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In the late 18th century, a Dutch scientist, Jan Ingenhousz, conducted a famous experiment which proved plants produced oxygen. He immersed various plants under water and observed them. He noticed that when they were placed in direct sunlight they released tiny bubbles of gas. When enough gas had accumulated in the container it was able to re-light a glowing splint, indicating the presence of oxygen. To show that it was the light energy and not the heat of sunlight which was necessary, Ingenhousz repeated the experiment with leaves placed near a fire.
This clip is from:
First broadcast:
14 June 2011

Classroom Ideas

Students could reproduce the experiment in class. They could examine the effect of light intensity on the rate of photosynthesis in waterweeds (for example Elodea), by measuring the amount of gas or bubbles given off. The design of Ingenhousz’ experiments can be discussed. The control of variables such as light and heat can be considered. The repeating of the experiments in order to consolidate the data and get more reliable results upon which to base a conclusion can be discussed.