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If you are not familiar with the parts of a cell, please visit our Animal Cell Page.
A cell is a lot like an egg. The yolk is like the nucleus, the white part is like the cytoplasm, and the shell is like the membrane. To see how the membrane works like a screen you can try this nifty experiment.
|
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| Two jars with lids. (make sure a raw egg can fit in both jars) |
| Masking tape |
| Meter tape |
| White Syrup |
| White Vinegar |
| Raw egg |
| Spoon |
| A piece of paper |
| A graduated cylinder or a device to measure liquid in the metric system |
Step One: Label the jars A and B. Measure two hundred mL of
vinegar into jar A.
Step Two: Place the measuring tape around the egg and
find the circumference of it.
Put the date and the measurement on the piece of paper and save
it.
Step Three: Carefully place the egg into the vinegar. Put the top on the jar and leave it for two days.
Step Four: After two days, remove the egg from the vinegar with a spoon and carefully rinse it in water. Use the measuring tape to find the circumference of the egg. Measure the vinegar with the graduated cylinder. Record the results on the piece of paper.
Step Five: Measure 200 mL of syrup into jar B. Place the egg into the jar of syrup. Place the lid on the jar and leave it for one day.
Step Six: Carefully remove the egg with the spoon from the syrup. Rinse it with water. Use the measuring tape to find the circumference of the egg. Measure the syrup remaining in the jar. Record the measurements on the same piece of paper used in steps two and four.
What Happened?
1. Did you see a change in the egg shell after being in the
vinegar? What happened and why did it happen?
2. What happened to the size of the egg after being in the syrup? Why did that happen?
If you're not sure about why things happened the way they did, click here to read about it.
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What happened?
1. After being in the vinegar, the egg grew larger. That's
because vinegar is actually a weak acid. The acid dissolved the
shell, which then allowed water to pass into the egg.
2. After being in the syrup, the egg grew smaller. That's because syrup is heavier (has a higher viscosity) than water. The pressure of the heavy syrup around the egg pushed the water back out of the cell and into the syrup.
Real cell membranes are usually made of fat and it's the chemical make-up of the membranes that allows materials to enter and leave the cells.