Thursday, 14 April 2016

Photosynthesis rate vs light colour in pond weed


LED full spectrum lamp
Couloures gel filters (red, green, blue)
Boiling tube
Clamp & stand
Sodium bicarbonate (Baking Soda)
Cabomba pond weed (Elodea may also be used)


Make up a 0.2% solution of the Sodium Bicarbonate and water to provide a source of Carbon Dioxide for the Cabomba.

Fill the boiling tube with the solution and add a piece of Cabomba such that there is 2cm of solution present above the Cabomba. Wrap a single layer of one of the gel filters around the boiling tube. Clamp this in place making sure the that clamp obscures as little of the Cabomba and solution as possible. Gently tap the tube to dislodge any gas introduced to the tube with the Cabomba.

Set up the LED lamp at a 5cm distance from the side of the boiling tube. A normal lamp can be used, however the temperature increase caused by using an incandescent lightbulb will introduce an error into your experiment as temperature also affects the photosynthesis rate. For improved results ambient lighting should be kept constant or the experiment should be done using the LED lamp as the only source of light.

Wait for the Cabomba to start producing bubbles. Start the stopclock and count the bubbles produced over a one minute period. Repeat measurement a further two times.

Repeat the entire experiment having removed the first colour filter and adding the next.

Ensure that the distance from the lamp to the boiling tube does not change so that the light intensity on the pond weed is constant - this will ensure the results are valid and make the experiment a fair test.