Diffusion — Science definition

Defined in 3 courses:

The net movement of particles from a crowded region to a sparse one, produced by random motion alone and costing the cell nothing. (Life Science & Scientific Inquiry)
Spreading caused by random particle motion. (Physical Science: Matter, Forces & Energy)
The net movement of particles from where they are more concentrated to where they are less concentrated, down the concentration gradient. (Life Science: Biology)

Where it is taught

Membrane Transport, Diffusion & Osmosis — Cells, Transport & Cellular Energy, Life Science & Scientific Inquiry, Grade 7
Gas Particles, Diffusion & Pressure — Phases of Matter, Physical Science: Matter, Forces & Energy, Grade 8
Cellular Transport — Cells, Membranes & Exchange, Life Science: Biology, Grade 10

In use

This is diffusion: the net movement of particles from where they are crowded to where they are sparse, produced by random motion and nothing else.
Membrane Transport, Diffusion & Osmosis

The simplest passive process is diffusion: particles in constant random motion naturally spread out until they are evenly mixed.
Cellular Transport

Questions using diffusion

Problem 1

Does diffusion equilibrium mean all particles stop?

Answer and explanation

No. Motion continues; opposing movements can balance so there is no net concentration change.

Problem 2

Does diffusion require every particle to move in the same direction?

Answer and explanation

No. Individual particles move in varying directions. The overall distribution changes because more particles start in one region than another.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 3

Osmosis is best defined as the diffusion of ___ across a selectively permeable membrane.

protein
water
oxygen
glucose

Answer and explanation

water

Osmosis specifically refers to the movement of water across a selectively permeable membrane toward the side with more solute.

Problem 4

A cell pumps ions against their gradient. What distinguishes this from facilitated diffusion? Show the reasoning, not just the conclusion.

Hints

State permeability and effective solute conditions; not every solute is trapped.

Answer and explanation

The pump uses coupled energy; facilitated diffusion moves particles down their electrochemical gradient.

Taught alongside

Elsewhere

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