PSL 431 Exam 1 Questions with
Complete Solutions
Define ICF and ECF. Draw a cell and indicate where each is found. - ANSWER-The
ICF is the Interstitial Cellular Fluid that has a high concentration in K+ and low
concentration in Na+ and Cl-. The ECF is the extracellular fluid that has a low
concentration in K+ and a slightly higher concentration in Cl-, and a high
concentration in Na+.
Compare the concentrations of Cl-, K+ and Na+ in the ICF and ECF - ANSWER-The
ICF is the Interstitial Cellular Fluid that has a high concentration in K+ and low
concentration in Na+ and Cl-. The ECF is the extracellular fluid that has a low
concentration in K+ and a slightly higher concentration in Cl-, and a high
concentration in Na
List the three types of proteins that can be associated with the plasma membrane. -
ANSWER--Transmembrane protein: anchored within membrane and pass through it,
have access inside and outside of the cell
-Integral protein: Inserted in the membrane, can either pass through or are anchored
so they only have access to one side of the cell
-Peripheral protein: hydrophilic regions that associate with the outer or inner polar
surface of the membrane, not anchored in it
Explain how the chemical structure of membrane-associated proteins determines if
they can be inserted into or pass through the plasma membrane. - ANSWER-The
chemical structure of membrane-associated proteins determines this because the
phospholipid bilayer of the plasma membrane contains a hydrophobic core with polar
heads; the proteins must be compatible with these polarities or else they will repel.
Give examples of solutes that move across the plasma membrane via Passive
Diffusion (e.g. need no protein helpers to move). Use what you know about the
composition of the plasma membrane to explain why they can be transported in this
way. - ANSWER-2 solutes that move across the plasma membrane via passive
diffusion are O2 and Glycerol, they can move because they are small, hydrophobic
and uncharged polar solutes which make them more lipid soluble and able to pass
through the plasma membrane's hydrophobic core and polar heads.
Give examples of solutes that move across the plasma membrane via Facilitated
Diffusion. Use what you know about the composition of the plasma membrane to
explain why these solutes cannot passively diffuse across the membrane. -
ANSWER-Glucose and Cl- are two solutes that move across the membrane via
facilitated diffusion because they are larger, and highly charged molecules which
make them less lipid soluble and unable to diffuse past the polar heads of the
plasma membrane and the hydrophobic core.
,Identify the types of solutes that move across the membrane according to Fick's
Law. - ANSWER-The types of solutes that move across the membrane according to
Fick's Law is are hydrophobic, uncharged polar solutes (with an exemption of water).
List the factors that impact transport of solutes across the plasma membrane via
Fick's Law. Predict how changing each factor will change the rate of transport. -
ANSWER--Concentration Gradient: more high to low concentration gradient
increases rate of diffusion
-Surface Area of Plasma Membrane: More surface area=quicker diffusion
-Lipid Solubility of a Substance: Easier to pass through lipid bilayer of plasma
membrane, increases rate of diffusion
-Molecular weight of substance: The smaller the molecule, the quicker it can diffuse
-Distance of diffusion: Less distance=faster diffusion rate
Discuss why the fact that "water follows non-permeable solute" impacts the volume
and shape of a cell. - ANSWER-When water follows a non-permeable solute, the
hydrostatic pressure increases, so the cell will changes shape and disperse, since it
is flexible, to help alleviate the high pressures
Define osmolarity and tonicity and identify how they differ from each other. Calculate
the osmolarity and the tonicity of a given solution, paying attention to which solutes
can dissociate in aqueous solution. - ANSWER-Osmolarity is the total concentration
of all solute particles free in a solution, while tonicity is the effect a solution has on
cell volume due to nonpermeable solutes. Osmolarity focuses on all solute particles
while tonicity focuses on nonpermeable solutes only.
Identify what types of solutes contribute to the tonicity of a solution. Give examples. -
ANSWER-Nonpermeable solutes such as NaCl, Na+, K+, Glucose, etc.
