5.6.5(Factors affecting rate of photosynthesis)

Name the 3 factors which limit photosynthesis

• CO2 conc

• Temperature

• Light intensity

Briefly describe 4 methods of measuring rate of photosynthesis

• Measuring the uptake of CO2 - immobilised algal balls in hydrogen carbonate indicator

• Measuring the production of O2 - Bubbling pondweed in a photosynthometer

• Measure rate of production of carbs by measuring change in dry mass

• Measure rare if LDR by measuring rate of decolourisation of DCPIP

What is meant by the term compensation point

• The point in the day when the rate of photosynthesis is equal to the rate of respiration

Describe, using the Calvin cycle, how decreasing light intensity affects rate of photosynthesis

• At low light inetnsity, less LDR reaction occurs, so less ATP and reduced NADP are synthesised

• Therefore less GP is reduced to TP

• Less TP is regenerated to RuBP

Describe and explain how the rate of photosynthesis changes as you increase the temperature

• Between 0-25C,the rate of photosynthesis doubles every 10C, due to increased KE, leading to increased ESCs forming

• Temperatures above 25C, rate of photosynthesis decreases due to photorespiration which occurs due to stomatal closure due to water stress : Oxygen acts as a competitive inhibitor for the active site of rubisco

• This means that products are oxygenated and not carboxylated so rate decreases

• When temp surpasses that of optimum temperature, enzymes begin to denature and no more ESCs can form, rate decreases

Describe how increasing CO2 conc. affects rate of photosynthesis

• As you increase conc. of CO2, the rate increases due to more ESCs forming, so more product

• CO2 is limiting factor here

• As rate increases, it eventually reaches an optimum where other factors become limiting factors, such as light intensity, temperature, conc. of Rubisco.

• Therefore, number of ESCs stays the same so rate plateaus

Describe, using the Calvin cycle, how decreasing the Conc. of CO2 affects rate of reaction

• As CO2 conc. decreases, less binds with rubisco to form GP

• Less GP reduced to TP

• Accumulation of RuBP