I selected links that provide background information about plants and water. Most provide general information about diffusion, osmosis or illustrate the pathways and processes involved. A few are more specific, and illustrate particular techniques and processes which are the same, or quite similar, to what we will do in the laboratory.

I will try to provide more specific information in the near future. However, you will learn much by studying the information available at the present sites. I recommend that you review the links as you prepare for lab and as you write your reports on your observations.

I. TRANSPIRATION

A. Intact Coleus Plant (Demonstration)

This first demonstration of transpiration consists of a potted Coleus plants that has roots, stems and leaves intact. One branch of the plant was inserted into a glass flask and the opening sealed with a cotton plug. Water evaporating (leaf transpiration) from the leaf will condense on the inside of the glass flask. A "control" flask sealed without a Coleus branch has no condensation, supporting the conclusion that the condensation originates from transpiration of the Coleus plant.

Transpiration is the loss of water vapor from the plant surface. Most transpiration occurs from leaves, especially from stomates (stomatal transpiration) when the stomates are open. When the stomates close, plants continue to transpire directly from the epidermal cells despite the cuticle layer that these cells usually have (cuticular transpiration). Tissues with a periderm often transpire via lenticels (lenticular transpiration).

B. Detached Coleus Branch - no roots (Demonstration)

In the demonstration of the intact plant, there is no way to determine if the moisture that is transpired is being pushed up the plant by the root system, or if it is being pulled up the plant by the shoot system. In this demonstration, the shoot of a vigorous Coleus plant has been cut from the root system, and the cut stem is inserted into a container of water. One branch of the plant was inserted into a glass flask (in a manner similar to that of the intact plant) and the opening sealed with a cotton plug. A "control" flask sealed without a Coleus branch has no condensation, supporting the conclusion that the condensation originates from transpiration of the Coleus plant.

If water evaporating (leaf transpiration) from the leaf will condenses on the inside of the glass flask, we will know that it was not pushed from below by the root system (the roots were removed), supporting the hypothesis that water is pulled up the plant from above by the shoot (shoot tension theory).

II. RATE OF XYLEM TRANSPORT

In lab Exercise 4 you allowed a red dye (eosin) to move up the stem of a young sunflower plant. Later, when you dissected the plant, you used the location of the red dye to mark the location of the xylem tissue that was transporting the eosin. Today, in a similar procedure you will allow eosin to move up the stems of an herbaceous and a woody stem. By noting the distance the dye travels in the stem in timed period, you will estimate the rate of transport of materials in the xylem.

A. Herbaceous Stem - Impatiens

Usually the eosin dye moves quite rapidly in the vascular tissues of the Impatiens plants that we use for this demonstration. The first students to try this should allow the eosin to move in the plant for 5 minutes. If the eosin reaches the top of the plant in this time period, subsequent trials by students should allow the eosin to move for shorter periods. If the eosin has not moved much distance, subsequent trials by students should be lengthened (perhaps to 10 minutes as suggested by the lab manual).

You will test the rate of movement in Impatiens stems subjected to three different conditions.

1. Leaves intact, exposed to air
2. Leaves intact, misted and contained in plastic bag
3. Leaves removed, exposed to air

Decide on the hypothesis that you are testing, and predict in advance what the results will be. In past years the results were variable, and not always as anticipated. Be prepared to explain what does happen.

B. Woody Stem - Yew or other Evergreen

I will cut branches of Yew (Taxus) from the bush outside of the Biology Office and place them immediately into a container of water. Transfer one branch of Yew into a container of eosin and allow the dye to move to determine the rate of xylem transport in this softwood species. I suggest that you allow movement to continue for at least an hour, perhaps longer, as movement is usually slow.

III. PLASMOLYSIS and OSMOTIC POTENTIAL

Rheo or Zebrina

The links lead to a variety of related sites. One provides images of plasmolyzed (flaccid) and normal plant cells. Another site, provides images and descriptions of Diffusion and Osmosis very similar to many of the observations you will make in the current lab. Many of the other links provide general information on osmosis, diffusion and related information.

IV. TURGOR and WATER POTENTIAL

Links under water potential lead to a series (a,b,c) of diagrams illustrating water potential.

V. OSMOSIS AND OSMOTIC PRESSURE

One link One link, Diffusion and Osmosis, includes a graph depicting weight changes from an experiment almost identical to that you will conduct with dialysis tubing. Well worth studying in advance, and reviewing again after you have conducted the experiment.

V. OSMOMETER - (Demonstration)

Several links, including Osmotic pressure provide an illustration and discussion of osmometers. These may assist you in interpreting results and understanding the principles involved.

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Assignment

               Assignment for Laboratory Exercise 9 -- Water
 

1.   Examine the materials on display in the room. These will
     include equipment and materials related to water and
     solutes.

2.   Work in teams as you perform parts I (Transpiration by intact
     stem and detached branch), II (Rate of Xylem Transport), III
     (Plasmolysis and Osmotic Potential), IV (Turgor and Water Potential)
     and V. (Osmosis and Osmotic Pressure). However, prepare your
     written reports individually.

3.  Submit a typewritten laboratory report to summarize the
     results of parts II, III and IV. The report should include
     computer graphs of the results.