AP Biology Questions on Active and Passive Transport in the Proximal Tubule

📚 Quick Study Guide

• 💧 Proximal Tubule: The first section of the nephron's tubule system in the kidney.
• 🚌 Reabsorption: The process by which water and solutes are moved from the filtrate back into the blood.
• ⚛️ Active Transport: Requires energy (ATP) to move substances against their concentration gradient. Examples include the reabsorption of glucose and amino acids.
• 🌊 Passive Transport: Does not require energy; substances move down their concentration gradient. Examples include the reabsorption of water via osmosis and the movement of ions through channels.
• ➕ Sodium (Na+): Actively transported out of the proximal tubule cells, creating an electrochemical gradient.
• ➖ Chloride (Cl-): Follows Na+ passively due to the electrochemical gradient.
• 💡 Water (H2O): Reabsorbed via osmosis, driven by the solute concentration gradient created by the active transport of Na+ and other solutes.
• 🍯 Glucose: Reabsorbed by secondary active transport, coupled with Na+ transport.

🧪 Practice Quiz

1. Which of the following transport mechanisms requires ATP to move substances across the cell membrane in the proximal tubule?
   1. A. Osmosis
   2. B. Facilitated diffusion
   3. C. Active transport
   4. D. Simple diffusion
2. What is the primary driving force for water reabsorption in the proximal tubule?
   1. A. Active transport of water
   2. B. Osmotic gradient created by solute reabsorption
   3. C. Hydrostatic pressure
   4. D. Facilitated diffusion of ions
3. Which ion is actively transported out of the proximal tubule cells, creating an electrochemical gradient?
   1. A. Potassium (K+)
   2. B. Sodium (Na+)
   3. C. Chloride (Cl-)
   4. D. Calcium (Ca2+)
4. How is glucose reabsorbed in the proximal tubule?
   1. A. Simple diffusion
   2. B. Facilitated diffusion
   3. C. Primary active transport
   4. D. Secondary active transport
5. Which of the following substances is reabsorbed via passive transport in the proximal tubule?
   1. A. Glucose
   2. B. Amino acids
   3. C. Sodium ions
   4. D. Water
6. What happens to the osmolarity of the filtrate as it passes through the proximal tubule?
   1. A. Increases
   2. B. Decreases
   3. C. Remains the same
   4. D. Becomes hypotonic
7. If active transport of sodium were inhibited in the proximal tubule, what would be the most likely consequence?
   1. A. Increased reabsorption of glucose
   2. B. Decreased reabsorption of water
   3. C. Increased secretion of potassium
   4. D. Decreased reabsorption of urea