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An Experiment Investigating the Factors Affecting Photosynthesis in Canadian Pondweed

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An Experiment Investigating the Factors Affecting Photosynthesis in Canadian Pondweed The experiment I am going to investigate involves exploring the effect certain limiting factors have on the rate of photosynthesis in Canadian pondweed. The formula for photosynthesis is as follows: 6CO2 + 6H2O = 6O2 + C6H12O6 Photosynthesis is the process in which green plants make use of the energy in sunlight to manufacture carbohydrates from carbon dioxide and water in the presence of chlorophyll. Water is absorbed by the roots and carried to the leaves by xylem tubes, and carbon dioxide is obtained from the air through the stomata and diffuses into the cells containing chlorophyll. Chlorophyll is a green pigment that is capable of converting sunlight energy into a latent form, stored in the plants food. Preliminary Work I am going to do this preliminary work so that I can find the boundaries for my experiment by finding the conditions needed for my experiment to work. There are three main limiting factors that could affect the rate of photosynthesis in my pondweed. These are: * CO2 levels - to adjust the amount of CO2 in the water I am using for my experiment I can add bicarbonate of soda. This will dissolve in the water and increase the amount of CO2 available for the plant to use during photosynthesis. * Light levels - these can be changed by the distance or strength of the light used during this experiment. ...read more.


Blue and red light is easily absorbed by the chlorophyll, but yellow and green light is reflected away from the chlorophyll, which decreases the amount of light absorbed, and therefore the rate of photosynthesis. Using the same light source throughout the experiment can control this, as well as maintaining the light intensity. I have decided that I will keep the temperature of my experiment at 20oC throughout, because this is approximately room temperature and therefore it will make it easier to maintain the temperature if the surroundings are at a similar temperature. I must also be careful in case the heat from the light I am using in the experiment heats up the water. I can counteract the effect of this by adding cold water. Apparatus * Beaker * Test tube * Filter funnel * Ruler * Pondweed * Water * Light * Stopwatch * Pen and pencil * Electronic scales Method 1) Set up apparatus as shown in diagram. 2) Measure amount of bicarbonate of soda to use. 3) Add bicarbonate of soda to water. 4) Start stopwatch. 5) Count the number of bubbles that the pondweed gives off in 60 seconds. 6) Record results. 7) Move light source 5cm after every experiment. 8) Repeat each section of the experiment 3 times. Diagram of Experiment Hypothesis I predict that as the distance of the light from the plant decreases (the light comes nearer to the pondweed), the rate of photosynthesis in the plant will increase. ...read more.


I would also have made sure that all the water I used in my experiment had an equal concentration of carbon dioxide in it because, although I added an equal amount of bicarbonate of soda to each experiment, there is no guarantee that each beaker of water had an equal amount of carbon dioxide dissolved in it at the beginning of the experiment. To counteract this I would... To gain more accurate results I would decrease the rate of photosynthesis by adding less bicarbonate of soda. This is because when the light source was at its closest to the plant, it became very difficult to accurately measure the number of bubbles being given off by the plant. Slowing the process down would decrease the chance of human error and therefore the accuracy of my results. It is likely that the bubbles that the pondweed gave off were not pure oxygen. If I were to do this experiment again I would test this with an oxygen probe. If I were to take this experiment further, I could experiment with fluorescent lights and halogen lights (Ultra Violet??), to see whether or not this affected the rate of photosynthesis in a different way to, for example, red or yellow light. I would also like to investigate what effect the pH level of the water can have on the rate of photosynthesis. The pH level affects enzymes in plants; therefore it should also affect the rate of photosynthesis. Louise Batty 11V ...read more.

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Here's what a teacher thought of this essay

3 star(s)

A fair GCSE account of an investigation into the effect of light intensity on the rate of photosynthesis. The writer includes most of the key components of a valid scientific investigation and collects some useful data.

A number of small improvements to the report would have increased its overall grade significantly. They include:

[1] A more detailed introduction focusing on the effect of increasing light intensity on the rate of photosynthesis;

[2] A clear hypothesis stating the relationship of the IV and DV over a wide range of light intensities (including the point at which light intensity is no longer a limiting factor);

[3] A more coherent treatment of controlled variables which includes both why and how they are controlled;

[4] A detailed analysis of the results which explores the reasons behind the discrepancy in values obtained for each of the three replicates.

Overall, a 3 star account.

Marked by teacher Ross Robertson 24/04/2013

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