Cell Membrane Transport

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Which of the following best describes the potassium equilibrium potential?

-94 mV

Which of the following can be used to determine an ion's equilibrium potential?

Nernst equations

A cotransporter uses an ions concentration gradient to move a second ion or molecule in the same directions the first.

True

Which of the following correctly describes cotransport of Y with sodium ?

Y and sodium both move into the cell

Which of the following does NOT directly determine the rate at which an ion will move passively across a membrane?

amount of ATP available

The potassium equilibrium potential is -94 mV. what does this means?

at -94 mV, the chemical force for potassium movement is opposed exactly by the electrical force

Which of the following transport mechanisms requires energy?

both primary and secondary active transport

The chemical force for which of the following ions is directed into the cell?

both sodium and calcium

Molecules with a relatively high lipid solubility are capable of crossing the membrane______

directly across the lipid bilayer

The osmotic pressure of a solution is an

indirect measure of its solute concentration

In active transport, the affinity of the carrier protein for the molecule being transported is greater in which side of the membrane?

on the side where the molecule is in lower concentration

When more then one ion species is present on both sides of the membrane, the chemical driving force acting on Na+ will include

sodium only

Sodium-linked glucose transport, where both Na+ and glucose are moving in the same direction, is an example of

support

Sodium permeability refers to a property of

the cell membrane

Which of the following statements about the Na+/K+ pump is FALSE?

the pumps activity is regulated through allosteric modulation

Which of the following is NOT true for all three of the following transport mechanisms: facilitated diffusion, primary active transport, and secondary active transport?

the transport mechanisms requires energy

The first step of the Na+/K+ pump's activity involves the binding of which of the following?

3 Na+ to their binding site on the inside of the cell

Primary active transporters are unique in their ability to couple the movement of ions directly to what?

ATP hydrolysis

Which of the following statements about the Ca+ pump is FALSE?

Calcium is actively transported from an organelle into the cytosol

Ions move passively down their electrochemical gradient

True

Osmosis occurs through aquaporins

True

Which of the following cells would have a greater electrical attraction for sodium ions to enter the cell?

cell with membrane potential= -90mV

Which of the following would NOT increase the rate of simple diffusion across the phospholipid bilayer of the plasma membrane?

greater number of protein carriers

Which of the following is NOT a determinant of the magnitude and direction of the equilibrium potential for an ion?

lipid solubility of the ion

Which of the following is a reflection of the unequal distribution of positive and negative ions across the plasma membrane?

membrane potential

Which of the following transport mechanisms is passive?

movement of sodium through ion channels

Comparing intracellular to extracellular fluid, the intracellular fluid has a _____ charge relative to the outside of a cell due to the presence of more ______ in that solution.

negative: anions

The flow of water across a membrane down its concentration gradient is called

osmosi

If a positively charged ion is more concentrated outside the cell, the forces required to balance the chemical gradient would be directed _______. Thus the equilibrium potential for this ion would be ______ charged.

outward: positively

In general, the molecules that move through specific carrier proteins are determined by which of the following?

the unique binding sites on the channel or carrier protein

If there is a difference in osmolarity between a cell and its environment, water will move ______ its osmotic pressure gradient.

up

What are aquaporins?

water channels

When solute is actively transported across epithelium, what usually follows?

water movement in the same direction

How will increases in the concentration difference of an uncharged molecule across a membrane affect the rate of diffusion between two compartments?

Diffusion rate will increase

Aquaporins are primary active transporters of water

False

At the resting membrane potential, a cell is at equilibrium

False

If the direction of the net flux of an ion is against its electrochemical gradient, then that transport is passive.

False

If the membrane potential is equal to the equilibrium potential for an ion, individual ions will not move across membrane in either direction.

False

In the presence of two or more ions, it is the sum of their concentration that determines the direction of movement of those ions across a membrane.

False

Ions can always move through the ion channels present in the plasma membrane as long as there is an electrochemical gradient to drive the movement

False

Large differences in water concentration are required to drive water across a membrane.

False

Phagosomes are formed following receptor- mediated endocytosis

False

Pumps can move ions in either direction, as long as it is against that ions electrochemical gradient

False

The movement of a molecule is determined by its energy state, with that molecule moving from a lower to a higher energy state.

False

When a substance crossing the membrane is driven by diffusion, the net flux of that molecule can be describes mathematically by_____-

Ficks law

Which of the following statements about glucose cotransport with sodium is true?

