Video Transcript

Which of the following chemical
equations correctly summarizes the reaction van Niel determined in photosynthetic
bacteria? (A) Six CO2 plus 12 H2O is
converted into C6H12O6 plus six H2O plus six O2. (B) Six CO2 plus 12 H2S is
converted into C6H12O6 plus six H2O plus 12 S. (C) Six O2 plus 12 H2S is converted
into C6H12 plus six O2 plus 12 S. Or (D) six CO2 plus six H2O is
converted into C6H12O6 plus six O2.

Cornelis Bernardus van Niel
determined the chemical equation by which photosynthetic bacteria produce their own
nutrients. What is this equation? In the 1930s, van Niel was studying
the process of photosynthesis. He compared the process of plant
photosynthesis with bacterial photosynthesis and was able to make some key
discoveries about plant photosynthesis from his observations of bacterial
photosynthesis.

What equation did van Niel
determine? Well, the photosynthesis equations
for plants and bacteria are almost identical, bar a few key differences. One difference is that bacteria use
hydrogen sulfide, H2S, as a reactant instead of water, H2O. Therefore, bacteria produce sulfur
as a product instead of oxygen. As a result, we can eliminate
answers (A), six CO2 plus 12 H2O is converted into C6H12O6 plus six H2O plus six O2,
and (D), six CO2 plus six H2O is converted into C6H12O6 plus six O2, because neither
of these equations include any sulfurous compounds. In fact, option (D) is precisely
the equation for photosynthesis in plants.

Now, let’s look at the
sulfur-containing answers. We can see that in option (C), six
O2 plus 12 H2S is converted into C6H12 plus six O2 plus 12 S, the products of the
reaction do not contain glucose, C6H12O6. An essential product of
photosynthesis in both plants and bacteria is glucose, which is the source of
nutrients for the organism. As a result of this, option (C)
must be incorrect.

The reactants of the remaining
equation are carbon dioxide and hydrogen sulfide. With the addition of light energy,
the organism produces glucose, water, and sulfur. This represents exactly the
equation for bacterial photosynthesis, and therefore the correct answer must be
(B). Six CO2 plus 12 H2S is converted
into C6H12O6 plus six H2O plus 12 S.

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