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Introduction

Biology HL Candidate name: Ieva Drulyte Date: ___________________ Effect of light intensity on the rate of photosynthesis of elodea D, DCP, CE Introduction Plants and some other organisms use a process called photosynthesis to produce all their own organic substances. The equation of Photosynthesis: Water + Carbon Dioxide (With the use of Chlorophyll and Light energy) --> Glucose + Oxygen. Photosynthesis uses only light energy and simple inorganic substances, and involves many stages controlled by enzymes. Since photosynthesis is a light dependent reaction, the intensity of light should affect the rate of photosynthesis. As one of the products of photosynthesis is oxygen, therefore the oxygen concentration will be measured to show the effects of photosynthesis. Design Aim: to find the effect of light intensity on the rate of photosynthesis of Canadian pondweed (Elodea Canadensis). Hypothesis: as the light intensity decreases, the rate of photosynthesis should also decrease. Variables: light intensity (independent variable) will be altered by changing the distance between the lamp and the plant, hence the rate of photosynthesis (dependent variable) will be measured by measuring the volume of oxygen produced by the plant in 10 minutes. Table 1 Controlled variables. ...read more.

Middle

Figure 1 Laboratory set. Data collection and processing Table 1 Raw data; volume of gas bubbles released per 10 minutes in different light intensity. Length from light source, cm (�0,05cm) Volume of oxygen produced per 10 min in each trial, mL (�0,005mL) Average, mL (�0,005) Deviation, mL (�0,005) 1 trial 2 trial 3 trial 4 trial 5 trial 10 0,73 0,79 0,67 0,65 0,80 0,728 0,067971 20 0,49 0,58 0,52 0,56 0,63 0,556 0,054129 30 0,29 0,36 0,40 0,42 0,39 0,372 0,050695 40 0,36 0,36 0,27 0,24 0,30 0,306 0,053666 50 0,03 0,06 0,02 0,07 0,04 0,044 0,020736 As the rate of photosynthesis increases, the volume of oxygen will also increase as it is a product of photosynthesis and vice versa. As the chart 1 shows only the changes in volume of oxygen released, therefore, the rate of photosynthesis can be calculated by dividing recordings from minutes, for example: The rate of photosynthesis when lamp is 10 cm away is: 0.728:10 = 0.0728 mL/min. Table 2 Processed data; average rate of photosynthesis in different conditions. Length from light source, cm (�0,05cm) Oxygen produced per 10 min; mL (�0,005) Rate of photosynthesis, mL/min (�0,005) ...read more.

Conclusion

The entire experiment could have been performed again, and the new results could be combined 1 Advanced Biology by Michael Kent, Oxford University Press if the same plant is used. But the photosynthetic rate of the same piece of pond weed would eventually decrease over time anyway. Repetitions would, however, improve the overall reliability of the results. Finally, results of an experiment might be affected by improper control of controlled variables as well. Some of controlled variables might not have been considered before the experiment, for example, while performing the experiment, some of the oxygen produced from photosynthesis may have dissolved into the water. Some oxygen may have even been used by micro-organisms living on the pond weed. Some oxygen is also used during the respiration of the plant. As I discussed minor improvements in the above passage, major suggestions for improvements of investigation could also be outlined. Investigating the effects of the quality of light on the rate of photosynthesis, for example, different colored light, could be used. This could have commercial benefit, as finding out the effect of the color of light on the rate of photosynthesis could aid plant rowers to find out which type(s) of light make(s) plants grow quickest. If not the color of light, other factors that alter the rate of photosynthesis, such as temperature or pH could be also investigated. ?? ?? ?? ?? 1 ...read more.

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