Which of the following statements concerning the role of redox reactions in photosynthesis and cellular respiration is true?
A) Photosynthesis involves only reductions, whereas respiration involves only oxidations.
B) Photosynthesis involves only oxidations, whereas respiration involves only reductions.
C) In photosynthesis, carbon dioxide is oxidized to form sugar, whereas in respiration, sugar is reduced to form carbon dioxide.
D) In photosynthesis, carbon dioxide is reduced to form sugar, whereas in respiration, sugar is oxidized to form carbon dioxide.
The correct answer and explanation is :
The correct answer is D): In photosynthesis, carbon dioxide is reduced to form sugar, whereas in respiration, sugar is oxidized to form carbon dioxide.
Explanation:
Photosynthesis and cellular respiration are two essential biochemical processes that involve redox (reduction-oxidation) reactions, where electrons are transferred between molecules. However, their roles in these processes are different.
- Photosynthesis:
- Photosynthesis occurs in plants, algae, and some bacteria, and its purpose is to convert light energy into chemical energy stored in glucose (a type of sugar).
- The overall reaction for photosynthesis can be simplified as:
[
6CO_2 + 6H_2O + light \ energy \rightarrow C_6H_{12}O_6 + 6O_2
] - In this process, carbon dioxide (CO₂) is reduced. This means that CO₂ gains electrons (and hydrogen ions) to form glucose (C₆H₁₂O₆). The reduction of carbon dioxide is a key part of photosynthesis, where energy from sunlight is used to convert CO₂ into organic molecules.
- Water (H₂O) is oxidized in photosynthesis. The hydrogen from water molecules is used to help reduce CO₂, and oxygen gas (O₂) is released as a byproduct.
- Cellular Respiration:
- Cellular respiration occurs in the cells of organisms and is the process by which energy stored in glucose is converted into usable energy in the form of ATP (adenosine triphosphate).
- The overall reaction for cellular respiration can be simplified as:
[
C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + energy (ATP)
] - In this process, glucose (C₆H₁₂O₆) is oxidized. This means that glucose loses electrons, ultimately being broken down into carbon dioxide (CO₂) and water (H₂O).
- Oxygen (O₂) is reduced in cellular respiration, as it accepts electrons to form water.
Key Difference:
- Photosynthesis: Carbon dioxide is reduced (gains electrons) to form sugar.
- Cellular Respiration: Glucose is oxidized (loses electrons) to form carbon dioxide.
Thus, the correct statement is that in photosynthesis, carbon dioxide is reduced to form sugar, while in cellular respiration, sugar is oxidized to form carbon dioxide.