4.1.2: Rate of photosynthesis
Not started yet — this one needs some love.
The rate of photosynthesis is affected by temperature, light intensity, carbon dioxide concentration and the amount of chlorophyll.
If light intensity increases, the rate of photosynthesis increases until another factor becomes limiting.
If carbon dioxide concentration increases, the rate increases until another factor becomes limiting.
Temperature increases the rate up to an optimum; above the optimum, enzymes denature and the rate falls.
Less chlorophyll reduces light absorption, so it can reduce the rate of photosynthesis.
(HT) Any one of the factors may be the limiting factor that prevents the rate increasing.
(HT) Light intensity follows the inverse square law: light intensity is inversely proportional to distance squared.
(HT) In greenhouses, adding heat, light or carbon dioxide must increase yield enough to maintain profit.
Common exam mistakes
Do not define a limiting factor as something that stops photosynthesis; it limits the rate when it is in short supply.
In graph questions, link the trend to the factor: for example, higher light intensity provides more energy until another factor limits the rate.
Do not explain a temperature plateau as denaturing; denaturing explains the fall above the optimum.
For inverse square law calculations, doubling the distance quarters the light intensity, not halves it.
Do not assume the best greenhouse condition is always the maximum; profit depends on both yield and the cost of heat, light or carbon dioxide.