Chapter 5-Membrane Dynamics
What is similar between facilitated diffusion and primary/secondary active transport? In both forms of transport ______________.
a membrane transport protein is involved
Match the transport process to its description. A. Active transport B. Passive transport Tends to create an equilibrium state
passive transport
Complete the calculation in step 3 and drag the appropriate solute amounts to the ECF and ICF columns.
ECF- 1085 mosmol ICF- 814 mosmol
Match the words in the left column to the appropriate blanks in the sentences on the right. Make certain each sentence is complete before submitting your answer.
*Membrane potential of -70 mV: the resting membrane potential of the cell *K+ permeability: the primary determinant of the resting membrane potential *Membrane potential of -90 mV: the point at which there is no net movement of K+ into or out of the cell *Na+ permeability: although it plays a role, it is not a primary determinant of the resting membrane potential
As with Part H, you have a total body concentration of 300 mOsM and body volume of 3 liters. You now add 2 liters of a 500 mOsM solution. The solution is equal parts NaCl (nonpenetrating) and urea (penetrating), so it has 250 mosmol/L NaCl and 250 mosmol/L urea. Answer the following questions about your new solution.
*The solution is hyper-osmotic to the body *what is the concentration of nonpenetrating solutes (NP) in the solution? 250 mosmol *what is the (NP) in the body? 300 mosmol *when the cells reach equilibrium after addition of the solution to the body, has cell volume increased, decreased, or stayed the same? Increased *based on your answer regarding water movement, the solution was hypo-tonic to the body's cells
What is the value for the resting membrane potential for most neurons?
-70 mV
Which answer choice has a higher so molarity than the other listed?
3 moles of substance V/L with a dissociation factor of 2.0
You have a total body concentration of 300 mOsM and total body volume of 3 liters. If you add 0.5 L of a solution containing 150 mosmol of NaCl to the body, what would the new total body concentration be?
300 mOsm
Osmolarity is a way of expressing solute concentration taking into account whether or not the solute in question dissociates into ions when dissolved in water. For example, suppose a hypothetical salt, AB, completely dissociates into A+ and B+ in water. One mole of AB in water would be one molar (1 M), but it would be 2 osmolarity (2 OsM) solution, because there would be 1 mole of each ion dissolved in that solution. Thus, osmolarity is the measure of the number of solutes per volume of solution. Some salts, like NaCl, will incompletely dissociate into their respective ions when dissolved in water. Using the same principles, one mole of NaCl dissolved in a liter of water would become a 1 molar (1 M) NaCl solution, but would also be a 1.8 osmolarity (1.8 OsM) solution. In the human body, we express the concentration in milliosmoles per liter (mOsM). Presuming that the salts listed below completely dissociate in water, which of the following solutions below has the highest osmolarity?
7 mM sodium chloride (NaCl)
Which type of molecular movement requires an input of energy (for example, from ATP)?
Active transport
Which of the following statements about vesicular transport processes into or out of the cell is (are) true?
All answers are correct -if a cell is to remain the same size, the rate of exocytosis must equal the rate of endocytosis -receptor-mediated endocytosis is triggered by the binding of a ligand to the receptor -proteins or lipids that have undergone endocytosis can be recycled back to the plasma membrane by exocytosis
Transport processes that can be saturated include __________________.
All answers are correct -primary active transport -secondary active transport -facilitated diffusion -movement of ions through some channels
The rate of diffusion, or flux, of particles across a membrane is dependent on ___________________.
All answers are correct -the membrane permeability -the surface area of the membrane -the steepness of the concentration gradient across the membrane
Which of the following will always be true of primary and secondary active transport?
At least one substance will move against its concentration gradient.
You have three separate beakers, each containing the following osmolarities. A. 10 OsM B. 13 OsM C. 7 OsM How would you describe the osmolarity of beaker A relative to beaker B?
Beaker A is hyposmotic to beaker B
Using the same beakers as Part E, how would you describe the osmolarity of beaker B relative to beaker C?
Beaker B is hyperosmotic to beaker C
Although osmolarity tells you the concentration of solute particles in solution, osmolarity cannot always tell you the direction of water movement across a membrane. To predict if water will move across a cell membrane, you need to know whether the solutes in the solution can cross that membrane. Solutes that can cross a cell membrane are said to be penetrating solutes, whereas solutes that cannot cross a cell membrane are said to nonpenetrating.
