How does light intensity affect photosynthesis?

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Zaka Ahmad 11m

Introduction

Photosynthesis is a very important process in nature. Photosynthesis is a biochemical reaction used to produce glucose using light energy, water and CO2 (Carbon Dioxide). A bye product of the reaction, photosynthesis, is Oxygen. It takes place in all green plants, which use the green chlorophyll, held in chloroplasts in the leaves, to trap light. The main site of photosynthesis is the palisade mesophyll cells in the leaf of a plant. It is these cells that contain the green chloroplasts and are very well adapted to do their task. They are near the upper side of the leaf where they can obtain the maximum amount of light, they are packed very closely together and as already mentioned contain green chloroplasts clustered towards the upper side too.

Plants photosynthesise to produce food chemicals that are needed to allow them to grow. The main reaction is to produce oxygen and glucose to be changed into energy during respiration. Glucose is stored in the form of starch which is insoluble and does not affect the osmosis taking pace in the plant. As plants respire both day and night this starch is often used up during the night when photosynthesis cannot take place. The uses of glucose within the plant are for active transpiration, cell division, the production of protein and the production of cellulose. Light energy is used to break down the bonds in water and carbon dioxide a then to make new bonds between atoms to form glucose and oxygen.

In photosynthesis the raw materials are carbon dioxide and water. They react to form the products of the reaction-oxygen and starch (glucose that has been stored). The reactions need energy and this comes from light. The green chloroplasts allow light to be used as energy and therefore both of these things are like helpers in the reaction. Glucose is formed firstly then turned into starch to be stored up for when it is needed.

Although photosynthesis is a complicated process it can be summed up in this equation:

Carbon Dioxide  +  Water     light        Glucose  + Oxygen

  6CO2                 +   6H2O      light         C6H12O6  +  6O2



It is important to the reaction that certain factors are present when it is occurring. We know that these are carbon dioxide, water, light and chlorophyll. Without these the reaction will not take place at all, but some of them also determine how quickly the reaction takes place. Water, carbon dioxide and light, along with temperature, all have a particular effect on the rate of photosynthesis. In terms of carbon dioxide the levels in the atmosphere do not really alter very much, but if people want to increase the rate of photosynthesis then sometimes carbon dioxide is added into greenhouses. Up to a certain point as temperature goes up so does the rate of reaction. After it reaches a certain point though the enzymes involved in the reaction become denatured and stop working properly. A drop in the amount of water present may cause photosynthesis to occur at only half the normal rate. The reason for this is the stomata are closing.

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The final factor which contributes is light. I decided to investigate how this affects the rate of reaction also.

Prediction

I predict that as the light intensity is increased the rate of photosynthesis will also increase. However at a certain point the light will reach a point where the rate will not increase any more. The chloroplasts will no longer be able to absorb any light so the rate will stay at its optimum level or even decrease. At this point light is no longer limiting.

This is a graph of my predicted results, it ...

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