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Investigating the affect light intensity has on photosynthesis

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Biology Coursework Investigating the affect light intensity has on photosynthesis Plan All living organisms need food. They need it as a source of raw materials to build new cells and tissues as they grow. They also need food as a source of energy. Food is a 'fuel', which drives essential living processes and brings about chemical changes. Animals take in food, digest it, and use the products to build their tissues or to produce energy, but plants, apart from a few insect-eating species, do not appear to take in food. This is because plants find food sources in water and the air. This is known as photosynthesis. Chlorophyll is a green substance found in the chloroplasts of plant cells. It absorbs sunlight and makes the energy from sunlight available for chemical reactions. Thus, chlorophyll converts light energy to chemical energy. Therefore photosynthesis is the building-up of food compounds from carbon dioxide and water by green plants using energy from sunlight, which is absorbed by chlorophyll. The products of photosynthesis are glucose and oxygen. There are many factors, which affect the rate of photosynthesis, including light intensity, temperature and carbon dioxide concentration. The maximum rate of photosynthesis will be constrained by a limiting factor. ...read more.


Preliminary I completed a preliminary investigation to test my basic idea and equipment. I placed the pondweed 5cm away from the lamp. At first no bubbles were given off and so I decided to increase the temperature of the water from around 17�C to 25�C. The pondweed started to give off bubbles and I collected 17 in a minute. I then moved the lamp 10cm away from the equipment and collected 9 bubbles in a minute. After completing my preliminary investigations I decided that the water I use in my experiments should be at 25�C to encourage photosynthesis. Therefore all the water I use must be at 25�C to ensure a fair test. I didn't experience any other problems with the equipment used in my preliminary investigation and so I decided I was ready to begin my experiments. Practical - Obtaining my evidence Aim: To discover what effect light intensity has on the rate of photosynthesis. Apparatus: Canadian pondweed, funnel, supports, a test tube, a beaker, water at 25�C, a lamp, a ruler and a bung. Method: 1) Fill a beaker with 700cm� of water at a temperature of 25�C. 2) Cut the Canadian pondweed into a 3cm segment. 3) Fill a test tube with water (also at 25�C) ...read more.


Firstly, the distance between the lamp and the Canadian pondweed was not measured to a high degree of accuracy. Ideally the distance should have been measured from the filament of the light bulb to the centre of the plant but this was not possible. Another inaccuracy was in the time keeping as there was often a small difference in when I began timing the minute, e.g. after the first bubble had been released or just before. Overall even though my experiment was open to some inaccuracies I believe it was accurate enough to support my predictions. To improve my results I could simply increase the length of time I measure the number of bubbles released to 5minutes although I would have to ensure that the water remained at the same temperature throughout. One way of doing this would be to place a Perspex block between the lamp and the plant, which would absorb most of the heat, while allowing the light energy to pass through. Another way of increasing the reliability of my results would be to take more readings. I would like to extend my investigations into light intensity and photosynthesis by investigating which colour of the spectrum produces the highest rate of photosynthesis and what effect halogen and fluorescent lights have on the rate of photosynthesis. Sources: G.C.S.E. Biology - D.G. Mackean Biology - Mary Jones & Geoff Jones ...read more.

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