Theory 36/Bioenergetics
Metabolic Rate Is an Area Ratio
The claim
Resting metabolic rate is set by the ratio of membrane area to cell volume rather than by mass, so a cell's cost per unit mass rises as it shrinks.
01The mechanism
Most resting cost maintains ion gradients across membranes; membrane area scales with the square of size while volume scales with the cube, so the ratio rises as cells shrink.
02Predictions
- P1Rate per unit mass should track the ratio.
- P2Mass alone should mispredict across cell sizes.
03Refutation
Rate tracking mass would restore the simple scaling.