Read How Fats Enter Respiration
Different fuels join respiration at different points, and energy yield depends on their reduction state and processing.
Living-system questions are solved by matching a structure or organism to its function, process and stated condition.
Why glucose is convenient
Glucose is a common fuel because it enters glycolysis directly. It is not the only fuel and is not the most energy-dense molecule by mass.
Follow triglyceride products
Lipases split fats into fatty acids and glycerol. Fatty acids undergo β-oxidation to acetyl-CoA; glycerol is converted to dihydroxyacetone phosphate and enters glycolysis. Fats yield roughly twice the energy per mass of carbohydrates.
Consider oxygen demand
More reduced substrates such as fats require more oxygen per carbon oxidised. Oxygen-rich organic acids can require less oxygen than carbohydrates.
Compare fuel yield with anaerobic access
Long-chain fatty acids are highly reduced and yield much more ATP on complete aerobic oxidation, at the cost of substantial oxygen use. Glucose is distinctive because glycolysis can supply energy anaerobically as well as feeding aerobic respiration. Distinguish high total yield from the ability to work without oxygen: fatty acid, then glucose. Choose D.
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- ✓Fat → fatty acids + glycerol.
- ✓Fatty acids → acetyl-CoA via β-oxidation.
- ✓Glycerol → dihydroxyacetone phosphate → glycolysis.
- ✓Fat is energy-dense; glucose enters the pathway readily.
- ✓Fatty acids yield high aerobic energy; glucose can support both aerobic and anaerobic energy production.
Do not confuse rapid pathway entry with total energy per gram.
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