Membrane Transport

Define simple diffusion

Movement directly through the lipid bilayer (passive)

State factors affecting rate of simple diffusion

Conc. gradient, solubility, size, charge and temperature

Define facilitated diffusion

Movement via a channel or carrier protein (passive)

State factors affecting rate of facilitated diffusion

Conc. gradient and availability of proteins

Define osmosis

Movement of water from low concentration to high concentration (passive)

State factors affecting rate of osmosis

Hydrostatic pressure (pressure exerted by liquid) and osmotic pressure (pressure exerted on a liquid by a dissolved solute too large to cross membrane - prevents water movement)

Define passive transport

Resulting from random motion and collisions moving down the concentration gradient (no energy required)

Define active transport

Movement of a molecule against the concentration gradient via a channel or carrier (from low conc. to high conc.)

Usually ions (e.g. Na+, K+, Ca2+, Mg2+, etc.)

Primary energy source = ATP
Secondary energy source = energy stored in ionic concentration gradient

Uses vesicle transport = substances transported in membrane-bound compartments

What particles pass through lipid bilayer by simple diffusion?

Small, uncharged and lipid soluble - high → low conc.

What particles pass through lipid bilayer by facilitated diffusion?

Large, charged and/or water soluble - high → low conc.

How does water pass through lipid bilayer

Osmosis via aquaporin (channel) - low solute/high water conc. → high solute/low water conc.

Define hypertonic

High water concentration and low solute concentration

Define hypotonic

Low water concentration and high solute concentration

Purpose of membrane transport

To transport nutrients into a cell and remove waste products

Define exocytosis

Release of fluids and/or solids from the cell via intracellular vesicles (requires ATP)

Define endocytosis

Packaging of extracellular materials into a vesicle to go into the cell (requires ATP)

Receptor-mediated, pinocytosis and phagocytosis

Define tonicity

How the solution affects cell volume, depends on the solute concentration outside the cell and solute permeability

Define isotonic solution

Same solute water concentration as inside the cell (no osmotic flow occurs)

Define hypertonic solution

Higher solute concentration/lower water concentration than inside the cell (cell loses water and shrivels - crenation)

Define hypotonic solution

Lower solute concentration/higher water concentration than inside the cell (cell gains water and swells - hemolysis)