Title: Rate of photosynthesis (light intensity) intensit y) Objective:
The objective of this experiment is to investigate the effect of different light intensities on the rate of photosynthesis Introduction
Biological principle Through photosynthesis, plants convert sunlight energy into organic molecules and oxygen, forming the basis of food for all organisms. In a series of reactions, light energy are absorbed by chlorophyll, carbon dioxide and water are combined to create food for plants and oxygen. Oxygen is only the by-product in the reaction. Design of the experiment The photosynthetic rate is often measured by the amount of carbon dioxide absorbed or oxygen released by a plant. In this experiment, the oxygen released by a plant is collected by the pipette. The volume of oxygen can be measured by the change in volume of gases in the pipette in a certain period of time. With increase in light intensity, photosynthesis begins, and some carbon dioxide from respiration is utilized in photosynthesis. As light intensity increases, there is an increase in the rate of photosynthesis, and this light intensity can be increased or decreased by bringing the source of light closer to or further away awa y from the plant. Hypothesis Hence, we can hypothesize that with increase in light intensity, the rate of photosynthesis would also increase. Variables The variables in the experiment are light intensity and the rate of photosynthesis. The independent variable is light intensity, which is adjusted by modifying the position of the lamp. The dependent variable is the rate of photosynthesis or the rate of bubble production which is affected by the varying light intensity and it is measured by the inverted pipette. The control variable is temperature, which is controlled by using water bath and measured me asured by thermometer. t hermometer. Another control variable is carbon dioxide (Na 2CO3) concentration and can be controlled replacing Na 2CO3 solution after each treatment. Assumption In the experiment, photosynthetic rate is measured by the amount of oxygen released. It is assumed that all the gases released from the plant and being collected is oxygen. Moreover, it is assumed that the heat from the light source does not affect the photosynthetic rate. The concentration Na 2CO3 solution used can provide excess carbon dioxide to the plant, therefore it is assumed that the change in carbon dioxide concentration does not limit the rate of photosynthesis.
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Apparatus & Materials
2 ml pipette
Thermometer
Pipette filler
Table lamp, 100W
Clip
Timer
Rubber tubing
1-metre ruler
Beaker, 500mL
5% Hydrogencarbonate solution
Boiling tube
Hydrilla plant (several)
Stand and Clamp
Procedure
1. Place the hydrilla in a test-tube filled with 5% hydrogencarbonate solution 2. Place the test-tube and the thermometer into the water bath 3. Fix the inverted pipette by the stand and clamp 4. Put the stalk of hydrilla into the pipette 5. Insert the pipette into the rubber tubing and clip the tubing tightly to avoid leakage of gas 6. Placed the lamp at a distance of 5cm, measured by the ruler, from the test-tube 7. Put the whole experimental set-up under the experimental condition for 5 minutes 4. Start the timer 6. Record initial reading and final reading after 5 minutes in a table 7. Repeat the above steps with the lamp at distances of 10cm, 15cm, 20cm and 25cm Result
Data collection Distance between lamp and
5
10
15
20
25
plant/cm Light intensity (1/distance between lamp and plant) Initial reading Final reading Volume of oxygen released Table: volume of oxygen released by the hydrilla under different light intensity Graph of volume of oxygen released against light intensity can be plotted in separate graph paper.
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Discussion
The above observations coincides with the hypothesis. The closer the lamp to the plant (hydrilla), the more the light intensity, and thus more the rate of photosynthesis, which is seen by the increased volume of oxygen produced by photosynthesis. Light is needed for photosynthesis as is seen by the following reaction equation: Carbon dioxide + Water
Glucose
+ Oxygen
CO2(g) + H2O(l) C6H12O6(s) + O2(g) In order to break the molecules of water and carbon dioxide, light energy is required. This is carried out through a series of reaction controlled by enzymes. Oxygen is released from the splitting of the water that combines with carbon dioxide to form glucose. Therefore, more the light intensity, the more splitting of water molecules takes place, and thus more oxygen is produced, indicating an increase in the rate of photosynthesis. Thus at a close intensity. Conclusion
Increase in light intensity will lead to increase in photosynthetic rate. Violet-blue and red light are most useful for the photosynthesis because the photosynthetic molecules of chloroplasts absorb violet-blue and red light (the colour most effective i n driving photosynthesis) and reflect or transmit green light. This is why leaves appear green.
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