All flashcards
Flashcard 1: What is secondary active transport (cotransport)?
Answer: Uses an ion gradient to drive another solute against its gradient. The electrochemical gradient of one ion, established by primary transport, energizes the coupled movement of another solute uphill.
Flashcard 2: What is the main function of aquaporins in membranes?
Answer: Increase water permeability to speed osmosis. Aquaporins form water-selective pores that enhance membrane permeability, facilitating rapid osmotic adjustments in cells.
Flashcard 3: Using π=iMRT, what happens to osmotic pressure if solute concentration M doubles (hold i, R, T constant)?
Answer: Osmotic pressure doubles. Since osmotic pressure is directly proportional to molar concentration in the van 't Hoff equation, doubling M doubles π.
Flashcard 4: What is the van 't Hoff equation for osmotic pressure (use ideal approximation)?
Answer: π=iMRT. This equation approximates osmotic pressure as proportional to van 't Hoff factor, molarity, gas constant, and temperature.
Flashcard 5: What is the term for red blood cell shrinkage with membrane wrinkling in a hypertonic solution?
Answer: Crenation. Water efflux in hypertonic conditions dehydrates the red blood cell, causing it to shrink and develop a scalloped appearance.
Flashcard 6: What is the term for red blood cell rupture after excessive swelling in a hypotonic solution?
Answer: Hemolysis. Excessive water influx in hypotonic conditions causes the red blood cell to swell beyond its membrane's capacity, leading to rupture.
Flashcard 7: What happens to an animal cell placed in an isotonic solution (assume steady state)?
Answer: No net water movement; cell volume remains constant. Equal effective osmolarities inside and outside the cell prevent an osmotic gradient, maintaining equilibrium.
Flashcard 8: Identify the tonicity of a solution that causes a cell to shrink due to net water efflux.
Answer: Hypertonic. Higher external solute concentration establishes an osmotic gradient pulling water out of the cell, reducing its volume.
Flashcard 9: Identify the tonicity of a solution that causes a cell to swell due to net water influx.
Answer: Hypotonic. Lower external solute concentration creates an osmotic gradient driving water into the cell, increasing its volume.
Flashcard 10: Which transport mechanism is saturable due to a finite number of binding sites: simple or facilitated diffusion?
Answer: Facilitated diffusion is saturable. Limited transporter proteins lead to a maximum transport rate when all binding sites are occupied at high solute concentrations.
Flashcard 11: What is primary active transport across a membrane?
Answer: Direct use of ATP hydrolysis to move solute against its gradient. ATP hydrolysis directly powers membrane pumps to transport solutes against their electrochemical gradients.
Flashcard 12: What is the difference between a symporter and an antiporter?
Answer: Symporter: same direction; Antiporter: opposite directions. Symporters couple the transport of two solutes in parallel, while antiporters exchange them in opposing directions across the membrane.
Flashcard 13: What is the net transport stoichiometry of the Na+/K+ ATPase per ATP hydrolyzed?
Answer: 3 Na+ out and 2 K+ in per ATP. This ratio establishes and maintains the sodium and potassium gradients crucial for membrane potential and cellular functions.
Flashcard 14: What is the immediate effect of the Na+/K+ ATPase on membrane charge (electrogenic or not)?
Answer: Electrogenic; net +1 charge moved out per cycle. The unequal ion exchange creates a net positive charge efflux, contributing to the resting membrane potential.
Flashcard 15: What is osmosis in biological membranes?
Answer: Net movement of water across a membrane toward higher solute. Water diffuses across semipermeable membranes from regions of lower to higher solute concentration to equalize water potential.
Flashcard 16: What is the definition of osmolarity?
Answer: Osmoles of solute per liter of solution. It quantifies the concentration of osmotically active particles that influence water movement across membranes.
Flashcard 17: What is the key distinction between osmolarity and osmolality?
Answer: Osmolarity: per L solution; Osmolality: per kg solvent. Osmolality measures solute particles per kilogram of solvent, making it less affected by temperature than osmolarity's volume-based measure.
Flashcard 18: What is tonicity, and which solutes determine it?
Answer: Effect on cell volume; determined by nonpenetrating solutes. Tonicity describes the solution's ability to alter cell volume via osmosis, influenced only by solutes that cannot cross the membrane.
Flashcard 19: What is the difference between passive transport and active transport across membranes?
Answer: Passive: down gradient; Active: requires energy to go up gradient. Passive transport occurs spontaneously along electrochemical gradients, while active transport uses cellular energy to move substances against them.
Flashcard 20: What is simple diffusion across a membrane?
Answer: Net movement down concentration gradient without a transport protein. Molecules move spontaneously from high to low concentration due to random thermal motion through the lipid bilayer without assistance.
Flashcard 21: Which property most strongly increases a solute's simple diffusion through a lipid bilayer?
Answer: High nonpolarity (lipid solubility). Nonpolar molecules dissolve readily in the hydrophobic core of the phospholipid bilayer, enhancing their diffusion rate.
Flashcard 22: What is facilitated diffusion across a membrane?
Answer: Passive movement down gradient via channels or carriers. Transport proteins assist hydrophilic or charged solutes in crossing the membrane along their concentration gradient without energy input.
Flashcard 23: What is the defining feature of a selectively permeable membrane in cells?
Answer: Allows some solutes to cross while restricting others. This property enables cells to maintain internal homeostasis by regulating the passage of molecules based on size, charge, or polarity.
Flashcard 24: What is the key functional difference between a channel and a carrier (transporter) protein?
Answer: Channels form pores; carriers bind solute and change conformation. Channels provide open pathways for rapid solute flow, whereas carriers undergo conformational changes to translocate bound solutes.