In Engelmann's experiment, a green filament lay across the spectrum made by a prism…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
In Engelmann's experiment, a green filament lay across the spectrum made by a prism. Bacteria that need oxygen were placed around it. (a) In which colours did the bacteria gather? (b) Why did they gather there? (c) In which colour would you expect the fewest bacteria? (d) What is the graph made from such an experiment called?
Need a reminder? The key ideaShow
Priestley (1770): a mint plant restores the air that a burning candle or an animal makes unfit. Ingenhousz (1779): sunlight is needed and only green parts release oxygen. Sachs (1854): glucose is made in green parts and stored as starch. Engelmann: bacteria gather in the blue and red regions of a prism spectrum, the first action spectrum. Van Niel: bacteria using H2S give out sulphur; in green plants the donor is water, so the oxygen comes from water. Overall: . Water is oxidised, carbon dioxide is reduced.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Where. The bacteria gathered in the blue and red regions.
Step 2. Why. In those regions the alga made the most oxygen, because chlorophyll absorbs these colours best. The bacteria need oxygen, so they went there.
Step 3. The fewest. In the green region, where the pigments absorb little.
Step 4. The graph. A graph of the rate of photosynthesis against wavelength is an action spectrum.
Answer: (a) blue and red; (b) most oxygen was made there; (c) green; (d) an action spectrum.
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