Membranes and PassiveMembranes and Passive TransportTransport

Ch. 6.2-6.3Ch. 6.2-6.3

Review

• Cell membranes are made up of some type of lipid• What is unique about the interaction of lipids and

water?• Lipids are hydrophobic, or water resistant, to

water!• Why do molecules like these work well for a cell’s

boundary?• Cell cytoplasm is mostly water and cell exterior is

mostly water --> water resistant molecule makes a good boundary layer

Objectives

1. Structure of cell membranes

2. Function of proteins in cell membranes

3. Relate diffusion to equilibrium

4. Describe passive transport

5. Relate osmosis to solute concentration

Phospholipid Molecule

• Structured like a fat molecule, but only 2 tails

• Hydrophilic Head• Hydrophobic Tail

Phospholipid Bilayer• Phospholipid Bilayer:

– Selectively permeable membrane

– surrounds cell

– Controls what goes in and out!

• Online Activity 6.3• Contains proteins

– What do these proteins do?

Function of Proteins in bilayer

• Cell communication • Assist with passage of

materials• Classroom analogy

– Light, heat, electricity, internet, etc.

Regulating Traffic

• Materials such as water, nutrients, dissolved gasses, ions and wastes must CONSTANTLY move in two-way traffic across membrane

• Cell membranes function like “gatekeepers”– Some molecules pass, others do not!

• How do they do this?

Ways to get materials across membrane

• Diffusion:– Movement of particles from HIGHER--> LOWER concentration

• The goal is to achieve an equilibrium• Equilibrium:

– in balance

• Perfume?

Ways to get materials across membrane

• Passive Transport:– Diffusion across a

membrane

– no energy

• Some molecules too big to get through membrane alone (sugars). Need help!

• What can help them?

Ways to get materials across membrane

• Facilitated Diffusion:– use of transport proteins– No energy

• Facilitated Diffusion animation

Are all substances able to pass through membrane?

• No!• Diffusion occurs through

a selectively permeable membrane

• Selectively permeable membrane: – Allows “select” substances

through

• Similar to a window screen: air but no mosquitoes

Water can pass, but sucrose too big

Three Ways to Get Materials Across Membrane

How does water get through?• Osmosis:

– Diffusion of H2O

• Hypertonic Solution:– Net water flow OUT of cell

• Hypotonic Solution:– Net water flow INTO cell

• Isotonic Solution:– Equal water flow

• Osmosis Animation• Sore throat, thirsty after

salty snacks