TRANSPORT OF MATERIAL ACROSS CELL MEMBRANE

Materials move across the membrane by passive or active transport mechanisms.

1. PASSIVE TRANSPORT

• Does not require energy.
• Movement occurs from high concentration → low concentration.

Types of Passive Transport

a) Diffusion
Movement of solute molecules from an area of high concentration to low concentration.

Two types:

• Simple Diffusion – substances pass directly through the membrane.
• Facilitated Diffusion – substances pass through transport proteins (carrier or channel proteins).

b) Osmosis
Movement of water molecules from high water concentration to low water concentration across a selectively permeable membrane.

2. ACTIVE TRANSPORT

• Requires energy (ATP).
• Movement occurs from low concentration → high concentration (against gradient).

Examples:

• Sodium-Potassium Pump
  Maintains ion balance inside nerve and muscle cells.

Bulk Transport

Used for movement of large particles or liquids.

a) Endocytosis ― Transport into the cell

• Phagocytosis – “cell eating”; uptake of solid particles.
• Pinocytosis – “cell drinking”; uptake of fluids.
• Receptor-mediated endocytosis – very specific uptake using receptors.

b) Exocytosis ― Transport out of the cell

• Used to release hormones, enzymes, waste, etc.