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Investigation into the effect of Light Intensity on Photosynthesis.

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Investigation into the effect of Light Intensity on Photosynthesis by Dominic Mulley Introduction Photosynthesis is the process that produces 'food' in plants. The 'food' that it produces is called glucose. Photosynthesis takes place in the leaves of all green plants. Leaves are especially to make photosynthesis: - Leaves are thin and flat to provide a large surface area to absorb as much sunlight as possible. - The palisade cells are near the top of the leaf and are packed with chlorophyll. - Guard cells control the movement of gases into and out of the leaf. They line the bottom of the leaf. An equation can be demonstrated to show how a plant produces photosynthesis and what substances it uses: Carbon + Water + Sunlight Glucose + oxygen Dioxide Chlorophyll 6CO2 + 6H2O + Sunlight C6H12O6 + 6O2 Chlorophyll The rate of photosynthesis depends on light intensity, carbon dioxide and temperature. Sometimes increasing these factors has little or no effect. This is because one of the other factors is so low that it limits the rate of photosynthesis. Scientists call this the limiting factor. Chlorophyll in green leaves uses light energy to perform photosynthesis. It can only do it as fast as the light energy is arriving. Chlorophyll only actually absorbs the red and blue ends of the visible light spectrum, but not the green light in the middle, which is reflected back. ...read more.


Here are the ways to achieve the maximum accuracy in this experiment: * The use of a water barrier efficiently in order to block out all heat. * The same plant should be used throughout the investigation. * The light intensity should be constant. * Distances must be measured accurately. * The table lamp is the only light source * The carbon dioxide concentration in the water containing the plant should remain constant during the investigation. Variables The only variables throughout the investigation should be the light intensity by moving the lamp or changing the voltage supply. Safety There is no specific safety for this experiment except electrical hazards and no safety equipment is necessary. Prediction I predict that the rate of gas produced (O2 in the form of bubbles) increases with an increase in light intensity and therefore more photosynthesis is being produced. Results For each distance three set-ups were made, this greatly increases the accuracy of the graph and makes it easier to find a positive correlation. The mean value of the 3-4 results are used for plotting graphs. Distance of lamp from pond weed (cm) Set - up Relative light Intensity (1/d�) Rate of photosynthesis 1 2 3 1/time (s) Mean 10 20 30 40 50 60 70 80 The results above are fairly accurate, however there are ways to improve the accuracy here: Source Error Remedy/Improvement The room temperature may fluctuate. ...read more.


2. Carbon Dioxide Concentration - This can be varied by using sodium hydrogen carbonate solution of different concentrations (e.g. 0-5%.) 3. Temperature - by connecting the measuring cylinder to a pipette, the apparatus can be put into a water bath. The following temperature range can be studied: 20-50�C Limiting Factors The rate of photosynthesis is affected by three factors: The Amount of Light (and the Wavelength) The chlorophyll uses light energy to perform photosynthesis. It can only do it as fast as the light energy is arriving. Chlorophyll actually only absorbs the red and blue ends of the visible light spectrum, but not the green light in the middle, which is reflected back. This is why the plant looks green. The Amount of Carbon Dioxide CO2 and water are the raw materials. Water is never really in short supply in a plant but only 0.003% of the air around is CO2 so it's actually pretty scarce as far as plants are concerned. The Temperature Chlorophyll is like an enzyme in that it works best when it's warm but not too hot. The rate of photosynthesis depends on how active the chlorophyll enzymes are, (at 45�C the enzymes die and photosynthesis can no longer take place.) At any given time one or the other of the above three factors will be the limiting factor which is keeping photosynthesis down at the rate it is. ...read more.

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