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Aim : To investigate the effect of light on the rate of photosynthesis

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Title: Photosynthesis Aim: To investigate the effect of light on the rate of photosynthesis. Apparatus: Test tube, graph paper, bung(rubber), dough, syringe, capillary tube. Materials: Elodea, tap water, pond water, petroleum jelly, hydrogen bicarbonate Method: A piece of well illuminated elodea about 10 cam long which already had bubbles emerging from it was obtained. A clean oblique cut was then made with a razor near the end of the stem, under the water, placing the plant in the same water as the pond weed. A pinch of hydrogen bicarbonate was added to the pond water in the test tube. The initial measurements were taken by placing a graph leaf on the test tube and recording the distance moved on the graph, between the tip (lower end) ...read more.


Observation: The rate of release of bubbles, this oxygen released, was greater (in mmmin-1) in the straight than in a dark area. Results: Table showing the distance (mm) moved of fluid in the tube with time (min) in light and dark condition Time/min Distance travelled/min Light Dark 5.0 0.10 o.o5 10.0 0.20 0.09 15.0 0.30 0.13 20.0 0.40 0.16 25.0 0.50 0.19 GRAPH SHOWING DISTANCE OF FLUID MOVED IN TUBE WITH TIME(min) Discussion: Photosynthesis consists of interconnected reactions. Thus the rate of this process is dependent upon the slowest reaction, which is in turn dependent on certain factors/condition. Such factors may be concentration of CO2, temperature and light intensity. ...read more.


This increase would continue until either light intensity started to decrease or the CO2 within the test tube was used up, the graph would have then leveled off with the decrease in CO2 concentration. On the other hand the Elodea in the dark (previously illuminated in pond) having both constant temperature and steady supply of CO2, still saw a decrease in the rate of oxygen evolved/ distance of fluid moved/ rate of photosynthesis, since light intensity was low and was therefore the limiting factor, lowering the rate of a particular reaction of photosynthesis. Conclusion: Since the rate of oxygen released increased with the increase of light intensity it may be concluded that the rate photosynthesis also increases (since the rate of photosynthesis is proportional to th release of oxygen) with increased light intensity. ...read more.

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