Biomedical Engineering Reference
In-Depth Information
Figure 2
. Effects of temperature (1000/(K) on mass-corrected resting metabolic rate, ln(
BM
-3/4
(W/g
3/4
)), for unicells (
A
), plants (
B
), multicellular invertebrates (
C
), fish (
D
), amphibians (
E
),
reptiles (
F
), and birds and mammals (
G
). Birds (black symbols) and mammals (open symbols)
are shown at normal body temperature (triangles) and during hibernation or torpor (squares).
This figure is reproduced with permission from Gillooly et al. (2000) (1).
whereas heart rate decreases as
M
-1/4
e
-
E/kT
, so the number of heartbeats per life-
time is approximately invariant, independent of size and temperature (lifetime
heartbeats ~1.5 x 10
9
for mammals). Hearts are not fundamental but the molecu-
lar machinery of aerobic metabolism is, and it also has an analogous invariant,
namely, the number of lifetime turnovers of the respiratory complex (~10
16
) (13).
Until recently most theoretical investigations focused on the metabolic rate
of a specific taxonomic class. The broader challenge is to understand the over-
whelming ubiquity and universality of quarter-power scaling with mass and the
exponential variation with temperature, and to connect the existence of these
scaling relationships to unifying principles that determine how life is structured
and the constraints under which it has evolved. In the second section of this
