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– ## Pre-LabDiffusionWicoff.docx
**## Pre-LabDiffusionWicoff.docx**
BIO 257 Module 3 Membrane Channels Pre-Lab Wicoff Name: _________________
Page1
Pre-Lab assignment for ___________________________ (add date here)
**Diffusion Pre-Lab**
**Learning Goals:** Students will be able to:
· Predict when particles will move through the membrane and when they will not.
· Identify which particle type will diffuse depending on which types of channels are present.
· Predict the rate of diffusion based on the number and type of channels present.
· Use evidence to defend their ideas.
In this pre-lab, you will drag the channels onto the membrane and then investigate what happens.
The concentration graphs will give you qualitative, relative information to help you understand diffusion.
1. What is the difference between qualitative and quantitative information?
2. What do you think of when you hear the word “diffusion”?
**Important modeling notes / simplifications:**
In a real cell, leakage channels are always open, whereas gated channels only open in response to some stimulus. Some gated channels respond to the presence of a certain substance (ligand gated), some respond to a change in membrane potential brought about by changes in ion concentrations (voltage gated), some respond to changes to tension in the cell membrane (mechanically gated), and some respond to light (light gated).
In real cells, channels do not actively move things through them; they only allow things to diffuse through them. This is true in the simulation too, though in some cases it may appear that an ion is being pulled across a channel. Make sure that you understand that the motion through the channels is passive – a result of diffusion – and that membrane channels do not ‘pump’ anything across the membrane.
Pre-Lab assignment for __June 6_________________________ (add date here)
**Diffusion Pre-Lab**
**Go to the PHET website for this simulation:**
[**https://phet.colorado.edu/sims/cheerpj/membrane-channels/latest/membrane-channels.html?simulation=membrane-channels**](https://phet.colorado.edu/sims/cheerpj/membrane-channels/latest/membrane-channels.html?simulation=membrane-channels)
1.
**Add 50 green particles (this does not need to be exact so don’t worry if you are out by 1 or 2).**
2.
**Slow the animation down and describe the motion of the green particles.** Is it random are pre-determined? What happens when the particles hit each other?
3. What does the membrane do?
4. What do you think a membrane is?
_Google membrane definition if you are unsure._
5.
**Click on the show concentrations box.**
6. How would you describe the concentration of the green particles on the top half of the membrane? (High or Low)
7. How would you describe the concentration of green particles below the membrane? (High or Low)
8.
**Add 3 evenly spaced gated channels to the membrane. Speed up the animation again and then click the Open Channels button.**
9. The process you are observing is the process of diffusion.
_Describe the process_ using the key words
**particle, movement, concentration, high and low**.
10.
**Closely observe the motion of the particles again** and
_describe why diffusion_ takes place.
11.
**Click on the reset all button and set up the green particles again. This time do the same thing with the blue particles.**
12. Speed up the animation to full speed. Open both gates and observe the concentrations. Wait for at least 1 minute.
_What happens to the concentration lines_ on both sides of the membrane?
**This is called**
**_the equilibrium point_. The concentrations will change somewhat on either side of the membrane but they will stay relatively equal.**
13.
**Watch this video on diffusion.** [http://www.youtube.com/watch?v=H7QsDs8ZRMI](http://www.youtube.com/watch?v=H7QsDs8ZRMI) (4:56)
14. Why do particles diffuse faster in a vacuum?
15. Why do nitrogen oxide particles travel faster than bromine particles?
16. How does temperature affect the rate of diffusion? Why do you think this is so? (It has to do with the speed of the particles.)
**Go back to the animation and press reset. Fill the top half with the maximum particles. Place 3 gated channels into the membrane. Set the animation speed to full speed then go to** [**http://www.online-stopwatch.com/**](http://www.online-stopwatch.com/) **and start the stop watch and open the channels at the same time. Time how long it takes to reach the equilibrium point.**
Reset the animation and do the same thing with 50 particles.
