Membrane Transport and Osmoregulation (2A) - Bio & Biochem

What is the term for red blood cell rupture after excessive swelling in a hypotonic solution?

Hemolysis. Excessive water influx in hypotonic conditions causes the red blood cell to swell beyond its membrane's capacity, leading to rupture.
What is the term for red blood cell shrinkage with membrane wrinkling in a hypertonic solution?

Crenation. Water efflux in hypertonic conditions dehydrates the red blood cell, causing it to shrink and develop a scalloped appearance.
What is facilitated diffusion across a membrane?

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.
What is the key functional difference between a channel and a carrier (transporter) protein?

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.
Which property most strongly increases a solute's simple diffusion through a lipid bilayer?

High nonpolarity (lipid solubility). Nonpolar molecules dissolve readily in the hydrophobic core of the phospholipid bilayer, enhancing their diffusion rate.
Which transport mechanism is saturable due to a finite number of binding sites: simple or facilitated diffusion?

Facilitated diffusion is saturable. Limited transporter proteins lead to a maximum transport rate when all binding sites are occupied at high solute concentrations.
What is the difference between passive transport and active transport across membranes?

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.
What is osmosis in biological membranes?

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.
What is simple diffusion across a membrane?

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.
What is the net transport stoichiometry of the Na $^+$ /K $^+$ ATPase per ATP hydrolyzed?

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.
What is primary active transport across a membrane?

Direct use of ATP hydrolysis to move solute against its gradient. ATP hydrolysis directly powers membrane pumps to transport solutes against their electrochemical gradients.
What is the definition of osmolarity?

Osmoles of solute per liter of solution. It quantifies the concentration of osmotically active particles that influence water movement across membranes.
Using $\pi=iMRT$ , what happens to osmotic pressure if solute concentration $M$ doubles (hold $i$ , $R$ , $T$ constant)?

Osmotic pressure doubles. Since osmotic pressure is directly proportional to molar concentration in the van 't Hoff equation, doubling $M$ doubles $\pi$ .
Identify the tonicity of a solution that causes a cell to swell due to net water influx.

Hypotonic. Lower external solute concentration creates an osmotic gradient driving water into the cell, increasing its volume.
What is the difference between a symporter and an antiporter?

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.
What is tonicity, and which solutes determine it?

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.
What is the van 't Hoff equation for osmotic pressure (use ideal approximation)?

$\pi=iMRT$ . This equation approximates osmotic pressure as proportional to van 't Hoff factor, molarity, gas constant, and temperature.
What is the key distinction between osmolarity and osmolality?

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.
What is the immediate effect of the Na $^+$ /K $^+$ ATPase on membrane charge (electrogenic or not)?

Electrogenic; net +1 charge moved out per cycle. The unequal ion exchange creates a net positive charge efflux, contributing to the resting membrane potential.
What is secondary active transport (cotransport)?

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.
What happens to an animal cell placed in an isotonic solution (assume steady state)?

No net water movement; cell volume remains constant. Equal effective osmolarities inside and outside the cell prevent an osmotic gradient, maintaining equilibrium.
Identify the tonicity of a solution that causes a cell to shrink due to net water efflux.

Hypertonic. Higher external solute concentration establishes an osmotic gradient pulling water out of the cell, reducing its volume.
What is the main function of aquaporins in membranes?

Increase water permeability to speed osmosis. Aquaporins form water-selective pores that enhance membrane permeability, facilitating rapid osmotic adjustments in cells.
What is the defining feature of a selectively permeable membrane in cells?

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.

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