Investigation into the colour of light needed to start a photosynthesis reaction

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Adrian Hall

Investigation into the colour of light needed to start a photosynthesis reaction

Diagrams

Method

The apparatus for this experiment will be setup as shown in the diagram, for all the experiments the coloured filter will be 5cm away from the white light bulb, which is a 60watt bulb, and the beaker will be 20cm away from the edge of the coloured filter. Just before the experiment takes place we will place the pond weed (which has been in darkness for at least 24 hours to stop it any photosynthesis) into the beaker. I will then place the funnel over the pond weed and place the test-tube into the beaker (like the diagram above) I will then fill the beaker up with cold tap water till it covers the bottom of the test tube (450ml). This is so that we can easily count the oxygen bubbles as they come off the pond weed. Now that the experiment is ready to start, I will turn on the light for one minute, then after the first minute I will count how many oxygen bubbles come from the pond weed in the second minute. I will repeat this stage again once 10 minutes has passed. The preliminary experiment was done to check my prediction of what I think will happen. For this I used red, green and blue filters. The main experiment will be done with more colours if it proves successful - I will repeat the experiment with more colours: red, orange, green, blue and purple filters. I will take three readings for the preliminary experiment and five for the main experiment so that I can take an average for each colour.

Fair Test

  • Pond weed is from the same pond.
  • Pond weed kept in dark for 24+ hours.
  • Pond weed stored in same conditions, darkness, temperature etc…
  • Same sized pieces of pond weed (~5cm)
  • Same temperatures (fridge, room and water)
  • Same room and cold water from the same tap.
  • Same light bulb, same strength bulb (60watt)
  • Same distance from light to filter, from filter to beaker.
  • Same equation (apart from colour of light filter)
    Carbon dioxide + Water
     Oxygen + Glucose
                                           ^
                                        Light
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Prediction

I think that the green filter will not allow the pond weed to start photosynthesis. This is because when white light hits a plant; all colours of light are absorbed, except the green which is reflected. This is why we see the pond weed as been green. On the diagram of the electromagnetic spectrum green light is in the middle, so I expect that the colours either side of green will provide enough energy for the pond weed to start photosynthesis and create oxygen bubbles. As colours either side of green are used as a filter, ...

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