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Investigation into the effect of differentconcentrations of carbon dioxide on the rate of photosynthesis

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Investigation into the effect of different concentrations of carbon dioxide on the rate of photosynthesis Aim To investigate into the effect of different carbon dioxide concentrations on the rate of photosynthesis. Introduction The investigation will be conducted using the method outlined in detail later on. In short, the water plant Elodea will be placed in a solution of altering hydrogencarbonate concentrations (0.02%, 0.04%, 0.06%, 0.08% and 0.1% as previous research has shown that concentrations above that start to damage the leaf.1) and the rate of photosynthesis will be measured by the volume of oxygen given off in a set amount of time, via a meniscus which is part of a photosynthometer apparatus set up. Prediction I predict that the rate of photosynthesis will increase as the concentration of carbon dioxide increases up to a certain point after which another factor limits the rate of photosynthesis e.g. light intensity or temperature. Variables -The independent variable is the concentration of carbon dioxide which will be manipulated to see what effect it has on the rate of photosynthesis. -The dependent variable is the volume of oxygen given off in the set amount of time. -The fixed control is the Elodea plant immersed in water with no added carbon dioxide in the form of hydrogen carbonate. ...read more.


The distance is critical and must be exactly the same in each experiment. Turn light in the room off and shut blinds. 7. Switch lamp on. Very carefully raise the plunger of the syringe to pull the meniscus to a point near the top of the capillary. Mark the position of the meniscus. The set up should now look like the diagram below. 8. Measure the distance travelled by the meniscus during the next three minutes. Repeat this three times. Record results and average the distance the meniscus moved in each three minute interval. 9. Repeat steps 5 to 8 with the plant in the range of hydrogen carbonate concentrations mentioned. (The first experiment was the control.) Justification The method used was the most appropriate for my investigation as it allowed the precise control of all variables that may effect the dependent variable in the study. Prior to this study, two preliminary experiments were carried out. The first was on light intensity and the latter was on wavelength. In the former, a photosynthometer much like the one in the method described earlier was set up, with the independent variable being the distance of the light from the plant. In the latter, a light source emitting different wavelengths was placed a certain length from the set up, one of which had a 'shade' plant and one of which had a 'sun' plant. ...read more.


That is how an increase in light intensity increases the rate of photosynthesis. For the light wavelength experiment, differences in absorbance can be explained in terms of what pigments are present, for example the pigment chlorophyll a has a peak absorption of about 430 nm and carotenoids peak at 450 and 500 nm. My prediction is justifiable in terms of diffusion. This is the net movement of molecules from an area of high concentration to an area of low concentration. It happens randomly due to the kinetic energy all molecules possess. Therefore, when carbon dioxide concentration is increased, this also increases the concentration gradient (it is steeper) between the carbon dioxide levels in the plant and immediately outside it. As a result, carbon dioxide will diffuse through the stomata on the leaves lower surface which are held open by guard cells. From there, they diffuse into the air spaces of the spongy mesophyll and eventually in the pallaside cells where they are used in the light independent stage of photosynthesis to make glucose. That is then the biological basis of how an increase in carbon dioxide concentration increases the rate of photosynthesis, making my prediction justified. 1 'Energy and Life', Cambridge University Press 1983 ...read more.

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