Plant Physiology

Plant Physiology (Biology 327) - Dr. Stephen G. Saupe; College of St. Benedict/ St. John's University; Biology Department; Collegeville, MN 56321; (320) 363 - 2782; (320) 363 - 3202, fax; ssaupe@csbsju.edu

Spuds McSaupe Studies Capillary Action

General: Today Spuds will help us understand the phenomenon of capillary action. The height a column of water will rise in a thin tube is related to the diameter of the tube by the following equation:

equation 1: h = 14.87/r where r = radius in μm and h = height in meters

Predictions: First, lets make some predictions. Based on Equation 1, we predict that:

water will travel further up a (narrower / wider) capillary tube
water will travel further up a (10 μL / 50 μL ) tube.
water will travel ________ mm up a tube that has a radius of 100 μL. (show your work)

Protocol:

Obtain three capillary tubes (10, 20, 50 μL). When the tubes are filled to the mark, they contain the specified volume.
Predict the height a column of water will rise in the tube. Record your prediction in the table. Hints: (a) you will not be able to measure the radius directly. Calculate the radius based on the equation for the volume of a cylinder, which volume (mm³ ) = π r² h (units in mm); and (b) 1 μL = 1 mm³
Place the capillary tube in water and measure the height to which the water column rises.

Data:

Table 1: Predicted and Actual Capillary Water Movement in Thin Tubes
	Tube volume (μL)
	10	20	50
Tube volume (mm³)
Length (mm)
radius (mm)
Radius (mm)
Predicted Height (m)
Predicted Height (mm)
Measured Height (mm)
% Difference

Conclusions:

How accurate were your predictions?
Explain why capillary action could not account for the movement of water to the top of tall trees.