Plants & Human Affairs (BIOL106)  -  Stephen G. Saupe, Ph.D.; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321; ssaupe@csbsju.edu; http://www.employees.csbsju.edu/ssaupe

Medium: Pre & Post Lab Assignments

PreLab:

1. Print & read copies of the lab exercise

2. On a separate sheet of paper, answer the following hypotheses (including a brief rationale):

   Hypotheses:

   1. The densest medium will be ___________ because.....

   2. The medium with the greatest pore space will likely be _________ because....

   3. The medium with the greatest water holding capacity will likely be _______ because....

   4. The medium with the greatest air space at field capacity will likely be _________ because....

   5. Mixing these media will result in ........

   6. As the density of the medium increases, the total pore space: ______ (increases, decreases, is not affected).

   7. As the density of the medium increases, the water held at field capacity:________ (increases, decreases, is not affected)

   8. As the density of the medium increases, the air space at field capacity:_________ (increases, decrease, is not affected).

Post Lab:

1. On a separate sheet of paper, complete Table 1

2. Turn in a graph with the following plots:  total pore space (y axis) versus density (x axis); water held at field capacity vs. density; air space at field capacity vs. density

3. Do the data support your hypotheses?  For each of the eight hypotheses, indicate if your data supported or rejected the hypothesis.  Offer a potential explanation(s).

4. Answer the following questions:

1. Vermiculite is a good medium for starting seeds.  Explain why with direct reference to your data.   

2. Perlite is a good medium for propagating cuttings of plants.  Explain why with direct reference to your data.

3. What is a possible disadvantage of a medium with too much air space?

4. Suggest a reason why sand is generally a major component of media for growing cacti and other succulents.

5. Vermiculite is reported to be able to retain 16 times its weight in water.  Do your data support this statement? (i.e., perform this calculation for your vermiculite sample.  Then briefly discuss your results).  Show your work.

6. In the greenhouse, a standard growing medium contains equal parts of soil, peat and vermiculite.  We hypothesized that a composite medium would exhibit properties that are the average of the individual components.  Do our data support this hypothesis?  Provide data to support or refute this hypothesis

Bonus Question:  Describe how we could determine the amount of "free water" in each medium when it is saturated. (2 points)

Last updated:  02/09/2005 / � Copyright  by SG Saupe / URL:http://www.employees.csbsju.edu/ssaupe/index.html