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:

1. Obtain three capillary tubes (10, 20, 50 μL).  When the tubes are filled to the mark, they contain the specified volume.

2. Predict the height a column of water will rise in each tube.  Record your predictions 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; where volume (mm3 ) = π r2 h (units in mm); and (b) 1  μL = 1 mm3

3. 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) Tube length (mm) Tube radius (mm) Tube radius (μm) Predicted height of water column (m) Predicted height (mm) Measured height (mm)

Conclusions:

1. How accurate were your predictions?

2. Explain why capillary action could not account for the movement of water to the top of tall trees.

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Last updated:  02/24/2009     � Copyright  by SG Saupe