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How does light affect the rate of Photosynthesis.

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BIOLOGY October 2003 HOW DOES LIGHT AFFECT THE RATE OF PHOTOSYNTHESIS GURDEEP SIAN INTRODUCTION Photosynthesis is the process that produces food in plants. The 'food' it produces is glucose. In order for photosynthesis take place you need a green plant sunlight and water. The carbon dioxide enters the leaf through the leaves, and the water goes through the roots of the plant. The water and carbon dioxide is mixed in the chloroplast, which is where the light is trapped. The mixture of carbon dioxide and water make the substance glucose which is sugar. The mixture of the two also gives off oxygen. Green plants use the light energy from the sun to combine carbon dioxide and water to make food. Light energy is converted into chemical energy and is stored in the food. The light used in photosynthesis is absorbed by a green pigment called chlorophyll. The three features that leaves have to make photosynthesis an efficient process are thinness, flatness and a large surface area to catch lots of sunlight. The leaf also has palisade cells are near the top of the leaf and are also packed wit chloroplasts. The guard cells on the leaf control the movement of gases into and out of the leaf. The four things needed for photosynthesis are: Light - This comes from the sun Chlorophyll - the green substance which is found in chloroplasts, Carbon dioxide - enters the leaf from the surrounding air, Water - comes from the soil, up the stem and into the leaf. ...read more.


0 10 20 30 40 50 60 70 80 90 100 FAIR TEST To ensure that only light intensity is affecting the rate of photosynthesis I will keep constant the following factors each time I repeat the experiment. The amount of pond weed: If there is more pond weed after the first recording and less pond weed after the second recording then the results will be imprecise. To keep the same amount of pond weed used at all times, I will use a top hand balance. The temperature of the water: Chlorophyll works like an enzyme because it works best when it's warm but not too hot. The rate of photosynthesis is determined on how hot the chlorophyll is. The amount of time that has passed when I record the results: The quantity of gas accumulated will vary a great deal if the results are recorded after dissimilar times. To keep the amount of time that has passed the same, I will use a stop watch. The power of the light bulb on the lamp: During the process photosynthesis light along with chlorophyll is used form glucose and oxygen. Glucose provides the energy needed for the plant, so light is an essential factor which affects the rate of photosynthesis. So it's important that the power of the light bulb remains the same otherwise the results will be inaccurate. ...read more.


When I setup the apparatus I used a measuring cylinder to collect the oxygen. Instead of using a measuring cylinder I could have used a gas syringe. A measuring cylinder measures in cm which is very efficient for collecting gas. A gas syringe is designed to measure gas and therefore will record far more accurate results. A gas syringe measures in cm� which is what gas is measured in and as a result is much more suitable for this experiment. An additional way to improve to my experiment would have been to perform the experiment in the dark as the rate of photosynthesis wouldn't have been contaminated with other sources of light. This would further improve the reliability of my results. In addition to my previous improvement, I would also keep the distance from the lamp to the water bath the same throughout the whole experiment but would also use a light filter. I would use a light filter because to vary the amount of light that gets through to the water bath using smaller intervals i.e. use a filter that only lets 5% of the light through, 10%, 15% etc. Taking into account all the improvements I would have made to this experiment I would predict that the more light there is then the quicker the rate of photosynthesis will take place. This is the same prediction as my previous experiment however my suggested opinions will improve the accuracy and reliability of my results. ...read more.

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