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An Investigate into the Effect of Light Intensity on The Rate of Photosynthesis

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An Investigate into the Effect of Light Intensity on The Rate of Photosynthesis Submitted by Simi Wang Aim The investigation aims to find the effect of light intensity on the rate of photosynthesis. Predication Before experiment, it is predicted that if the light intensity is increased the rate of photosynthesis will increase. Why? Chlorophyll Carbon Dioxide + Water Sugar + oxygen Sunlight Chlorophyll Sunlight Figure 1. Formula for Photosynthesis As shown in figure 1, in order for any plant to photosynthesis it needs three main raw materials: 1. Water 2. Carbon Dioxide 3. Light These are also known as 'limiting factors' of photosynthesis (another limiting factor that has not been mentioned above is temperature). Therefore, if the limiting factors are increased, the rate of photosynthesis should also increase. From figure 1, it can be concluded that photosynthesis couldn't happen without light. This is proven from a previous experiment, comparing a plant that has all the raw materials to photosynthesis, with a plant that has light limited. The result of this experiment was that when iodine solution, is added to the decolourised plant with all the right raw material to photosynthesis, it turned blue-black, which means glucose had been produced. And when iodine solution is added to the decolourised plant with limited light, it stayed reddish brown, which showed that glucose had not been produced. ...read more.


Do this twice and work out an average. Meanwhile, measure the temperature of the water after the acclimating time. 8. Repeat procedure 7 after placing the lamp at each of the following distances from the weed: * 15 cm * 25 cm * 35 cm * 45 cm In order to make this experiment safely the following must be kept strictly: * Do not fill the water to the top of the beaker to avoid spilling out on the floor, which might cause an accident when some one slips on it. * When blowing into the water, blow gently to avoid water being blown out of the beaker. * Place the wire of the lamp far away from any sink or water to avoid any electrical conduction, which would cause a serious accident. To make this experiment fairly, and the most accurate result could be obtained, the following key factors must be take into account: * The amount of water used must be the same in every experiment. * The same piece of weed must be used in each of the experiments. * The acclimatising time before each experiment undertaken must be the same. * When removing the lamp to different distance, it is essential to place the lamp as accurate as possible. ...read more.


The above causes could be limited by adopting the following methods: 1. To overcome the effect of unwanted light sources, the experiment needs to be done independently in a dark room. 2. To eliminate the heat effect from lamp, it is suggested that a column of water is fixed between lamp and test beaker shown in figure 5. Figure 5. A method of preventing temperature as a cause of the rate of photosynthesis. 3. To reduce the errors of counting the bubbles, the two measuring method below can be employed: * Stoke count - one stroke every 5 bubbles Or * Only count for 15 second and multiply the result by 4. 4. To avoid the effect of carbon dioxide concentration in the experimental results, fill beaker with water of the same concentration of CO2 in every experiment. In addition, the following measures should be helpful to make experiment more accurate: * Measure the volume of oxygen give off instead of counting the number of bubbles given off so it would be more accurate. Figure 6. Measuring the volume of oxygen. * Make multi-experiment at the same test condition. The further suggestion is given below for further extended experiment: 1. Using different wattage of bulb to change the intensity of light. 2. Using different colours of light to see which of the light in the spectrum is most effective at photosynthesis. 3. Increase the volume of carbon dioxide in the water to see if the rate of photosynthesis would change. ...read more.

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