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(g) (i) factors affecting photosynthesis. (ii) practical investigations into factors affecting the rate of photosynthesis

Terms in this set (13)

State what is meant by the term 'limiting factor'
- neccessary factor for photosynthesis which is in short supply, reducing the rate
State 5 factors that affect the rate of photosynthesis
1) light intensity - needed as an energy source
2) CO₂ concentration - needed as a source of carbon
3) temperature - affects the rate of enzyme-controlled reactions
4) whether the stomata are open or closed - let CO₂ in
5) water availability - needed as a source of hydrogen
Describe how increasing light intensity affects the rate of photosynthesis
- rate of ATP and reduced NADP production increases
Describe how increasing carbon dioxide concentration affects the rate of photosynthesis
- rate of carbon fixation in the Calvin cycle and, therefore, the rate of TP production increase
Describe how increasing temperature affects the rate of photosynthesis
- rate of enzyme-controlled reactions (e.g. carbon fixation) increases until the point at which proteins denature
Explain how graphs of the rate of photosynthesis under different environmental conditions can show what is limiting the rate of photosynthesis under a particular set of conditions
- rate of photosynthesis increases as a certain factor (e.g. light intensity) increases, until the point at which another factor (e.g. CO₂ concentration) becomes limiting
Explain why water availability itself is not considered to be a limiting factor
- for water availability to have become low enough to limit the rate of photosynthesis, the plant will already have closed its stomata and stopped photosynthesis
State the law of limiting factors
- rate of a physiological process will be limited by the factor which is in shortest supply
Describe how the rate of photosynthesis can be measured
- by calculating the rate of O₂ produced, CO₂ used, or increase in dry mass of plant
Describe a step by step method to investigate how one environmental factor affects the rate of photosynthesis
1) set up the apparatus pictured
2) add NaHCO₃ to provide CO₂
3) keep the pond weed illuminated
4) leave the apparatus for 10 minutes or so before readings are taken
5) set the software to take readings at desired intervals for the required length of time
Describe the effect of reducing light intensity on the Calvin cycle
1) rate of light-dependent stage of photosynthesis is reduced
2) quantity of ATP and reduced NADP produced is reduced
3) as ATP and reduced NADP are needed to convert GP to TP, the concentration of GP will increase and the concentration of TP will decrease
4) as there will be less TP to regenerate RuBP, the concentration of RuBP will also decrease
Describe the effect of reducing temperature on the Calvin cycle
1) enzyme and substrate molecules have less kinetic energy
2) there are fewer successful collisions and so a reduced rate of reaction
3) concentration of GP, TP, and RuBP is reduced
Describe the effect of reducing CO₂ concentration on the Calvin cycle
1) less CO₂ is fixed
2) concentration of GP and TP is reduced
3) concentration of RuBP is increased as it is still being formed from TP but not being used to fix CO₂
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