Glucose and sodium both move into the cell

The movement of a number of molecules across the apical surface of the epithelial cell by secondary transporters is coupled to the ______- gradient that is maintained by the _____ on the basolateral surface of the epithelial cell

Na+: Na+/K+ pump

Which of the following statements about primary active transport is FALSE?

The Ca2+ pump always moves calcium into the extracellular fluid

An anion has an equilibrium potential of -40mV. What direction are the chemical and electrical forces acting on the anion at the rating membrane potential (-70mV)?

The chemical force is directed into the cell and the electrical force is directed out of the cell

In secondary active transport with sodium, which of the following is FALSE?

The molecule being transported moves down its electrochemical gradient

At resting membrane potential, leakage of sodium ions into the cell and potassium ions out of the cell is balanced by the action of the Na+/K+ pump.

True

In facilitated diffusion, the carrier protein has equal affinity for the molecule being transported on both sides of the membrane

True

Most of the time, the body is neutral with respect to its electrical charge due to the equal distribution of anions and cations within the body.

True

Oxygen is able to move across the cell membrane based upon its thermal energy

True

Primary active transporters are similar to carriers, with the exception that they are able to use energy to move ions against their electrochemical gradient

True

The driving force for simple diffusion is the electrochemical gradient.

True

The movement of water across a membrane is always a passive process

True

The rate at which molecules are actively transported across a membrane is determined by the rate of transport of individual pumps and the number of pumps in the membrane.

True

The hydrolysis of ATP on the Na+/K+ pump results in

a conformational change that exposes the Na+ binding site to the outside of the cell

In facilitated diffusion

a molecule is moved down its concentration gradient with the assistance of a protein carrier molecule, and no energy is required

The equilibrium potential describes the membrane potential where what two forces are balanced?

chemical and electrical

A carrier is a transmembrane protein that moves molecules across the membrane through

conformational changes in the carrier proteins

Most water molecules that cross the plasma membrane do so by

diffusion through aquaporins

Molecules tend to move spontaneously _______ their chemical gradient

down

Of the gradients listed below, which is the most accurate description of the force that ultimately determines the movement of ions across the membrane ?

electrochemical gradient

In addition to functioning as a transporter, primary active transporters also function as ________ in order to make use of energy

enzymes

One way that membrane surface area is increased is absorptive cells in through increasing the ________ of the apical membrane

folding

When molecules are passively transported across a membrane, the direction of their movement is dictated by the molecules tendency to move

from higher to lower energy

The concentration of sodium is greater in the extracellular fluid compared to the intracellular fluid. If the membrane potential was equal to the equilibrium potential for sodium, then what would be the direction of the electrochemical force acting on sodium?

no force

If a negatively charged ion is more concentrated outside the cell, the forces required to balance the chemical gradient would be directed ______. Thus, the equilibrium potential for this ion would be ______ charged.

outward: negatively

The extent of ion movement through the _____ space between epithelial cells is determined by the extent of _____ coupling between neighboring epithelial cells

paracellular: tight junctional

Movement of water through aquaporins occurs by what process?

passive transport

Which of the following is found in greater concentration inside the cell than outside?

potassium

Which of the following will NOT increase the net flux of an ion across a membrane?

reduced surface area

What transport process couples the movement of an ions against its electrochemical gradient to another ion that is moving down its electrochemical gradient that was established using cellular energy (ATP)?

secondary active transport

The unequal distribution of charge in solutions on either side of a membrane will lead to a ______ of charge across the membrane and a ______ of counter ions in a region close to the membrane.

separation: clustering

Which of the following is NOT required to determine equilibrium potential of a particular ion?

size of the ion

Which of the following pairs of characteristics is more likely to make a substance diffuse through the cell membrane ?

small, non polar molecule

Oxygen diffuses from blood into cells down its concentration gradient. As cells become more active and oxidative phosphorylation increases in the cell, which of the following occurs?

the concentration gradient for oxygen increases and oxygen movement into the cell increases.

Na+ is released from its binding site on the Na+/K+ pump as a result of

the conformational change decreasing the affinity of the Na+ binding site

During cotransport of glucose with sodium , sodium increases the affinity of the carrier molecule for glucose when the binding site is facing which side?

the extracellular fluid

What is the main difference between primary and secondary active transport?

the form of energy (ATP vs. electrochemical gradient) used to move molecules across the membrane

Which of the following factors does NOT directly affect the direction or magnitude of the electrical driving force?

the molecular weight of an ion


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