Cell does not change size- 3 mOsmol, Isotonic Cell swells- 0 mOsmol, hypotonic Cell shrinks- 10 mOsmol, hypertonic
What is the most important distinction between the membrane transporters known as channel proteins and those known as carrier proteins?
Channel proteins create water-filled passages for small molecules that do not bind to the protein. Carrier proteins transport larger molecules by binding to them.
As the solute concentration of a solution increases, __________.
the water concentration decreases and the osmotic pressure increases
In the digestive system, Vitamin B12 bound to intrinsic factor (B12-IF) is absorbed through the epithelium of the small intestine and delivered into the extracellular fluid on the basolateral membrane of the epithelium by a process called transcytosis. This process begins on the apical surface of the epithelial cell when the B12-IF binds to receptors, and is engulfed into the cell. What is the type of membrane transport at the apical surface of the epithelium?
Endocytosis
The movement of molecules into a cell in an indentation of the cell membrane and formation of a small vehicle is called _______________.
Endocytosis
What type of membrane transport is used in the following scenario? Neurons will release signaling molecules called neurotransmitters in order to communicate with other neurons or with organs. In the axon terminal of many neurons are storage vesicles of these neurotransmitters called synaptic vesicles. When an electrical signal known as an action potential is propagated to the axon terminal, the synaptic vesicles fuse with the neuronal membrane and the neurotransmitters is released.
Exocytosis
If many solutes are constantly being pumped into or out of cells, why don't the intracellular concentrations of these solutes change?
For any given solute, the rate of active transport in one direction is equal to the passive movement (leak) of the solute in the opposite direction.
Water will always move from _____________ areas to __________ areas, if the membrane is permeable to water.
Hypotonic, hypertonic
Which of the following statements provides an accurate comparison between facilitated diffusion and simple diffusion?
In both facilitated and simple diffusion, substances move down their concentration gradient.
Which of the following statements makes an accurate comparison between primary and secondary active transport?
In primary active transport ATP is directly utilized, while in secondary active transport the potential energy of a concentration gradient is utilized.
You have a beaker containing 1 L of 1 mOsM glucose. Add or subtract the solutions or solute listed below, then determine the concentration of the mixed solution. Use the equation solute/volume = concentration (S/V = concentration) for each item to find the concentration of the added solution. Remember that you cannot just add concentrations. You must first consider the sum of the solutes, then consider the total volume before expressing the value as the concentration (solute amount/total volume) of the mixed solution. Drag the solutions to the correct box to indicate whether the final concentration of the mixed solution has increased, decreased, or remained the same.
Increase- remove 0.5 L of water, add 1 mosmol of KCl Decrease- add 1 L of pure water, add 0.5 mosmol NaCl and 1 L water Same- add 0.5 mosmol glucose and 0.5 L water, add 1 mosmol NaCl and 1 L water
Passive transport refers to a process that requires no
Input of energy
Identify whether each of the following is a component of the intracellular fluid or extracellular fluid by dragging the box into the appropriate compartment.
Intracellular fluid- cytosol of a red blood cell, cytoplasm of a neuron Extracellular fluid- blood plasma, interstitial fluid
A cell containing 300 mOsm of non-penetrating solutes per liter is placed in a solution containing 200 mOsm of non-penetrating solutes per liter and 100 mOsm of the penetrating solute area per liter. The solution can be said to be _________________ with respect to the cell.
Iso-osmotic and hypotonic
Based on the scenario in Part H, the added solution was ________________ osmotic compared to the original 300 mOsM concentration of the body.
Isosmotic
First, how does the solution's concentration compare to that of the body? Is the solution we are adding hyposmotic, isosmotic, or hyperosmotic?
Isosmotic
What is the mechanism of action of the cystic fibrosis transmembrane conductance regulator (CFTR)?
It allows for the active pumping of chloride from the intracellular fluid to the extracellular fluid
The permeability of a membrane to a particular solute is related to which two variables, and what is the relationship?
It is directly proportional to lipid solubility and inversely proportional to the size of the solute
Identify which of the following is the correct definition of primary active transport.
It is mediated by a protein that directly uses ATP energy in order to move a substance against its concentration gradient.
The membranes of neurons at rest are very permeable to _____ but only slightly permeable to _____.
K+, Na+
Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?
Leak channels
An increase in which of the following would increase the rate of diffusion of oxygen molecules across pulmonary cell membranes?
