H. Biology
C.7
Unit 3. Studies of a living plant cell
Background information.
Name ______________________________________
Since plants lead a stationary existence, it is appropriate that their cells should have rather rigid cell walls for support. Elodea is a genus of aquatic plants often called the waterweeds. Elodea is native to North
America and is also widely used as aquarium vegetation. It lives in freshwater. An older name for this genus is Anacharis, which serves as a common name in North America.
Procedure.
Remove a fresh, green leaf from an Elodea plant. Hold the leaf in your hand a few minutes to warm it.
Mount the whole leaf in a drop of pond water on a slide and carefully add a cover glass. Examine all areas of the leaf with the low power of your microscope. Then select a portion where the cells are clearly visible, center it in the field and bring it into focus under high power. Draw and label the cells in the circle below. Include, cell wall, chloroplasts, cytoplasm and nucleus.
Analysis.
1.
High power field of view is .4 mm = 400 u = 400,000 nm. Measure the length and width of the typical Elodea cell. (Show your work!)
2.
Estimate the size of a chloroplast! (About how many would equal the length of a cell?)

Part 2. Osmosis in Elodea
Use the leaf from part 1 or make a new slide if necessary. Observe your leaf under medium power
(100X). Locate a good example of a typical plant cell. While you are observing this cell have your partner add a drop of salt water to the edge of the cover slip near the leaf. Observe the changes which take place in the next minute or two. Use the space below to draw a diagram of the cell after the changes. Label the
cell wall, cell membrane, and chloroplasts. You may wish to observe the same experiment at 400X. Use a clean slide and a fresh leaf.
1.
How have the cells changed after the addition of the salt water?
2.
Develop some ideas that would explain why this would happen.
3.
Hypothesize as to what would happen if you had used distilled water instead of salt water.

Part 2. Cytoplasmic streaming.
Using clean materials, make a new slide of an Elodea leaf. Leave your slide on your microscope stage with the light on. After 15 minutes have passed look at your slide of the elodea leaf again. Look for cells where the chloroplasts are streaming around the cell.
1.
Are all the chloroplasts moving in the same direction? If so describe that movement.
2.
Are they all moving at the same rate? How fast are they moving? (How long to complete one circuit?
3.
Chloroplasts do not have any structure for locomotion. Account for their movement.
Analysis.
1.
In general how do the sizes of the plant cells we have studied compare with the animal cells?
2.
Why do plant cells show cytoplasmic streaming and animal cells do not?
3.
Why would it be important to plants to be able to move the chloroplasts around the cell?
4.
Look up cytoplasmic streaming in Elodea, cytoskeleton, myosin and actin and use this information to explain how the chloroplasts stream around the cell.