Onion Cell Plasmolysis Lab

Aspect 1

We did this lab in order to show the effects of plasmolysis on plant cells to help enhance the understanding of diffusion and water potential. Knowing that plasmolysis involves the shrinking of the cytoplasm in a cell wall after diffusion of water in hypertonic solutions, I predict that both the area and the perimeter of the cell will decrease in size.

The independent variable is the perimeter of the cell. The dependent variable is the area of the cell. The control is the amount of salt in the water.

Aspect 2 and 3

The first step was to cut out a piece of onion and remove a single layer of the purple tissue. The layer was then placed on a slide and a drop of water was added. Then we used a microscope to find the onion cells under 40X and then 100X. Next, we placed a paper towel along one edge of the slide and added drops of 15% NaCl (salt) solution and replaced the fresh water. After plasmolysis took place, we observed the cell, took a picture and analyzed the results using Image J.

For complete instructions see Mrs. Keel’s teacherweb page at: http://teacherweb.com/TX/westwoodhighschool/Keel/photo2.stm

Aspect 4

Area

Cell Initial Area (mm2)

Final Area (mm2)

1 0.0742 0.0442

2 0.1050 0.0697

3 0.1297 0.0830

PerimeterCell Initial

Perimeter (mm)

Final Perimeter (mm)

1 1.2474 0.95412 1.4850 1.13543 1.7713 1.4671

Area and Perimeter Percent Change

-40.43

-33.62-36.01

-23.51

-23.54

-17.17

-70

-60

-50

-40

-30

-20

-10

0

1 2 3

Cell

Per

cen

t C

han

ge

Perimeter

Area

Aspect 5

Area Percent Change

10.0442 – 0.0742

X 100 = -40.43% 0.0742

20.0697 – 0.1050

X 100 = -33.62% 0.1050

30.0830 – 0.1297

X 100 = -36.01% 0.1297

Perimeter Percent Change

10.9541– 1.2474

X 100 = -23.51%1.2474

21.1354 – 1.4850

X 100 = -23.54%1.4850

31.4671 – 1.7713

X 100 = -17.17%1.7713

Aspect 6

Aspect 7

My original hypothesis was correct in that both the final perimeter and area were less than the starting values. This occurred because water moved out of the cell, into the hypertonic, meaning a high solute concentration, salt solution, which led to the shrinking of the cytoplasm, a process called plasmolysis. If the solution added had been hypotonic, meaning it had a low solute concentration, then plasmolysis would not have occurred, and the perimeter and area would not have increased.

The percent change in area was much more drastic than that of the perimeter. This occurred because the area is dependent upon the perimeter and is affected more by changes in the cell wall shape.

Aspect 8

In our experiment, we made a few mistakes. When we took our picture of the onion cells after plasmolysis occurred, we zoomed in to get a better shot. This skewed our results in Image J because the picture was enlarged creating a bigger perimeter and area.

Another error that occurred was the tracing of the cell wall in Image J. It was very difficult to accurately outline each cell, making the results inaccurate.

Aspect 9

Some improvements that could have been made to our experiment would have been a more accurately sized picture to analyze and being more careful in outlining the cell wall in Image J. By fixing these two things, our results would have been much clearer and provided a better outcome.