Video Transcript
After his experiments using
photosynthetic bacteria, what did van Niel assume about photosynthesis in green
plants? (A) The reactions were highly
similar, but instead of glucose being formed, it would be sucrose. (B) The reactions were highly
similar, but instead of carbon dioxide being a reactant, it would be oxygen. (C) The reactions were highly
similar, but instead of hydrogen sulfide being broken down, it would be water. (D) The reactions would be
completely identical. Or (E) the reactions would be
completely different.
van Niel was a scientist who
studied photosynthesis in green and purple sulfur bacteria. To help us answer this question,
let’s have a look at the equation for photosynthesis in these bacteria. During this reaction, carbon
dioxide and hydrogen sulfide are converted into glucose, water, and sulfur. The sulfur is produced when
hydrogen sulfide is broken down, so the hydrogen atoms can be used to make glucose
and water. Now, let’s compare this process to
the equation for photosynthesis in green plants. We can see that the equations are
very similar. The major difference is that in
plants, instead of hydrogen sulfide being a key reactant, water is. And instead of sulfur being
produced, oxygen is.
If we apply the same logic as
before to the equation for photosynthesis in plants, we can assume that the oxygen
produced comes from the breakdown of water. Now, let’s use these equations to
eliminate some of the answer options. We can immediately exclude options
(D) and (E). The reactions are not completely
identical, but neither are they completely different. We can see that in both equations,
glucose is a product, so option (A) cannot be correct. And in both cases, carbon dioxide
is a reactant, not a product. So finally, we can eliminate option
(B).
van Niel applied his knowledge of
photosynthesis in green and purple sulfur bacteria to the process in green plants
and made the assumption that the oxygen produced would’ve come from water. So the correct answer is (C). The reactions were highly similar,
but instead of hydrogen sulfide being broken down, it would be water.
