[Chapter 6: Cell Membranes]

Cell Transport
Old Books: Periods 1 & 5
New Books: Period 7
Read pp. 114-123.
Read 113- 122.


Membrane permeability (ability to allow chemicals to pass / not pass across it):

permeable- holes in membrane are large & all molecules pass through.

semi-permeable- smaller holes in membrane allow only small molecules to pass through.

non-permeable - no holes in membrane. Nothing passes through.

Examples of Cell Transport

Passive Transport - Movement of molecules from high to low concentration. Needs no energy input.

Active Transport - Movement of molecules from low to high concentration (opposite the flow of diffusion). Needs input of energy (ATP).

Examples of Passive Transport:

1. Diffusion: Random movement of any molecules from higher to lower concentration.

Animation: [Diffusion / Osmosis #1] [Diffusion / Osmosis #2 (french language)] [Ion Channels- Diffusion (french language)]

2. Osmosis: Diffusion of water across a membrane. Occurs from high concentration of H2O to low conc. H2O, (or low solute conc. to high solute conc.).

Terms Associated with Osmosis in Cells:

Hypertonic: (hyper = more / tonic = solute)

a) Any solution having more solute (less H2O) than inside cell. More water flows out of cell so cell shrinks.


Hypotonic: (hypo = less / tonic = solute)

a) Any solution having less solute (more H2O) than the cell contents. Water diffuses into the cell (which has more solute, less H2O) so cell expands.


Isotonic: (iso = equal / tonic = solute)

2 solutions with equal concentrations of solute and water. Net flow of water between the 2 is equal. We say both are in equilibrium. H2O diffusion still occurs in both directions at equilibrium.

Animations: [Hypertonic/Hypotonic/Isotonic]


3. Facilitated Diffusion: passive transport (no energy required).

Passage of molecules from high to low concentration (diffusion) across membrane via binding to a membrane protein which carries it across.

Animation: [Facillitated Diffusion]

4. Ion channels: Special channel proteins allow ions to pass through membrane w/out interacting with hydrophobic lipid tails.

[To Active Transport]

Online Reviews of Passive & Active Transport:

A. Passive Transport



Osmosis in an Isotonic Environment: (www.cat.cc.md.us) -

Osmosis in a Hypertonic Environment:

Osmosis in a Hypotonic Environment:

Facillitated Diffusion (no ATP used......from high to low concentration)

Transport (In french, but does a good job illustrating diffusion, passage through protein channels, cotransport, Na/K pumps, endocytosis & exocytosis.)


B. Active Transport

Active Transport: (McGraw-Hill) - 4 Animations & Audio of CoTransport, Na/K Pump, Endocytosis & Exocytosis, and Proton Pump.

Sodium/Potassium Pump: (No text with it but a good animation of this important form of Active Transport)

CoTransport (passage of Na into the cell helps bring Glucose (G) in too!)

Sodium/Potassium Pump combined with Cotransport (The sodium/potassium pump is often coupled with Cotransport to power the active transport of glucose into a cell)


Phagocytosis: Shows both an animation as well as 2 short movie clips of amoebas ingesting other organisms via phagocytosis.

Receptor-mediated Endocytosis: The molecule to be moved into the cell must match up with a receptor on the membrane surface to be moved in.


Exocytosis: (BBC Education)