THE CELL MEMBRANE AND

PASSIVE TRANSPORT

LEARNING GOALS:

We need to understand the basic process of transport across a plasma membrane.

We are learning ... That the cell has a semi-permeable

membrane To understand the difference between

passive and active transport

CELL MEMBRANE Controls what goes in and out of the cell

Cell membrane is composed of different structures:

Phospholipid bilayerProtein ChannelsCarbohydratesCholesterol

Together these structures make up the Fluid Mosaic Model

FLUID MOSAIC MODEL

THE CELL MEMBRANE IS SEMI-PERMEABLE

The cell membrane selects substances to enter and leave the cell (semi-permeable)

What is entering? Water and uncharged molecules

(E.g. O2, CO2)

What is leaving? Water and waste (E.g. Fatty Acids)

FEATURES OF THE CELL MEMBRANE

Phospholipid Bilayer:holds components of the cell together

Proteins:transport specific substances across

membrane and aids in signaling

Cholesterol:keeps fluidity of the cell membrane

Carbohydrates:identifies molecules entering the cell

PHOSPHOLIPID STRUCTURE

HYDROPHOBIC:WATER HATING

HYDROPHILIC: WATER LOVING

TRANSPORTSubstances can be transported across cell

membrane in 2 different ways:

1. PASSIVE TRANSPORT requires no energy Substances travel from high to low

concentration

2. ACTIVE TRANSPORT requires energy Substances travel from low to high

concentration

PASSIVE TRANSPORT: SIMPLE DIFFUSION

Movement of molecules from a region of high to low concentration

No energy needed

Stops when the concentration of particles are equal everywhere EQUILIBRIUM

Small molecules travel across the phospholipid bilayer in this fashion

I

FACTORS THAT AFFECT SIMPLE DIFFUSION

1. TEMPERATURE: Molecules move faster and reach

equilibrium quicker

2. CONCENTRATION: The bigger difference in concentration, the

faster the rate of diffusion

3. SIZE OF MOLECULE: Smaller molecules diffuse faster than

large molecules

PASSIVE TRANPORT:FACILITATED DIFFUSION

Diffusion with the aid of membrane proteins

Proteins are very selective:

Bind to an identified molecule and transport it across the cell membrane

(ex. Na+ and Cl-Ions)

Energy not needed

DIFFUSION OF WATER:OSMOSIS

The diffusion of water across a selectively permeable membrane

Occurs when water concentrations differ on either side of the cell membrane

Water moves to ensure that the concentration of water is equal on both sides of the cell membrane EQUILIBRIUM

OSMOSIS

TYPES OF SOLUTIONS:There are three different types of

solutions:

1. ISOTONIC SOLUTION2. HYPERTONIC SOLUTION3. HYPOTONIC SOLUTION

ISOTONIC SOLUTIONSCONDITIONS:equal concentration

inside and out

WATER MOVEMENT: water molecules go in

and out of the cell at the same rate

No net movement

CELL SIZE: stays the same

HYPERTONIC SOLUTIONCONDITIONS:The solution has a

higher concentration of solute than inside the cell

WATER MOVEMENT: Water will move out of the cell

CELL SIZE: cells will shrink and shrivel

HYPOTONIC SOLUTIONCONDITIONS:The solution has a lower

concentration of solute than inside of the cell

WATER MOVEMENT:Water will move inside

the cell

CELL SIZE:expands and swells

ANIMATIONShttp://www.northland.cc.mn.us/biology/biology1111/animations/passive1.swf

http://bcs.whfreeman.com/thelifewire/content/chp05/0502001.html

http://biology-animations.blogspot.com/2011/06/cell-membrane-passive-transport.html

http://www.teachersdomain.org/asset/tdc02_int_membraneweb/

HOME / IN CLASS WORK Read pages 62-70

Answer questions on:

Page 63 # 10, 11 Page 68 # 13, 14 Page 70 # 16-18 page 71# 1-2, 5-6, 9