Active transport Knowledge-Based Practice

Questions

1. 1.

   Which type of membrane transport protein couples the downhill movement of one solute to the uphill transport of a different solute in the opposite direction across the cell membrane?

   • A) Symporter
   • B) Antiporter
   • C) Uniporter
   • D) Gated ion channel
2. 2.

   Which of the following membrane transport processes would be directly and immediately halted if a cell were exposed to a metabolic poison that completely inhibits ATP synthesis?

   • A) Movement of oxygen molecules across the phospholipid bilayer down a concentration gradient
   • B) Rapid transit of water molecules through transmembrane aquaporin channels
   • C) Downhill transport of glucose into erythrocytes via facilitated diffusion
   • D) Pumping of ions across the plasma membrane against their electrochemical gradient
3. 3.

   Which of the following serves as the direct energy source that drives the movement of a solute against its concentration gradient in secondary active transport?

   • A) The direct hydrolysis of ATP by the cotransporter protein
   • B) The thermal energy generated by cytoplasmic metabolic reactions
   • C) The mechanical tension exerted by cytoskeletal microfilaments on the membrane
   • D) The electrochemical potential difference of an ion established by primary active transport
4. 4.

   In animal cells, the sodium-potassium pump ($\text{Na}^+/\text{K}^+$ ATPase) uses energy from ATP hydrolysis to maintain vital electrochemical gradients across the plasma membrane. Which of the following correctly describes the direction and stoichiometry of ion movement per cycle of this pump?

   • A) 3 $\text{Na}^+$ ions are pumped out of the cell and 2 $\text{K}^+$ ions are pumped into the cell.
   • B) 2 $\text{Na}^+$ ions are pumped out of the cell and 3 $\text{K}^+$ ions are pumped into the cell.
   • C) 3 $\text{Na}^+$ ions are pumped into the cell and 2 $\text{K}^+$ ions are pumped out of the cell.
   • D) 2 $\text{Na}^+$ ions are pumped into the cell and 3 $\text{K}^+$ ions are pumped out of the cell.
5. 5.

   Which of the following statements correctly characterizes primary active transport across a cell membrane?

   • A) It moves water molecules through channel proteins strictly along their osmotic gradient without consuming metabolic energy.
   • B) It relies solely on thermal kinetic energy to diffuse small nonpolar molecules directly across the phospholipid bilayer.
   • C) It moves specific solutes against their concentration gradient through transmembrane pumps coupled to ATP hydrolysis.
   • D) It enables the downhill transport of polar solutes across the membrane via carrier proteins without metabolic input.

Answers and step-by-step solutions appear after you finish the test.