---
title: "Concentration Gradient — AP Bio Definition & Exam Guide"
description: "A concentration gradient is the difference in a substance's concentration between two regions, and it drives diffusion, osmosis, and active transport in AP Bio Unit 2."
canonical: "https://fiveable.me/ap-bio/key-terms/concentration-gradient"
type: "key-term"
subject: "AP Biology"
---

# Concentration Gradient — AP Bio Definition & Exam Guide

## Definition

A concentration gradient occurs when there is a difference in concentration of a particular substance between two regions. Substances will naturally move from areas of high concentration to areas of low concentration until equilibrium is reached.

## Related Study Guides

- [2.8 Mechanisms of Transport](/ap-bio/unit-2/tonicity-osmoregulation/study-guide/CCENUydXNVb7K4P7ikp7)
- [2.7 Tonicity and Osmoregulation](/ap-bio/unit-2/tonicity-osmoregulation/study-guide/i3qUckt9PGfT4pQlHq5B)

## Review

### Related Terms

- [Diffusion](/ap-bio/key-terms/diffusion): This refers to how particles spread out from an area of high concentration to an area of low concentration.
- [Osmosis](/ap-bio/key-terms/osmosis): A special type of diffusion involving water molecules moving across a semi-permeable membrane from an area with more water (low solute concentration) towards less water (high solute concentration).
- Equilibrium: The state where concentrations are equal throughout a space; no net movement occurs once this state has been reached.