The Elodea plant has the parts that
would typically be found in a plant cell. In this exercise we will identify those parts and see what happens when you subject this plant to plasmolysis.
Show
ImageJ application.
Elodea
- Normal:
Go to File, Open Samples Open the image Elodea1.
In this low power view under the microscope it is possible to see a number
of individual cells. You may also see that there is more than one layer
of cells.
Close Elodea 1 and Open Elodea2. In this more highly magnified view it is possible to identify a number of the typical plant parts.
1. Name
three structures that are shown in this plant cell that you would not expect
to find in an animal cell?
It is not possible to see the cell membrane because it is pushed up against
the cell wall. Also, the central vacuole cannot be clearly distinguished
from the cell cytoplasm. In a living elodea cell you can “roughly”
tell where the vacuole is by where the moving chloroplasts are not able
to go.
If you were to surround this group of plant cells with salt water then the
water inside the plant would move from where there is more water (less salt)
through the cell wall and membrane to the outside where there is less water
(more salt). This process of water movement from a high concentration of
water to a lesser concentration of water is called osmosis. When the water
movement is out from a cell this form of osmosis is specifically called
plasmolysis.
Close
Elodea2 and Open ElodeaP.
This is a view of a cell that has undergone plasmolysis. It is now possible to see the cytoplasm which has contracted around the chloroplasts and the other cellular structures. Most of the water that has left the cell has been from the vacuole. It is possible to roughly calculate the size of the vacuole by measuring the area of the space between the cell membrane and the cell wall. To do that we will first calibrate the image.
Calibrating
the image.
Keep ElodeaP
open and also open image
Scale. This Scale image is a photograph of a micrometer slide
that you saw earlier on this page. The large gap is 0.1 mm. or 100 microns.
The closely spaced lines on the left are 10 microns apart. Use the Rectangle
Selection 
tool and
select a 10 micron area. (It should look like the piece that is immediately
above the label 10 microns. Notice how the selection is made through the
middle of the micrometer line to middle for the next line.) Then go to Copy
under Edit on the Menu.
2. Why is the copy portion selected in this manner?
Paste
the 10 micron portion in the lower left portion 
of
the ElodeaP image.
Calibrating
the image.
Go to your Line
tool. Drag the tool
across the scale bar. Then go to Set Scale under Analyze.
Put micrometers for "Unit of Measurement" and 10 for "Known
Distance".
Then go to Set Measurements under Analyze and only check "Area" and "Perimeter".
Measure the length and perimeter of the cell that is in the center and Record results in Table 1.
Area is automatically calculated if you have area checked under Set Measurements. (Be sure the lines connect when you do the perimeter.)
Measure using
the Freehand Selection 
tool around the cell membrane and Record results in Table
1. If you subtract the area inside the cytoplasm from the area of
the entire cell you will have the approximate area of the cell that was
originally occupied by the cell vacuole.
1. What % of the cell is occupied by the vacuole?
2. Can you see any problems with calculating the area of the cell vacuole
in this manner?
Results
1. Name three structures that are shown in this plant cell that you would not expect to find in an animal cell?
Table 1:
1. What % of the cell is occupied by the vacuole? (Show your work)
2. Can you see any problems with calculating the area of the cell vacuole in this manner?
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