Cell Transport Demo (Dialysis Tubing/Passive Transport) & (Egg Cells/Osmosis)
34 classwork points
Name:
Date:
Do you think all substances pass in and out of a cell membrane with equal ease?
What would cause some substances to move in and out easily and prevent others from moving at
all? What makes substances move from one area to another? In this activity, you will examine these
questions by using a model for a cell membrane. In this laboratory exercise you will use dialysis
tubing as a model for a cell membrane. You will determine if starch and iodine molecules can pass
through the cell membrane. You will decide if the cell membrane is permeable, impermeable, or
semipermeable.
Dialysis Tubing: Passive Transport (diffusion & osmosis)
Pre-Lab Questions
1.
2.
3.
4.
5.
What color is the starch solution? _______________
What color is iodine? _________________
What color will iodine turn in the presence of starch? ____________
What is the mass of the bag in the beginning? ______________ g
Draw the before set-up (label everything with a name and a color)
Before Drawing: (2pts)
6. How long did we let the dialysis tubing sit in the beaker? _________
7. Draw everything again now that it has had an opportunity to react.
After Drawing: (2pts)
8. What color is the starch inside the dialysis tubing bag? _________
9. What color is the water and iodine in the beaker? ____________
10. Where did we put iodine when we started this lab? ___________
11. Did the iodine move through the process of diffusion? ________? How do you
know?
___________________________________________________________________________________
_________________________________________________
12. You put starch in the bag in the beginning, was starch able to move out of the
bag? _________ How do you know?
________________________________________________________________________________
______________________________________________________
13. What is the mass of the bag in the end? ______________ g
14. Was water able to move through the process of osmosis? ________ How do you
know?
________________________________________________________________________________
______________________________________________________
15. What word should we use to describe the type of membrane the dialysis tubing
is? ______________________
16. Why are we correct to use the word that we did in number 15?
________________________________________________________________________________
______________________________________________________
Egg Cells: Osmosis (Isotonic, Hypertonic, Hypotonic)
The purpose of this lab is to demonstrate what happens when an animal cell is exposed to varying
osmotic conditions.
Questions:
What happens when a cell is subjected to a solution where the water concentration is higher
than that inside a cell (hypotonic solution)?
What happens when a cell is subjected to a solution where the water concentration is lower
than that inside a cell (hypertonic solution)?
What happens when a cell is subjected to a solution where the water concentration is equal
to that inside a cell (isotonic solution)?
The cell is like a salty sea that is mostly water. The cell membrane in an animal cell is both a
protective barrier and a filter to keep unwanted materials out and bring needed materials inside.
Water can move freely through the cell membrane with osmosis. So can small molecules such as
sodium and calcium ions. Large molecules like polysaccharides and proteins need assistance in
moving through the cell membrane. In this experiment, you will be looking at the movement of
water via osmosis by using an egg as a model for the cell. Eggs are approximately 90% water, corn
syrup is made up of approximately 25% water.
Your teacher has soaked the eggs in vinegar. This dissolves the hard shell and leaves a soft outer
covering that acts like the cell membrane of a cell – it is a semi-permeable membrane.
1. Complete the data table as the teacher shows you the cells. (2pts)
Soaking Solution
Mass start
(grams)
Mass end
(grams) after 24
hours
Difference in Mass
(end-start)
Subtract
% Change in
Mass*
Water
Vinegar
Corn Syrup
* Calculate % Change in Weight = Difference in Weight x 100
NEGATIVE)
Weight start
(CAN BE POSITIVE OR
Analysis Questions (2 points each):
1. Which of the solutions was hypertonic to the egg? ________________________
What is your evidence?
2. Which of the solutions was hypotonic to the egg? ________________________
What is your evidence?
3. Which of the solutions was isotonic to the egg? ________________________
What is your evidence?
4. Which “cell” gained mass? ________________________
Explain why this happened (use water/solute concentration in your explanation).
5. Which “cell” lost mass? ________________________
Explain why this happened (use water/solute concentration in your explanation).
6. Which “cell” stayed at about the same mass? ________________________
Explain why this happened (use water/solute concentration in your explanation).
7. The membrane around your egg acted as a semipermeable membrane – explain why using
the corn syrup “cell” as an example (hint: corn syrup ingredients include large
polysaccharides & water).