The Affect Of Light On Photosynthesis.

Carbon Dioxide + Water                               Glucose + Oxygen

    There are three equally significant factors that affect the rate of photosynthesis, they are:

• The amount of carbon dioxide
• The temperature
• The amount of light  

I now wish to investigate the affect the above has on photosynthesis, in particular light. To do this I will need:

• A test tube  
• A lamp
• A ruler
• A piece of elodea plant.
• 50ml water

    There are a few variables I could change within the light experiment, these include:

• The distance between the light source and the elodea plant
• The time the experiment is carried out for

    I will keep the time as my fixed variable and change the distance between the light source and the elodea plant.  First I will obtain a test tube of 50ml water (at room temp) and in it I will place a 7.5cm cut piece of elodea plant. Then I will place it 5cm away from a 60-watt lamp and time 1 minute. This will to get the lamp heated up and the plant photosynthesis, so the results will not be recorded. This should help the accuracy of my first set of results. Then I will start the timer again and wait one minute.  During this time I will count the number of oxygen bubble rise from the top of the plant. As oxygen is a by-product of photosynthesis, it should show the rate at which the plant is photosynthesising. After 1 min I will move the test tube another 5 cm away from the lamp. I will move it 5 times, and repeat each experiment three times. This will not only give me a good range but it will also give me more accurate results as I can find the average.

   

From looking at PG 19 of CGP AQA Modular Science Revision guide I know that the less the amount of light energy the slower the photosynthesis rate.  When the amount of light energy gets to a certain point the rate of photosynthesis can not get any faster as the chlorophyll can only work at a certain speed.  This is a rough graph showing the rate of photosynthesis compared to the light intensity.  

 

    As the light intensity increases the rate of photosynthesis gets faster, until a point where at the level of photosynthesis stays the same. I predict that in my experiment the further away the plant is from the lamp, the less quickly it will photosynthesise.

Results:

         

    All my results almost form a straight line. The above graph shows that the further away the plant is from a light source, or the weaker the light intensity, the slower the rate of reactivity.

    This happened because the water and the carbon dioxide went into the plant. When the light energy was given the chlorophyll started to work to produce glucose and oxygen as a by-product. The closer the plant was to the lamp, the more light was available and more chemical energy was able to produced faster. So the further away the light source, the less the concentration of the light and the slower the plant could photosynthesis.

    I think the results I got support my prediction, as what I just said is the same as in my prediction.

    I think my result were accurate as none were odd or to far from the line of best fit. This meant I could easily conclude. I think my range of results also made it easier, as there was enough to comment on. If I were to improve my experiment I would have more people counting the bubbles at the same time just to double check the accuracy.

    To extend my enquiry I would start with my plant a lot closer to the lamp, and move it more gradually. This would test the theory that after a certain point no matter how much the light level is increased the rate of photosynthesis will not speed up. As it is used for