Name:
Date:
Partners’ Names:
Period:
_________
Biology Laboratory
Diffusion and Osmosis
BACKGROUND / PRE-LAB QUESTIONS:
1. Name three things that an animal cell needs to take inside in order to survive.
,
,
2. Name two things the animal cell needs to remove from the internal environment in order to survive.
,
3. What is the outer boundary that surrounds all cells and controls what moves in and out?
_______
4. This outer boundary only allows certain substances to pass and not others and is therefore said to be:
5. What is diffusion?
6. What is osmosis?
7. What type of transport is osmosis and diffusion?
8. What is not required in this type of transport?
9. Compare the tonicity (solute and solvent concentration) in the following types of solutions:
a. Isotonic Solution:
b. Hypertonic Solution:
c. Hypotonic Solution:
PURPOSE:
1. To observe how a selectively permeable membrane works.
2. To observe osmosis in cells placed in varying solutions of salt concentrations.
MATERIALS:
Two eggs
Vinegar
Marking Pen
Two (2) Beakers
Two (2) Plastic Cups
Balances
Red Onion Slice
Graduated Cylinder
Dialysis Tubing
String
Water Bath
Four (4) Test Tubes
Iodine
Glass Rod
15% NaCl Solution
Corn Syrup
Microscope
Cover Slips
Molasses
Starch-Glucose Mixture
Two Medicine Droppers
Glass Tubing
Microscope Slide
1
PROCEDURE:
Part A: Egg Experiment
Day 1: Egg Experiment
1. Using a marking pen, mark one cup “water” and a second cup “syrup.” Also label your cups with your
names.
2. Place an egg in each cup. Determine the mass of each egg to the nearest 0.1 gram. Record the mass:
a. Day 1: Mass of “water” egg:
b. Day 1: Mass of “syrup” egg:
3. Pour enough vinegar into both of the cups to cover each egg.
4. Place your cups on one of the sides of the room.
5. Hypothesize on what will happen to the eggs overnight?
a. Hypothesis:
Day 2: Egg Experiment
1. Observe each of eggs.
a. Observation:
2. Pour the vinegar into the sink and carefully remove your eggs.
a. Remember which egg is the “water” egg and which is the “syrup” egg.
3. Turn the water on first and wash your eggs off gently. Also, wash your cups out with water.
4. Dry your eggs and your cups. Return each egg to the proper cup.
5. Determine the mass of each egg to the nearest 0.1 gram. Record the mass:
a. Day 2: Mass of “water” egg:
b. Day 2: Mass of “syrup” egg:
6. Add syrup to the “syrup” cup until the egg is covered.
7. Add water to the “water” cup until the egg is covered.
8. Wash off the tray on the balance with a Clorox wipe.
9. Without the shell, the membrane surrounding the egg now acts like the
of the cell. Hypothesize how the mass will change in each egg over the next 24 hours based on the
solutions they are placed.
a. Hypothesis:
Day 3:
1. Remove the eggs from the cups. Carefully rinse the eggs and the cups with water. (Turn water on first!)
2. Dry the eggs and the cups. Return each egg to its proper cup.
3. Determine the mass of each egg to the nearest 0.1 gram. Record the mass.
a. Day 3: Mass of the “water” egg:
b. Day 3: Mass of the “syrup” egg:
4. You may pop the eggs in the sink. Do NOT leave the membrane in the sink, put it in the garbage! Wash
the insides down the drain with plenty of water.
5. Throw the cups away and wash the tray on the balance with a Clorox wipe.
2
Part B: Diffusion through a Selectively Permeable Membrane
1. Soak a section of dialysis tubing in water for a few minutes until it is soft and pliable.
2. Rub the ends together to separate the two sides. After you separate the sides, reinsert it into the water to
make it easier to open.
3. Insert a glass rod to hold it open.
4. Twist one end and fold it over. Clasp the end closed with a clip (you may use string if a clip is not
available). Make sure this is secure; you do not want this end to leak!
5. Remove the glass rod and fill the dialysis bag ¾ full with the Starch-Glucose mixture.
6. Put a knot in the top of the back (or tie it with string).
7. Rinse the outside of the bag. Place the bag in a beaker of water using a beaker clamp.
8. Pour 5 ml of Iodine into the beaker until it turns amber (tea-like).
a. Observation of Solution in Dialysis Bag:
_______________________________________________________________________
b. Observation of Solution in Beaker:
______
________________________________________________________________________
9. ***Wait 25 minutes***. While you are waiting, BEGIN WORKING ON PART C!!!
