Question

In the history of photosynthetic research, the empirical reaction of photosynthesis was first proposed for green plants (equation 1), followed by another reaction for purple sulfur bacteria (equation 2), leading to a generalized equation for photosynthesis (equation 3), where \( {H}_2{A} \) in equation 3 is a generalized electron donor.
\[ {CO}_2 + {H}_2{O} \xrightarrow{{light}} {(CH}_2{O)} + {O}_2 \quad {(equation 1)} \] \[ {CO}_2 + 2{H}_2{S} \xrightarrow{{light}} {(CH}_2{O)} + {H}_2{O} + 2{S} \quad {(equation 2)} \] \[ {CO}_2 + 2{H}_2{A} \xrightarrow{{light}} {(CH}_2{O)} + {H}_2{O} + 2{A} \quad {(equation 3)} \] Where \( {H}_2{A} \) in equation 3 is a generalized electron donor. Which one of the following statements is DISPROVEN by equation 3?
 

• A. The source of oxygen produced in photosynthesis in green plants is COsubscript{2}
• B. The source of oxygen produced in photosynthesis in green plants is Hsubscript{2}O
• C. Light is essential in every form of photosynthesis
• D. Glucose is the end product in all forms of photosynthesis

Hint:

In photosynthesis, the source of oxygen in green plants is water, not carbon dioxide. Remember that oxygen is released during the splitting of water molecules in the light-dependent reactions of photosynthesis.

Answer 1

The Correct Option is A

In equation 3, the generalized equation for photosynthesis, it is clear that the oxygen produced is not derived from carbon dioxide (COsubscript{2}) but from the electron donor \( {H}_2{A} \). This disproves the statement that oxygen comes from COsubscript{2}, which is true for the original green plant photosynthesis equation (equation 1). 
Therefore, statement (A) is disproven. 
Let's analyze the other options: 
- (B) The source of oxygen produced in photosynthesis in green plants is Hsubscript{2O}: This statement is true for green plants. In the empirical reaction for green plants (equation 1), oxygen is released from water (Hsubscript{2}O) as the electron donor, not from COsubscript{2}. Hence, statement (B) is not disproven. 
- (C) Light is essential in every form of photosynthesis: Light is indeed essential for all forms of photosynthesis, as shown in equations (1), (2), and (3), where the reactions are driven by light energy. Hence, statement (C) is not disproven. 
- (D) Glucose is the end product in all forms of photosynthesis: While glucose is the major product of photosynthesis in green plants, in certain forms of photosynthesis (like in purple sulfur bacteria, equation 2), the end product is a simple carbohydrate (CHsubscript{2}O), not glucose. However, the statement is more related to the generalized nature of photosynthesis and is not disproven. 
Thus, the correct answer is (A), as equation 3 disproves the idea that oxygen comes from COsubscript{2} in photosynthesis.