Diffusion and Osmosis

Life Science: Molecular

Vocabulary Diffusion

Facilitated DiffusionOsmosisOsmotic Pressure Tonicity

Cell MembraneThe cell membrane is a semi-permeable lipid bilayer. – Semi-permeable means it lets some things pass

through it. – Lipid means fat (phospholipid to be exact) – Bilayer means there are 2 layers

Cell Membrane

Cell Membrane

Cell Membrane

The cell membrane maintains the internal environment of the cell, by moving molecules from one side to the other.

PhospholipidThe cell membrane is composed phospholipids, which have hydrophilic heads and hydrophobic tails.

Cell membrane

Proteins

Protein channel Lipid bilayer

Carbohydrate chains

Lipid Bilayer

Phospholipids spontaneously arrange into a double layered membrane in a fluid environment.

Fluid Mosaic Model

Membrane ProteinsProteins embedded within the membrane allow materials to move in and out of the cell.

Classes of membrane proteins – peripheral proteins

• loosely bound to surface of membrane • ex: cell surface identity marker (antigens)

– integral proteins • penetrate through the cell membrane • ex: transport proteins

Membrane Proteins

Passive TransportDiffusion is the movement of molecules from an area of high concentration to an area of low concentration.

Passive TransportIn a cell... Diffusion moves small, uncharged molecules across the cell membrane until equilibrium is reached.

Facilitated Diffusion

High Concentration

Low Concentration

Cell Membrane

Facilitated diffusion is the movement of large or charged particles such as ions, sugars, and salts through protein channels across the cell membrane.

High Concentration to Low Concentration

Passive Transport

Osmosis: Facilitated DiffusionOsmosis is the diffusion of water through a selectively permeable membrane. Many cells contain water channel proteins called aquaporins that allow water to pass directly through the membrane.

Osmosis: Facilitated DiffusionThere is a net movement of water from low to high solute concentration, or high to low water concentration.

How Osmosis Works

The net movement of water into or out of a cell produces a force known as osmotic pressure.

Osmotic Pressure

Osmotic PressureOsmosis is a force that exerts a pressure on the more concentrated side of a cell membrane.

Solution ConcentrationsTonicity is a measure of the osmotic pressure gradient of two solutions separated by a semipermeable membrane. • Hypertonic - Having a higher concentration than another

solution. • Hypotonic - Having a lower concentration than another

solution. • Isotonic - Having the same amount of dissolved solute as

another solution.

Comparing Solutions• A cell placed in a hypertonic solution will decrease

in volume. • A cell placed in a hypotonic solution will increase in

volume. • A cell placed in an isotonic solution will not change

in volume.

Hyper, Hypo, or Isotonic?

Normal Red Blood Cell