alleryStart learning →Which statement describes simple diffusion in the nephron?
AIt moves solute up its gradient using ATP energy
BIt moves solute down its gradient without energy
CIt needs a channel protein but no energy at all
DIt moves water across a semipermeable membrane
Answer & Solution
Correct answer: B. It moves solute down its gradient without energy
1. Simple diffusion carries a substance from higher to lower concentration, down its gradient.
2. It requires no energy, and the substance only needs to be soluble.
3. Facilitated diffusion also runs downhill but needs a specific channel or carrier protein.
4. Active transport is the one that spends ATP to move a substance from low to high concentration.
5. Water crossing a semipermeable membrane is osmosis, which is described separately.
_Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 25 "The Urinary System", section 25.6 Tubular Reabsorption_
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