
Concept explainers
What do some photosynthetic bacteria use as a source of electrons instead of water?
a. oxygen (O2)
b. hydrogen sulfide (H2S)
c. organic compounds (e.g., CH3COO–)
d. nitrate (NO3–)

Introduction:
In the photophosphorylation reaction, electrons are required. These electrons are acquired from water molecules. The molecule is split and oxygen is generated as a by-product.
Answer to Problem 1TYK
Correct answer:
Some of the photosynthetic bacteria use hydrogen sulfide (H2S) instead of water as a source of electrons.
Explanation of Solution
Explanation/Justification for the correct answer:
Option (b) is given that hydrogen sulfide is used an alternative source of energy by some photosynthetic bacteria instead of water. Some of the bacteria may not use water molecule as a source of electrons and use hydrogen sulfide instead. For example, a sulfur bacteria Thiobacillus oxidizes sulfur by sulfate production required for growth of plants. Some of them also use other different molecules such as iron ions. Hence, Option (b) is correct.
Explanation for incorrect answers:
Option (a) is given that oxygen (O2) is used an alternative source of energy by some photosynthetic bacteria instead of water. In this process, oxygen is released as a by-product and does not act as an electron source. So, it is a wrong answer.
Option (c) is given that organic compounds like acetate are used as an alternative source of energy by some photosynthetic bacteria instead of water. The organic compounds such as acetate ions also do not provide electrons. So, it is a wrong answer.
Option (d) is given that nitrate
Hence, options (a), (c), and (d) are incorrect.
Thus, some photosynthetic bacteria use hydrogen sulfide as an alternative source of energy.
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Chapter 26 Solutions
Biological Science, Loose-leaf Edition (7th Edition)
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