17. Which one was faster? How does concentration affect the rate of diffusion?
18. How do you think the thickness of the membrane would affect the rate of diffusion? Why?
19. How do you think the surface are of the membrane would affect the rate of diffusion? Why?
| | |
| — | — |
| PHET Membrane channels Pre-Lab | Wicoff |
**## Pre-LabDiffusionWicoff.docx**
BIO 257 Module 3 Membrane Channels Pre-Lab Wicoff Name: _________________
Page1
Pre-Lab assignment for ___________________________ (add date here)
**Diffusion Pre-Lab**
**Learning Goals:** Students will be able to:
· Predict when particles will move through the membrane and when they will not.
· Identify which particle type will diffuse depending on which types of channels are present.
· Predict the rate of diffusion based on the number and type of channels present.
· Use evidence to defend their ideas.
In this pre-lab, you will drag the channels onto the membrane and then investigate what happens.
The concentration graphs will give you qualitative, relative information to help you understand diffusion.
1. What is the difference between qualitative and quantitative information?
2. What do you think of when you hear the word “diffusion”?
**Important modeling notes / simplifications:**
In a real cell, leakage channels are always open, whereas gated channels only open in response to some stimulus. Some gated channels respond to the presence of a certain substance (ligand gated), some respond to a change in membrane potential brought about by changes in ion concentrations (voltage gated), some respond to changes to tension in the cell membrane (mechanically gated), and some respond to light (light gated).
In real cells, channels do not actively move things through them; they only allow things to diffuse through them. This is true in the simulation too, though in some cases it may appear that an ion is being pulled across a channel. Make sure that you understand that the motion through the channels is passive – a result of diffusion – and that membrane channels do not ‘pump’ anything across the membrane.
Pre-Lab assignment for __June 6_________________________ (add date here)
**Diffusion Pre-Lab**
**Go to the PHET website for this simulation:**
[**https://phet.colorado.edu/sims/cheerpj/membrane-channels/latest/membrane-channels.html?simulation=membrane-channels**](https://phet.colorado.edu/sims/cheerpj/membrane-channels/latest/membrane-channels.html?simulation=membrane-channels)
1.
**Add 50 green particles (this does not need to be exact so don’t worry if you are out by 1 or 2).**
2.
**Slow the animation down and describe the motion of the green particles.** Is it random are pre-determined? What happens when the particles hit each other?
3. What does the membrane do?
4. What do you think a membrane is?
_Google membrane definition if you are unsure._
5.
**Click on the show concentrations box.**
6. How would you describe the concentration of the green particles on the top half of the membrane? (High or Low)
7. How would you describe the concentration of green particles below the membrane? (High or Low)
8.
**Add 3 evenly spaced gated channels to the membrane. Speed up the animation again and then click the Open Channels button.**
9. The process you are observing is the process of diffusion.
_Describe the process_ using the key words
**particle, movement, concentration, high and low**.
10.
**Closely observe the motion of the particles again** and
_describe why diffusion_ takes place.
11.
**Click on the reset all button and set up the green particles again. This time do the same thing with the blue particles.**
12. Speed up the animation to full speed. Open both gates and observe the concentrations. Wait for at least 1 minute.
_What happens to the concentration lines_ on both sides of the membrane?
**This is called**
**_the equilibrium point_. The concentrations will change somewhat on either side of the membrane but they will stay relatively equal.**
13.
**Watch this video on diffusion.** [http://www.youtube.com/watch?v=H7QsDs8ZRMI](http://www.youtube.com/watch?v=H7QsDs8ZRMI) (4:56)
14. Why do particles diffuse faster in a vacuum?
15. Why do nitrogen oxide particles travel faster than bromine particles?
16. How does temperature affect the rate of diffusion? Why do you think this is so? (It has to do with the speed of the particles.)
**Go back to the animation and press reset. Fill the top half with the maximum particles. Place 3 gated channels into the membrane. Set the animation speed to full speed then go to** [**http://www.online-stopwatch.com/**](http://www.online-stopwatch.com/) **and start the stop watch and open the channels at the same time. Time how long it takes to reach the equilibrium point.**
Reset the animation and do the same thing with 50 particles.
17. Which one was faster? How does concentration affect the rate of diffusion?
18. How do you think the thickness of the membrane would affect the rate of diffusion? Why?
19. How do you think the surface are of the membrane would affect the rate of diffusion? Why?
| | |
| — | — |
| PHET Membrane channels Pre-Lab | Wicoff |