Question

Which would be the last substrate to be used in respiration?

• A. Carbohydrate
• B. Protein
• C. Fat
• D. Organic acids

Answer 1

Answer: (B)

Protein

• The most common respiratory substrate is carbohydrate, followed by fat and protein.
• Carbohydrates are the first substrates for respiration because of their high respiratory quotient and high production of ATP.
• Fats have a lower respiratory quotient but higher energy yield than carbohydrates.
• The last substrate to be used in respiration would be protein because of low respiratory quotient and low ATP yield than carbohydrates. Proteins require ATP to be consumed for converting to amino acids and then to acetyl CoA to enter Krebs' cycle. Thus, they are used as last resorts for energy in stressful conditions.
• So the answer is 'Protein'.