a cell it is very fast. The average instantaneous velocity of a particle in solution—that is, the velocity between its very frequent collisions—is v = (kT/m)½where k = 1.38 × 1
“Diffusion” sounds slow—and over everyday distances it is—but on the
scale of a cell it is very fast. The average instantaneous velocity of a particle
in solution—that is, the velocity between its very frequent collisions—is
v = (kT/m)½where k = 1.38 × 10–16 g cm2/K sec2, T = temperature in K (37°C is 310 K),
and m = mass in g/molecule.
Calculate the instantaneous velocity of a water molecule (molecular
mass = 18 daltons), a glucose molecule (molecular mass = 180 daltons),
and a myoglobin molecule (molecular mass = 15,000 daltons) at 37°C.
Just for fun, convert these numbers into kilometers/hour. Before you do
any calculations, you might try to guess whether the molecules are moving at a slow crawl (<1 km/hr), an easy walk (5 km/hr), or a record-setting sprint (40 km/hr)
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