WorksheetsCell Membrane Transport Questions
Total questions: 56
Worksheet time: 31mins
Which of the following substances is found in large amounts in the extracellular fluid but only in a small amount in the intracellular fluid?
Potassium
Phosphate
Proteins
Sodium
The cell membrane is almost entirely composed of a lipid bilayer with many protein molecules, many of which penetrate all the way through the membrane. This lipid bilayer serves as a barrier against the movement of:
Lipid-soluble substances
Water molecules and water-soluble substances
Gases like oxygen and carbon dioxide
Steroid hormones
Which type of membrane protein forms watery spaces all the way through the molecule, allowing free movement of water and selected ions or molecules?
Channel proteins
Carrier proteins
Receptor proteins
Enzyme proteins
Facilitated diffusion requires the interaction of a carrier protein that aids passage of molecules or ions by:
Creating a membrane opening without interaction.
Moving substances against an energy gradient.
Binding chemically with them and shuttling them through the membrane.
Using ATP to power movement.
What is the primary energy source that causes diffusion?
ATP hydrolysis
The normal kinetic motion of matter
Electrical potential differences
Concentration gradients maintained by pumps
Simple diffusion through the cell membrane can occur via two pathways: through the interstices of the lipid bilayer if the diffusing substance is lipid-soluble, and through:
Carrier proteins.
Watery channels that penetrate large transport proteins.
Active transport pumps.
Ligand-gated receptors.
Aquaporins are protein pores known to permit rapid passage of which substance through cell membranes, while excluding hydrated ions?
Glucose
Sodium
Water
Amino acids
The high selectivity of potassium channels for potassium ions over sodium ions is largely explained by:
The larger molecular diameter of potassium ions.
Carbonyl oxygens in the selectivity filter interacting with dehydrated potassium ions but not smaller sodium ions.
Strong negative charges attracting only potassium ions.
The presence of a specific carrier protein for potassium.
Gating of protein channels can be controlled in two principal ways: voltage gating and:
Mechanical gating.
Pressure gating.
Chemical (ligand) gating.
Osmotic gating.
The patch clamp method is a technique used to record:
Ion current flow through single protein channels.
The overall electrical potential of an entire cell.
The rate of ATP synthesis in mitochondria.
Muscle contraction forces.
A key difference between simple diffusion and facilitated diffusion is that the rate of facilitated diffusion:
Increases proportionately with concentration, like simple diffusion.
Approaches a maximum (Vmax) as the concentration of the diffusing substance increases.
Is determined solely by the velocity of kinetic motion.
Does not require carrier proteins.
Which of the following substances are specifically mentioned as crossing cell membranes by facilitated diffusion?
Sodium and chloride ions
Glucose and most amino acids
Phosphates and proteins
Oxygen and carbon dioxide
The net rate of diffusion of a substance into a cell is directly proportional to the:
Velocity of kinetic motion.
Number and sizes of membrane openings.
Concentration on the outside minus the concentration on the inside.
Molecular mass of the substance.
The Nernst potential for a specific ion is the diffusion potential across a membrane that:
Creates a net movement of the ion.
Exactly opposes the net diffusion of that particular ion through the membrane.
Is determined solely by the membrane's permeability to that ion.
Requires active transport to be established.
The process of net movement of water caused by a concentration difference of water across a cell membrane, leading to cell swelling or shrinking, is called:
Diffusion
Active transport
Facilitated diffusion
Osmosis
One osmole is defined as:
1 gram of any solute.
1 gram molecular weight of a solute that does not dissociate.
1 gram molecular weight of osmotically active solute.
The total number of particles in a liter of solution.
The normal osmolality of the extracellular and intracellular fluids is about:
19.3 milliosmoles per kilogram of water
100 milliosmoles per kilogram of water
300 milliosmoles per kilogram of water
5790 milliosmoles per kilogram of water
Active transport is characterized by the movement of ions or other substances across the membrane:
Only through watery channels.
Down an energy gradient.
In combination with a carrier protein against an energy gradient, requiring additional energy.
Directly through the lipid bilayer.
The sodium-potassium (Na+-K+) pump is a primary active transport mechanism responsible for:
Pumping sodium ions inward and potassium ions outward.
