Fluid Mosaic Model

The plasma membrane is primarily composed of a bilayer of phospholipids, with proteins and other molecules embedded within. This composition allows the membrane to be fluid and selectively permeable.

• Phospholipid Bilayer: Forms the basic structure, with hydrophilic heads facing outward and hydrophobic tails inward.
• Proteins: Integral and peripheral proteins serve functions in transport, signal transduction, and cell recognition.
• Cholesterol: Helps maintain fluidity and stability by preventing the fatty acid chains from sticking together.

Transport mechanisms are processes that control the movement of substances across the cell membrane. These include passive transport (such as diffusion and osmosis) and active transport, which requires energy.

• Passive Transport: Includes diffusion, osmosis, and facilitated diffusion, moving substances down their concentration gradient without energy use.
• Active Transport: Moves substances against their concentration gradient, requiring ATP (e.g., sodium-potassium pump).
• Endocytosis and Exocytosis: Processes for moving large molecules or particles into (endocytosis) or out of (exocytosis) the cell.