Answers to AQA GCSE Limiting factors interacting (Biology)
Practice Questions
1.What is meant by limiting factor in photosynthesis?
The factor in the shortest supply that restricts the rate of photosynthesis.
2. Why does increasing light intensity not always increase the rate of photosynthesis?
Because another factor (such as carbon dioxide concentration or temperature) may be limiting.
3.If light intensity is high but carbon dioxide concentration is low, which factor limits photosynthesis?
Carbon dioxide concentration.
4. Why must all factors be considered together when studying photosynthesis?
Because photosynthesis depends on all factors and the rate is limited by whichever factor is in shortest supply.
5.What does a plateau on a photosynthesis rate graph show?
That the factor being increased is no longer limiting and another factor is limiting the rate.
6.A graph shows rate of photosynthesis against light intensity at low and high CO₂.
6a)At low light intensity, which factor is limiting for both curves?
Light intensity.
6b)On the same graph, why does the curve at high CO₂ reach a higher maximum rate?
Because carbon dioxide is not limiting, allowing a higher rate before another factor limits.
6c)Why do both curves eventually plateau even at high light intensity?
Because another factor, such as temperature or enzyme activity, becomes limiting.
6d)A student increases CO₂ concentration but sees no increase in photosynthesis rate. Give a possible limiting factor.
Light intensity or temperature.
7.How does low temperature limit the rate of photosynthesis?
It reduces enzyme activity, so reactions occur more slowly.
8. Why does photosynthesis decrease at temperatures above the optimum?
Enzymes denature and can no longer catalyse reactions effectively.
Factors affecting the rate of photosynthesis
Measuring & calculating rates of photosynthesis
Inverse square law and photosynthesis
Economics of enhancing the conditions in greenhouses
Investigating the effect of light intensity on the rate of photosynthesis