Cell Membrane &
Passive Transport
Diffusion
Facilitated 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 gradient
Dynamic 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 low
B. Passive Transportrequires 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 semipermeable 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.Plants wilt
B.animal cell shrink-Plasmolysis
A.
B.
C.
Salt “Sucks” or dehydrates
the water
in plant cells- TurgurPressure
Animal Cells would swell and
burst
Discuss this picture
What organ goes through the process of
osmosis?
Osmosis
Key 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/SSS3
EtKAzYc
Measuring for Molar Solutions
To make 300 mL of a 0.5M NaOH solution.
Convert 300 mL = 0.3 L
_________
concentration
____________
X
__________
_________g__
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 MW
Determine the molecular weight of the solute
The formula weight can be determined using a periodic table or by looking
at a chemical reagent bottle