Which of the following statements best describes the relationship between photosynthesis and respiration? O A. Photosynthesis is catabolic; respiration is anabolic OB. Respiration runs the biochemical pathways of photosynthesis in reverse O C. Photosynthesis occurs only in plants; respiration only occurs in animals OD. Photosynthesis stores energy in complex organic molecules; respiration releases energy from complex organic molecules
The Correct Answer and Explanation is:
The correct answer is:
D. Photosynthesis stores energy in complex organic molecules; respiration releases energy from complex organic molecules.
Explanation:
Photosynthesis and respiration are two fundamental biochemical processes that sustain life on Earth. They are closely interconnected but serve opposite functions in the energy cycle of living organisms.
Photosynthesis is an anabolic process, meaning it builds complex molecules from simpler ones. Specifically, plants, algae, and some bacteria capture light energy from the sun and convert it into chemical energy stored in glucose, a complex organic molecule. The simplified overall chemical equation for photosynthesis is:
$$
6 \text{CO}2 + 6 \text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}{12}\text{O}_6 + 6 \text{O}_2
$$
In this process, carbon dioxide and water are combined, using energy from sunlight, to form glucose and oxygen. The glucose molecule stores potential energy in its chemical bonds.
Respiration, on the other hand, is a catabolic process—it breaks down complex molecules into simpler ones to release energy. This process occurs in nearly all living organisms, including plants, animals, fungi, and many microorganisms. Cellular respiration breaks down glucose (or other organic molecules) to produce energy in the form of adenosine triphosphate (ATP), which powers cellular activities. The simplified equation for aerobic respiration is essentially the reverse of photosynthesis:
$$
\text{C}6\text{H}{12}\text{O}_6 + 6 \text{O}_2 \rightarrow 6 \text{CO}_2 + 6 \text{H}_2\text{O} + \text{energy} (ATP)
$$
Through respiration, the energy stored in glucose is released and converted into a usable form for the cell.
Why the other options are incorrect:
- A. Photosynthesis is catabolic; respiration is anabolic.
This is false. Photosynthesis is anabolic (building glucose), while respiration is catabolic (breaking glucose down). - B. Respiration runs the biochemical pathways of photosynthesis in reverse.
While the overall chemical equations look like reverses, the pathways themselves are different and involve distinct enzymes, intermediates, and organelles. Respiration and photosynthesis are not simply reverse reactions but complementary processes. - C. Photosynthesis occurs only in plants; respiration only occurs in animals.
This is incorrect because photosynthesis also occurs in algae and certain bacteria, not just plants. Respiration occurs in almost all organisms, including plants, animals, fungi, and many microorganisms.
Summary:
Photosynthesis captures energy and stores it by synthesizing glucose molecules, while respiration releases that stored energy by breaking glucose down into simpler molecules, enabling cells to perform their functions. These processes form a biological energy cycle that supports life on Earth.
