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An Investigation To Show How Light Intensity Effects The Rate Of Photosynthesis

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An Investigation To Show How Light Intensity Effects The Rate Of Photosynthesis Aim The aim of my investigation is to see how the light intensity will effect the rate of photosynthesis in a plant. Introduction Photosynthesis is a biochemical reaction that occurs in the presence of sunlight and takes place in the chloroplasts of green cells. In all biochemical reactions, energy is required to split the bonds between the reactants. In photosynthesis, this energy comes in the form of sunlight energy, which is absorbed by the chloroplast and is released to provide energy to combine the raw materials, carbon dioxide (from the air) and water to form simple sugars and oxygen (which is the by-product.) Photosynthesis can be defined as the production of simple sugars resulting from the reaction of when the raw materials (CO2 and H2O react together forming sugar and oxygen (by-product)) in the presence of sunlight and chlorophyll. The chemical equation for this is It is a known fact that all plants require sunlight to photosynthesis and without it, the plants would die. I know this from my preliminary work and experiments that I did in year nine, where I took two plants and placed them in exactly the same conditions, except one was deprived of sunlight. At the end of my experiment, I discovered that the plant deprived of sunlight died, whilst the other survived. This shows the importance of light intensity to a plant. I predict the as the intensity of light is increased, so will the rate of photosynthesis. This is because as light, which is the energy, falls on the chloroplast in a leaf, it is trapped by the chlorophyll, which then makes the energy available for chemical reactions in the plant. ...read more.


In order to conduct a fair experiment, the only factors I will change is the distance of the lamp, hence the light intensity. Experimental variable- light intensity is the variable that is going to be explored in this investigation. Therefore I will vary it by increasing and decreasing the distance from the light source to the plant. Carbon dioxide concentration- the concentration of carbon dioxide can effect the rate of photosynthesis because the greater the levels of carbon dioxide, the more CO2 diffuse into the plant. As a result the rate of photosynthesis will rise up to a certain point where the limiting factors theory comes in. this variable will be kept constant by adding a fixed amount of sodium hydrogen carbonate to the beaker and plant. This experiment should be completed within an hour, so the plant does not use up a significant percentage of the CO2. Water- water is required on the photosynthesis reaction. When plants lack water, their stomata close to prevent further water loss. At the same time, closing the stomata cells does not allow CO2 to diffuse into the leaf. A lack of Water is therefore linked to the Co2 factor. Water needs to be kept constant by keeping the same amount of water in the beaker. Temperature- enzymes are also used in photosynthesis and the respiration of plants. Therefore increasing the temperature will increase emyme reactions, to a certain point, which in turn will increase the rate of photosynthesis. However when the temperature reaches above 45 degrees, the enzyme will denature and reactions will stop. Therefore it is essential to keep the temperature at a constant level. Safety * Wear overalls * Do not put any equipment into your mouth. ...read more.


Thus I can form a conclusion, which supports my prediction that as the light intensity increases; the rate of photosynthesis will also increase. The reason for this, as stated in the prediction, is because, as light, which is the energy, falls on the chloroplast in a leaf, it is trapped by the chlorophyll, which then makes the energy available for chemical reactions in the plant. This is because when chlorophyll absorbs light energy, the light energy cannot be immediately used for energy conversion. Instead the light energy is transferred to a special protein environment where energy conversion occurs. This happens by using the energy of a photon to transfer electrons from the chlorophyll pigment to the next. When enough light has been harnessed at the a reaction centre, ATP can be synthesised from ADP. During this reaction, oxygen is produced as a by-product and it is the oxygen bubbles that can be measured to give an indication of the rate of photosynthesis. Thus as the amount of sunlight, or in this case the light from the lamp, falls on the plant, more energy is absorbed, so more energy is available for the chemical reaction. As a result photosynthesis will occur at a faster rate in a given time which will be indicated through the amount of oxygen produced as the by-product of this reaction, in a given time. Therefore the rate of photosynthesis will be directly proportional to the light intensity until a certain level is reached and then the rate of photosynthesis will not increase further. This is due to the law of limiting factor theory; which is that if a reaction (in this case the photosynthesis reaction) depends on a number of factors being favourable, then the rate is limited by the factors that is the closest to its minimum value. ...read more.

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