Name Standard 2.1 Lab
Passive Transport Lab:
How can you determine whether solutes are diffusing across a membrane?
Introduction
A cell membrane is a ___________ _____________ barrier, which means that some particles can pass through the cell membrane while other particles are held back. When solutes move across the membrane without energy it is a form of passive transport called _____________. When solutes diffuse, they move from an area of __________concentration to an area of _________concentration.
Diffusion can occur faster if solutes can move through an open protein channels. This is called
_______________diffusion.
In this lab, you will make a cell using dialysis tubing to represent the cell membrane. Dialysis tubing is a synthetic (man-made) membrane used in kidney dialysis. Dialysis is the process of filtering wastes from the blood of a person who has experienced kidney failure. The smallest blood vessels called
______________ in the kidneys filter nitrogen and other waste from your blood then make__________ to be excreted from your body. The dialysis tubing acts like the small tubules in the kidney collecting waste out of sick patients. The tubing has small openings or pores that act like the ___________ channels to allow the passage molecules.
Your synthetic cell will contain a starch solution. Remember starch is a polymer of carbohydrates called a ____________________. When starch is present it turns iodine from brown to blue/black. You will use iodine to determine which molecules diffuse through the pores.
Synthetic Cell
First predict what will happen to the starch and to the iodine: Which solutes will move across the membrane? (here are some pictures to help!)
Starch: polymer
Iodine & Water molecule
Write your Hypothesis: If a cell containing starch is placed into an iodine solution…
_________________________________________________________________________________

Materials
• dialysis tubing
• scissors
• metric ruler
• 250-mL beakers
• string
•10-mL graduated cylinders
Safety
• 1% starch solution
• iodine solution
• forceps
Iodine solution can irritate the eyes and skin and can stain clothing. WEAR
GOGGLES! Rinse off any solution that spills on your skin or clothing. Do not direct the points of the scissors toward yourself or others. Use the scissors only as instructed.
Pre-Lab Questions
1. How will you know whether starch has diffused across the membrane?
2. How will you know whether iodine has diffused across the membrane?
3. How is a window screen similar to a cell membrane?
Procedure
In Part A , you will determine whether the dialysis membrane is permeable to starch or to iodine.
1.
Put on your goggles. Obtain a 10cm length of dialysis tubing.
2.
Add 200 mL of water to a 250-mL beaker.
3.
Soak the tubing in the water for one minute.
4.
Remove the tubing from the water. Twist 3 cm of the tubing at one end. Use a string to tightly tie off this end.
5.
Roll the unsealed end of the tubing between your fingers until it opens.
6.
Pour 6 ml of starch solution into the tubing with a graduated cylinder.
7.
Twist 3 cm of the tubing at the other end. Use a string to tightly tie off this end.
Honors: use a triple beam balance to determine the mass of your cell.
8.
Use tap water to thoroughly rinse the outside of the tubing!!!!
9.
Place the “cell” in the beaker. The tubing must be completely covered with water.
10. Add 2 drops of iodine solution to the water in the beaker.
-Record your initial observations in Data Table 1.
-Wait 10 minutes, and then record your final observations.
Honors only: remove your “cell” and determine the mass after experiment.
11. Remove and dispose of the tubing as instructed by your teacher.

Data Table 1
Color
Inside Tubing
Is starch present?
Is iodine present?
Color
Outside Tubing
Is starch present?
Is iodine present?
Initial
Final
All levels: You will be writing a LAB REPORT for this lab. It is important to complete the lab report and pass it in ON TIME.
All Levels: Use Rubric on next page:
Honors only Extension:
Mass of cell before passive transport
Mass of cell after passive transport
Conclude on the date from the table above. Describe what happened to the cell’s mass with specific numbers. Then further describe the cell process(es) that occurred in order for the mass to change.

Salem High School Rubric for Lab Reports
Introduction
(First Paragraph)
Std: SIS1
 In a written paragraph the student introduces all important concepts, key terms and background information.
 Identifies the purpose of the lab
 Concludes the paragraph with a clear and concise hypothesis statement.
8/8/4=20
Std: SIS2
Experimental
Procedure
(Second Paragraph)
 Provides a written paragraph of the exact procedure step by step.
 Provides a neat, labeled visual of set-up under the written directions.
 Clearly distinguishes control & variable portions of the experiment in the written and visual portions.
 Identifies all materials and equipment used. (in the paragraph/ on the visual/or list separately)
Results
(Graph)
5 pts each= 20
 Graphs data with the x and y axis clearly labeled Std: SIS3
 Includes a title above the graph or table
 Includes a key with any calculations, formulas (if needed)
 Includes one statement briefly explaining what the graph presents
(underneath graph) (This is not where you discuss results save that for conclusion)
Example: This graph shows the rate of X in ABC solution.
5 pts each=20

Conclusion:
(Third Paragraph)
Std: SIS4
 Clearly defines whether or not the results of the lab support or refute the hypothesis. Data/numbers from the lab must be used!
DO the math for the reader and explain!
 Discusses possible sources of error and ways to improve the lab in future
 Demonstrates clear understanding of how the information is relevant . Uses Key
Terms from class and connects back to introductory purpose and global issues.
8/4/8 pts each=20
Analyze and Conclude
1. In Part A, why did the iodine enter the tube? Why didn’t the starch enter the beaker?
2. Use what you know about the structure of starch molecules to explain your results.
3. What substance other than iodine moved across the membrane in Part A? In which direction did this substance move, and why?
4. Describe a function of a cell membrane that cannot be modeled with dialysis tubing.
5. When Alyssa did Part A of the experiment, she observed the solution outside the tubing turn black. What error might have happened?