Indicate how a Hypo-osmotic and Hyperosmotic solution compare to normal
osmolarity of body fluids. - ANSWER-A hypo-osmotic solution is anything less than
300 mOsm/L, while a hyperosmotic solution is anything greater than 300 mOsm/L
Indicate how a Hypotonic and Hypertonic solution compare to normal osmolarity of
body fluids. Diagram which way each solution would cause water to move across the
plasma membrane and how it would affect cell size. - ANSWER-A hypo-osmotic
solution means there is a lower concentration of non-permeable solutes which
causes the cells to swell. A hyperosmotic solution means there is a higher
concentration of non-permeable solutes which causes cells to shrink.
Describe how Facilitated Diffusion and Active Transport differ in regards to transport
of solutes across the plasma membrane. Give examples of proteins that mediate
each type of transport. - ANSWER-Facilitated diffusion uses channel proteins that
allow solutes such as ion to go in and out of the cell and are driven by an
electrochemical gradient. Active transport uses carrier proteins that can transport
ions and other solutes, they are slower and driven via concentration gradient; they
are never closed.
• Compare and contrast Leak, Ligand-Gated and Voltage-Gated Channels in terms
of their structure and gating. - ANSWER-Leak channels are always open and allow
, for constant ion flux as long as there is a concentration gradient. Ligand-gated
channels are opened and closed by ligand binding, while voltage-gated channels
open and close by membrane voltage of a cell.
Compare and contrast channels vs. carrier proteins in terms of the solutes they
transport, rate of transport, open/closed state and limits of transport. - ANSWER-
Channels can provide fast transport and is usually selective for a specific type of
ion/charge, the transport can be in or out of the cell depending on concentration
gradient and whether the channel is open. Carrier proteins can transport both ions
and solutes and is slower than channels, the carriers are never closed and open to
at least one side of the membrane, they have specific binding and competitive
binding due to the limited number of proteins and binding sites available in the
membrane.
Explain why transport via a carrier protein is saturable. Predict how you could
increase transport via a carrier protein transport system. - ANSWER-Transport via a
carrier protein is saturable because there is a limited amount of carrier proteins,
therefore a limited amount of binding sites in a cell membrane. You could increase
transport via a carrier protein transport system by increasing the surface area of the
plasma membrane to provide more binding sites and area for more carrier proteins.
Compare and contrast Uniporters, Symporters and Antiporters in terms of the
number of solutes transported and their directions. (Drawing them might help for
your explanation.) - ANSWER-Uniporters transport 1 molecule in 1 direction.
Symporters transport 2 or more molecules in the same direction, while antiporters
transport 2 or more molecules in opposite directions.
Describe how large proteins are transported across the plasma membrane. -
ANSWER-Large proteins are transported across the plasma membrane via
membrane-mediated transport. This includes endocytosis (in) or exocytosis (out). A
piece of the plasma membrane surrounds the protein and pinches off (forms a
vesicle).
Describe the relative distribution of charged solutes inside and outside the cell, and
how this determines the cell's membrane potential. - ANSWER-There is a relative
negative charge inside the cell compared to the outside of the cell. The cell's
membrane potential is the difference between either side of the membrane.
List the two forces that govern movement of an ion across the plasma membrane.
Explain why both of these forces specifically act on ions. (Hint: how are ions different
than other solutes?) - ANSWER-The two forces that govern movement of an ion
across the plasma membrane are concentration force and electrical force. Ions want
to travel down their concentration gradient and electrical force: opposite charges
attract, like charges repel.
