How does light intensity affect the rate of photosynthesis?

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How does light intensity affect the rate of photosynthesis?

Poorly Pondweed


1) How does light intensity affect the rate of photosynthesis?

2) How does temperature affect the rate of photosynthesis?


carbon dioxide + water glucose + oxygen



6CO2 + 6H2O àààààà C6H12O6 + 602



I predict that the more intense the light, the higher the rate of photosynthesis. To photosynthesise, plants need light. It provides the energy for the process to happen. Chlorophyll is an enzyme and it speeds up the reaction. If a plant does not get enough of either of these things, photosynthesis will not happen as quickly, if at all. Therefore, I predict that when the light is not very intense we will not see so many bubbles being produced. This is because the plant will not have so much energy (derived from light) to activate photosynthesis. All reactions require a certain activation energy, and if this is not reached the reaction will occur more slowly.

I think that as we move the lamp away (and therefore reduce the light intensity) from the elodea pondweed the number of bubbles produced will decrease steadily. For instance, say at 10cm distance 50 bubbles are counted, it is likely that at 20cm distance 25 bubbles will be counted, as the lamp is twice the distance away. This means the rate of photosynthesis is halved. I think that if we move the lamp any further away than 50cm no bubbles at all will be produced because there will simply not be enough light for photosynthesis to work.

I predict that for temperature, it will not be a case of an increase in x = an increase in y. I predict that there will be a peak where photosynthesis happens the quickest at around 40-50°C. Chlorophyll is an enzyme, therefore it requires some heat to work, but if it is overheated it stops working. Enzymes work rather like a lock and key. It is important that they are a very specific shape for their purpose...
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