Lab How DOES CARBON DIOXIDE ENTER A LEAF by steepslope9876


									       Stomata Lab: How DOES CARBON DIOXIDE ENTER A LEAF?
Objectives: On your test you will be expected to describe how leaves regulate gas exchange. Be able to write the equation for
photosynthesis and describe where each requirement comes from and what happens to each product. Also be able to name the various
parts of the leaf.

Procedure: You are now to perform the first part of this experiment. Your teacher will point out where the Zebrina plant is kept. You
will need to strip off a small peace of the UNDER SURFACE of the leaf and use this to make a wet mount. This must be
accomplished in a specific manner as follow: First, place 2 drops of distilled water on a clean slide. To get only the thin, transparent,
red surface cells, the EPIDERMIS, hold the leaf with the under surface facing you and tear the leaf in such as way as to cause the thin
red EPIDERMIS to peel away from the rest of the leaf. Obtain a piece of epidermis that is large enough to work. Add a cover slip. Try
to eliminate any large bubbles. Examine on 4X and 10X.

Answer the following questions in you lab comp book.

1.   When you see anything that might resemble pores, draw them on 10X on your own paper. You should see many cells of the
     Epidermis and see structures like those drawn below:

     Examine a number of the structures you suspected to be pores. Can you find any of them with an “opening” in the center? Locate
     one that seems typical of the rest but appears to be open and examine it on 40X.

2.   Draw an enlarged view of one of these structures as viewed on 40X (see example below).

3.   If any of the structures in the above drawing were omitted from your drawing, put them into your
     drawing. Learn the following terms associated with the drawing at the right: structure “a” is the
     STOMATA or STOMA (This is the open “space” itself). Structures “B” are 2 bean-shaped cells
     called GUARD CELLS. They are caplable of pening and closing the STOMA. Look again at your

4.   What colors are structures C and D?

5.   Do any of the cells in the epidermis that surround the 2 guard cells contain chloroplasts? (See your slide for the answer). Also
     notice, on your slide as in the drawing, that the inner surface of the 2 GUARD CELLS are much thicker than any other surface in
     the epidermis.
The next PROBLEM you must tackle is: By what mechanism can the cytoplasm filled guard cells, which contain no muscle-like fibers,
open and close? You will be able to partly solve this problem yourself by performing a simple experiment and by recalling some of
the concepts that you already know about diffusion and photosynthesis.

6.   Write the equation for photosynthesis on your own paper.

The Cells carrying out this process are right below the stomata opening where they can absorb the CO 2 that passes through the stomata
openings. As the equation states, the process continues as long as the light is provided. At night, the process stops. As CO 2 is entering
the leaf during the day, precious water vapor will be lost. To obtain CO 2 the plant pays a price, which in this case, is the loss of water
vapor. Over a ton of water evaporates from stomata of leaves of an average size tree on a warm day.

7.   At night when the leaf cannot carry out photosynthesis, and thus does not need CO 2 what logical occurances would prevent
     additional water loss?

How can these GUARD CELLS open and close? You can simulate night conditions by replacing the distilled water on your slide with
a glucose solution. Find an open stomata on 40X, then replace the water with moving the position of the slide or cover slip as follows:
Firs, add 2 drops of 5% glucose solution next to the cover slip with a dropper so that the solution touches the edge of the cover slip.
Second, tough a small piece of paper towel to the other side of the cover slip as shown in the drawing at the right. This will cause the
glucose solution to move under the cover slip and around the epidermis. OBSERVE WITH YOUR MICROSCOPE while the solution
moves over the cells.

8.   OBSERVE ANY CHANGES in the stomata apparatus. Describe your observations of at least 7 different stoma as viewd on 40X
     for a period of at least 5 minutes.

Analyze what has happened and how the GUARD CELLS are able to change shape and open or close the STOMA when a cell is
placed in 5% glucose solution.

9.   This 5% glucose solution is what % water?

10. If guard cells that contain more than 95% water are placed in 95% water, what happens to the water within the guard cells?

Recall that in the 5% glucose (95% H2O) solution, the stoma closes. Therefore, water leaving the guard cells must be related to their

11. What happens with respect to water movement, when guard cells that are less than 100% water are placed in a solution of 100%
    distilled water?

Review the terms and main concepts in this lab and be ready for your chapter test. Review the structures of the stoma.

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