A LITTLE LIGHTBULB MOMENT
Cell biology, genetics and molecular biology
Osmosis and tonicity
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Water moves toward the side with more dissolved solute
The idea behind the cue
Osmosis is the net movement of water across a semipermeable membrane toward the side with higher effective solute concentration. Tonicity describes how a solution affects cell volume: hypotonic swells cells, hypertonic shrinks cells, isotonic leaves volume unchanged.
Practice this flashcard →Make it memorable
Short & simple
Water moves toward the side with more dissolved solute
Acronym
OHHI — Overdressed Hippos Hug Igloos.
Story
Two fish tanks share a wall. One side is packed with sugar syrup, and water drifts over like curious tourists trying to dilute the crowd.
Connect the pieces
- O (Overdressed) → Osmosis: Water moves across a semipermeable membrane toward the side with higher effective solute concentration.
- H (Hippos) → Hypotonic: A hypotonic solution makes cells swell.
- H (Hug) → Hypertonic: A hypertonic solution makes cells shrink.
- I (Igloos) → Isotonic: An isotonic solution leaves cell volume unchanged.
- Overdressed · Osmosis: Water moves across a semipermeable membrane toward the side with higher effective solute concentration.
- Hippos · Hypotonic: A hypotonic solution makes cells swell.
- Hug · Hypertonic: A hypertonic solution makes cells shrink.
- Igloos · Isotonic: An isotonic solution leaves cell volume unchanged.
Know the limits
Tonicity compares effective solutes across a membrane; it is not always identical to total osmolarity.
Further reading · OpenStax science and mathematics textbooks ↗Check your understanding
A red blood cell placed in a hypertonic solution will most likely
A. swell as water enters
B. shrink as water leaves
C. stay unchanged because ions cannot move
D. burst immediately from osmotic influx
Reveal explanation
shrink as water leaves
In a hypertonic environment, water moves out of the cell, causing it to shrink.