OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What is the primary function of respiration in living organisms?

1. To absorb nutrients from food

2. To synthesize proteins from amino acids

3. To release energy from the food consumed

4. To form glucose from carbon dioxide

The correct answer is: To release energy from the food consumed

Respiration is a vital process in living organisms that primarily serves the function of releasing energy from the food consumed. This energy is essential for various life processes, including growth, movement, and maintaining homeostasis. During respiration, glucose, which is a product of food digestion, is broken down in the presence of oxygen (in aerobic respiration) to produce carbon dioxide, water, and energy in the form of ATP (adenosine triphosphate). This energy can then be utilized for cellular functions, enabling organisms to perform necessary activities that sustain life. The focus on energy release distinguishes respiration from other biological processes such as nutrient absorption or protein synthesis, which, while important, are not the core purpose of respiration itself. The formation of glucose from carbon dioxide is actually part of photosynthesis, primarily occurring in plants, rather than respiration. Thus, the primary function of respiration is accurately captured by the option concerning energy release from consumed food.