TRANSPORT ACROSS THE
MEMBRANE
UNIT G
Power Point Notes
THINGS I NEED TO KNOW: (Chapter 4, pp. 65-76)
G1. Apply knowledge of organic molecules to explain the structure and function of the fluidmosaic 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.
VOCABULARY
_____ 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
PLASMA MEMBRANE
A) __________________________: Controls what comes in and out of the cell.
Does not let large, charged or polar things through without help.
B) FLUID MOSAIC MODEL: The _____________________, thus allowing small
non-polar molecules to slip through.
C) INTEGRAL PROTEINS: ______________ specific larger and charged
_____________________________ of the cell. Can act as ‘tunnels’ or will
change shape.
Everything that is transported across the cell membrane takes
place by one of two fundamental processes:
1. ______________ transport moves molecules from a _________ to ____________
in order to establish equilibrium.
The molecules may or may not need to use a _________ channel or carrier.
2. ______________ transport moves molecules from _______ to _______,
__________ the concentration gradient and this process requires __________ in the
form of ATP.
SIMPLE DIFFUSION
Simple Diffusion is a _________ process ( ______ energy required). Some substances will diffuse
through membranes as if the membranes weren’t even there.
Molecules diffuse until they ______________ distributed.
The molecules move from an area of __________________.
EXAMPLES of molecules that easily cross cell membranes by simple diffusion are:
__________________ _________________________________________________.
The rate of diffusion will be increased when there is :
1. _________________: the difference in [ ] between two areas (the [ ] gradient) causes
diffusion. The __________ ______________________, the __________ the diffusion.
2. _________________: smaller substances diffuse more _____________. Large molecules
(such as starches and proteins) simply cannot diffuse through.
3. __________________: a substance’s shape may _____________ it from diffusing rapidly,
where others may have a shape that aids their diffusion.
4. ________________________: the lower the viscosity, the more _____________ molecules
can move through it.
5. ______________________: currents will aid diffusion. Like the wind in air,
______________________ (constant movement of the cytoplasm) will aid diffusion in the cell.
6. _______________: _________-soluble molecules will dissolve through the phospholipid
bilayer ____________, as will gases like CO2 and O2.
7. _______________: ___________ will diffuse, but because of its polarity, it will _________
pass through the non-polar phospholipids. Instead, water passes though specialized
__________________ channels.
OSMOSIS
Osmosis is the ____________________ across a
selectively permeable membrane driven by a
______________________ _____________________
on the two sides of the membrane.
A selectively permeable membrane is one that allows
unrestricted passage of _________, but not solute
molecules or ions.
So it is the ____________ _____________ to create
equilibrium!!!
•
Osmosis requires ____ ENERGY.
•
Osmosis is the net movement of WATER molecules from the
area of _________ of water to the area of _________ of water
until it is _____________________.
•
Because membranes often __________________ the
movement of some molecules, particularly large ones, the water
(_____________) must be the one to _______________.
•
•
To cross the membrane, water
must move through a
___________________.
In certain cellular conditions, these protein channels can be
opened or closed (ie: in the _____________, _______
____________________) depending on how much water is
needed by the body.
TONICITY OF A SOLUTION
The tonicity of a solution will affect the size & shape of cells:
I.__________________________:
1. the solution concentration is __________ 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 _______________
_______________ of water.
II. _________________________:
1. The solution ____________ the cell is more concentrated than inside.
2. There is more water inside the cell and the water will move _________
of the cell.
3. This causes the cell to ____________
*Memory Trick...
III. __________________________:
1. The concentration _________ the cell is more concentrated than outside.
2. Therefore there is more water outside of the cell, and water will move
________ the cell.
3. This will cause the cell to __________.
4. *Memory Trick...
MEMORY TRICK: If you eat a lot of sugar (ie: solute) you get _____________. The solution with a
lot of solute is called __________________.
Water always moves towards the _________________________________.
HYPEROSMOTIC = MORE [ SOLUTES ]’d
When we speak of plants, we speak
of ______________________.
Which of these cells is in a hypertonic
solution? Hypotonic?
FACILITATED DIFFUSION
Facilitated Transport: Some molecules are ________ normally able to pass through the
lipid membrane, and need _______________ _____________ to help them move across.
This does ___________________ when moving from [H] to [L] (with the concentration gradient).
Molecules that need help to move through the plasma membrane are either _____________
_____________________________________.
The protein channels and carriers are very ___________________________________.
Each protein channel or protein carrier will allow only ___________ ______________ to pass through
it.
Many channels contain a “____________” 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 _____________ cells.
ACTIVE TRANSPORT
Active Transport: the movement of polar, large, and charged molecules moving __________ the [ ]
gradient (___________).
EXAMPLES of molecules that move this way are all of the things that require protein carriers to
move across the plasma membrane.
__________ (like Na+ and K+ in cells, and iodine) and _____________________________...
Examples of Active Transport
Example 1: the ______________ accumulates iodine as it is needed to manufacture the hormone
thyroxin.
The ____________ concentration can be as much as 25 times
more concentrated in the thyroid than in blood.
Example 2: a _____________ (mostly in nerve membranes).
These function to restore electrical order in a nerve after an
impulse has traveled along it.
Example 3: In order ____________ in the mitochondria, a proton
pump (hydrogen ion) is required.
ENDOCYTOSIS
Endocytosis: (“Endo” means “________”).
Endocytosis is the taking in of molecules or particles by ________________ of the cell membrane
forming a vesicle.
This ____________________.
There are two types of
endocytosis:
1. _____________ (cell drinking): small molecules are ingested and a vesicle is immediately
formed. This is seen in _________________ cells (villi)
2. ______________ (cell eating): large particles, (visible with light microscope) are invaginated
into the cell (ie: ______ _______________________________).
EXOCYTOSIS
Exocytosis: (“Exo” means “_______”.)
• Exocytosis is the _____________ of endocytosis.
• This is where a cell _______________ ________ of a vesicle outside of the cell.
• These contents may be _____________________________, or some other product for
secretion.
• This also ___________________.
• Example: vesicles from the _________ fuse with the plasma membrane and the proteins are
released outside of the cell.
CELL SIZE
Cells exist individually, or in groups forming tissues, organs, and eventually organisms.
Their ___________ 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
The materials it ________________, and the ____________ 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 ____________ _______________________ than the
surface area.
The bigger the cell, the _________________ and the more it needs to get rid of.
If the cell gets __________, there will ___________________ on the plasma ______________ 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 _________________________________ .
When cells grow larger, if they don’t want to die, the only real solution is to ______________.
Once a cell has divided, the surface area to volume ratio will ________________ and the problem is
solved.