Maintaining sodium and potassium concentration differences across the cell membrane and establishing a negative electrical voltage inside the cells.
Equalizing sodium and potassium concentrations across the membrane.
Facilitating diffusion of sodium and potassium.
The Na+-K+ pump is considered electrogenic because it:
Cleaves ATP to release energy.
Moves three Na+ ions to the exterior for every two K+ ions moved to the interior, creating a net positive charge deficit inside.
Is composed of two separate globular proteins.
Is activated when a cell begins to swell.
An example of secondary active transport is the co-transport of glucose and amino acids, which uses the diffusion energy of which ion?
Potassium
Calcium
Hydrogen
Sodium
The resting membrane potential of large nerve fibers when not transmitting signals is approximately:
+35 millivolts
0 millivolts
-70 millivolts
-94 millivolts
In a resting nerve cell, the K+ "leak" channels are far more permeable to which ion compared to the other?
Potassium than to sodium
Sodium than to potassium
Chloride than to potassium
Calcium than to sodium
If the nerve membrane were permeable only to potassium ions, with a 35:1 ratio of inside to outside concentration, the calculated Nernst potential would be:
+61 millivolts
-61 millivolts
-94 millivolts
+94 millivolts
The Goldman equation is used to calculate the diffusion potential when a membrane is permeable to several different ions. It depends on the polarity of the electrical charge of each ion, the concentration of the respective ions, and the:
Permeability of the membrane to each ion.
Temperature of the membrane.
Size of the ion channels.
Activity of the Na+-K+ pump.
The depolarization stage of a nerve action potential is primarily caused by:
Rapid outflow of potassium ions.
Closure of sodium channels.
Rapid diffusion of positively charged sodium ions to the interior of the axon.
Increased permeability to chloride ions.
The voltage-gated sodium channel has an activation gate and an inactivation gate. During the normal resting membrane state (-70mV), the activation gate is:
Open
Slowly opening
Closed
Inactivated
The threshold for stimulation of a large nerve fiber, which usually causes the explosive development of an action potential, is ap
The threshold for stimulation of a large nerve fiber, which usually causes the explosive development of an action potential, is approximately:
-70 millivolts
-55 millivolts
0 millivolts
+35 millivolts
The transmission of the depolarization process along a nerve or muscle fiber is called a nerve or muscle:
Repolarization
Hyperpolarization
Plateau
Impulse
The all-or-nothing principle states that once an action potential has been elicited at any point on the membrane of a normal fiber:
It travels only in one direction.
The depolarization process travels over the entire membrane if conditions are right, but not at all if conditions are not right.
Its strength is proportional to the stimulus intensity.
It depends on the size of the nerve fiber.
To re-establish the sodium and potassium ionic gradients after action potentials are completed, the Na+-K+ pump requires energy derived from:
Glucose directly
Glycolysis
The adenosine triphosphate (ATP) energy system of the cell.
The flow of ions down their concentration gradients.
In heart muscle fibers, the plateau phase of the action potential is largely responsible for prolonged contraction and is mainly caused by the prolonged opening of:
Fast sodium channels.
Voltage-activated calcium-sodium channels (slow channels).
Voltage-gated potassium channels.
Acetylcholine-gated channels.
The myelin sheath in myelinated nerve fibers significantly increases the velocity of nerve transmission and conserves energy for the axon by:
Directly conducting action potentials.
Acting as an electrical insulator, allowing action potentials to jump from node to node.
Increasing the diameter of the axon.
Promoting continuous depolarization.
The maximum rate at which a large myelinated nerve fiber can transmit impulses per second is approximately:
100
500
1000
2500
The period during which a second action potential cannot be elicited, even with a strong stimulus, is called the:
Latent period
Absolute refractory period
Relative refractory period
Hyperpolarization period
Local anesthetics like procaine and tetracaine primarily decrease nerve excitability by acting directly on the:
Potassium channels.
Activation gates of the sodium channels, making them more difficult to open.
Calcium channels.
Inactivation gates of the sodium channels.
What is the typical resting membrane potential of smooth muscle cells?
