Like us, goldfish need oxygen to survive. The gas produced under water by weed in a pond is collected in a test tube. When a freshly extinguished splint is put into the tube, the splint relights. This proves the gas inside the tube is oxygen.
The clip illustrates the fact that plants give off oxygen and could be used as part of a topic on plants. The clip could be used to reinforce the fact that this gas is emitted when green plants photosynthesise, thus underlining animals and their dependence on green plants for survival. Pupils could be asked to predict what gas is within the bubble produced from the pondweed. The clip could also be paused at the point when the gas is collected in a test tube. Can the children suggest a way to test what gas is in the tube? After watching the igniting of the recently lit splint, the subject of the necessity of oxygen to light a fire (fire triangle) could be discussed.