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Investigate a factor that affects the rate of photosynthesis.

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Introduction

Photosynthesis Aim: To investigate a factor that affects the rate of photosynthesis. A piece of pondweed will be cut and placed into a beaker containing water and sodium hydrogen carbonate. A lamp will be shined on to the pondweed and the amount of bubbles released from the plant will be counted. The lamp will be adjusted to different distances from the plant to try and obtain different results. Green plants are the only living things that can make their own food. They do this using a process called photosynthesis, which means, "making things with light." During the process of photosynthesis, the energy from the sun is turned into chemical energy. The chemical energy is used to join carbon dioxide and water. In the process, sugar and oxygen are created. This process takes place mainly in the leaves of the plant. Leaves contain a substance called chlorophyll that traps the sun's energy. The chlorophyll is a bright green colour, which explains why plants are green. Through the process of photosynthesis, plants convert the light energy into stored energy. Because green plants can manufacture their own food, plants are called autotrophs or self-nourishing. Photosynthesis is possible because green plants contain an energy- capturing substance called chlorophyll. The plant gets its green colour because chlorophyll is green. Many types of seaweed and other plants that do not appear to be green also have chlorophyll and therefore can convert the sun's energy into food. In these plants the greenness is hidden by other pigments. The chlorophyll captures the light energy and uses this energy to build carbohydrates from simple raw materials (water, carbon dioxide and minerals). ...read more.

Middle

This variable can be fixed by adding a fixed amount of sodium hydrogen carbonate to the beaker and plant. The experiment should also be completed in one session and under two hours so the plant does not use up a significant percentage of the CO2. Water- Water is required in the photosynthetic reaction. When plants lack water, their stomata close to prevent further water loss. At the same time, closing the stomata cells doesn't allow CO2 to diffuse into the leaf. Water is also therefore, linked to the carbon dioxide factor. Water can be kept a constant by keeping the same amount of water in the beaker. Plant- Different plant species have different photosynthetic rates due to the different leaf structures of the plants. Even plants of the same species may have slightly different rates of photosynthesis since there may be more or less chlorophyll in the leaves to absorb light. The size of the plant is also important since this would affect the amount of surface area for gas exchange. The only solution to controlling this variable is by using the same plant throughout the experiment. Temperature - Enzymes are used in the photosynthesis reactions of a plant. Therefore, temperature will increase the rate of photosynthesis, until a point at which the enzymes denature. I am therefore going to perform the experiment at room temperature, checking the temperature frequently, in case the heat given off from the light should slightly raise the temperature, in which case I shall simply refill the beaker with more water after each experiment. Method 1.Set up the apparatus as shown in the diagram but leaving out the pond weed, funnel, test tube, water, and the sodium hydrogen carbonate. ...read more.

Conclusion

If during a repeated experiment, counting bubbles is still used, there is a smaller chance for human error when counting within a smaller time frame. If the capillary tube option was to be chosen, volume should be measured for a smaller time frame to reduce the overall time to complete the experiment. Also, during high rates of photosynthesis, it would still be difficult and impractical to measure the volume of oxygen produced for a long duration. Due to the nature and convenience of the experiment, it could be easily modified to investigate another variable of photosynthesis. Since sodium hydrogen carbonate (NaHCO3) is used to provide the pondweed with carbon dioxide. Performing the experiment with different volumes of NaHCO3 could vary the amount of CO2. The plant would be kept at a constant distance from the lamp and a constant volume of water would be added to the sodium hydrogen carbonate. Another experiment using almost identical apparatus would be to vary the colour of the light the plant absorbs. Using translucent colour filters in front the lamps could vary this. Since light wave length has already been identified as a variable of photosynthesis, it would be interesting to actually test it. The only problem of this experiment is that there is no way to define or "measure" the colour of light. Wavelength would be a solution but this cannot be measured with available equipment. We only have a general idea of how to class colours. Because of this, the coloured light experiment should not be taken as seriously as light intensity or carbon dioxide. Results Table Distance from lamp (cm) No. Of bubbles Average 1 2 3 100 1 2 2 1.6 80 3 6 6 5 60 5 8 9 7.3 40 14 10 11 11.6 20 17 17 200 78 ...read more.

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