Download Osmosis in a Plant

Osmosis in a Plant
Now that you have seen what happens to eggs and potatoes when they are
exposed to salt water, you will now discover what happens to plant cells under the same
conditions. The plant you are using is either Elodea or Anacharis. These plants are good
to study because they have leaves that are only two cells thick. It is easy to see individual
cells. Also, because these are water plants, they lack a protective covering over their
leaves that would make the cells harder to see. The plants are easily obtained at aquarium
stores where they are popular choices for fish tanks. Like all cells, plant cells are
surrounded by membranes, but these are covered, in turn, by tough cell walls. The cell
walls are made of strong cellulose that helps give the cells their shape. You might think
of the plant cells as each fitting inside a tough, protective box.
The membranes around cells are semi-permeable. In this case, water—but not
salt—can move back and forth. How will this affect the cells?
If you have not used the microscope this year, review its use with your instructor before
starting the lab.
Questions:
1. Do you predict the cells will be affected, when changed from fresh water to salt
water?
2. If you predict they will change, what do you think the change will be? Why? If
you predict they will not change, what were your reasons for choosing this
answer?
3. What would the picture of the moving salt and water look like on the molecular
level? Draw a labeled diagram with arrows showing how things are moving.
Safety:
Remember: never taste experimental materials unless expressly told to do so by
your instructor. Wash your hands with soap after each lab activity. Leave your lab
area in the same condition as you found it.
Materials:
1 microscope
1 slide
1 cover slip
1 Elodea or Anacharis leaf
salt water
dropper
paper towel
salt
Procedure:
1. Remove one leaf from your water plant and place it on a slide.
2. Add 2 drops of tap water with a dropper and cover with a cover slip.
3. Draw the views under both low and then high power, labeling each drawing with the
name of the plant, the water used (tap water), and the magnification of the view.
4. Remove the cover slip.
5. With the edge of a paper towel, gently blot up most of the water.
6. Add two drops of salt water with a dropper and cover with a cover slip.
7. Rinse out the dropper with fresh tap water.
8. Wait 5 minutes.
9. Observe the leaf cells again, under both low and then high power.
10. Draw the views under both low and high power, labeling the name of the plant, the
type of water used (salt water), and the magnification of the view.
11. Clean the slide and cover slip and dispose of the leaf in the trash.
Questions:
1. What changes, if any, did you observe? Was your prediction correct?
2. What explanation can you give for these results? (HINT: reread the introduction
to this section).
3. What do you think might happen, if you had used sugar syrup, instead of salt
water? Why?
4. What do you think might have happened if you had used pure distilled water
instead of tap water?
5. What clues have you gained from this activity that might help you to predict what
will happen in your egg experiment?
6. How has this experiment shown how osmosis can work in living cells?