If a molecule diffusing through extracellular fluid travels 1 mm in 1 sec, how long will it take that molecule to diffuse 1 cm?

To determine the time, we can simply do dimensional analysis from the given values. We are given the distance the fluid travels per sec and we are given the required distance to travel. Therefore, we simply divide the required distance with the rate given. It is important to take note with the units.

t =.01 m /.001 m/s = 10 s