Which respiratory substrate releases the greatest amount of energy per gram when oxidised?
Correct answer: A. Fat
- A. Fat
- B. Carbohydrate
- C. Protein
- D. Nucleic acid
Explanation
Fat yields roughly 9 kcal per gram against about 4 for carbohydrate and protein, because its carbon atoms are far more reduced and so give up more electrons to the transport chain. This energy density is why fat rather than glycogen is the body's long term store and why migrating birds and hibernating mammals rely on it. Nucleic acids are informational molecules and are not used as fuel.
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About Cellular Respiration
Cellular respiration releases energy from glucose through glycolysis, the link reaction, the Krebs cycle and the electron transport chain, producing ATP. The pathway differs in oxygen availability: aerobic respiration uses oxygen and yields more ATP, while anaerobic respiration produces much less ATP and forms lactic acid in muscles or ethanol and carbon dioxide in yeast.
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