BIOL 2160 Exam 2 Crousillac Test
Questions and All Correct Answers
2025-2026 Updated.
In the semi-permeable plasma membrane, how do nonpolar molecules get across it? - Answer
Passive transport (they freely diffuse)
In the semi-permeable plasma membrane, how do polar molecules get across it? - Answer
Active transport (they need carrier proteins)
In the semi-permeable plasma membrane, the heads of the phospholipid bilayer are ___, and
the tails are ___. - Answer hydrophilic (polar); hydrophobic (nonpolar)
The membrane potential describes the charge where? - Answer Inside the cell, as compared
to the outside
What is the membrane potential always approaching? - Answer The equilibrium potential (a
number) of the MOST permeable ion
What does "membrane potential is negative" mean? - Answer The intracellular fluid is
slightly more negative, and the extracellular fluid is slightly more positive
What is the equilibrium potential? - Answer the membrane potential in which the electrical
driving force is equal and opposite to the chemical driving force, making the electrochemical
driving force zero
The equilibrium potential can also called described as the number it takes to ___ - Answer
change the electrochemical gradient
NA+'s equilibrium potential is - Answer +55 mV
K+'s equilibrium potential is - Answer -94 mV
Passive transport (does or does not?) require energy, moves from an area of ___ concentration
to an area of ____ concentration, and is energetically ___. - Answer Does not; high to low;
downhill
,Active transport (does or does not) require energy, moves from an area of ___ concentration to
an area of ___ concentration, and is energetically. - Answer Does; low to high; uphill
Driving force is the difference in ___ - Answer energy across a membrane (does it push from
higher to lower or lower to higher?)
The direction of net flux is passive transport is - Answer DOWN its electrochemical gradient
In passive transport, what is the carriers' preference, and which way is the carrier most likely to
transport molecules in the absence of an electrochemical gradient? - Answer No preference,
so equally likely to transport molecules in either direction in the absence of an electrochemical
gradient.
More solute= - Answer more energy
Carrier proteins in passive transport have what kind of affinity for molecules? - Answer Equal
affinities for molecules on either side of the membrane
Transport proteins in active transport have what kind of affinity for molecules? - Answer
Have greater affinity for one molecule when the binding site is open to its side than for the
other molecule when the binding site is closed to its side
Difference in diffusion through ion channels and facilitated diffusion is? - Answer An empty
channel's binding sites are accessible from both sides of the membrane at the same time. A
carrier's site is only accessible from one site at one time.
What are the 3 mechanisms are passive transport? - Answer Simple diffusion, facilitated
diffusion, and diffusion through ion channels.
Simple diffusion's special entry way?
Disclaimer:
Don't judge me for saying "special entryway"...that is Crousillac's exact quoted terminology. -
Answer Does not require a special entryway
Why does simple diffusion occur? - Answer Because of random thermal motion
, How do molecules move across the membrane in simple diffusion? What is the net movement?
- Answer Freely; down the electrochemical gradient
What is the rate of simple diffusion determined by? - Answer Driving force, membrane
surface area, and membrane permeability
What affect will a warmer temperature have on the molecules' rate of diffusion? - Answer
The hotter it is, the more energy there is, therefore the more movement there is, so faster rate
of diffusion.
What is the special entryway in facilitated diffusion? - Answer Molecules bind to specific
carrier proteins in the membrane
What is the net movement of molecules in facilitated diffusion? - Answer Down the
electrochemical gradient
What do the molecules do to the carrier proteins when they bind to them during facilitated
diffusion? - Answer Change the shape of the carrier protein when it binds to it
What is the (:special entryway:) in diffusion through ion channels - Answer Molecules flow
through pores in specific protein channels in the membrane
Another way to think of chemical gradient is - Answer Concentration gradient
Why do ions naturally try to flow from high to low concentrations? - Answer Because of their
chemical (concentration) gradient
Why do Na+ and K+ ions not cross the membrane easily, therefore requiring an ion channel to
pass through? - Answer Because they have a charge
ps it's positive
ps good luck on the test
What happens as a result of K+ and Na+ ions not being able to use simple diffusion? - Answer
The ion concentrations never even out
What is the net flow of molecules in diffusion through ion channels? - Answer Down the
electrochemical gradient
Questions and All Correct Answers
2025-2026 Updated.
