= Solution
On a moving step, the largest speed resolved by the discrete model is the distance per interval,
$$
\boxed{v_{\max}=\delta/\tau=0.20\,\mu\mathrm m/\mathrm s
=2.0\times10^{-5}\,\mathrm{cm}/\mathrm s}.
$$
This is a step-averaged speed; the model does not specify motion within the interval. Use the cell length $a=2r=20\,\mu\mathrm m=2.0\times10^{-3}\,\mathrm{cm}$ in the stated <Reynolds number> formula. In consistent centimetre–gram–second units,
$$
\boxed{R_{\max}=\frac{av_{\max}\rho}{\eta}
=\frac{(2.0\times10^{-3})(2.0\times10^{-5})(1)}{10^{-2}}
=4.0\times10^{-6}}.
$$
Thus viscous effects dominate inertia overwhelmingly. The surrounding flow is in the <Stokes flow> regime: sustained movement needs applied forces, and inertial coasting is negligible. Using radius rather than the specified length as the characteristic size would halve the <Reynolds number>, without changing that physical conclusion.
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