Membrane surface area, the oxygen concentration inside the lung, and temperature
The concentration of which two ions are highest outside the cell
Na+ and Cl-
The concentrations of which two ions are highest outside the cell.
Na+ and Cl-
The concentrations of which two ions are highest outside the cell?
Na+ and Cl-
If a cell's Vm=-70 mV and E(Na+)=+50 mV, which way will Na+ ions move across the cell membrane?
Na+ ions will move into the cell
Which of the following molecules would not diffuse through cell membranes easily?
Na+ ions, glucose
The Na+-K+ pump actively transports both sodium and potassium ions across the membrane to compensate for their constant leakage. In which direction is each ion pumped?
Na+ is pumped out of the cell and K+ is pumped into the cell.
What prevents the Na+ and K+ gradients from dissipating?
Na+/K+ ATPase
After adding the solution from Part H to the body, would you expect cell size to change?
No, the solution is isotonic
How will the solute we are adding in the solution be distributed among the body compartments? In other words, does the solution contain penetrating solutes that enter cells, nonpenetrating solutes that stay in the ECF, or a combination of both?
Nonpenetrating
Predict what you think will happen to the ions in each compartment as soon as we allow potassium to move.
One ion moves down its gradients.
Let's consider a scenario in which the resting membrane potential changes from -70 mV to +70 mV, but the concentrations of all ions in the intracellular and extracellular fluids are unchanged. Predict how this change in membrane potential affects the movement of Na+. The electrical gradient for Na+ would tend to move Na+ _____________ while the chemical gradient for Na+ would tend to move Na+ __________________.
Out; in
Which of the following types of molecules would be most likely to pass through the plasma membrane by means of simple diffusion?
Oxygen - nonpolar
Match the type of transport with its description. A. secretion B. paracellular transport C. transcellular transport D. absorption Between adjacent cells
Paracellular transport
White blood cells engulf bacteria in a process known as _________________.
Phagocytosis
If a cell were to become depleted of its ATP, which type of membrane transport would be most directly and immediately affected?
Primary active transport
In skeletal muscle, the sarcoplasmic reticulum stores a very high concentration of Ca+. When Ca+ is released into the cytosol of muscle to facilitate contraction, it needs to be removed and pumped back into the sarcoplasmic reticulum so that skeletal muscle can return to its relaxed state. The Ca+ is moved from cytosol and pumped back into the sarcoplasmic reticulum where its concentration is much higher. What type of membrane transport does this represent?
Primary active transport
Overall, Na+ and glucose transport into epithelial cells ________________.
Requires energy
Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane. What is the name given to this potential difference?
Resting membrane potential (RMP)
According to Fick's law of diffusion, diffusion rate is proportional to the surface area of the membrane, the concentration gradient, and which other variable?
The permeability of the membrane
Use the following scenario to answer the question. A beaker containing two fluid compartments separated by a semipermeable membrane is filled with distilled water. In compartment A you place 15mM of NaCl and in compartment B you place 25 mM of NaCl. The membrane is permeable to both sodium and chloride. Initially, which side has the higher osmotic pressure? As time goes on will the water levels change and if so how?
Side B has a higher osmotic pressure; the water levels will not change
Which is NOT a type of mediated transport?
Simple diffusion
The resting membrane potential depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. Identify these two factors.
The presence of concentration gradients and leak channels
Take a second and use the information given about the starting conditions to fill in the values for total body solute, volume, and osmolarity.
Solute: 900 Volume: 3 Osmolarity: 300
Active transport of substances across membranes requires ATP because
Substances are moved against the concentration gradient (uphill)
Which of the following statements is false with regard to primary/secondary active transport?
Substances will always move down their concentration gradient.
Why would tasting salty sweat on the foreheads of babies lead a midwife to assume that the baby might be afflicted with cystic fibrosis?
The CFTR allows for chloride to leave the sweat and re-enter the cells, creating a hypotonic sweat.
How is the function of the CFTR altered in someone with cystic fibrosis?
The CFTR channel is absent.
Which of the following statements about epithelial transport in the intestines is (are) true?
The Na+/K+ ATPase is found only in the basolateral membrane of intestinal epithelial cells and the movement of Na+ ions across the apical membrane of intestinal epithelial cells is dependent on the electrochemical gradient created by the Na+/K+ ATPase
On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you?
The inside surface of the plasma membrane is much more negatively charged than the outside surface
Which of the following statements about the Na-K pump is (are) true?
