BIO 152 - final exam ACTUAL UPDATED
Exam Questions and CORRECT Answers
Voltage pg 257 - CORRECT ANSWER - If you have two compartments with KCl one has
high concentration and the other low (blue is K+ gold is Cl-)
The membrane is selectively permeable to one of the ions (K+)
The K+ will diffuse through the membrane (down its gradient high to low concentration and take
its positive charge with it, developing a negative membrane on the other side)
This does not make the cell negative it is just a small charge
A voltage is a measure of the electrical potential energy between two points
Because cells have differentially permeable membranes and have different concentrations of ions
in and out they create a membrane potential.
The electrical potential is a voltage
Charge separation pg 257 - CORRECT ANSWER - Because both ions have a charge, as
the potassium leaves you will get a "charge separation" the left will become more negative (with
respect to the right).
This charge has an attractive force on the K+.
Very few ions are moving - there is no major flow of ions
Electrical potential pg 257 - CORRECT ANSWER - So now you have a concentration
gradient in which the K+ "wants" to go to the right and a charge that makes the K+ "want" to go
left.
They can be balanced charge vs. concentration.
This is an electrical potential (same thing as voltage)
This charge separation is the membrane potential it can be harnessed to do work.
It can also be measured in millivolts
Chemical gradient making it go out )high to low) and electrical gradient making it move back in
(low to high)
,Nerst potential: - CORRECT ANSWER - electrical potential for one ion and balances the
chemical potential for that ion
Q: If the membrane were selectively permeable to Cl- instead of K+ what can you say about the
charge separation?
A. There's no gradient for Cl- so no potential would develop
B. There would be a charge separation with positive charge on the right
C. There would be a charge separation with positive on the left
D. There would be a charge separation with negative on the left - CORRECT ANSWER -
C
Q: Again blue is K+ and gold is Cl- What would happen if this membrane were permeable to
both ions?
A. A membrane potential would develop but it wouldn't have charge
B. No membrane potential would develop because both ions would equilibrate.
C. The Cl- ions would go one way and the K+ ions would go the other because they don't like
each other
D. The membrane potential would oscillate - CORRECT ANSWER -B
Concentration gradient - CORRECT ANSWER - A particular concentration gradient can
be held in place by a particular voltage:
Voltage = concentration gradient (some constants)
Note: we are going to look at how one ion contributes to the membrane potential. But the
potential comes from all ions in solution
Nernst - CORRECT ANSWER - You can calculate the Nernst potential for a single ion
across a membrane using the Nernst Equation. With cells it's usually negative inside.
E is the voltage, R=universal gas, T is temp, z is charge and F is faraday's constant
This version of the equation works with a univalent cation (+ ION) at body temperature and
standard pressure.
62mV(log Co/Ci)
,If anion add a negative: - CORRECT ANSWER - -62mV(log Co/Ci)
What would you predict would be the Nernst Potential in a cell in which there's 100 mM K+
inside and 5 mM K+ outside (ignore other ions for now)?
A. -81
B. 81
C. -1.3
D. 1.3 - CORRECT ANSWER -A
(will be negative bc potassium will diffuse out leaving the neg charge behind)
Q: A cell with a potassium permeable membrane is 100 mM K in and 5 mM K out. If I raise the
external K+ to 20 mM, what should happen to the Nernst potential?
A. It would become more positive.
B. It would become more negative.
C. There would be no change. - CORRECT ANSWER -A
(less potential energy in the gradient)
For a positive ion as your outside concentration increases with respect to your inside
concentration, the Nernst potential becomes more - CORRECT ANSWER - positive
Q: If my inside concentration is 100 mM, what does my outside concentration need to be to get a
Nernst potential of 0 mV?
A. 200
B. 100
C. 50 - CORRECT ANSWER -B
Q: A cell with a potassium permeable membrane is 100 mM K + in and 5 mM K + out will have
a Nernst Potential of -81 mV. A different cell with a SODIUM permeable membrane is 5 mM
Na+ in and 100 mM Na+ out. What will its Nernst potential be?
, A. The same as K+ because they are the same charge
B. More negative that -80 mV
C. More positive that -80 mV, but still negative
D. 0
E. 81 mV - CORRECT ANSWER -E
Q; A normal mammalian neuron has a extracellular K+ concentration of 5 mM and intracellular
of 140 mM. For Na+ those values are 15 mM in and 120 mM out. What is the sodium Nernst
potential? )
A. 62 mV
B. -56 mV
C. 56 mV
D. -62 mV - CORRECT ANSWER -C
In most mammalian cells these are the Nernst potentials for sodium and potassium (draw pg 262)
- CORRECT ANSWER -
The total membrane potential arises from - CORRECT ANSWER - the gradients of all
ions
However, the _____ of the given ion tells you how important it is - CORRECT
ANSWER - permeability
Important membrane potential/Nerst potential concepts - CORRECT ANSWER -
Permeability comes from protein channels in the plasma membrane. More channels=more
permeability
Alterations in concentration only matter with regards to permeability (assuming osmotic balance)
membrane potential is close to the nerst potential for potassium
The resting membrane potential is close to, but not the same as the ___. This is due to
Exam Questions and CORRECT Answers
Voltage pg 257 - CORRECT ANSWER - If you have two compartments with KCl one has
high concentration and the other low (blue is K+ gold is Cl-)
The membrane is selectively permeable to one of the ions (K+)
The K+ will diffuse through the membrane (down its gradient high to low concentration and take
its positive charge with it, developing a negative membrane on the other side)
This does not make the cell negative it is just a small charge
A voltage is a measure of the electrical potential energy between two points
Because cells have differentially permeable membranes and have different concentrations of ions
in and out they create a membrane potential.
