Problem 1 - AP Psychology Premium Prep 2021

Question

Movement of substances into the cell is largely dependent on the size, polarity, and concentration gradient of the substance. Which of the following represents an example of active transport of a substance into a cell? (A) Diffusion of oxygen into erythrocytes (red blood cells) in the alveolar capillaries of the lungs \(\quad\) (B) Influx of sodium ions through a voltage- gated ion channel in a neuron cell during an action potential (C) The sodium-potassium pump, which restores resting membrane potentials in neurons through the use of ATP (D) Osmosis of water into an epithelial cell lining the lumen of the small intestine

Step-by-Step Solution

Answer

The correct answer is \((C)\) The sodium-potassium pump, which restores resting membrane potentials in neurons through the use of ATP, as it represents an example of active transport.

Step 1: Understand the difference between active and passive transport

Active transport requires energy (usually in the form of ATP) to move substances against their concentration gradient, whereas passive transport does not require energy and substances move along their concentration gradient.

Step 2: Analyze the given options

(A) Diffusion of oxygen into erythrocytes (red blood cells) in the alveolar capillaries of the lungs: This is a passive transport mechanism, as oxygen moves along its concentration gradient from high concentration in the alveoli to lower concentration in the erythrocytes. (B) Influx of sodium ions through a voltage-gated ion channel in a neuron cell during an action potential: This is also a passive transport mechanism, as sodium ions move along their concentration gradient from high concentration outside the neuron to lower concentration inside the neuron. (C) The sodium-potassium pump, which restores resting membrane potentials in neurons through the use of ATP: This is an active transport mechanism, as it requires energy (ATP) to move sodium and potassium ions against their concentration gradients to maintain resting membrane potentials. (D) Osmosis of water into an epithelial cell lining the lumen of the small intestine: This is a passive transport mechanism, as water moves along its concentration gradient from an area of low solute concentration in the lumen to an area of higher solute concentration inside the epithelial cell.

Step 3: Select the correct option

Based on the analysis in Step 2, the correct answer is (C) The sodium-potassium pump, which restores resting membrane potentials in neurons through the use of ATP, as it represents an example of active transport.