Think about the cell model. What part of the egg is the shell

Upon the successful completion of the lab, the learners should be able to:

Define the following terms: diffusion, osmosis, equilibrium, tonicity, turgor pressure, plasmolysis

Describe what drives simple diffusion (why do the molecules move?)

List the factors that may affect the speed of simple diffusion

List which molecules, in general, can freely diffuse across the plasma membrane of a cell

Describe what drives osmosis (why do water molecules move?)

Explain why water moves out of a cell when the cell is placed in a hypertonic solution

Explain why water moves into a cell when the cell is placed in a hypotonic solution

Describe what physically happens to a cell if water leaves the cell

Describe what physically happens to a cell if water enters the cell

Introduction

Can all substances move in both directions through a cell membrane?

The cell membrane determines what diffuses into a cell. Many cells are semi-permeable, which means not all substances can pass through the cell membrane. The amount of a substance that diffuses through a membrane is influenced by concentration and time. A chicken egg is just one gigantic cell. We will use it to further our learning about cell membranes and diffusion.

Problem: How does a cell membrane work?

Hypotheses: Formulate a hypotheses for the experiment.

Write a hypothesis as to what you think will happen to the egg when you check on it in 2 days.

Write a hypothesis as to what you think will happen to the egg when you check on it in 3 days.

Write a hypothesis as to what you think will happen to the egg when you check on it in 4 days.

Write a hypothesis as to what you think will happen to the egg when you check on it in 5 days.

Write a hypothesis as to what you think will happen to the egg when you check on it in 6 days.

Materials: 1 egg, 250 ml glass container, vinegar, water, salt, 30 cm of string, scissors, ruler, wooden splint

Method:

1- Record the date and day.

Use a string to measure the circumference of the egg 3 times: width and length.

Using a ruler, measure in cm the length of the string. Record the data in the table provided in step 5. Find the average of the 3 measurements.

Write several observations about your egg.

Cover raw egg with vinegar in a 250 ml container. Draw a diagram of your egg each time you checked it (label the solutions). Draw arrows showing which way water moved by osmosis. The arrows will show how water entered or left the egg, depending upon which solution it was in.

2- Record the date and day. Be very careful not to poke or squeeze your egg for even a little bit! Drain egg and very carefully use a string to measure the circumference of the egg 3 times: width and length. Using a ruler, measure in cm the length of the string. Write this data down in your notebook. Find the average of the 3 measurements. Write several observations about your egg. Fill beaker with 100ml of water and 25 ml of salt. Stir the solution well with a wooden splint. Place egg back in container. Write a hypothesis as to what you think will happen to the egg when you check on it next. Draw a diagram of your egg each time you checked it (label the solutions). Draw arrows showing which way water moved by osmosis. The arrows will show how water entered or left the egg, depending upon which solution it was in.

3- Record the date and day. Be very careful not to poke or squeeze your egg for even a little bit!  Drain egg and very carefully use a string to measure the circumference of the egg 3 times: width and length. Using a ruler, measure in cm the length of the string. Write this data down in your table. Find the average of the 3 measurements. Write several observations about your egg. Place egg back in beaker. Replace with fresh water. Write a hypothesis as to what you think will happen to the egg when you check on it next. Draw a diagram of your egg each time you checked it (label the solutions). Draw arrows showing which way water moved by osmosis. The arrows will show how water entered or left the egg, depending upon which solution it was in.

4- Record the date and day. Be very careful not to poke or squeeze your egg for even a little bit!  Drain egg and very carefully use a string to measure the circumference of the egg 3 times: width and length. Using a ruler, measure in cm the length of the string. Write this data down in your table. Find the average of the 3 measurements. Draw a diagram of your egg each time you checked it (label the solutions). Draw arrows showing which way water moved by osmosis. The arrows will show how water entered or left the egg, depending upon which solution it was in. Write several observations about your egg. Discard of egg in Ziploc bag.

5-Use this table to write your data in each day you check your egg.

Day: __________ Date:__________

Analyze and Conclude

1. Define diffusion and osmosis.
2. Why is the cell membrane a necessary part of the cell?
3. Think about the cell model. What part of the egg is the shell? What part of the egg is the layer under the shell? What is the yolk? What is the “white” part of the egg?
4. Why does the egg change size from one day to the next? Use words like: molecules, low, concentration, high, and move. What part do the different types of solutions play in the change in size?
5. What would happen if you placed a grape in a dish of pure water? What would happen if you soaked the grape in water mixed with a large amount of sugar?
6. Describe what drives simple diffusion (why do the molecules move?)
7. Explain why water moves out of a cell when the cell is placed in a hypertonic solution
8. Explain why water moves into a cell when the cell is placed in a hypotonic solution
9. Describe what physically happens to a cell if water leaves the cell
10. Describe what physically happens to a cell if water enters the cell

Write a conclusion that talks about diffusion and the egg. Be sure to note each change in size (number value) and why the change in size occurs in the Results Listed and Explained part of your conclusion.

Define the following terms: diffusion, osmosis, equilibrium, tonicity, turgor pressure, plasmolysis