Download Supplemental File S3. Acting Transport-Think-pair

Lights, Camera, Acting Transport!
Think-Pair-Share Prompts
ANSWER KEY
LIGHTS, CAMERA, ACTING TRANSPORT!
The following Think-Pair-Share prompts are designed to help students think about the concepts covered in
each act of the Lights, Camera, Acting Transport! activity. Helpful references are Sections 7.1-7.3 in the
Campbell textbook or Sections 5.1-5.4 in Raven.
ACT I
Suggested T-P-S Prompt 1
What is your molecular “ID”? For members of the “public,” think about size, polarity, and charge. Should
you be allowed to enter at the main entrance? If not, what might you need to cross the membrane? For
membrane components, think about what substances you will allow to cross and why.
Varies according to role.
ACT II
Suggested T-P-S Prompt 2
What is a membrane potential and what is its purpose?
“Membrane potential” refers to the electrical potential energy (i.e., voltage) stored across a biological
membrane when positive and negative charges are separated. It results from an unequal distribution of
ions on either side of the membrane. Its purpose is to store electrical potential energy that can be used by
the cell to do work.
How will you distribute the Na+ and K+ ions to mimic a real membrane potential?
There should be a higher concentration of Na+ outside than inside, a higher concentration of K+ inside
than outside, and an overall net positive charge outside of the cell.
Is the inside of the cell positive, neutral, or negative in relation to the outside?
Negative.
Is the concentration of Na+ inside of the cell higher than, equal to, or lower than outside of the cell?
Lower.
Is the concentration of K+ inside of the cell higher than, equal to, or lower than outside of the cell?
Higher.
Suggested T-P-S Prompt 3
If you are an ion, consider whether you are “inclined” to cross the membrane under current conditions.
Why or why not?
If allowed, Na+ would flow into the cell down its electrochemical gradient. The possible movement of K + is
less straightforward as the concentration gradient of K+ would make it likely that K+ would flow out of the
cell, but the electrical component of this electrochemical gradient might make movement inward more
likely. This is a good opportunity to reiterate that the movement of ions is a result of both of these forces.
Based on the new cast members, what might you require to move?
Varies according to role. Na+ ions could move down an electrochemical gradient with a Na+ channel; K+
ions could move down an electrochemical gradient with a K+ channel; and both could be moved with a
Na+/K+ pump.
If you are one of the new cast members, consider who you are and what you do. Where should you be
located? How might you interact with the other members of the cast?
Varies according to role. The ions should be distributed according to the stage instructions on the board.
The Na+/K+ pump and ion channels would belong in the membrane; and ATP would belong inside of the
cell.
ACT III
Suggested T-P-S Prompt 4
Is co-transport active or passive?
Active.
What force drives the movement of molecules in co-transport?
The membrane potential.
Using the template on the board as a starting point, sketch the opening positions of all cast members.
Lights, Camera, Acting Transport!
Think-Pair-Share Prompts
ANSWER KEY
The cotransporter should be in the membrane. There may be some variability in students’ exact
distributions of Na+ and glucose, but there should be more glucose inside of the cell and more Na + outside
of the cell.
Suggested T-P-S Prompt 5
What role will your character play?
Varies according to role.
How will electrochemical and concentration gradients influence your actions and the movement of other
characters?
Varies according to role. The cotransporter will not be affected directly, but will allow movement of Na +
and glucose into the cell as long as the membrane potential for Na+ exists. Na+ outside of the cell would
move down its electrochemical gradient to enter the cell, if there is a membrane protein that will allow this
(e.g., the cotransporter). Glucose would flow out of the cell if allowed to move down its electrochemical
gradient.
Who gets to move and why?
As long as the electrochemical gradient exists for Na+, Na+ and glucose can enter the cell together through
the cotransporter. Glucose “gets” to move against its electrochemical gradient because this work is being
powered by the membrane potential and Na+ moving with its gradient.
How do you think a Na+/glucose cotransporter might work?
This is a thought question so answers will vary. This cotransporter is a symporter that moves one glucose
molecule into the cell against its gradient for every two Na + ions that move into the cell along their
gradient.