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Summary A Level OCR A Biology - 17.4 Factors Affecting Photosynthesis
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🌷17.4 Factors affecting
Photosynthesis
Class Bio
Created @Apr 9, 2021 10:20 AM
Date of Exam @Apr 27, 2021
Exam Questions done?
Reviewed
Teacher Mrs Batchelor
Type Sub-topic
Photosynthesis is a multi-step reaction pathway that takes
place in plants. It is affected by various environmental
factors. Plants are affected by changes in temperature and the
availability of raw materials required for photosynthesis.
Plants obtain carbon dioxide through open stomata but this
also involves the loss of water by transpiration. However, the
loss of water vapour results in the transport of important
ions and minerals from the soil to the leaves.
17.4 Factors affecting Photosynthesis 1
, A balance between these different processes has to be
maintained and this can be upset by changes in the environment
of the plant.
limiting factors
When one of the factors needed for a plant to photosynthesise
is in short supply, it reduces the rate of photosynthesis, and
is therefore a limiting factor.
The factors that affect the rate of photosynthesis are:
Light intensity - light is needed as an energy source. As
light intensity increases, ATP and reduced NADP are
produced at a higher rate.
Carbon dioxide concentration - carbon dioxide is needed as
a source of carbon, so if all other conditions are met,
increasing the carbon dioxide concentration increases the
rate of carbon fixation in the Calvin cycle and, therefore,
the rate of TP production.
Temperature - affects the rate of enzyme-controlled
reactions. As temperature increases, the rate of enzyme
activity increases until the point at which the proteins
denature. However, the rate of photorespiration also
increases above 25C meaning higher photosynthetic rates may
not be seen at higher temperatures even if enzymes are not
actually denatured.
Stomata on plant leaves and other surfaces will close to avoid
water loss by transpiration when plants undergo water stress.
The closure of stomata stops the diffusion of carbon dioxide
into the plant, reducing the rate of the light-independent
reaction, and eventually stopping photosynthesis.
Although water is required for photosynthesis it is never
considered a limiting factor because for water potential to
have become low enough to limit the rate of photosynthesis the
plant will already have closed its stomata and ceased
photosynthesis. Plants, except those with adaptations to
17.4 Factors affecting Photosynthesis 2
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