Name

Period Date

INTRODUCTION

Cells have an outer covering called a cell membrane. The cell membrane controls what moves into and out of cells. The cell membrane allows only certain materials to pass through; this is a property known as semi-permeability. Food and oxygen pass through the cell membrane by the process of diffusion. Diffusion is the movement of substances from an area where there is a lot to an area where there is a little. The movement of water in this way is called osmosis. Osmosis is a special form of diffusion.

Why do diffusion and osmosis occur? The ability to maintain a stable internal state is called homeostasis. All living organisms need to maintain this balance to survive. Diffusion and osmosis allow cells to balance their internal chemistry with changes in their environment.

OBJECTIVES

  • Observe osmosis of water across a semi-permeable membrane.
  • Observe diffusion of food coloring across a semi-permeable membrane.
  • Measure the amount of water that moves across the egg membrane.
  • SAFETY: BE SURE TO WASH YOUR HANDS AFTER HANDLING RAW EGGS.

PRE-LAB: Define the following terms.

Cell membrane
Diffusion
Osmosis
Semi-permeable
Homeostasis

MATERIALS

1 large plastic cup150 mL acetic acid (vinegar)

Petri dish150 mL Karo’s syrup

Triple beam balanceFood coloring

100 mL graduated cylinderWater

Permanent markerPaper towels

Raw egg

PROCEDURE: Check off each step as you complete it.

PART A – OSMOSIS INTO THE EGG

Label the plastic cup with your name and period.

Measure 150 mL of acetic acid and place it in the cup.

Mark the cup at the 150 mL level for future reference.

Observe the shape and texture of your raw egg. Record in the Observation Table.

Mass the Petri dish using the triple beam balance. Record in the Data Table.

Mass the Petri dish and raw egg together and record.

Subtract the mass of the Petri dish to determine the mass of the raw egg alone and record.

Gently roll the raw egg into the acetic acid and cover with your Petri dish.

Leave the egg undisturbed for at least two days.

PART B – OSMOSIS OUT OF THE EGG

After two days observe your egg and record any changes.

Dab off any excess liquid and mass your egg again. Record the new mass.

Leave your egg on the Petri dish, empty the acetic acid in the sink and thoroughly rinse your cup.

Using the mark on the cup, put 150 mL of Karo’s syrup into the cup.

Very gently, roll the egg into the syrup. Do not push it down, it will sink naturally.

Leave the egg undisturbed for at least two days.

PART C – DIFFUSION OF PIGMENT MOLECULES

After two days observe your egg and record any changes.

Dab off any excess liquid and mass your egg again. Record the new mass.

Leave your egg on the Petri dish, empty the syrup in the sink and thoroughly rinse your cup.

Using the mark on the cup, put 150 mL of water in the cup and 15 drops of food coloring.

Very gently, place the egg in the colored water.

Leave your egg undisturbed for at least two days.

PART D – FINAL OBSERVATIONS

After two days observe your egg and record any changes.

Dab off any excess liquid and mass your egg again. Record the new mass.

Leave your egg on the Petri dish, empty the water in the sink and thoroughly rinse your cup.

In the empty cup carefully break the egg and observe the inside. Record both the color of the egg white and the yolk.

Dispose of all materials in the garbage and disinfect any equipment that has come in contact with the egg.

DATA TABLE:

Mass of Petri dish (g)
Mass of Petri dish and egg (g)
Mass of egg alone (g)
Mass of egg after acetic acid (g)
Mass of egg after syrup (g)
Mass of egg after colored water (g)

OBSERVATION TABLE:

Original egg
Egg after acetic acid
Egg after syrup
Egg after colored water
Inside of egg

PART A – MOVEMENT INTO THE EGG(sketch)

PART B – MOVEMENT OUT OF THE EGG(sketch)

PART C – MOVEMENT INTO THE EGG(sketch)

ANALYSIS

  1. Vinegar is made of acetic acid and water. Describe what happened to the shell of the egg after soaking in this acid. Why did this occur?
  2. What process occurred as the egg soaked in an acetic acid solution (check one):  Diffusion Osmosis
  3. What process occurred as the egg soaked in a syrup solution (check one): Diffusion Osmosis
  4. Describe what happened to the egg white after soaking in colored water.
  5. By what process does water enter the egg white (check one): Diffusion Osmosis
  6. By what process do color pigments enter the egg white (check one): Diffusion Osmosis
  7. Was the yolk sac permeable or impermeable, explain?
  8. Would a cell place in syrup lose or gain water? Why?
  9. Why are fresh fruits sometimes sprinkled with water at the supermarket and what process is occurring? (Hint: Think about how they are sold.)
  10. Explain how the process of diffusion can be used to stain a slide for viewing under a microscope.