-80 to -90 millivolts
-70 millivolts
-50 to -60 millivolts
+30 millivolts
Skeletal muscle fibers are composed of several hundred to several thousand myofibrils, which in turn are made up of approximately:
1500 actin filaments and 3000 myosin filaments.
1500 myosin filaments and 3000 actin filaments.
Equal numbers of actin and myosin filaments.
Only actin filaments.
In the sarcomere, the dark bands that contain myosin filaments and the overlapping ends of actin filaments are called:
I bands
Z disks
H zones
A bands
The Z disk in a myofibril serves the purpose of:
Bundling myosin tails together.
Attaching the ends of actin filaments and connecting myofibrils to one another across the muscle fiber.
Forming cross-bridges.
Storing calcium ions.
When a muscle fiber is contracted to approximately 2 micrometers in sarcomere length, it is capable of generating its:
Minimum force of contraction.
Zero force of contraction.
Greatest force of contraction.
Only passive tension.
The sarcoplasmic reticulum in skeletal muscle is specialized for:
Synthesizing contractile proteins.
Conducting action potentials into the muscle fiber.
Regulating calcium storage, release, and reuptake for muscle contraction.
Producing ATP for muscle contraction.
The general mechanism of muscle contraction begins with an action potential traveling along a motor nerve, leading to the secretion of which neurotransmitter at the neuromuscular junction?
Norepinephrine
Dopamine
Acetylcholine
Serotonin
Muscle contraction occurs by a 'sliding filament mechanism,' where:
Myosin filaments shorten.
Actin filaments are pulled inward among the myosin filaments.
The Z disks move farther apart.
The cross-bridges shorten.
The myosin head contains ATPase activity and binds with ATP before contraction. The energy from ATP cleavage is then used to:
Release ADP and phosphate.
Cause the myosin head to detach from actin.
Cause a conformational change in the head, tilting it for the power stroke.
Uncover active sites on the actin filament.
What is the function of tropomyosin in the resting state of skeletal muscle?
It binds strongly with calcium ions.
It forms the Z disk.
It lies on top of the active sites of the actin strands, preventing attraction between actin and myosin.
It generates the power stroke.
The 'walk-along' (ratchet) mechanism describes how the heads of the cross-bridges:
Attach to active sites, detach, and remain extended.
Bend back and forth and, step by step, walk along the actin filament, pulling it toward the myosin filament center.
Only attach to the myosin filament body.
Transport ATP to the actin filament.
The Fenn effect states that when a muscle contracts:
More work is performed, less ATP is cleaved.
The more work performed by the muscle, the more ATP that is cleaved.
ATP is synthesized rather than cleaved.
Calcium ions are always released.
What is the first and fastest source of energy used to reconstitute ATP during intense muscle contraction?
Glycolysis
Oxidative metabolism
Phosphocreatine
Stored ADP
Glycolysis is an important energy source for muscle contraction because it:
Provides the most ATP for long-term contraction.
Can occur even in the absence of oxygen and produces ATP rapidly.
Produces no end products that accumulate in muscle cells.
Is activated by insulin.
The efficiency of muscle contraction, defined as the percentage of energy input converted into work, is typically less than 25%, with the remainder becoming:
ADP
Heat
Lactic acid
Pyruvic acid
A muscle contraction is described as isometric when the muscle:
Does not shorten during contraction but creates tension.
Shortens while maintaining constant tension.
Lifts a weight against a fixed load.
Expends energy without producing force.
A motor unit consists of:
A single muscle fiber and its sarcolemma.
All the myofibrils within a muscle.
A single motor neuron and all the skeletal muscle fibers it innervates.
The entire muscle, regardless of innervation.
The 'size principle' of multiple fiber summation in muscle contraction refers to the fact that:
Larger motor units are always excited first.
Smaller motor units are stimulated in preference to larger ones during weak signals, allowing fine gradations of force.
All motor units contract synchronously.
Muscle force is independent of motor unit size.
Tetanization occurs in muscle contraction when the frequency of stimulation is so high that:
Individual twitch contractions are clearly visible.
The muscle fatigues rapidly.
Successive contractions fuse together, appearing as a completely smooth and continuous contraction.
Calcium ions are rapidly pumped back into the sarcoplasmic reticulum between stimuli.
