Questions: Cellular Respiration Introduction

Question 1

What is the relationship between photosynthesis and cellular respiration?

• A. They are the same process
• B. They are reverse processes — the outputs of one are the inputs of the other
• C. Photosynthesis occurs only in plants, and cellular respiration occurs only in animals
• D. They have no relationship

Answer: (B)

Photosynthesis takes in CO₂ and H₂O and produces glucose and O₂. Cellular respiration takes in glucose and O₂ and produces CO₂ and H₂O. The outputs of one are the inputs of the other, forming a cycle. However, they are NOT opposites that cancel out — photosynthesis stores energy (from sunlight) in glucose, while cellular respiration releases that stored energy for cells to use.

Question 2

Plants perform photosynthesis but do not perform cellular respiration.

• T. True
• F. False

Answer: False

Plants perform BOTH photosynthesis and cellular respiration. During the day, photosynthesis dominates — plants produce more oxygen and glucose than they use. But plant cells have mitochondria and continuously perform cellular respiration to release energy from glucose for their own growth and life processes, day and night.

Question 3

Explain why cellular respiration is not the same as breathing, even though the two are related.

Model answer: Breathing is the mechanical process of moving air in and out of the lungs — inhaling oxygen and exhaling carbon dioxide. Cellular respiration is the chemical process inside cells where glucose is broken down using oxygen to release energy, with carbon dioxide and water produced as waste. Breathing supplies the oxygen that cellular respiration needs and removes the CO₂ it produces, but they are different processes at different levels.

This distinction is important because cellular respiration happens in every cell of the body, not just in the lungs. The lungs handle gas exchange with the environment; mitochondria handle the energy-releasing chemistry. Organisms without lungs (like plants and single-celled organisms) still perform cellular respiration.