3.1 Diffusion
Understanding the NET movement of particles down a concentration gradient
Syllabus Definition (CORE)
Diffusion is the NET movement of particles from a region of their higher concentration to a region of their lower concentration (i.e. down a concentration gradient), as a result of their random movement.
Energy Source for Diffusion
The energy for diffusion comes from the kinetic energy of random movement of molecules and ions.
Baby Steps Explanation: Particles are not trying to spread out or balance concentrations. They are simply bouncing around randomly because they have kinetic energy. When there are more particles in one area, more will randomly bounce into the lower concentration area than the other way around. This creates the NET movement.
Examiner Trap Warning
- ✗WRONG: Particles move from high to low concentration
- ✓CORRECT: NET movement of particles from higher to lower concentration
The word NET is crucial because particles move randomly in all directions, but MORE move from high to low than low to high.
Movement Through Cells
Some substances move into and out of cells by diffusion through the cell membrane.
Importance in Living Organisms
Diffusion is essential for the movement of gases (O₂, CO₂) and solutes in living organisms.
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