The location of the binding sites on the Na-K pump dictates the direction of solute movement
Facilitated diffusion differs from simple diffusion in what way(s)?
The rate of facilitated diffusion depends on the number of carriers in the membrane.
Which of the following statements about facilitated diffusion is (are) true?
The rate of facilitated diffusion is directly dependent on the number of carrier proteins for a solute and the rate of facilitated diffusion is directly dependent on the concentration gradient of the solute across the membrane
A cell has a mutation in a sodium ion leak channel, and sodium cannot diffuse through the channel. What would you expect to happen to the resting membrane potential difference?
The resting membrane potential difference would be more negative, because there would be less diffusion of positively charged sodium ions into the cell
The fluid compartments of the human body are in osmotic equilibrium. This means that the ICF and the ECF have the same total solute concentrations, despite the differences in their specific solute composition. Osmotic equilibrium occurs because water passes freely through cell membranes using open channels or the water channels called aquaporins. If the osmolarity in one compartment changes, water moves by osmosis to bring the two compartments back to osmotic equilibrium. Water moves down its own gradient into the compartment with the higher osmolarity until both compartments have the same solute-to-volume ratio (or osmolarity). Which of the following statements correctly describes the relationship between intracellular fluid (ICF) and extracellular fluid (ECF)?
The types of solutes and their distribution between the ICF and ECF are not the same.
What will occur if solution A, containing 400 mosmol/L nonpenetrating solute, were separated by a biological membrane from solution B, containing 600 mosmol/L nonpenetrating solute?
The volume of B would increase
The plasma membrane is much more permeable to K+ than to Na+. Why?
There are many more K+ leak channels than Na+ leak channels in the plasma membrane.
In comparing a solution to a fluid in a cell, a hypertonic solution always has _____________.
a higher concentration of non-penetrating solutes than that in the cell
Which of the following conditions would lead to the fastest rate of oxygen diffusion into a cell?
a large concentration gradient and a thin membrane
Why is the thick mucus in Daniel's lungs a sign that he might have cystic fibrosis?
Without the CFTR, mucus cannot be thinned.
In order for water to be absorbed by epithelial cells,
aquaporins must be present in the cell membranes and the concentration of impermeable solutes must be higher on the inside of the cell
During depolarization, which gradient(s) move(s) Na+ into the cell?
both the electrical and chemical gradients
The difference between carrier and channel proteins is that
channel proteins create a continuous passage between intra- and extracellular compartments
The inside of a resting cell is slightly negative relative to the outside. This is an example of
electrical disequilibrium
In the process of __________________, membrane-bound receptors will recognize and bind to specific structures on a bacterium, which will result in the cell taking that bacteria into a vesicle.
endocytosis
Water toxicity occurs when __________.
extracellular fluids become hypotonic, causing brain cells to swell
Substances that readily dissolve in water and do not readily dissolve in lipids are
hydrophilic and lipophobic
In people with diabetes mellitus, glucose is not being transported into cells at the normal rate. This buildup of glucose in the plasma causes the extracellular fluid to become
hypertonic and hyperosmotic
A cell placed in a solution of unknown composition soon swelled up and burst, so the solution must have been __________ to the cell when it was originally placed in the solution.
hypotonic and of an undetermined relative osmolarity
The membrane potential of most cells
is negative, except when there is a change in membrane permeability to ions
Which of the following does not require the use of ATP?
osmosis
Energy released by the hydrolysis of ATP is used to move K+ and Na+ across cell membranes. This process is called ___________________.
primary active transport
Transport processes that require an energy source include _________________.
primary active transport and secondary active transport
Substances that are going to move against their concentration gradient (from low concentration to high concentration) will use which type(s) of membrane transport?
primary or secondary active transport
Cations will ________ each other.
repel
Which of the following transport mechanisms may be utilized to move glucose across cell membranes?
secondary active transport and facilitated diffusion
Examples of active transport may include _________________.
the movement of Na+ ions out of cells and the movement of glucose molecules into intestinal epithelial cells
The term simple diffusion can be used to describe __________, from areas of high concentration to areas of lower concentration.
the movement of oxygen molecules across the cell membrane and the movement of oxygen molecules in air
With cystic fibrosis, breathing is difficult because __________.
the osmotic pressure of the fluid on the luminal side of the respiratory surface favors water transport out of cells and the movement of Cl- ions is impeded due to a lack of chloride transporters
