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Factors effecting the rate of photosynthesis

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Saved by Tanya
on November 6, 2009 at 6:38:08 pm


These are the factors.





At first as light intensity is increased, the rate of photosynthesis is increased but then it plateaus because of limiting factors.  Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the speed of photosynthesis.




rate of photosynthesis plotted against carbon dioxide concentration. the rate begins to slow as the carbon dioxide concentration continues to increase


Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide. If CO2 is added the graph will keep going up until about .10% CO2. At this point the graph will plateau out. 




rate of photosynthesis plotted against temperature. the rate begins to slow as the temperature continues to increase

If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it gets too hot.

Furthermore, the rate drops if the temperature is too high because photosynthesis requires an enzyme, in both light and light independent reactions. The light reactions use ATP synthase, while Rubisco is found in the "dark reactions". Since these are both enzymes, a temperature too high will cause them to denature, which brings down the rate. The optimal temperature that gives the highest rate of reactions is 25 degrees Celcius.

This picture shows the details in the photosynthesis process, and how temperature affects it more specifcally at certain points. For example, it points and helps us to visualize that at 25 degrees C, the rate is at its optimum. This explains why the area saturated with the most plant life surrounds the equator in rainforests, due to the optimal temperature that plants have adapted to taking advantage of. 



Water effects the rate of photosynthesis because water is one of the reactants in the photosynthesis reaction. If not enough water is being pulled out of the ground via the roots and up the plant through the xylem, then the leaves and plant might become dehydrated. If this happens, then the stoma on the leaves of the plant will close shut in order to conserve the water in the plant, as water is constantly exiting the plant through the stoma. When the stoma of the plant are shut, this also prevents CO2 in the air from entering the plant, and as a result, the rate of photosynthesis plummets.







This is a picture of a closed and open stoma. The top picture is a closed stoma and the bottom picture  is an open stoma.




The effect of humidity on the rate of photosynthesis in a plant is very similar to that of water. If there is a lot of humidity in the air around the plant, less water from the plant evaporates. This allows the plant to open its stoma wider because there is no risk of losing excessive amounts of water. Because of this, the rate of photosynthesis increases as the humidity increases. Another factor of the humidity in the air is that the ground can be more moist, so the plant's roots can extract more water from the ground.


This diagram looks at the 3 (main) factors that effect the rate of photosynthesis as a whole.

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