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  • Level: GCSE
  • Subject: Science
  • Document length: 5153 words

Confirm which factors increases or decreases the rate of photosynthesis.

Extracts from this essay...


Introduction Aim My aim in this coursework is to investigate the factors, which affect photosynthesis. My aim is to confirm which factors increases or decreases the rate of photosynthesis. The factors are * Carbon dioxide, * Chlorophyll * Light intensity * Water The building-up of complex food molecules from simpler substances is called a synthesis and it needs enzymes and energy to make it occur. Enzymes those are present in the plant's cells and the energy for the first stages in the synthesis comes from sunlight. The process is, therefore, called photosynthesis ('photo' means light). Photosynthesis is the main type of auto tropic nutrition. There are two fundamentally different methods of nutrition. Animals and certain other organisms take in ready-made organic substances; this is known as heterotrophic nutrition. Other organisms, notably plants, take in simple inorganic substances which they then build up into complex organics substances, this is known as auto tropic nutrition. The importance of photosynthesis Heterotrophs, including humans, all depend on photosynthesis for making their food. The manufacturing of sugar (starch) during the process of photosynthesis is astounding. For example: a hectare of maize can convert as much as 10 000 kg of carbon form carbon dioxide into the carbon of sugar in a year, giving a total yield of 25 000 kg of sugar per year. This example is a fact that was ascertained by my previous Biology teacher. For photosynthesis to take place a plant requires carbon dioxide, water, light, chlorophyll and a suitable temperature. The necessity for these factors can be demonstrated by simple experiments either on whole plants or single leaves. The main product that is produced during the process of photosynthesis is sugar, although this is often built up into starch for storage. As an indication of whether or not photosynthesis has been taking place, leaves are tested for starch. At first the plant has to be de-starch a plant.


* Now these two conical flasks must be air tight, so no gases (i.e.: carbon dioxide) can penetrate through the gaps. * A rubber bung is then used; it is split in half so that it can fit around the stem of the leave firmly and be air tight as possible. * The plant is then placed in the light for several hours and then both leaves are tested for starch. * The starch test was then carried out and the results were observed and recorded. Safety Precautions While conducting this experiment many harmful substances and dangerous equipment were used. Therefore safety precautions were taken place. Below are the safety precautions: * During the experiment Iodine was used, this substance us very dangerous towards the skin, it can change colour of the skin. Therefore Lab coats, plastic gloves and goggles were worn to protect the bare skin. * Ethylated spirit is also very harmful upon bare skin. It can actually burn human skin, to protect the hands plastic gloves were worn. Goggles were worn to protect eyes and large lab coats were worn to protect any other bare skin. Results The plants that was given no carbon dioxide they had no starch in that plant, but the other plant that received al the necessary substances showed signs of starch. This proves that carbon dioxide is necessary for photosynthesis to occur. It was found that the control leaf (Key C) had found to form a significant quantity of starch, the other leaf was found to have little starch present. A plant will have no starch when only three factors for photosynthesis are present (light, water and chlorophyll) and no carbon dioxide is in attendance. All four factors are required for photosynthesis to produce starch. Conclusion It has been concluded this experiment was a successful investigation. It has been proved that carbon dioxide is required for photosynthesis to transpire.


One is just a branch. The roots are removed to ensure that the plant could not absorb any water. The apparatus is assembled like the diagram shown below: Method * Both plants are kept within a dark room for about two-three days (this is to de-starch the plant). * The branch is provided with carbon dioxide and still has its chlorophyll, but it is not given water. * The other has carbon dioxide water and chlorophyll. * Once the other plant is taken out the dark room and de starched they are subjected to 6 hours of artificial light or alternatively sunlight. * This means that the plants is deprived from light * Then the starch test is carried out * The results are observed and recorded. Starch test Apparatus required during the experiment * Boiling H2O in a beaker * Beaker * Ethanol (alcohol) * Test tube * Heatproof mat * Tripod * Iodine * Bunsen burner This starch test shows us that if the plant contained starch or not. The process of the starch test is shown below: Results The branch that did not receive any water did not have any starch present in it, the other plant that had received water had signs of starch present in it. This is concluded that water is necessary for photosynthesis to take place. Conclusion The prediction that I had stated earlier was correct. The branch that did not receive any water did not show signs of starch. But the plant that had received water did show signs of starch present in it. Evaluation The experiment was first conducted with two normal plants. One plant was not supplied with water and was not in soil. This is proved that it was in effective. Little starch was present in the plant without water. I think that my prediction may have been incorrect. Although this result was not satisfactory, one of the plants had their roots removed and then there were no signs of starch so it can be concluded that the plant may have obtained water form the water vapour in the air.

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