Capillary rise can be used to describe how far water will rise above a water table because the interconnected pores in the soil act like capillary tubes. This means that deep-rooted plants in the desert need only grow to the top of the “capillary fringe” in order to get water; they do not have to extend all the way down to the water table.

a. Assuming that interconnected pores can be represented as a continuous capillary tube, how high is the capillary rise in a soil consisting of a silty soil, with a pore diameter of 10 μm?

b. Is the capillary rise higher in fine sand (pore diam. approx. 0.1 mm), or in fi ne gravel (pore diam. approx. 3 mm)?

c. Root cells extract water from soil using capillarity. For root cells to extract water from the capillary zone, do the pores in a root need to be smaller than, or greater than, the pores in the soil? Ignore osmotic effects.