CELL MEMBRANE TRANSPORT

Fluid Mosaic Model

Model describing the cell membrane as a flexible phospholipid bilayer with embedded proteins, carbohydrates, and cholesterol.

Why is it called "fluid"?

Phospholipids and proteins can move sideways within the membrane.

Why is it called "mosaic"?

The membrane is made of many different molecules arranged together.

Phospholipid

Molecule with a hydrophilic phosphate head and two hydrophobic fatty acid tails; forms the main structure of the membrane.

Hydrophilic

Water-loving; attracted to water.

Hydrophobic

Water-fearing; repelled by water.

Phospholipid Head

Hydrophilic phosphate region that faces water.

Phospholipid Tails

Hydrophobic fatty acid region that faces inward away from water.

Phospholipid Bilayer

Double layer of phospholipids that forms the cell membrane.

Protein

Membrane component that transports substances, acts as a receptor, or functions as an enzyme.

Glycoprotein

Protein with attached carbohydrate chain used for cell recognition and communication.

Glycolipid

Lipid with attached carbohydrate chain used for cell recognition and membrane stability.

Carbohydrate Chains

Molecules that act as identification tags for cell recognition.

Cholesterol

Molecule that helps maintain membrane fluidity and stability.

Selective Permeability

Property of the membrane that allows some substances to pass while restricting others.

Passive Transport

Movement of substances across the membrane without ATP; moves down the concentration gradient.

Diffusion

Movement of particles from an area of high concentration to an area of low concentration.

Concentration Gradient

Difference in concentration between two areas.

Examples of Diffusion

Oxygen entering cells and carbon dioxide leaving cells.

Osmosis

Diffusion of water across a selectively permeable membrane.

Direction of Osmosis

Water moves from high water concentration (low solute concentration) to low water concentration (high solute concentration).

Facilitated Transport (Facilitated Diffusion)

Passive movement of substances through channel or carrier proteins from high to low concentration.

Channel Protein

Protein that forms a passageway for specific molecules or ions.

Carrier Protein

Protein that changes shape to move substances across the membrane.

Examples of Facilitated Transport

Glucose, ions, and other large or charged molecules.

Active Transport

Movement of substances from low concentration to high concentration using ATP and carrier proteins.

ATP

Energy molecule used to power active transport.

Sodium-Potassium Pump

Example of active transport that moves sodium and potassium ions against their concentration gradients.

Endocytosis

Process by which a cell takes substances into the cell using vesicles; requires ATP.

Phagocytosis

"Cell eating"; endocytosis of large solid particles.

Example of Phagocytosis

White blood cells engulfing bacteria.

Pinocytosis

"Cell drinking"; endocytosis of liquids and dissolved substances.

Exocytosis

Process by which a cell releases substances using vesicles; requires ATP.

Examples of Exocytosis

Hormones, neurotransmitters, proteins, and waste products leaving the cell.

Diffusion vs Active Transport

Diffusion moves high→low concentration without ATP; active transport moves low→high concentration using ATP.

Facilitated Transport vs Diffusion

Both move high→low concentration without ATP, but facilitated transport requires membrane proteins.

Osmosis vs Diffusion

Osmosis involves only water; diffusion involves other particles.

Hypertonic Solution

Environment with a higher solute concentration outside the cell than inside.

Effect of Hypertonic Solution on Animal Cells

Water leaves the cell and the cell shrinks (crenation).

Hypotonic Solution

Environment with a lower solute concentration outside the cell than inside.

Effect of Hypotonic Solution on Animal Cells

Water enters the cell and the cell swells or may burst (lysis).

Isotonic Solution

Environment with equal solute concentration inside and outside the cell.

Effect of Isotonic Solution on Animal Cells

No net movement of water; cell stays the same size.

Factors Affecting Diffusion Rate

Temperature, molecule size, charge, concentration gradient, and pressure gradient.

Temperature and Diffusion

Higher temperature increases diffusion rate.

Molecule Size and Diffusion

Smaller molecules diffuse faster than larger molecules.

Charge and Diffusion

Charged molecules diffuse more slowly and often require transport proteins.

Concentration Gradient and Diffusion

A steeper gradient increases diffusion rate.

Pressure Gradient and Diffusion

A greater pressure difference increases diffusion rate.

Transport Process Using No ATP and No Protein

Diffusion.

Transport Process Using No ATP but Protein

Facilitated Transport.

Transport Process Using ATP and Protein

Active Transport.

Transport Process Used for Water Only

Osmosis.

Transport Process Used for Large Particles Entering Cell

Endocytosis.

Transport Process Used for Large Particles Leaving Cell

Exocytosis.

Small Non-Polar Molecules

Molecules such as oxygen and carbon dioxide that can diffuse directly through the phospholipid bilayer.

Large or Charged Molecules

Molecules that usually require channel or carrier proteins to cross the membrane.