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Science Lab Worksheet
Catholic Schoolhouse
Lab I: Osmosis and Plant Cell Size
Describe in your own words the following terms as they are used in the laboratory.
Basic terms
Plant cellPlasma membraneCell wallDiffusionOsmosisAdvanced terms
ConcentrationSolventSoluteSolutionSurface areaVolumeTurgid-
1
FlaccidOsmosis Data Collection
• Record your data in the following table as instructed by your tutor.
• Write the colors of the dye in the left column.
• Make a prediction before the experiment. Which dyes do you think will migrate the
fastest & slowest? Why do you think that?
• Record the diameters of diffusion (in millimeters) in the corresponding boxes. If
you are late in recording a measurement, be sure to record the exact time.
• If you used paper disks, you should record the diameter of the disk in the “0”
column; if you used toothpicks, record the actual measurement.
Table A. Rate of Food Coloring Diffusion
Color
0
10
20
Time (min)
30
40
50
60
Advanced: Using a graphing program (such as Excel), construct a line graph of the
diameter versus time for all the food dyes. Determine the slope (m) of each line
(y=mx+b). (The slopes will be <1 and in units of mm/min.) You may multiply each of
the slopes by 60 min/h to obtain larger values in units of mm/h.
Questions to consider:
Which colors diffused the fastest? The slowest?
Was your prediction right?
Does that mean your explanation is right, too? Explain.
2
Table B. Determining the size of cells
Type of
Ball
Diameter
(D)
Radius (r)
Surface
Area (SA)
Volume (V)
Ratio
(SA/V)
• Rank the balls according to their size, from smallest to largest. Which one has the
largest SA/V ratio?
• What might a smaller SA/V ratio mean for a very large cell with respect to rates of
diffusion? (Hint: imagine you are an ant in the very center of a ball, and you want to
get out. Compare being in a small ball or a large ball.)
• Why does the amount of surface area matter for a cell?
Application:
• Microvilli are microscopic, fingerlike projections in the small intestine that greatly
increase the surface area of cells there to improve nutrient absorption. Can you
think of part(s) of a plant where lots of surface area would be necessary? Explain.
3
Part C: Demonstration of salted celery
Make observations about the celery stalks placed in water and salt-water. How do
they each feel, particularly at the base of the stalk? Why do you think this happened?
• What was the overall direction of the diffusion of water (osmosis) in the celery
stalk placed in salt water?
Application:
1. Florists tell their customers to give their flowers fresh cuts and new water to
keep them healthy longer. Why?
2. Your friend’s father is growing tomato plants in pots, but he is frustrated
because they are flaccid and wilting. He cannot understand it because he has
fertilized them with lots of potassium salts, which are good for plants. What
has happened? Can you think of a way to help rescue his plants?
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