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

What substances can cells use as substrates for respiration?

1. Only glucose

2. Carbohydrates, proteins, and lipids

3. Only carbohydrates

4. Only proteins and lipids

The correct answer is: Carbohydrates, proteins, and lipids

Cells can utilize a variety of substrates for respiration, which is essential for producing energy in the form of ATP. While glucose is a primary source, as a carbohydrate, cells can also derive energy from other carbohydrates, proteins, and lipids. Carbohydrates such as fructose and sucrose can be broken down through glycolysis, much like glucose. Proteins can be deaminated, removing an amino group, and the remaining carbon skeletons can enter the respiratory pathways. Lipids, primarily triglycerides, are broken down into glycerol and fatty acids; both components can then be converted into intermediates that participate in cellular respiration. This versatility in substrates allows cells to adapt to varying nutrient availability and energy demands, demonstrating the metabolic flexibility necessary for survival in different environments. Thus, the correct answer encompasses the broad range of substances cells can utilize for respiration, affirming that not just glucose, but also proteins and lipids play crucial roles as substrates.