Which of the following statements best describes the relationship between photosynthesis and cellular respiration: a. photosynthesis produces organic molecules that are oxidized during cellular respiration to produce ATP. b. plants and other photosynthetic organisms get energy from photosynthesis and animals get energy from cellular respiration. c. photosynthesis and cellular respiration use CO2 and H2O as substrates d. photosynthesis and cellular respiration are exergonic, energy releasing reactions.
The Correct Answer and Explanation is:
The correct answer is:
a. photosynthesis produces organic molecules that are oxidized during cellular respiration to produce ATP.
Explanation:
Photosynthesis and cellular respiration are fundamentally connected biochemical processes that together sustain life by managing energy flow in ecosystems.
Photosynthesis is a process used primarily by plants, algae, and some bacteria to convert light energy from the sun into chemical energy stored in organic molecules such as glucose. The overall photosynthesis equation 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 used as raw materials, and with the energy from sunlight, they are converted into glucose (an organic molecule) and oxygen. Glucose stores energy in its chemical bonds.
Cellular respiration occurs in almost all living organisms, including plants and animals. It is the process of breaking down glucose to release stored energy for cellular functions. The general equation for cellular respiration is essentially the reverse of photosynthesis:
$$
\text{C}6\text{H}{12}\text{O}_6 + 6 \text{O}_2 \rightarrow 6 \text{CO}_2 + 6 \text{H}_2\text{O} + \text{energy (ATP)}
$$
During cellular respiration, glucose molecules are oxidized, meaning their electrons are removed and passed along the electron transport chain, which ultimately produces ATP (adenosine triphosphate), the main energy currency of cells.
Why other options are incorrect:
- b. It’s incorrect to say that only plants get energy from photosynthesis and animals from cellular respiration. Plants also perform cellular respiration to use the glucose they produce. Animals cannot perform photosynthesis.
- c. Photosynthesis and cellular respiration do not both use CO₂ and H₂O as substrates. Photosynthesis uses CO₂ and H₂O as inputs, while cellular respiration uses glucose and O₂ as inputs.
- d. Photosynthesis is an endergonic (energy-consuming) process because it requires sunlight to drive the synthesis of glucose, whereas cellular respiration is exergonic (energy-releasing) as it breaks down glucose to produce ATP.
Summary:
Photosynthesis and cellular respiration form a biological cycle: photosynthesis captures energy to create glucose, while cellular respiration releases energy from glucose for cellular activities. This interdependent relationship maintains energy flow and the balance of oxygen and carbon dioxide in the atmosphere.
