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How light intensity affects the rate of photosynthesis.

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Introduction

HOW LIGHT INTENSITY AFFECTS THE RATE OF PHOTOSYNTHESIS. Photosynthesis is the process in which plants make their own food using light. To make the food they also require Carbon Dioxide, Chlorophyll and water. This can be shown in an equation: Carbon + Water light Glucose + Oxygen. Dioxide Chlorophyll The balanced word equation for this is: 6CO2 + 6H2O C6H12O6 + 6O2 The plant takes in light energy from the sun, using the palisade cells, which are situated in the leaf. The cells contain Chlorophyll, which is the green substance inside the leaf, and also chloroplasts, which trap the sun's energy. This then reacts with the water. The plant uses light energy to separate 1 hydrogen atom from the water. This gives the OH - ion, which is hydroxyl, and the H+ ion that is hydrogen. These are then unsatisfied bonds so they join together to form 2 water molecules, 1 oxygen and 4 hydrogen molecules. (The hydrogen ions are turned into glucose), this means that the more light there is, the more water is split and hence there is more oxygen. This is all part of the light stage. The light stage involves this splitting of water and also the production of ATP, this is a source of energy which is later used in the dark stage. The light stage traps the sunlight and converts it into chemical energy. Oxygen produced in the light stage is evolved as oxygen gas, and the hydrogen reduces the carbon dioxide to carbohydrate. ...read more.

Middle

Add a spatula of sodium hydrogen carbonate to the boiling tube. 3) Place the beaker on 0cm, switch the lamp on and wait until tiny bubbles appear. When this occurs begin timing the experiment for 1 minute, record your results. 4) Move the beaker to 5cm and repeat the experiment. Keep moving the beaker up 5 cm each time. Use the stirring rod to stir the water in the beaker throughout the experiment so that the heat is evenly spread. 5) When you have a full table of results, repeat the whole experiment again so that your experiment is more accurate and work out the average. To make sure my experiment is a fair test I will keep certain things the same, I will do the experiment twice to make sure it is accurate, I will only have 1 variable throughout the experiment, this will be the distance of the light source. The temperature will be approximately 23 degrees (room temp.) because more oxygen will be produced. I will use the same piece of pondweed, the same lamp and the same amount of water each time. I will be changing the light intensity in my experiment, as this is what my investigation is based on. I will do this by moving the pondweed further away each time. In my investigation I will measure how many bubbles of oxygen are given off in one minute. ...read more.

Conclusion

As the plant bubbled very quickly near the start, it is possible that I did not manage to count all of the bubbles or I could have miscounted. These could all cause 1 result to be out. I could make my experiment better by making sure I used the same piece of pondweed each time, the same size, the same light - incase the 1 bulb was stronger than the other, the same amount of water each time. I could also repeat my experiment a few more times using different lengths to get more results and hence a more accurate graph. I think my experiment was good enough to give the conclusion that light intensity affects the rate of photosynthesis because my experiment was as fair as possible and I didn't make many errors. My graph also proves this because it is a curved line, which shows the light intensity, and rate of photosynthesis are proportional to one another. There are some other experiments I could carry out to extend my investigation such as, investigating the other limiting factors (carbon dioxide concentration and temperature) which affect photosynthesis rate. I could also extend the light intensity experiment by using different types of lights such as fluorescent or halogen lights. I could also investigate how different coloured pigments absorb the light more, for example black absorbs light and white reflects it, and chlorophyll is a green substance so maybe a green pigment would affect the rate of photosynthesis. ...read more.

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