A red blood cell in a hypotonic solution

Answer: Swells (water moves in by osmosis); may lyse Hypotonic surroundings → water flows into the cell. Animal cells have no wall, so excessive swelling causes lysis.

Why does the student calculate percent change in mass rather than absolute mass change?

Answer: To control for slight differences in initial cylinder mass Cylinders are not exactly equal in initial mass. Normalizing to percent change ((final - initial)/initial 100) makes results comparable across samples and removes systematic bias from cutting variation.

A plant cell in a hypotonic solution becomes thanks to its cell wall.

Answer: Turgid (firm) Water enters, vacuole swells, but the cell wall resists bursting — the cell becomes turgid.

AP Biology · Topic 2.8

Tonicity and Osmoregulation Practice

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

Practice questions

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Sample questions

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Sample 1difficulty 2/5
$A red blood cell in a hypotonic solution$
- A
  $Stays normal (no net water movement); shape held$
- B
  $Swells (water moves in by osmosis); may lyse$
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- C
  $Becomes turgid (water in against cell wall); no lysis$
- D
  $Shrinks (water moves out by osmosis); may crenate$
Why
$Hypotonic surroundings \to water flows into the cell. Animal cells have no wall, so excessive swelling causes lysis.$
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Sample 2difficulty 2/5
$A student cuts six cylinders from a single potato using a cork borer, blots them dry, and weighs each. One cylinder is placed in each of six beakers containing sucrose solutions at 0.0, 0.1, 0.2, 0.3, 0.5, and 1.0 M. After 90 minutes, cylinders are blotted and reweighed. Percent change in mass is calculated for each cylinder.$
$Why does the student calculate percent change in mass rather than absolute mass change?$
- A
  $Because absolute mass change cannot be calculated$
- B
  $To control for slight differences in initial cylinder mass$
  check_circle
- C
  $To convert mass into moles of water$
- D
  $Because percent change is the only measurable variable$
Why
$Cylinders are not exactly equal in initial mass. Normalizing to percent change ((final - initial)/initial * 100) makes results comparable across samples and removes systematic bias from cutting variation.$
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Sample 3difficulty 2/5
$A plant cell in a hypotonic solution becomes _______ thanks to its cell wall.$
- A
  $Turgid (firm)$
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- B
  $Plasmolyzed$
- C
  $Lysed (burst)$
- D
  $Flaccid (limp)$
Why
$Water enters, vacuole swells, but the cell wall resists bursting — the cell becomes turgid.$
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Sample 4difficulty 2/5
$Potato cores of equal mass were submerged in sucrose solutions of 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 M for 24 hours. The percent change in mass was recorded.$
$Approximately what is the molarity of the potato cytoplasm?$
- A
  $About 1.0 M$
- B
  $About 0.8 M$
- C
  $About 0.3 M$
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- D
  $About 0.0 M$
Why
$The line crosses zero percent mass change near 0.3 M, the isotonic point where water flux is balanced.$
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Sample 5difficulty 2/5
$Osmosis is the diffusion of$
- A
  $Glucose into cells via facilitated transport$
- B
  $Water across a selectively permeable membrane$
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- C
  $Solute particles down their concentration gradient$
- D
  $Ions through voltage-gated channel proteins$
Why
$Water moves toward higher solute concentration (= lower water concentration) through a selectively permeable membrane.$
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