Stahl-Biology
Osmosis Lab / 1

Observing Osmosis Lab

Introduction

The cell membrane is an organelle that every cell contains. Its function is to provide a barrier and to act as the doorman, only allowing certain molecules to enter, while keeping others out, also known as being selectively permeable. There are two types of transport across the cell membrane, one that does not require energy such as passive transport (diffusion, osmosis, and facilitated diffusion) and one that requires energy or active transport (endocytosis and exocytosis).

Oxygen and carbon dioxide are two molecules that move through the cell membrane through the process of diffusion. Diffusion is the movement of molecules from an area of high concentration to an area of low concentration, until equilibrium is reached. Osmosis is another type of diffusion and occurs when water moves from an area of high to low concentration.

In this lab you will be observing osmosis taking place in a normal chicken egg with the shell removed. The shell of the egg will be removed by soaking it in vinegar. Egg shells are composed of a base, calcium carbonate and when they are exposed to high acidity such as the acetic acid in vinegar, the shell dissolves while releasing carbon dioxide (the bubbles you see). The goal of this experiment is to soak eggs in various solutions and to measure and compare the changes in cell size.

Pre-lab questions:

  1. Define diffusion and osmosis.
  1. What is the function of the cell membrane?
  1. What does selective permeability mean?
  1. What do you think would happen to a shell less egg if water passed into the egg cell?
  1. What do you think would happen to the egg if water passed out of the cell?
  1. What substances do you think need to pass though the shell in order for a chick to properly develop?
  1. In the cell membrane malfunctioned, what do you think would happen to the chick inside?

Materials:

  • 3 Raw eggs
  • Masking tape and marker
  • Tap water
  • Vinegar
  • Corn syrup
  • Coca Cola
  • Metric tape
  • Balance
  • Plastic container
  • Beaker / container to hold egg
  • Spoon
  • Paper towels

Predictions-

How do you think the egg will respond when it’s soaked in-

  1. Vinegar-______
  2. Corn Syrup-______
  3. Salt Water-______
  4. Coca cola-______

Procedure:

Step 1-Making Shell-less Eggs

1. Place the eggs in the container so they are not touching.

2. Add enough vinegar to cover the eggs. Notice bubbles

form on the eggs. Cover the container, refrigerate, and let

the eggs sit in the vinegar for 24 hours.

3. Use a large spoon to carefully scoop the eggs out of the

vinegar. The egg membrane may be the only thing holding

the egg together and it is not as durable as the shell.

4. Pour out the vinegar. Put the eggs back in the container

and cover them with fresh vinegar, cover container. Leave

the eggs in the refrigerator for another 24 hours.

5. Scoop the eggs out again and rinse them carefully. If any

of the membranes have broken, throw those eggs away.

6. When done, you will have an egg without a shell. It looks

like an egg, but it’s translucent—the membrane is flexible.

Step 2 / Day 2- Observing Osmosis

  1. Open the jar and pour off the vinegar. Use a spoon to remove the egg and gently pat it dry with a paper towel.
  2. Measure and record the diameter with the measuring tape, weigh it, and document its appearance. Do this for each egg.
  3. Record all information on your data table.
  4. Label the three jars: Corn syrup, tap water, and Coca cola.
  5. Place egg #1 into a container and cover the egg with corn syrup. Cover with saran wrap.
  6. Place egg #2 into a container and cover the egg with tap water. Cover with saran wrap.
  7. Place egg #3 into a container and cover the egg with Coca Cola. Cover with saran wrap.
  8. Refrigerate for 24 hours.

Step 3 / Day 3- Let’s check them out!

  1. Open the jars and pour off the liquid. Do one at a time to prevent any spills or accidents.
  2. Using a spoon, remove the eggs and gently pat them dry with a paper towel.
  3. Measure and record the diameter with the measuring tape, weigh it, and document its appearance. Do this for each egg.
  4. Record all information on your data table.

Step 4 / Day 4- Let’s see what happens!

  1. Take the egg that was in the corn syrup, pat it dry, and place it into a clean beaker of tap water, cover it, and refrigerate for 24 hours.

Step 5 / Day 5- What happened?

  1. Record what happened. ______

Results:

Data Table:

Date / Liquid / Circumference in cm. before 24 hours in solution / Circumference in cm. after 24 hours in solution / Weight in grams before solution / Weight in grams after solution / Observational Drawings- what it looked like / Change in weight in grams / Change in circumference in cm.
Corn Syrup
Tap Water
Coca Cola

Graphing:

  1. Create two bar graphs that compare the circumference in centimeters, as well as the weight in grams of the three solutions.
  2. Then make another bar graph comparing the weight before and after the soaking of the egg in the three solutions.
  3. You should have three graphs total. Complete on the graph paper provided.

Analysis Questions-

  1. What liquid caused the egg to swell?
  1. What liquid caused the egg to shrivel or shrink?
  1. What process caused this to happen?
  1. What happened to the egg in the Coca cola?
  1. Describe what happened when you placed the egg that was in the corn syrup back into regular water.
  1. Compare the results of all three solutions and egg reactions. Be specific.