We had an oxygenating aquarium plant (Cabomba), lamps, a supply of hot and cold water, and thermometers - and various other things which were handy. Our mission: to investigate factors affecting the rate of photosynthesis. We followed the classic Nuffield Practical Science method to investigate the rate of photosynthesis.
Our pondweed cuttings were inserted into a test tube of water, cut stem facing upwards. The test tube was placed in a beaker of water. We moved the beaker towards the lamp until bubbles started to appear from the cut end of the stem. We counted the number of bubbles arising in a minute, then tried varying one condition to see how it affected the rate of photosynthesis.
Some groups measured distance from the lamp to the pondweed beaker.
Some tried varying the water temperature:
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| Adjusting the temperature of the water bath |
Light Colour
One group tried changing the colour of light reaching the plant, by placing coloured filters in front of the lamp:
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| Placing coloured filters between lamp and plant |
Counting Bubbles
The rate of bubbles produced was our measure of the rate of photosynthesis. It was quite tricky to determine because we had to position the plant so that the bubbles were produced at a countable rate, not a stream of tiny bubbles. Usually one person took charge of timing and another counted.
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| Using a timer to determine the rate of bubbles produced. |
There was lots of effort to take accurate readings and record observations.
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