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The effect of light intensity on cyclosis on Elodea leaf cells

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The effect of light intensity on Cyclosis in Elodea leaf cells: Research Question: What is the effect of light intensity on the speed of movement of chloroplast (rate of cyclosis) in Elodea? * Independent variable; Light intensity (Lux) * Dependent variable; time taken for a chloroplast to move a measured distance. (s) * Controlled variables; temperature (oC), volume of water (mm3), using same leaf, CO2 (ppm.) Hypothesis: As light intensity exposed on an Elodea cell increases, rate of cyclosis inside the cell increases. Apparatus used: * Glass slides to view specimen * Elodea leaf (fresh from plant) * Microscope * Stopwatch * 3 lamps Procedures: One leaf was taken from an Elodea plant and examined under a light microscope at a magnification of around 400x. A cell was then located which performed cyclosis, and was exposed to the light produced by 1 lamp. 5 recordings were taken of the time taken for one chloroplast to move from one end of the cell to the other. ...read more.


130 8.76 12.90 No entry 14.65 12.24 No entry 130 8.87 10.62 No entry 17.76 11.58 No entry 130 7.32 11.23 No entry Avg: 22.67 17.06 16.51 130 6.36 8.70 8.96 Standard deviation: 2.04 2.62 2.68 (To calculate speed: Distance/time) Interpretation: The graph shows a trend where the rate of cyclosis increases (generally) as light intensity increases (i.e. when increasing the number of lamps) because graph lines of 'speed with 3 lamps' or speed of chloroplast with light from 3 lamps is higher than with 2 lamps or 1, and the speed of chloroplast is greater with 2 lamps than 1 lamp because its line is above the line for 1 lamp. Errors: Random errors: As seen in the graph, the 5th measurement of 'speed with 3 lamps' was an extreme value due to a large 'pileup of chloroplasts inside the cell leading to a very long time taken for the chloroplast to move the required distance. ...read more.


To control temperature, the experiment can be carried out in a closed laboratory with no air circulation. Temperature can be measured periodically to make sure temperature stays constant. Water supply can be controlled by keeping a drop of water next to the specimen and using blotting paper to suck water into the slide. CO2 concentration can be controlled by not breathing onto the specimen and keeping it in a closed container. Using the same leaf avoids differences in measurements due to different chloroplast concentration or size of the cell. Conclusion: Through this experiment one can conclude that the rate of cyclosis increases as light intensity increases. The graph formed by the collected data shows how the speed at which chloroplast moves in increasing light intensities increases. The data thereby supports the hypothesis as chloroplast moved at an average of 6.36um/s while being exposed to the light of one lamp but 8.96um/s with 3 lamps. Though there were some extreme values, they can be accounted for by the errors explained earlier. ?? ?? ?? ?? Money 1 ...read more.

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