Question at position 2 Which of the following may have the highest metabolic rate per unit mass?FatHeartMuscleBone单项选择题
A
Fat
B
Heart
C
Muscle
D
Bone

Question

Question at position 2 Which of the following may have the highest metabolic rate per unit mass?FatHeartMuscleBone

BlackTom AI · Accepted Answer

Cardiac muscle (heart) has the highest metabolic rate per unit mass among the choices because it is continuously active and has very high energy demands.

1. Relevant knowledge points and concepts
- Metabolic rate per unit mass depends on cellular activity, ATP demand, and mitochondrial density. 
- Tissues that contract continuously or maintain ionic gradients without interruption consume more ATP per gram. 
- Adipose tissue (fat) stores energy and is metabolically quiescent per gram; bone has metabolic activity for remodeling but low basal energy demand; skeletal muscle can have high total energy use but, per gram at rest, is less active than cardiac muscle.

2. Step-by-step reasoning
- Identify functional role: the heart continuously pumps blood without rest, requiring constant ATP for contractile work and ion pumping. 
- Link to cellular machinery: cardiac myocytes are densely packed with mitochondria and have high capillary perfusion to supply oxygen and substrates. 
- Compare relative demands: skeletal muscle is active intermittently (depends on exercise) so its resting per-gram metabolic rate is lower than heart; fat primarily stores triglycerides and has low baseline ATP turnover; bone’s remodeling processes are metabolically modest per mass.

3. Calculations / intermediate steps
- No numerical calculation is required to rank these tissues qualitatively. The logical intermediate steps are: continuous activity → high ATP demand → high mitochondrial content and O2 consumption → high metabolic rate per gram.

4. Why the correct answer is correct
- The heart’s continuous contractile and ionic work demands sustained ATP production, making its basal metabolic rate per unit mass higher than fat, skeletal muscle (at rest), and bone.

5. Why the other options are incorrect
- Fat: primarily an energy store, low basal metabolism per gram. 
- Muscle (skeletal): can have high total metabolic output during exercise, but per gram at rest it is lower than cardiac muscle. 
- Bone: metabolic activity for remodeling exists but overall energy turnover per unit mass is low.

6. Conclusion
- Therefore, Heart is the correct choice, matching the provided answer.

Question at position 2 Which of the following may have the highest metabolic rate per unit mass?FatHeartMuscleBone单项选择题

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