B8 Photosynthesis Flashcards
Method
1) Place sodium hydrogen carbonate solution into the boiling tube which encourages the pondweed to photosynthesise. .
2)You could use a test tube holder for the tube.
3) Place a piece of pondweed into the solution, right below the level.
4) Cut, while underwater, with dissecting scissors, the stem of the pondweed, to see the oxygen bubbles produced. Cut the pondweed at an angle for a nice stream of oxygen bubbles. To measure the rate of photosynthesis, count the number of bubbles of oxygen gas produced in one minute.
5)Move the end of the ruler to be directly in line with the bulb, angle the tube to be in line with the 10cm mark on the ruler. Turn on the light and give the pondweed a bit of time to adjust to the brightness of the light. Then measure the rate of photosynthesis, by using a timer to count for one minute the amount of bubbles produced from the hot surface. To keep it a fair test, count the bubbles from the end of the stem.
6) Repeat the experiment by moving the pondweed to be 20cm from light source and repeat the experiment. Repeat the experiment four more times.
Independent variable
Light intensity - to affect this change the distance between the pondweed and light intensity
Control variables - improve the experiment
LED light bulbs don’t give off heat energy which may affect the rate of photosynthesis
Turn off overhead lights so there’s only one light source
To keep it a fair test, count the bubbles from the end of the stem.
Could collect gas, one error could be that assuming every oxygen bubble produced is the same volume, so we could collect the volume of oxygen to measure it more accurately.
How to measure the volume of oxygen(alternative method)
1) Use a beaker full of water, take pondweed and trap it inder a glass funnel - place it in the bottom of the beaker.
2) With the light source close, the pondweed will photosynthesise, but to collect oxygen take a boiling tube of water, turn it upside down and place it over the top of the funnel. As the bubbles of the oxygen are produced, they pass into the boiling tube, displace the water and enough oxygen will be collected to measure the volume.
