membrane permeability

Membrane Permeability 012-10971 r1.04

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IntroductionJournals and Snapshots

Membrane Permeability

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Lab ChallengesWhat types of substances are able to pass through a semi-permeable membrane?


Background• The contents of a cell are separated from the outside environment by a

membrane.

• The cell membrane, also called plasma membrane, consists mostly of phospholipids and proteins. Phospholipids have 2 distinct regions: a hydrophilic head and a hydrophobic tail. They form a bilayer by arranging themselves tail to tail, so only their hydrophilic heads are exposed to the aqueous environment inside and outside the cell.


Self Check

1. Phospholipids arrange themselves in a bilayer because they have ____________________.

a) hydrophobic tails and hydrophilic heads

b) hydrophilic tails and hydrophobic tails

c) opposite charges

d) bipolar DNA


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Self Check

...Background• In some cases, the cell membrane acts as a passive barrier and substances can

move in and out of the cell based on concentration gradient. Water, carbon dioxide, oxygen, cholesterol and other small polar molecules are able to diffuse passively across the membrane.

• In other cases the membrane can be very selective about what is able to enter and leave. Substances that cannot diffuse through the membrane must pass through a protein channel. Some protein channels act as an open gateway that specific substances can pass through. Other protein channels require energy input and act as pumps to move substances against the concentration gradient.


Self Check

2. Substances that cannot diffuse directly through the phospholipid bilayer but go through a(n) ____________.

a) ion gate

b) water pore

c) carbohydrate chain

d) protein channel


Self Check

Safety• Use all standard laboratory safety procedures.

• Wear safety glasses and lab coats or aprons.

• Dispose of chemicals and solutions as instructed.


Materials and EquipmentCollect all of these materials before beginning the lab.

• pH sensor• Beaker, 250 mL• Large Base and Support Rod• Utility clamp (2)• Lugol's Iodine• 0.1 M Hydrochloric Acid• 0.1 M Sodium Hydroxide

• Starch Solution• Dialysis Tubing, 15cm length (2)• Magnetic stirrer and stir bar• Wash Bottle• Distilled Water• Binder clip• String


The steps to the left are part of the procedure for this lab activity. They are not in the right order. Determine the correct sequence of the steps, then take a snapshot of this page.

Sequencing Challenge

A. Record data and then determine the change in pH for each data run.

B. Lower the dialysis tubing into the water.

C. Prepare the dialysis bags.

D. Add distilled water to the beaker and turn on the magnetic stirrer.


Setup: Dialysis Bags (HCl and Starch)

1. Tie one end of one piece of dialysis tubing with string to create a bag. Rub the tubing between your fingers to open the top of the bag.

2. Pour 15 mL of 0.1 M HCl (hydrochloric acid), and 5 mL of the starch solution into the bag.

Note: Wash your hands. The oils on your skin can clog the pores of the tubing.

Caution: HCl is corrosive and can ruin clothing, and cause skin and eye irritation. Notify your teacher of any skin/eye contact.

3. Fold over the open end of the bag and use a binder clip, or string, to secure it shut.


Setup: Dialysis Bags (NaOH)4. Tie one end of a second piece of dialysis tubing with string to create a bag.

Rub the tubing between your fingers to open the top of the bag.

5. Pour 15 mL of 0.1 M NaOH (sodium hydroxide). Caution: NaOH is corrosive and can ruin clothing, and cause skin and eye irritation. Notify your teacher of any skin/eye contact.

6. Fold over the open end of the bag and use a binder clip, or string, to secure it shut.

7. Rinse both bags under a gentle stream of water and place aside on a labeled paper towel.


Setup: Hydrogen Ions1. Connect a pH sensor to the SPARK Science Learning

System.

2. Place a spin bar into a 250 mL beaker and place the beaker on the magnetic stirrer.

3. Use a base, support rod and clamp to position the pH probe low in the beaker, but not touching the stir bar.

4. Use a second clamp to suspend the dialysis bag containing the HCL and starch above the beaker.

5. Add 100mL of water and 25 drops of Lugol's iodine to the beaker. Adjust the pH probe so it is in the water.


Q1: What will happen to the pH in the beaker when the HCl bag is lowered into it? Draw your prediction on the graph provided*.

*To Draw a Prediction: 1. Tap to open the tool

palette.2. Tap then use your finger

to draw your prediction.3. Tap when finished.4. If you make a mistake, tap

to clear your prediction.


Q4: Will the iodine molecules move into the bag? How will you know if they do?

Q3: Will the starch molecules move out of the bag? How will you know if they do?

