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Biology Coursework : Rate of Photosynthesis

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Biology Coursework : Rate of Photosynthesis Aim To investigate a factor that affects the rate of photosynthesis. Outline A piece of pond weed will be cut and placed into a beaker containing water and sodium hydrogen carbonate. A lamp will be shined on to the pond weed and the amount of bubbles released from the plant will be counted for 1 minute. The lamp will be adjusted to different distances from the plant to try and obtain different results. Background In Previous experiments leading up to this one, we have seen that plants are able to photosynthesis better when there is plenty of light. As long as there are no other limiting factors this should be true. When chlorophyll absorbs light energy, the light energy cannot be immediately used for energy conversion. Instead the light energy is transferred to a special protein environment where energy conversion occurs. This happens by using the energy of a photon to transfer electrons from a chlorophyll pigment to the next. When enough light energy has been harnessed at a reaction centre, ATP can be synthesized from ADP. During this reaction, oxygen is produced as a by-product and it is the oxygen bubbles that are being measured in the experiment. The greater the light intensity, the more light energy that can be transferred and harnessed to fuel reaction in photosynthesis. Diagram Photosynthesis Equation: 6CO2 + 6H2O light energy & chlorophyll C6H12O6 + 6O2 Variables: Experimental Variable- Light intensity is to be the variable explored in this investigation. ...read more.


5. Put in the measured amount of Sodium Hydrogen Carbonate 6. Place the ruler so that the "0" measurement is aligned with the side of the beaker. (Distance measured from side of beaker to edge of light bulb) 7.) Take a control test with the lamp off. This means no light is present, and there should not be any bubbles. 8.) Place the lamp directly in front of the plant so that it is the desired distance away from the beaker. 9.) With the light shining on the plant, record the number of bubbles emitted in a 1 minute duration. Switch off the lamp and wait for another minute before taking another reading. 10.) Take 2 readings at the current distance and move the lamp 5 cm further away from the plant. 11.) Repeat steps 8 and 9 until 2 readings from at least 5 intervals of 5 cm have been taken. 12.) Proceed to the data analysis stage. Results Distance Bubbles1 Bubbles2 Bubbles3 0 5 10 15 20 25 30 Conclusion From the results that I have gathered I can state that an increase in light intensity certainly does increase the rate of photosynthesis. As was also expected in my prediction, the relationship between light intensity and the rate of photosynthesis was non-linear. From both graphs there is a best-fit curved line. This means that the rate of photosynthesis increases at an exponential rate. ...read more.


Some oxygen is also used during the respiration of the plant. But since only bubbles were counted, the volume of bubbles was not as important. During the high intensities I had experienced counting difficulties of the bubbles being produced. There are also factors affecting accuracy at low light intensities. With low light intensity, the pond weed receives some light energy from background light such as sunlight seeping through curtains or the light from the lamp of another student's experiment. To eliminate most all background light, the experiment must be performed in a completely dark room. Even then, some of the light from the lamp in my experiment would reflect of the table and reach the plant though this amount of light is probably insignificant in affecting the rate of photosynthesis. Temperature was also another factor that was controlled by the lamp being used. Even though a perspex sheet was used in front of the lamp to prevent some heat from reaching the plant, not all the heat can be blocked. The method of the experiment could probably also be improved to obtain more reliable results. I had originally chosen to count the number of bubbles in one minute but this produced miscounts in the readings. 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. During high rates of photosynthesis, it would still be difficult and impractical to measure the volume of oxygen produced for a long duration. ...read more.

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Here's what a teacher thought of this essay

3 star(s)

This is an average write up which contains good background information on photosynthesis and limiting factors. There are no results or graph included so it is difficult to establish whether the conclusion is reliable.

3 stars.

Marked by teacher Louise Star 08/01/2013

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