Simple diffusion moves molecules

Answer: Down their concentration gradient without ATP Passive: high → low concentration; no energy input required.

The transport process shown is BEST classified as:

Answer: Simple diffusion (passive transport down a gradient) Solutes move from high to low concentration without ATP - the defining feature of simple diffusion (passive transport).

Why is the Na⁺/K⁺ pump considered "primary" active transport?

Answer: It directly hydrolyzes ATP to drive transport against a gradient Primary active transport directly couples ATP hydrolysis to transport. Secondary uses an existing ion gradient (built by primary pumps) as the energy source.

AP Biology · Topic 2.6

Membrane Transport Practice

Part of Cell Structure and Function.(ENE-1.F)

Practice questions

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Sample questions

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Sample 1difficulty 1/5
$Simple diffusion moves molecules$
- A
  $Down their concentration gradient without ATP$
  check_circle
- B
  $Against the concentration gradient using ATP$
- C
  $Only through protein channels$
- D
  $Only across nuclear membranes$
Why
$Passive: high \to low concentration; no energy input required.$
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Sample 2difficulty 2/5
$A student observes that small nonpolar O2 molecules accumulate inside a cell whenever the extracellular O2 concentration is higher than inside, even when the cell's metabolism is blocked by a poison that depletes ATP. The teacher asks the student to identify the kind of transport responsible.$
$The transport process shown is BEST classified as:$
- A
  $Simple diffusion (passive transport down a gradient)$
  check_circle
- B
  $Active transport against a gradient$
- C
  $Exocytosis$
- D
  $Endocytosis$
Why
$Solutes move from high to low concentration without ATP - the defining feature of simple diffusion (passive transport).$
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Sample 3difficulty 2/5
$Why is the Na⁺/K⁺ pump considered "primary" active transport?$
- A
  $It uses sunlight energy directly as its source of power for transport$
- B
  $It directly hydrolyzes ATP to drive transport against a gradient$
  check_circle
- C
  $It depends on a preexisting ion gradient maintained by another transporter$
- D
  $It is the most abundant transport pump found in eukaryotic plasma membranes$
Why
$Primary active transport directly couples ATP hydrolysis to transport. Secondary uses an existing ion gradient (built by primary pumps) as the energy source.$
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Sample 4difficulty 2/5
$The right-hand process (with ATP, moving solute against the gradient) is$
- A
  $Active transport$
  check_circle
- B
  $Osmosis$
- C
  $Facilitated diffusion$
- D
  $Simple diffusion$
Why
$Active transport uses ATP to pump solutes against their concentration gradient — e.g., the Na⁺/K⁺ pump.$
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Sample 5difficulty 2/5
$A red blood cell placed in pure water will$
- A
  $Become turgid$
- B
  $Swell and lyse$
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- C
  $Shrink$
- D
  $Maintain its shape$
Why
$Pure water is hypotonic to the cell's interior; water rushes in, rupturing the membrane (no cell wall to resist).$
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