Describe the ICF and ECF concentration of Na+ and K+ for a cell if it were at
equilibrium vs. steady state. Identify the protein that keeps cells at steady state and
describe how it works. - ANSWER-The ICF has a relatively high concentration of K+
and low concentration of Na+, the ECF has a low concentration of K+ and high
Complete Solutions
Define ICF and ECF. Draw a cell and indicate where each is found. - ANSWER-The
ICF is the Interstitial Cellular Fluid that has a high concentration in K+ and low
concentration in Na+ and Cl-. The ECF is the extracellular fluid that has a low
concentration in K+ and a slightly higher concentration in Cl-, and a high
concentration in Na+.
Compare the concentrations of Cl-, K+ and Na+ in the ICF and ECF - ANSWER-The
ICF is the Interstitial Cellular Fluid that has a high concentration in K+ and low
concentration in Na+ and Cl-. The ECF is the extracellular fluid that has a low
concentration in K+ and a slightly higher concentration in Cl-, and a high
concentration in Na
List the three types of proteins that can be associated with the plasma membrane. -
ANSWER--Transmembrane protein: anchored within membrane and pass through it,
have access inside and outside of the cell
-Integral protein: Inserted in the membrane, can either pass through or are anchored
so they only have access to one side of the cell
-Peripheral protein: hydrophilic regions that associate with the outer or inner polar
surface of the membrane, not anchored in it
Explain how the chemical structure of membrane-associated proteins determines if
they can be inserted into or pass through the plasma membrane. - ANSWER-The
chemical structure of membrane-associated proteins determines this because the
phospholipid bilayer of the plasma membrane contains a hydrophobic core with polar
heads; the proteins must be compatible with these polarities or else they will repel.
Give examples of solutes that move across the plasma membrane via Passive
Diffusion (e.g. need no protein helpers to move). Use what you know about the
composition of the plasma membrane to explain why they can be transported in this
way. - ANSWER-2 solutes that move across the plasma membrane via passive
diffusion are O2 and Glycerol, they can move because they are small, hydrophobic
and uncharged polar solutes which make them more lipid soluble and able to pass
through the plasma membrane's hydrophobic core and polar heads.
Give examples of solutes that move across the plasma membrane via Facilitated
Diffusion. Use what you know about the composition of the plasma membrane to
explain why these solutes cannot passively diffuse across the membrane. -
ANSWER-Glucose and Cl- are two solutes that move across the membrane via
facilitated diffusion because they are larger, and highly charged molecules which
make them less lipid soluble and unable to diffuse past the polar heads of the
plasma membrane and the hydrophobic core.
,Identify the types of solutes that move across the membrane according to Fick's
Law. - ANSWER-The types of solutes that move across the membrane according to
Fick's Law is are hydrophobic, uncharged polar solutes (with an exemption of water).
List the factors that impact transport of solutes across the plasma membrane via
Fick's Law. Predict how changing each factor will change the rate of transport. -
ANSWER--Concentration Gradient: more high to low concentration gradient
increases rate of diffusion
-Surface Area of Plasma Membrane: More surface area=quicker diffusion
-Lipid Solubility of a Substance: Easier to pass through lipid bilayer of plasma
membrane, increases rate of diffusion
-Molecular weight of substance: The smaller the molecule, the quicker it can diffuse
-Distance of diffusion: Less distance=faster diffusion rate
Discuss why the fact that "water follows non-permeable solute" impacts the volume
and shape of a cell. - ANSWER-When water follows a non-permeable solute, the
hydrostatic pressure increases, so the cell will changes shape and disperse, since it
is flexible, to help alleviate the high pressures
Define osmolarity and tonicity and identify how they differ from each other. Calculate
the osmolarity and the tonicity of a given solution, paying attention to which solutes
can dissociate in aqueous solution. - ANSWER-Osmolarity is the total concentration
of all solute particles free in a solution, while tonicity is the effect a solution has on
cell volume due to nonpermeable solutes. Osmolarity focuses on all solute particles
while tonicity focuses on nonpermeable solutes only.
Identify what types of solutes contribute to the tonicity of a solution. Give examples. -
ANSWER-Nonpermeable solutes such as NaCl, Na+, K+, Glucose, etc.