In the semi-permeable plasma membrane, how do nonpolar molecules get across it? - Answer
Passive transport (they freely diffuse)
In the semi-permeable plasma membrane, how do polar molecules get across it? - Answer
Active transport (they need carrier proteins)
In the semi-permeable plasma membrane, the heads of the phospholipid bilayer are ___, and
the tails are ___. - Answer hydrophilic (polar); hydrophobic (nonpolar)
The membrane potential describes the charge where? - Answer Inside the cell, as compared
to the outside
What is the membrane potential always approaching? - Answer The equilibrium potential (a
number) of the MOST permeable ion
What does "membrane potential is negative" mean? - Answer The intracellular fluid is
slightly more negative, and the extracellular fluid is slightly more positive
What is the equilibrium potential? - Answer the membrane potential in which the electrical
driving force is equal and opposite to the chemical driving force, making the electrochemical
driving force zero
The equilibrium potential can also called described as the number it takes to ___ - Answer
change the electrochemical gradient
NA+'s equilibrium potential is - Answer +55 mV
K+'s equilibrium potential is - Answer -94 mV
Passive transport (does or does not?) require energy, moves from an area of ___ concentration
to an area of ____ concentration, and is energetically ___. - Answer Does not; high to low;
downhill
,Active transport (does or does not) require energy, moves from an area of ___ concentration to
an area of ___ concentration, and is energetically. - Answer Does; low to high; uphill
Driving force is the difference in ___ - Answer energy across a membrane (does it push from
higher to lower or lower to higher?)
The direction of net flux is passive transport is - Answer DOWN its electrochemical gradient
In passive transport, what is the carriers' preference, and which way is the carrier most likely to
transport molecules in the absence of an electrochemical gradient? - Answer No preference,
so equally likely to transport molecules in either direction in the absence of an electrochemical
gradient.
More solute= - Answer more energy
Carrier proteins in passive transport have what kind of affinity for molecules? - Answer Equal
affinities for molecules on either side of the membrane
Transport proteins in active transport have what kind of affinity for molecules? - Answer
Have greater affinity for one molecule when the binding site is open to its side than for the
other molecule when the binding site is closed to its side
Difference in diffusion through ion channels and facilitated diffusion is? - Answer An empty
channel's binding sites are accessible from both sides of the membrane at the same time. A
carrier's site is only accessible from one site at one time.
What are the 3 mechanisms are passive transport? - Answer Simple diffusion, facilitated
diffusion, and diffusion through ion channels.
Simple diffusion's special entry way?
Disclaimer:
Don't judge me for saying "special entryway"...that is Crousillac's exact quoted terminology. -
Answer Does not require a special entryway
Why does simple diffusion occur? - Answer Because of random thermal motion
, How do molecules move across the membrane in simple diffusion? What is the net movement?
- Answer Freely; down the electrochemical gradient
What is the rate of simple diffusion determined by? - Answer Driving force, membrane
surface area, and membrane permeability
What affect will a warmer temperature have on the molecules' rate of diffusion? - Answer
The hotter it is, the more energy there is, therefore the more movement there is, so faster rate
of diffusion.
What is the special entryway in facilitated diffusion? - Answer Molecules bind to specific
carrier proteins in the membrane
What is the net movement of molecules in facilitated diffusion? - Answer Down the
electrochemical gradient
What do the molecules do to the carrier proteins when they bind to them during facilitated
diffusion? - Answer Change the shape of the carrier protein when it binds to it
What is the (:special entryway:) in diffusion through ion channels - Answer Molecules flow
through pores in specific protein channels in the membrane
Another way to think of chemical gradient is - Answer Concentration gradient
Why do ions naturally try to flow from high to low concentrations? - Answer Because of their
chemical (concentration) gradient
Why do Na+ and K+ ions not cross the membrane easily, therefore requiring an ion channel to
pass through? - Answer Because they have a charge
ps it's positive
ps good luck on the test
What happens as a result of K+ and Na+ ions not being able to use simple diffusion? - Answer
The ion concentrations never even out
What is the net flow of molecules in diffusion through ion channels? - Answer Down the
electrochemical gradient
