Question at position 14 Indirect calorimetry is based upon the concept that Oxygen is used in ATP production and ___ is a by-product of ATP production.NADHFADH2WaterCarbon dioxide单项选择题
A
NADH
B
FADH2
C
Water
D
Carbon dioxide

Question

Question at position 14 Indirect calorimetry is based upon the concept that Oxygen is used in ATP production and ___ is a by-product of ATP production.NADHFADH2WaterCarbon dioxide

BlackTom AI · Accepted Answer

During aerobic respiration, molecular oxygen accepts electrons at the end of the electron transport chain while oxidative decarboxylation reactions in the TCA cycle release carbon dioxide.

1) Relevant knowledge points and concepts
- Indirect calorimetry estimates metabolic rate by measuring O2 consumption (VO2) and CO2 production (VCO2).
- Cellular respiration: glycolysis, pyruvate oxidation, and the tricarboxylic acid (TCA) cycle produce reduced carriers (NADH, FADH2). The electron transport chain uses O2 as the final electron acceptor, producing water. CO2 is produced chiefly in oxidative decarboxylation steps (pyruvate → acetyl-CoA and multiple TCA cycle steps).
- Respiratory quotient (RQ) = VCO2 / VO2, which reveals substrate use (carbohydrate RQ ≈1.0, fat RQ ≈0.7).

2) Step-by-step reasoning
- Indirect calorimetry relies on measuring gases exchanged between organism and environment; the measurable outputs are O2 consumed and CO2 produced.
- Although NADH and FADH2 are central to ATP production, they are intermediate electron carriers generated inside the cell, not gaseous by-products expelled.
- Water is indeed formed when O2 is reduced in the electron transport chain, but it remains largely within the body and is not the primary gaseous marker used for calorimetry.
- Carbon dioxide is produced by the oxidation of carbon substrates and is the gaseous waste product that correlates directly with substrate oxidation and can be measured in expired air.

3) Calculations / examples (intermediate steps)
- Glucose oxidation: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O → RQ = VCO2/VO2 = 6/6 = 1.0
- Palmitate oxidation: C16H32O2 + 23 O2 → 16 CO2 + 16 H2O → RQ = 16/23 ≈ 0.70

4) Why the correct answer is correct
- Indirect calorimetry measures VO2 and VCO2; CO2 is the by-product of substrate oxidation and is exhaled, allowing indirect energy expenditure calculation.

5) Why other options are incorrect
- NADH and FADH2: reduced electron carriers (not exhaled by-products).
- Water: produced but not the primary exhaled gaseous marker used in indirect calorimetry.

6) Conclusion
Carbon dioxide is the by-product relevant to indirect calorimetry; this matches the provided correct answer: Carbon dioxide.

Question at position 14 Indirect calorimetry is based upon the concept that Oxygen is used in ATP production and ___ is a by-product of ATP production.NADHFADH2WaterCarbon dioxide单项选择题

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