cell transport/permeability *FINISH

diffusion

• The movement of particles (like molecules or ions) from an area of high concentration to low concentration until evenly spread out.

Simple diffusion

• Direct movement of small, nonpolar molecules (like oxygen, carbon dioxide) through the cell membrane without help.

Readily dissolve in lipids

Facilitated Diffusion

• Movement of larger or charged molecules (like glucose or ions) across the membrane through transport proteins.

• Still passive (high → low, no energy).

• Uses: Channel proteins or carrier proteins

passive transport

• Movement of substances across a cell membrane without using energy (ATP).

• How: Relies on natural concentration gradients (high → low).

• Types include:

  • Simple diffusion

  • Facilitated diffusion

  • Osmosis

active transport

• Movement of substances across a membrane against the concentration gradient (low → high).

• Energy use: Requires ATP (cellular energy).

• Example: Sodium-potassium pump in nerve cells.

Osmosis

A special type of diffusion—the movement of water molecules across a selectively permeable membrane from high water concentration (low solute) → low water concentration (high solute).

HIGH water (low solute) to LOW water (high solute)