PRESCRIBED LEARNING OUTCOMES (Chapter 4, pp. 65-76)
G1. Apply knowledge of organic molecules to explain the structure and
function of the fluid-mosaic model
G2. Explain why the cell membrane is described as “selectively
permeable”
G3. Compare and contrast the following: diffusion, facilitated transport,
osmosis, and active transport.
G4. Explain factors that affect the rate of diffusion across a cell
membrane.
G5. Describe endocytosis, including phagocytosis and pinocytosis, and
contrast it with exocytosis.
G6. Predict the effects of hypertonic, isotonic, and hypotonic
environments on animal cells
G7. Demonstrate an understanding of the relationship and significance
of surface area to volume, with reference to cell size.
_____ Active transport
_____ ATP energy
_____ Blood antigen
_____ Concentration gradient
_____ Crenate
_____ Diffusion
_____ Endocytosis
_____ Exocytosis
_____ Facilitated transport
_____ Glycolipid
_____ Glycoprotein
_____ Hemolysis
_____ Hypertonic
_____ Hypotonic
_____ Isotonic
_____ Na/K pump
_____ Neuron
_____ Osmosis
_____ Osmotic pressure
_____ Phagocytosis
_____ Phospholipid
_____ Pinocytosis
_____ Polarity
_____ Protein channels
_____ Receptor sites
_____ Selectively permeable
_____ Solubility
_____ Solute
_____ Solvent
_____ Surface area/volume ratio
_____ Thyroid gland
_____ Thyroxin
_____ Tonicity
_____ Turgor pressure
_____ Villi
_____ Viscosity
SELECTIVELY PERMEABLE: Controls what comes in and out
of the cell. Does not let large, charged or polar things through
without help.
FLUID MOSAIC MODEL: The phospholipids move, thus
allowing small non-polar molecules to slip through.
GLYCOLIPIDS and GLYCOPROTEINS: Act as
receptors – receive info. from body to tell cell
what to do.
INTEGRAL PROTEINS: assists specific larger and charged
molecules to move in and out of the cell. Can act as ‘tunnels’
or will change shape.
CHOLESTEROL: Reduces membrane fluidity by reducing
phospholipid movement. Also stops the membrane from
becoming solid at room temperatures.
CYTOSKELETON: A cytoskeleton acts as a framework that
gives the cell it's shape. It also serves as a monorail to
transport organelles around the cell.
Everything that is transported across the cell membrane
takes place by one of two fundamental processes:
1. Passive transport moves
molecules from a [high] to
[low] in order to establish
equilibrium.
The molecules may or may
not need to use a protein
channel or carrier.
2. Active transport moves molecules from [low] to [high],
AGAINST the concentration gradient and this process
requires energy in the form of ATP.
Simple Diffusion is a passive process ( no energy required).
Some substances will diffuse through
membranes as if the membranes
weren’t even there.
Molecules diffuse until they are
evenly distributed.
The molecules move from an area of [high] to [low].
EXAMPLES of molecules that easily cross cell membranes
by simple diffusion are: oxygen, carbon dioxide, alcohols,
fatty acids, glycerol, and urea.
Fatty Acids, Glycerol,
Alcohol & Urea
The rate of diffusion will be increased when there is :
1. Concentration: the difference in [ ] between two areas
(the [ ] gradient) causes diffusion. The greater the
difference in concentration, the faster the diffusion.
2. Molecular size: smaller substances diffuse more quickly.
Large molecules (such as starches and proteins) simply
cannot diffuse through.
3. Shape of Ion/Molecule: a substance’s shape may prevent
it from diffusing rapidly, where others may have a shape
that aids their diffusion.
4. Viscosity of the Medium: the lower the viscosity, the more
slowly molecules can move through it.
5. Movement of the Medium: currents will aid diffusion. Like
the wind in air, cytoplasmic steaming (constant movement
of the cytoplasm) will aid diffusion in the cell.
6. Solubility: lipid - soluble molecules will dissolve through
the phospholipid bilayer easily, as will gases like CO2 and
O2.
7. Polarity: water will diffuse, but because of its polarity, it will
not pass through the non-polar phospholipids. Instead,
water passes though specialized protein ion channels.
Osmosis is the diffusion of water across a selectively
permeable membrane driven by a difference in the
concentration of solutes on the two sides of the membrane.
A selectively permeable
membrane is one that
allows unrestricted
passage of water, but not
solute molecules or ions.
So it is the WATER THAT
MOVES to create
equilibrium!!!
•
Osmosis requires NO ENERGY.
•
Osmosis is the net movement of
WATER molecules from the area
of [high] of water to the area of
[low] of water until it is equally
distributed.
•
Because membranes often
restrict or prevent the movement
of some molecules, particularly
large ones, the water (solvent)
must be the one to move.
