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Question Video: Recalling the Correct Chemical Equation for Photosynthesis in Bacteria Biology

Which of the following chemical equations correctly summarizes the reaction Van Niel determined in photosynthetic bacteria? [A] 6CO₂ + 12H₂O ⟶ C₆H₁₂O₆ + 6H₂O + 6O₂ [B] 6CO₂ + 12H₂S ⟶ C₆H₁₂O₆ + 6H₂O + 12S [C] 6O₂ + 12H₂S ⟶ C₆H₁₂ + 6O₂ + 12S [D] 6CO₂ + 6H₂O ⟶ C₆H₁₂O₆ + 6O₂

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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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