GCSE Biology Revision "Required Practical 6: Photosynthesis"

Experimental Setup and Method00:00:01

The video introduces the required practical for investigating light intensity and photosynthesis. It details using a boiling tube placed 10cm from an LED light to avoid heat interference. Sodium hydrogen carbonate solution provides carbon dioxide, and pond weed is added to produce oxygen bubbles. After a five-minute acclimatization period, bubbles are counted for one minute, repeated three times to find a mean, and then repeated at distances of 20, 30, and 40 centimeters.

Problems and Improved Equipment00:01:46

Two main problems with counting bubbles are identified: they may be too fast to count accurately and they are not always the same size. To solve this, the video suggests measuring the volume of oxygen produced using a measuring cylinder filled with water to catch the bubbles instead of counting them.

The Inverse Square Law00:02:21

For higher tier students, the video explains that plotting results against distance reveals the inverse square law. If the distance from the light source is doubled, the number of bubbles per minute falls by a factor of four. This occurs because light intensity falls by four times when distance doubles, directly reducing the rate of oxygen production.