•To cross the membrane,
water must move through
a protein ion channel.
•In certain cellular
conditions, these protein
channels can be opened
or closed (ie: in the
kidneys, large
intestines) depending on
how much water is
needed by the body.
The tonicity of a solution will affect the size & shape of cells:
ISOTONIC SOLUTION:
1. the solution concentration is
equal on both sides of the
membrane .
2. There is no net concentration
difference across the cell
membrane
3. Water moves back and forth,
but there is no net gain or
loss of water.
HYPERTONIC SOLUTION:
1. The solution outside the cell
is more concentrated than
inside.
2. There is more water inside
the cell and the water will
move out of the cell.
3. This causes the cell to
shrink
4. *Memory Trick... Hyper
people get skinny!
HYPOTONIC SOLUTION:
1. The concentration inside the
cell is more concentrated than
outside.
2. Therefore there is more water
outside of the cell, and water
will move into the cell.
3. This will cause the cell to
swell.
4. *Memory Trick... Hippos are
FAT!
In Biology we usually talk about the SOLUTION’S tonicity,
NOT the cells!
*MEMORY TRICK: If you eat a lot of sugar (ie: solute)
you get HYPER. The solution with a lot of solute is
called HYPEROSMOTIC.
When we speak of plants, we speak of TURGOR PRESSURE.
Which of these cells is in a hypertonic solution? Hypotonic?
Facilitated Transport: Some molecules are not
normally able to pass through the lipid membrane,
and need channel or carrier proteins to help
them move across.
This does not require energy when moving
from [H] to [L] (with the concentration gradient).
Molecules that need help to move through the
plasma membrane are either charged, polar,
or too large.
If molecules are POLAR, CHARGED, or TOO LARGE they
need a protein the help them across the membrane
EXAMPLES: sugars, amino acids, ions, nucleotides ….
Each protein
channel or protein
carrier will allow
only ONE TYPE
OF MOLECULE to
pass through it.
Many channels contain a “gate” which control the channel's
permeability.
When the gate is open, the channel transports, and when the
gate is closed, the channel is closed.
These gates are extremely important in the nerve cells.
Active Transport: the movement of
polar, large, and charged molecules
moving against the [ ] gradient
(uphill).
EXAMPLES of molecules that
move this way are all of the things
that require protein carriers to move
across the plasma membrane.
ions (like Na+ and K+ in cells, and
iodine) and sugars, amino acids,
nucleotides...
Example 1: the thyroid gland accumulates
iodine as it is needed to manufacture the
hormone thyroxin.
The iodine concentration can be as much as 25
times more concentrated in the thyroid than in
blood.
Example 2: a Na/K pump (mostly in nerve membranes).
These function to restore electrical order in a nerve after an
impulse has traveled along it.
Example 3: In order to make ATP in the mitochondria, a
proton pump (hydrogen ion) is required.
Endocytosis: (“Endo” means “in”).
Endocytosis is the taking in of molecules or particles by
invagination of the cell membrane forming a vesicle.
This requires energy.
There are two types of endocytosis:
1. pinocytosis (cell drinking): small
molecules are ingested and a vesicle is
immediately formed. This is seen in
small intestine cells (villi)
2. phagocytosis (cell eating): large
particles, (visible with light microscope)
are invaginated into the cell (ie: white
blood cells ‘eat’ bacteria).
Exocytosis: (“Exo” means “out”.)
•Exocytosis is the reverse of
endocytosis.
•This is where a cell releases the
contents of a vesicle outside of the cell.
•These contents may be wastes, proteins, hormones, or
some other product for secretion.
•This also requires energy.
•Example: vesicles from the Golgi fuse with the plasma
membrane and the proteins are released outside of the cell.
Cells exist individually, or in groups
forming tissues, organs, and
eventually organisms.
Their size is a very important
factor for their survival.
Cells are the size they are because
that is the size they have to be
in order to function
effectively.
The materials it needs to use, and the wastes it needs to
remove must pass in and out of the cell through the cell
membrane.
As a cell grows, it suffers the possibility of the volume
increasing faster than the surface area.
The bigger the cell, the more it needs and the more it needs
to get rid of.
If the cell gets too big, there will not be enough room on the
plasma membrane for things to get in and out quickly
enough to maintain the cell.
Why? Its surface area has not kept up to its volume size.
When the volume of a cell increases, the amount of surface
area does not increase in the same proportion.
When cells grow larger,
if they don’t want to
die, the only real
solution is to divide.
Once a cell has divided,
the surface area to
volume ratio will
increase and the
problem is solved.
*When you see questions regarding surface area to
volume ratio, think of a water balloon.
(ie: when you squish a water balloon, it has the same
volume, but the surface area is increased!)