10. Swirl a glucose test strip around in the beaker, remove and compare color.
a. Did the test strip change to indicate a positive test?
b. Observation of Solution in Dialysis Bag:
c. Observation of Solution in Beaker:
11. Wash liquids down the sink. Throw away the dialysis tubing and test strip. Clean the beaker.
Part C: Osmosis
1. Soak a section of dialysis tubing in water for a few minutes until it is soft and pliable.
2. Rub the ends together to separate the two sides. After you separate the sides, reinsert it into the water to
make it easier to open.
3. Insert a glass rod to hold it open.
4. Twist one end and fold it over. Clasp the end closed with a clip (you may use string if a clip is not
available). Make sure this is secure; you do not want this end to leak!
5. Remove the glass rod and fill the dialysis bag ¾ full with molasses. Careful, it starts to pour slowly but
then comes out fast! PLEASE DO NOT SPILL MOLASSES!!! This process requires that the team
work together and really take care in what you are doing.
6. Insert the glass tubing into the top of the bag. Make sure the tube does not touch the bottom of the bag!
Tie the top of the bag tightly around the glass tubing with a piece of string.
7. Rinse the outside of the bag with water. Do not get any water into the bag.
8. Place the bag into the beaker of water. The water should not go above the bag. Prop the bag in an
upright position so the glass tube is straight up and down vertically.
9. Observe and mark the location of the liquid in the glass tubing at the start of experiment.
a. Observation:
10. Wait 30 minutes and make another observation of the liquid in the glass tubing.
a. Observation:
11. Wash liquids down the sink. Throw away dialysis tubing. Clean and dry the beaker, the glass rod, and
the glass tubing with soap and water.
3
Part D: Red Onion in Different Solutions
1. Make a wet mount of a piece of red onion. No wrinkles, no bubbles.
2. Examine the onion under medium and high power. Pick the one which gives you the clearest view.
Draw.
Which power are you observing and drawing:
3. Stay under the power you picked in #2. Place 1 drop of NaCl solution at the end of the cover slip.
Continue adding one drop every 30 seconds, until you see a change.
Draw.
Explain your observation:
4. Place a piece of paper towel at the edge of the cover slip and soak up (and get rid of) the salt water.
5. Place one drop of plain water at the edge of the cover slip and continue every 30 seconds until you see a
change. Draw.
Explain your observation:
4
DISCUSSION:
Part A: Egg Experiment
1. What effect did the vinegar have on the egg?
2. What kind material(s) moved through the egg membrane?
3. What is the tonicity of the syrup solution? Explain.
_______
______________________________________________________________________________
4. What is the tonicity of the water solution? Explain.
_______
______________________________________________________________________________
5. Explain, in detail, what happened to each egg and why.
a. Water Egg:
b. Syrup Egg:
6. This experiment was an example of what type of passive transport?
Part B: Diffusion through a Selectively Permeable Membrane
1. What was the solution you put in the dialysis bag?
2. Why was it necessary to wash the dialysis bag with water before putting it in the beaker?
3. The test strip tests for the presence of:
a. What type of carbohydrate is this?
b. Was the test positive or negative?
Explain:
4. Explain, in detail, what happened in order to give you this result.
5. Iodine tests for the presence of:
a. What type of carbohydrate is this?
5
6. Compare the color of the water in the beaker and the inside of the dialysis bag.
7. Which of those two liquids shows a positive test?
Explain:
8. Explain, in detail, what happened in order to give you this result. Make sure to include the difference
between the beaker and bag and why they are different.
9. How did the type of carbohydrate affect this experiment?
Part C: Osmosis
1. What happened to the size of the dialysis bag?
2. Why?
3. What happened inside the glass tubing?
______
4. What force caused the change in the glass tubing?
5. What force will eventually stop the change in the glass tubing?
Part D: Red Onion in Different Solutions
1. What process occurred in the red onion cells when NaCl solution was added?
2. What evidence do you have that this occurred?
_____________
______________________________________________________________________________
3. What process occurred in the red onion cells when the water was added?
4. What evidence do you have that this occurred?
_____________
______________________________________________________________________________
6
CONCLUSION:
Explain what you learned during this lab.
______
______
______
______
______
______
7