Cells

Structure of Plasma Membrane

1 Phospholipid Bilayer: Hydrophilic heads face outward; hydrophobic tails face inward.
2 Proteins: Integral (span membrane can not move) and peripheral (surface)
Fluid Mosaic Model: Flexible and proteins/lipids move laterally.

Functions of Plasma Membrane

Selective Permeability: Controls substance entry/exit.
Cell Communication: Receptors for signals.
Structural Support: Maintains cell shape and integrity.

Permeability of the Plasma Membrane (Easy)

Small Nonpolar Molecules: Pass easily (e.g., oxygen, carbon dioxide).

Small Polar Molecules: Pass if small (e.g., water, urea).

Permeability of the Plasma Membrane (Restricted Molecules)

Large Polar Molecules: Require assistance (e.g., glucose).

Ions: Need specific channels/pumps (e.g., sodium, potassium).

Isotonic

Equal solute concentration (e.g., normal saline).

Hypotonic

Lower solute concentration outside (e.g., distilled water); cell swells.

Hypertonic

Higher solute concentration outside (e.g., concentrated saline); cell shrinks.