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WorksheetsLecutre 2
Total questions: 40
Worksheet time: 20mins
Which molecules can freely diffuse across lipid bilayers?
Ions
Glucose
Steroid hormones
Amino acids
Lipid bilayers are generally impermeable to:
Small hydrophobic molecules
Ions and large polar molecules
Steroid hormones
O₂ and CO₂
The two main classes of membrane transport proteins are:
Receptors and enzymes
Transporters and channels
Symports and antiports
Pumps and receptors
Passive transport moves molecules:
Against their electrochemical gradient
Along their electrochemical gradient
Independently of gradients
By consuming ATP directly
Active transport requires:
ATP hydrolysis or energy coupling
No energy input
Only concentration gradient
Only osmosis
The difference in ion concentrations across membranes generates:
Hydrostatic pressure
Osmotic balance
Membrane potential
Enzymatic activity
Resting membrane potential in most animal cells is:
+200 mV
0 mV
Between –20 and –200 mV
+60 mV
Which ions are most important in generating the resting potential?
Na⁺ and Ca²⁺
K⁺ and Cl⁻
K⁺ and Na⁺ leak channels
Mg²⁺ only
The electrochemical gradient combines:
Concentration and electrical gradients
Osmotic pressure and ATP
Enzyme activity and diffusion
Voltage-gated and ligand-gated channels
Osmosis refers to:
Movement of ions against gradients
Passive water movement down concentration gradient
Active water pumping
Passive glucose uptake
Passive transporters are also called:
Pumps
Carriers
Symports
ATPases
Which pump expels 3 Na⁺ and imports 2 K⁺ per ATP hydrolyzed?
Proton pump
Na⁺/K⁺ ATPase
Ca²⁺ ATPase
Glucose–Na⁺ symport
The Na⁺/K⁺ pump helps maintain:
Equal Na⁺ and K⁺ inside and outside
High Na⁺ inside, high K⁺ outside
High Na⁺ outside, high K⁺ inside
Only Ca²⁺ balance
Ca²⁺ pumps keep cytosolic Ca²⁺:
Very high
Very low
Equal to extracellular
Only in mitochondria
Gradient-driven pumps use:
Light energy
One solute’s gradient to transport another
ATP only
Osmotic pressure
A glucose–Na⁺ symporter uses:
ATP directly
Na⁺ gradient to import glucose
H⁺ gradient
Facilitated diffusion only
In plants and fungi, the primary electrochemical gradient is generated by:
Na⁺ pumps
H⁺ pumps
Ca²⁺ pumps
Cl⁻ channels
Antiporters transport:
Two solutes in same direction
One solute only
Two solutes in opposite directions
Only ions
Ion channels differ from transporters because:
They undergo conformational change each cycle
They allow rapid passive ion flow
They consume ATP
They are non-selective
Ion selectivity depends on:
Channel size, shape, and charge
ATP binding
Membrane proteins only
Number of glycolipids
Ion channels are usually:
Always open
Gated (voltage, ligand, mechanical stimuli)
Non-specific to ions
ATP-dependent
K⁺ leak channels are critical for:
Generating resting potential
Transporting glucose
Blocking Na⁺ entry
Triggering exocytosis
An action potential is triggered when:
Na⁺ channels close
Membrane depolarizes past threshold
K⁺ leak channels open
ATP is depleted
Depolarization occurs due to:
Na⁺ influx
K⁺ efflux
Cl⁻ influx
Ca²⁺ efflux
Repolarization is due to:
Na⁺ channel inactivation, K⁺ efflux
Na⁺ influx
Ca²⁺ release
ATP hydrolysis
Hyperpolarization occurs because:
Na⁺ channels stay open
K⁺ channels remain open longer
Ca²⁺ channels activate
Cl⁻ influx increases
Voltage-gated Ca²⁺ channels in nerve terminals:
Maintain resting potential
Convert electrical signal into chemical signal (neurotransmitter release)
Pump Ca²⁺ into ER
Block vesicle fusion
Transmitter-gated ion channels convert:
Electrical → electrical signals
Chemical → electrical signals
ATP → ion movement
Osmotic pressure → signaling
The acetylcholine receptor in skeletal muscle opens when:
ATP binds
Acetylcholine binds
Na⁺ concentration increases
Voltage threshold is crossed
Most psychoactive drugs act by:
Blocking Na⁺/K⁺ pump
Binding neurotransmitter receptors
Altering glycolipids
Degrading ion channels
Which ion is used as primary electrochemical gradient in animals vs plants?
Na⁺ in both
H⁺ in both
Na⁺ in animals, H⁺ in plants/fungi
K⁺ in plants, Na⁺ in animals
Which of the following is not passive transport?
Diffusion of O₂
Facilitated glucose transport
Na⁺/K⁺ ATPase activity
Ion channel opening
Which best explains why Na⁺ is ideal for creating gradients in animals?
High cytosolic concentration
Low cytosolic concentration, steep gradient
Ca²⁺ blocking
Equal distribution across membrane
Which process is directly linked to nerve impulse propagation?
Na⁺ channel opening → depolarization
Ca²⁺ pump
Glucose symporter
Na⁺/K⁺ pump immediate action
Resting potential is primarily governed by:
Equal distribution of all ions
K⁺ leak channels and Na⁺/K⁺ ATPase
Ca²⁺ pumps
Random ion movement
Mechanically-gated channels are found in:
Muscle contraction
Auditory hair cells
Gut glucose transport
RBCs only
A drug that blocks K⁺ channels would:
Prevent depolarization
Prolong depolarization/reduce repolarization
Stop neurotransmitter release
Hyperpolarize cell
In neurons, action potentials propagate because:
Each patch of membrane triggers the next via local depolarization
Na⁺/K⁺ pumps rapidly pump ions
ATP flows down axon
Channels open only at dendrites
Why is neurotransmission a two-step signal conversion?
Electrical → chemical → electrical
Chemical → mechanical → chemical
Electrical → osmotic → chemical
Mechanical → electrical → ATP
The complexity of synaptic signaling underlies:
Simple reflexes only
Thinking, learning, memory
DNA replication
Only muscle contraction
