Cell Membrane & Passive Transport

DiffusionFacilitated Diffusion

Osmosis

I. The Cell Membrane

• Also known as a Plasma Membrane.

• Semi-permeable membrane (picket fence)

• Made of:– two layers of

phospholipids.– Proteins– Carbohydrates– cholesterol

Cell Membrane

Characteristics:• Controls what enters and leaves the cell.• Provides some Structure and Support.• Allows the cell to maintain Homeostasis.• Phospholipid Bilayer:

– Two layers of lipids, proteins and carbohydrate chains.– Phosphate- head faces outward, while the lipid tails face

inward. (remember oil and water don’t mix)

• Considered a fluid mosaic structure due to lots of different types of molecules that assemble to form a function

What does this and a cell membrane have in common?

Structure:1. Two Layers:

a. Cholesterol found between the phospholipids. Creates a strong and flexible structure.b. The Bilayer is Selective (semi-permeable) and only allows certain molecules to pass through.

2. Integral (transport) proteins help in communication between cells.3. Carbohydrate chains are attached to integral proteins found on the outside layer of the membrane.a. Carbohydrates act as chemical identifiers (name tags), that allow one cell to identify another.

Cell Membrane

Types of proteins and Carbohydrates within cell membrane:– Protein channel - allows specific large molecules to

enter or leave cell (facilitated diffusion).

– Communication – cell to cell

– Carbohydrate chains – chemical identifiers

Two concepts we have to know:

Concentration gradientDynamic EQUILIBRIUM

2 other words you need to know solute and solvent

Simple Diffusion• Moving from a High (more particles) concentration

to a Low (less particles) concentration.• Diffusion does not require energy to move solutes

(molecules) in and out.

• Impermeable membrane – “brick wall”, nothing enters or leaves.

• Semi-permeable – (picket fence), some can get through.

• To find an equilibrium, balance, between both sides.

• To find homeostasis (same amount on both sides).

High low

Diffusion

A. Diffusion – High to lowB. Passive Transport-

requires no energy

Facilitated Diffusion

• The movement of molecules through a protein channel.– Can not move through the phospholipid Bilayer due

to either being very large or has a polar charge.– Channel proteins move molecules across the

membrane very fast and only allow specific types to enter or leave by them.

– Using a protein channel for facilitated diffusion does not require ATP energy.

Molecule move through the channel from a high to low concentration.

Facilitated Diffusion

• Channel proteins act as pore. • Molecules will from through

channel.

• What does diffusion and facilitated diffusion have in common?

Osmosis:The diffusion of water across a semi-permeable membrane from an area of high concentration to an area of low concentration.

1. Isotonic Solution – concentration of solutes is the same inside and outside the cell. Water flows in and out of the cell.

2. Hypertonic Solution – Concentration of solute is higher outside the cell. Water moves out of the cell.

3. Hypotonic Solution – Concentration of solute is higher inside the cell and water moves into the cell.

A. Salt “Sucks” or dehydrates the water

B. in plant cells- Turgur-Pressure

C. Animal Cells would swell and burst

A.Plants wiltB.animal cell shrink-Plasmolysis

Discuss this picture

What organ goes through the process of osmosis?

OsmosisKey terms: 1.Turgid – rigid, full, swollen ex: A plant standing up after watering.2. Lyse – To break apart, burst or separate. Ex: popping a balloon, when filled with too much helium.3. Shrink – to shrivel up. Dehydrate, To get smaller. Ex: a grape sitting in the sun turning into a raisin.

Active Transport

• When solutes move against the concentration gradient and requires ATP (cell energy).

• Low -> high concentrations– Transports small molecules or ions (polar)

molecules through proteins called carrier proteins.– One specific type of active transport is the

Sodium/Potassium Pump.

• What is the difference between passive and active transport?

Lab over diffusion and osmosis

• Egg osmosis video demonstration

http://youtu.be/SSS3EtKAzYc

Measuring for Molar SolutionsTo make 300 mL of a 0.5M NaOH solution.

Convert 300 mL = 0.3 L

_________ ____________ __________ _________g__

concentration X volume desired X molecular weight = mass of solute

desired (mol/L) (L) (g/mol) (g)

Molecular Weight ?

Moles are used to count molecules and atoms since they are too small to count individually. 1 mole equals the amount of molecules that gives a mass, in grams, equal to that substance’s molecular or formula weight.

The formula weight (FW or MW) can be determined using a periodic table or by looking at a chemical reagent bottle.

For Molar Solutions you need the MWDetermine the molecular weight of the solute

The formula weight can be determined using a periodic table or by looking at a chemical reagent bottle