesis with reference to carbon dioxide concentration, light intensity and temperature.

2. Law of limiting factors The limiting factor for a metabolic process is the factor that is present at the lowest or least favourable value.

3. Carbon dioxide concentration Average carbon dioxide content of the atmosphere is 0.03-0.04% Increase in CO 2 up to 0.5% will increase the rate of photosynthesis BUT optimum is 0.1% 0.1 0.5 Carbon dioxide conc Rate of photo synth esis

4. With reference to the graph: What makes 0.1% the optimum figure? Why is there little point in recording rates above the 0.5% CO 2 concentration?

5. Light intensity Experiments carried out by Blackmann At low light intensities, the rate of photosynthesis increases as light increases Beyond 20 kilolux the rate levels off

6. Effect of light Allows opening of stomata so CO 2 can enter Absorbed by chlorophyll  excites electrons Splits water molecules  photolysis

7. Light intensity and the compensation point

8. Effect of temperature Mostly affects enzyme controlled reactions of Calvin cycle At high light intensity, increase in temperature increase in rate. At low light intensity, little change. Above 30 o C photosynthesis is reduced at both high and low light intensity- can you suggest why?

9. Effect of temp. and light together Rate of photo synthesi s Temperature/ o C High light intensity Low light intensity

10. What temperature is likely to be the optimum temperature at high light intensity? What is likely to be the temperature at which photosynthesis stops? Explain why this happens. Now do questions on p67

11. Graphs and quiz http://www.cix.co.uk/~argus/Dreambio/ferti lisers%20and%20crops/limiting%20factors. htmhttp://www.cix.co.uk/~argus/Dreambio/ferti lisers%20and%20crops/limiting%20factors. htm