Observing Plasmolysis in Onion Cells (Allium cepa)

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Observing Plasmolysis in Onion Cells (Allium cepa)

I. Introduction

Plasmolysis is the process in plant cells in which the cytoplasm is separated from the cell wall as a result of water loss through osmosis.

Osmosis is a type of passive transport involving movement of water molecules across a partially permeable membrane.

1. Research question

How does 15% NaCl solution affect the appearance of onion cells?

2. Hypothesis

If onion cells are submerged in solutions of NaCl of different concentrations, then cells will lose water and the plasma membrane will shrink. This is because the process of osmosis will take place. Because of a difference between solute concentrations on either side of a partially permeable membrane, the movement of water molecules will occur.

II. Materials and methods

1. Materials

Light microscope


Cover slips

Small beakers (50 ± 5 ml)




Weighing scale (± 0.1 g)

Automatic pipette (100-1000 ±50 µm)

15% NaCl solution, 10 ml

Tap water

Red onion

Yellow onion

2. Method

a. Obtain a small piece of the yellow onion using a scalpel.

b. Peel off the outer layer cells using forceps.

c. Mount the tissue in a few drops of tap water.

d. Set up the light microscope and observe the cells in 10 times magnification.

e. Draw the few of these cells seen in distilled water.

f. Weigh 1,5 g of NaCl using the spatula and weighing scale.

g. Add some water to the beaker and make sure that all substance dissolves in water.

h. Add distilled water up to the line 10 ml.

i. Obtain small pieces of both yellow and red onion.

j. Peel off the outer layer cells using forceps.

k. Set up two more slides, this time using a few drops of 15% NaCl solution.

l. Observe the...