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Investigate how light intensity affects the rate of photosynthesis.

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Introduction

Biology SC1 Introduction Plants also take in energy, like humans, who get their energy from raw materials-such as food, however plants do not seem to be in taking food their mostly common source of raw materials comes from the soil. A statement from GCSE Biology states'...Experiments show that the weight gained by a growing plant is far greater than the weight lost by the soil it is growing in.' This statement implies that there must be an increase in the raw materials such as water and air. A hypothesis to show a source of food in plants is from the air, water and soil salts. Glucose contains three elements carbon, hydrogen, and oxygen (C6H12O6). The carbon and oxygen is mainly supplied by (CO2) from the air and the hydrogen from water (H2O), in the soil. What is photosynthesis? Photosynthesis the building up of complicated food molecules from simple substances better known as 'synthesis.' In order for this process to take place, it requires enzymes and energy. The first stage where synthesis begins is from the sun. The sun supplies the plant as a source of light, which is essential for photosynthesis. This is where we get the word 'photo' from as it means 'light'. ...read more.

Middle

Method > Collect the above apparatus. Make sure they are washed in clean water using detergent as otherwise bubbles may stick to the apparatus. > Using a measuring tube collect 10cm3 of sodium hydrogen carbonate. > Add it to250cm3of water (H2O) The reason for this is to maintain the level of carbon dioxide (CO2) > Collect 5cm of Canadian pondweed (Elodea) > Place this into a beaker but DO NOT PUT IT IN THE WATER AND NaHCO3 SOLUTION JUST YET! > The reason for this is because the rest of the apparatus has not been set up and it will make the results unreliable. > Attach the photosynthometer to the stand + clamp. > Set it up as shown in the diagram. > Keep the metre stick in a secure place avoid it from moving. (A suggestion you keep it stuck down by using a bit of masking tape at the bottom of it.) > Have the lamp ready to switch on. BUT NOT YET! > When ready put Elodea in the solution (water and NaHCO3) and attach it to the micro-burette. > Turn on the lamp, which should be at the appropriate distance on the meter stick. ...read more.

Conclusion

Instead of using the sophisticated apparatus: photosynathermetre and the graduated capillary tube I could have simply used a beaker, test tube, stop watch, a lamp, a metre stick and the same solution (water and NaCHO3). However this experiment would have been inaccurate because I would have had to count the bubbles myself and measure the gas quantity. The other disadvantages I may encounter would be the following: > When the lamp is at its furthest distance (100cm) from the Elodea the bubbles are going to reduce by quantity and size, therefore the bubbles maybe too small to see which would have made them difficult to count as a result. > The lamp could be too close to the test tube and heat up the water quickly making the temperature to be inaccurate and the rate of photosynthesis would vary. > When the lamp is at its closest distance (0cm) from the Elodea the bubbles are going to be rapidly produced therefore once again making it difficult to count. > If the lamp heated the water up, the temperature would have increased giving me two limiting factors: temperature and light intensity, instead of just one. This would have gone against my hypothesis. > The whole experiment would not be as accurate as the photosynthometer. The main advantage in using the above apparatus' has been that it is easy to set-up and use. ...read more.

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