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


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. This procedure was repeated with 2 lamps and 3 lamps giving 15 readings. The cell length was then measured by finding the length being viewed under the magnification and divided by the number of cells that fit into that length. The results were recorded along with the results of 2 other peoples and the speed calculated:

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Rate of cyclosis under increasing light intensity:

(To calculate speed: Distance/time)


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 ...

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