---
title: "Osmosis — AP Biology Definition & Exam Guide"
description: "Osmosis is the passive movement of water across a semi-permeable membrane toward higher solute concentration, central to AP Bio Unit 2 transport and tonicity questions."
canonical: "https://fiveable.me/ap-bio/key-terms/osmosis"
type: "key-term"
subject: "AP Biology"
---

# Osmosis — AP Biology Definition & Exam Guide

## Definition

The movement of water from an area of low solute concentration to an area of high solute concentration across a semi-permeable membrane.

## Related Study Guides

- [2.6 Facilitated Diffusion](/ap-bio/unit-2/membrane-transport/study-guide/7yV52dtD7Vj7ZadTEd2P)
- [2.8 Mechanisms of Transport](/ap-bio/unit-2/tonicity-osmoregulation/study-guide/CCENUydXNVb7K4P7ikp7)
- [2.9 Cell Compartmentalization](/ap-bio/unit-2/mechanisms-transport/study-guide/sMlGCA9J4sGVE7S24xBM)

## Review

### Related Terms

- [Hypertonic Solution](/ap-bio/key-terms/hypertonic-solution): This is like a super popular concert - it has more solutes (people) so water (other attendees) wants to go there.
- [Hypotonic Solution](/ap-bio/key-terms/hypotonic-solution): This is like a less popular concert - it has fewer solutes so water tends to leave this area.
- [Isotonic Solution](/ap-bio/key-terms/isotonic-solution): This is like two concerts with equal popularity - water doesn't preferentially move towards either because they have equal amounts of solutes.