Osmosis Lab - Rubber Egg Objectives: To demonstrate the semi-permeability of a c

Question

Osmosis Lab - Rubber Egg
Objectives:
To demonstrate the semi-permeability of a cell membrane To lay ground-work for discussion of osteoporosis
Materials Needed:
1 raw egg in its shell
clear vinegar
3 wide-mouth jars or plastic cups
corn syrup
water
Procedure:
Measure and record the circumference around the center of the egg.
Record the appearance of the egg.
lace the egg inside the jar. DO NOT crack the shell.
Cover the egg with vinegar.
Observe immediately, and then periodically for the next 72 hours.
Remove the egg after 72 hours and measure its circumference.
Compare the appearance of the egg before and after being in the vinegar.
Put corn syrup in a clean jar and then place the egg in the jar and let it sit over night.
Compare the appearance of the egg before and after the syrup.
Put fresh water (tap or distilled works) in a clean jar and place the egg in the jar and let it sit over night.
Compare the appearance of the egg before and after the syrup.
Strategy:
The egg has a hard shell on the outside and the circumference will vary. Bubbles start forming on the surface of the egg's shell immediately and increase in number with time. After 72 hours, the shell will be gone and portions of it may be seen floating on the surface of the vinegar. The egg remains intact because of the thin see-through membrane. The size of the egg has increased.
The shell of the egg is made of calcium carbonate, commonly called limestone. When vinegar chemically reacts with the limestone, one of the products is carbon dioxide gas, those bubbles seen on the egg. The membrane around the egg does not dissolve in vinegar, but becomes more rubbery. The increased size is due to osmosis, the movement of water through a cell membrane. The water in the vinegar moves through the thin membrane into the egg because the water inside the egg has more materials dissolved in it than does the vinegar. Water will always move through a membrane in the direction where there are more dissolved materials. The contents of the egg stayed inside the membrane because the molecules were too large to pass through the tiny homes. This selectiveness of materials moving through the membrane is called semi-permeability.
Journal Question:
1. Explain your observations in detail in terms of concentration gradient, diffusion, osmosis, osmotic pressure, passive transport, and active transport.

Explanation / Answer

Answer:

In the rubber egg lab also known as the osmosis lab, I first measured the circumference of the egg which was 6 inches. The egg had no cracks and was hard. I placed the egg in the vinegar and within seconds the egg started to bubble. These bubbles were carbon dioxide. After 72 hours, the shell of the egg had started to dissolve or flake. This would be considered passive transport as the vinegar diffused across the egg shell without any force.

72 hours into the experiment, the membrane was exposed and had a circumference of 8 inches. Before the egg had a shell and you couldn't see through it. But once the vinegar acted as an acetic acid it broke down the shell and left a yellow membrane that felt like rubber. This is an example of diffusion. I then placed the egg in another container and put corn syrup on the egg for 24 hours. The egg had shriveled and shrunk, the water had left the egg and went to the syrup. This is what caused the egg to shrink.

The corn syrup is essentially pure sugar with very little water, so the osmotic pressure is very low. I then placed the shriveled egg in water and waited for another 24 hours. After observation, the egg had no wrinkles and swelled back up. The water had moved through the membrane inside the egg making the proportion of molecules equal which caused the egg to swell. This is an example of osmosis.

Also when the egg was placed in the water, the egg expanded. This was because of the interior of the eggs must have had a higher solute concentration than their surrounding environment of distilled water. This would be an example of concentration gradient. Active transport occurs against the gradient and requires an input of energy.

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