Indicate how a Hypo-osmotic and Hyperosmotic solution compare to normal
osmolarity of body fluids. - ANSWER-A hypo-osmotic solution is anything less than
300 mOsm/L, while a hyperosmotic solution is anything greater than 300 mOsm/L
Indicate how a Hypotonic and Hypertonic solution compare to normal osmolarity of
body fluids. Diagram which way each solution would cause water to move across the
plasma membrane and how it would affect cell size. - ANSWER-A hypo-osmotic
solution means there is a lower concentration of non-permeable solutes which
causes the cells to swell. A hyperosmotic solution means there is a higher
concentration of non-permeable solutes which causes cells to shrink.
Describe how Facilitated Diffusion and Active Transport differ in regards to transport
of solutes across the plasma membrane. Give examples of proteins that mediate
each type of transport. - ANSWER-Facilitated diffusion uses channel proteins that
allow solutes such as ion to go in and out of the cell and are driven by an
electrochemical gradient. Active transport uses carrier proteins that can transport
ions and other solutes, they are slower and driven via concentration gradient; they
are never closed.
• Compare and contrast Leak, Ligand-Gated and Voltage-Gated Channels in terms
of their structure and gating. - ANSWER-Leak channels are always open and allow
, for constant ion flux as long as there is a concentration gradient. Ligand-gated
channels are opened and closed by ligand binding, while voltage-gated channels
open and close by membrane voltage of a cell.
Compare and contrast channels vs. carrier proteins in terms of the solutes they
transport, rate of transport, open/closed state and limits of transport. - ANSWER-
Channels can provide fast transport and is usually selective for a specific type of
ion/charge, the transport can be in or out of the cell depending on concentration
gradient and whether the channel is open. Carrier proteins can transport both ions
and solutes and is slower than channels, the carriers are never closed and open to
at least one side of the membrane, they have specific binding and competitive
binding due to the limited number of proteins and binding sites available in the
membrane.
Explain why transport via a carrier protein is saturable. Predict how you could
increase transport via a carrier protein transport system. - ANSWER-Transport via a
carrier protein is saturable because there is a limited amount of carrier proteins,
therefore a limited amount of binding sites in a cell membrane. You could increase
transport via a carrier protein transport system by increasing the surface area of the
plasma membrane to provide more binding sites and area for more carrier proteins.
Compare and contrast Uniporters, Symporters and Antiporters in terms of the
number of solutes transported and their directions. (Drawing them might help for
your explanation.) - ANSWER-Uniporters transport 1 molecule in 1 direction.
Symporters transport 2 or more molecules in the same direction, while antiporters
transport 2 or more molecules in opposite directions.
Describe how large proteins are transported across the plasma membrane. -
ANSWER-Large proteins are transported across the plasma membrane via
membrane-mediated transport. This includes endocytosis (in) or exocytosis (out). A
piece of the plasma membrane surrounds the protein and pinches off (forms a
vesicle).
Describe the relative distribution of charged solutes inside and outside the cell, and
how this determines the cell's membrane potential. - ANSWER-There is a relative
negative charge inside the cell compared to the outside of the cell. The cell's
membrane potential is the difference between either side of the membrane.
List the two forces that govern movement of an ion across the plasma membrane.
Explain why both of these forces specifically act on ions. (Hint: how are ions different
than other solutes?) - ANSWER-The two forces that govern movement of an ion
across the plasma membrane are concentration force and electrical force. Ions want
to travel down their concentration gradient and electrical force: opposite charges
attract, like charges repel.
Describe the ICF and ECF concentration of Na+ and K+ for a cell if it were at
equilibrium vs. steady state. Identify the protein that keeps cells at steady state and
describe how it works. - ANSWER-The ICF has a relatively high concentration of K+
and low concentration of Na+, the ECF has a low concentration of K+ and high