Q2: Will the hydrogen ions move out of the bag? How will you know if they do?


Collect Data: HCl1. Turn on the magnetic

stirrer.2. Tap to start collecting

data.3. Wait 60 seconds and

lower the dialysis bag into the water.

4. After 300 seconds, tap to stop data collection.


5. Enter any color change observations in the data table.*

*To Enter Data into a Table: 6. Tap to open the tool

palette.7. Tap then tap a cell in

the data table to highlight it in yellow.

8. Tap to open the Keyboard screen.


Setup: Hydroxide Ions1. Dispose of the HCl bag and clean out the 250 mL

beaker.

2. Place a spin bar into the beaker and place the beaker on the magnetic stirrer.

3. Use a base, support rod and a clamp to position the pH probe low inside the beaker, but not touching the stir bar.

4. Use a second clamp to suspend the dialysis bag containing the NaOH above the beaker.

5. Adjust the pH probe so it is in the water.


Q5: What will happen to the pH in the beaker when the NaOH bag is lowered into it? Draw your prediction in the graph*.

*To Draw a Prediction: 1. Tap to open the tool

palette.2. Tap then use your

finger to draw your prediction.

3. Tap when finished.4. If you make a mistake,

tap to clear your prediction.


Collect Data: NaOH1. Turn on the magnetic

stirrer.2. Tap to start collecting

data.3. Wait 60 seconds and lower

the dialysis bag into the water.

4. After 300 seconds, tap to stop data collection.


Data AnalysisMembrane Permeability

1. Determine initial pH, final pH and the change in pH for each run.*

Note: Enter these values on the next page.

* To Find the X- and Y-Values of a Data Point:

2. Tap to open the tools palette.

3. Tap and then tap a data point.

4. Tap or to select nearby data points.

Data Analysis2. Record initial pH, final

pH, and the change in pH for each run in the table.

*To Enter Data into a Table: 3. Tap to open the tool

palette.4. Tap then tap a cell in

the data table to highlight it in yellow.

5. Tap to open the Keyboard screen.


Analysis1. Describe what happened to the pH in the beaker during the soaking of the HCl

bag. What does this indicate about the permeability of H+ ions to the membrane?


2. Describe what happened to the pH in the beaker during the soaking of the NaOH bag. What does this indicate about the permeability of OH- ions to the membrane?


Analysis

3. Describe what happened between the starch and iodine. Was iodine abe to move into the bag? Was starch able to move out of the bag? Explain your answer and support it with data.


Analysis

4. This lab is demonstrating diffusion and semi-permeable membranes. Define these concepts.


Analysis

Synthesis1. How could the diffusion rate be increased?


2. How could you use a series of molecules to determine the size of the pores in the membrane?


Synthesis

3. How does this membrane model differ from a real cell membrane? What structures are present in a real cell membrane that regulate what can enter and exit the cell?


Synthesis

4. Does this model illustrate active or passive transport? Explain your answer.


Synthesis

Multiple Choice1. Despite differences in cell types, all cells have a

_________________.

a) cell wall

b) cell membrane

c) golgi apparatus

d) endoplasmic reticulum


Multiple Choice2. The membrane of a cell will allow water, oxygen,

carbon dioxide, and glucose to pass through. However, other substances are blocked from entering. This type of membrane is called:

a) semi-permeableb) perforatedc) permeabled) non-permeable


Multiple Choice3. Cell membranes are constructed mostly of

a) protein channels.b) carbohydrate channels.c) lipid bilayers.d) hydrophobic regions


= starch = glucose

Multiple Choice4. Look at the diagram to the right and choose the

correct statement.

The membrane is permeable to glucose, but not permeable to starch

a) Glucose will move from right to left.b) Starch will move from right to left.c) Salt will move from right to leftd) No molecules will move in any direction.


You have completed the lab.Congratulations!

Please remember to follow your teacher's instructions for cleaning-up and submitting your lab.


Images are taken from PASCO documentation, public domain clip art, or Wikimedia Foundation Commons.

http://commons.wikimedia.org/wiki/Image:Semipermeable_membrane.pnghttp://www.freeclipartnow.com/office/paper-shredder.jpg.htmlhttp://commons.wikimedia.org/wiki/File:Bilayer_scheme.svghttp://commons.wikimedia.org/wiki/File:Cell_membrane_detailed_diagram_3.svg

ReferencesMembrane Permeability

membrane permeability

Documents

plasma membrane

membrane permeability012

lab page

cell membrane acts

semipermeable membrane

page ofthis lab

lab coats

cover page