BACKGROUNDBACKGROUND
Materials move into and out of cells freely, especially water. Such a high percentage of our bodies, and thus our cells, is water, that it becomes obvious that maintaining proper water balance in the cell (body) is vital to life. Water moves into and out of the cells based on the concentration gradient of the solution surrounding the cell compared to the cell. If a solution is Hypertonic, it has more dissolved particles in solution than the cell. Because cells strive to maintain a balance between it's internal environment and external environment. So to balance the concentrations, the cell loses water and shrivels. To much, and the cell dies. In Hypotonic solutions, the opposite scenario exists and cells gain water, swelling and bursting.
Plant cells, by virtue of their cell wall, do not burst. Instead, as the cell membrane pushes up against the cell wall, a pressure is formed, called turgor, which stops the influx of water, thus stoping osmosis. In this lab, you will use this knowledge to predict the environmental condition of two samples by viewing their cellular structure under the microscope.
1. Examine two specimens of Elodea that have been kept ina hypeertonic and hypotonic environment. Both are unknown to you. Making visual observations of the plant, predict which has been kept in the hypertonic solution.
Visual Observations:
Prediction/Hypothesis:
2.Get a microscope and make two wet mount slides of the Elodea: one of sample A and the other of sample B. View the two at 400X magnification. Below is an example of what you may have seen:
| Sample A | Sample B |
 |
 |
Based on our knowledge from the previous lab:
A. Which of the two samples were kept in a hypertonic solution?
B. State the reason why you believe this to be the case?
Notes for your Lab Report:In this lab you were to predict what kind of solution (salt
water or fresh) a plant was kept in by examining the cells of
the plant for any signs of osmosis having occured. In this lab
report you are to discuss the lab procedure as well as use the
concept of osmosis to describe the reasoning behind your hypothesis
and conclusion.
Purpose:
See above.
define osmosis
detail basic plant cell anatomy
explain what hypertonic and hypotonic
are and how they relate to osmosis and cells Hypothesis:
what do you predict will physically
happen to the cells in the hypertonic and hypotonic solution
why do you think these will be
the results that you will observe; be specific as to what you
expect to see Procedure:
describe the steps involoved
include what you were going to
look for as evidence of osmosis occuring Results:
what did you observe on side A
and slide B
how did the two slides differ
draw a picture of a representitive
cell from each slide Analysis:
which plant had been placed in
a hypertonic environment
detail why you suspect this to
be the case
describe the osmotic event that
occured, using the sample as evidence Conclusion:
restate purpose, hypothesis, and
what your results show..... relative to the problem at hand It is important that you look at cell structure and the basics
of osmosis in your report. Do not tell me only about the lab procedure
and results. You MUST explain what happened (and why you expected
certain results) by using the concept of osmosis!!