Video Transcript
The equation for photosynthesis is
six CO2 plus six H2O produces C6H12O6 plus six O2. Which reactant did Van Niel assume
was the source of the oxygen produced?
To answer this question, let’s take
a look at some of the work Van Niel did. Van Niel was a Dutch-American
microbiologist who studied photosynthesis in green and purple sulfur bacteria. These bacteria perform
photosynthesis like plants. But unlike plants, they contain
bacteriochlorophyll instead of chlorophyll as the pigment that absorbs sunlight for
use in the reaction. In plants, photosynthesis is a
process that converts water and carbon dioxide into glucose and oxygen using light
energy. The green and purple bacteria,
however, use carbon dioxide and hydrogen sulfide in their photosynthesis reactions
to produce glucose, water, and sulfur.
Van Niel compared the reactions
between the plants and the green and purple bacteria. As we can see, the
hydrogen-containing reactants in the photosynthesis reactions differ. But they both use carbon
dioxide. The products formed from these
reactions also differ. The green and purple bacteria
produce water and sulfur, whereas plants produce oxygen. But both reactions produce
glucose. So we can see that these reactions
have some similarities and some differences.
Van Niel assumed that as plants
produce oxygen in this reaction while green and purple bacteria do not and instead
produce sulfur, the oxygen the plants were producing must come from the different
reactant in plants, which is water. So the correct answer to this
question is water. Van Niel assumed that the source of
the oxygen was water.