The electrical potential is a voltage
Charge separation pg 257 - CORRECT ANSWER - Because both ions have a charge, as
the potassium leaves you will get a "charge separation" the left will become more negative (with
respect to the right).
This charge has an attractive force on the K+.
Very few ions are moving - there is no major flow of ions
Electrical potential pg 257 - CORRECT ANSWER - So now you have a concentration
gradient in which the K+ "wants" to go to the right and a charge that makes the K+ "want" to go
left.
They can be balanced charge vs. concentration.
This is an electrical potential (same thing as voltage)
This charge separation is the membrane potential it can be harnessed to do work.
It can also be measured in millivolts
Chemical gradient making it go out )high to low) and electrical gradient making it move back in
(low to high)
,Nerst potential: - CORRECT ANSWER - electrical potential for one ion and balances the
chemical potential for that ion
Q: If the membrane were selectively permeable to Cl- instead of K+ what can you say about the
charge separation?
A. There's no gradient for Cl- so no potential would develop
B. There would be a charge separation with positive charge on the right
C. There would be a charge separation with positive on the left
D. There would be a charge separation with negative on the left - CORRECT ANSWER -
C
Q: Again blue is K+ and gold is Cl- What would happen if this membrane were permeable to
both ions?
A. A membrane potential would develop but it wouldn't have charge
B. No membrane potential would develop because both ions would equilibrate.
C. The Cl- ions would go one way and the K+ ions would go the other because they don't like
each other
D. The membrane potential would oscillate - CORRECT ANSWER -B
Concentration gradient - CORRECT ANSWER - A particular concentration gradient can
be held in place by a particular voltage:
Voltage = concentration gradient (some constants)
Note: we are going to look at how one ion contributes to the membrane potential. But the
potential comes from all ions in solution
Nernst - CORRECT ANSWER - You can calculate the Nernst potential for a single ion
across a membrane using the Nernst Equation. With cells it's usually negative inside.
E is the voltage, R=universal gas, T is temp, z is charge and F is faraday's constant
This version of the equation works with a univalent cation (+ ION) at body temperature and
standard pressure.
62mV(log Co/Ci)
,If anion add a negative: - CORRECT ANSWER - -62mV(log Co/Ci)
What would you predict would be the Nernst Potential in a cell in which there's 100 mM K+
inside and 5 mM K+ outside (ignore other ions for now)?
A. -81
B. 81
C. -1.3
D. 1.3 - CORRECT ANSWER -A
(will be negative bc potassium will diffuse out leaving the neg charge behind)
Q: A cell with a potassium permeable membrane is 100 mM K in and 5 mM K out. If I raise the
external K+ to 20 mM, what should happen to the Nernst potential?
A. It would become more positive.
B. It would become more negative.
C. There would be no change. - CORRECT ANSWER -A
(less potential energy in the gradient)
For a positive ion as your outside concentration increases with respect to your inside
concentration, the Nernst potential becomes more - CORRECT ANSWER - positive
Q: If my inside concentration is 100 mM, what does my outside concentration need to be to get a
Nernst potential of 0 mV?
A. 200
B. 100
C. 50 - CORRECT ANSWER -B
Q: A cell with a potassium permeable membrane is 100 mM K + in and 5 mM K + out will have
a Nernst Potential of -81 mV. A different cell with a SODIUM permeable membrane is 5 mM
Na+ in and 100 mM Na+ out. What will its Nernst potential be?
, A. The same as K+ because they are the same charge
B. More negative that -80 mV
C. More positive that -80 mV, but still negative
D. 0
E. 81 mV - CORRECT ANSWER -E
Q; A normal mammalian neuron has a extracellular K+ concentration of 5 mM and intracellular
of 140 mM. For Na+ those values are 15 mM in and 120 mM out. What is the sodium Nernst
potential? )
A. 62 mV
B. -56 mV
C. 56 mV
D. -62 mV - CORRECT ANSWER -C
In most mammalian cells these are the Nernst potentials for sodium and potassium (draw pg 262)
- CORRECT ANSWER -
The total membrane potential arises from - CORRECT ANSWER - the gradients of all
ions
However, the _____ of the given ion tells you how important it is - CORRECT
ANSWER - permeability
Important membrane potential/Nerst potential concepts - CORRECT ANSWER -
Permeability comes from protein channels in the plasma membrane. More channels=more
permeability
Alterations in concentration only matter with regards to permeability (assuming osmotic balance)
membrane potential is close to the nerst potential for potassium
The resting membrane potential is close to, but not the same as the ___. This is due to
