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Cell Membranes
•The cell / plasma membrane is _____________________________________________.
Selective in that it allows ____________ things in and some things out of the cell. Recall
that phospholipids have hydrophobic _______________ and hydrophilic ___________.
The term to describe this property is _________________________________________.
•An early model of the cell membrane is pictured on the left below. This model is called
the “_____________________________ model”. While it is inaccurate, it got other
scientists thinking about what makes up the cell membrane.
•The current and accurate cell membrane model is on the right above. This model is
called the ___________________________ model. Fluid because the cell membrane is
not ________________________________.
Q: What components of the cell membrane are in a “mosaic pattern”?
________________________________________________________________________
•The fluid property of the cell membrane allows the phospholipids to move easily in a
___________________________ direction. Sometimes however, the phospholipids can
___________________________ across the membrane.
•The _______________________ hydrocarbon tails that have double bonds give the cell
membrane more fluidity. While the _______________________ hydrocarbon tails make
the cell membrane more rigid.
Q: Image C above shows cholesterol (a steroid/ lipid) in the cell membrane. At room
temperature what does adding cholesterol to the cell membrane do to the cell membrane?
________________________________________________________________________
Q: Same question, but what happens if you add cholesterol to the cell membrane at low
temperatures? ___________________________________________________________
•This property allows _______________________ that live in very cold climates to still
maintain plasma membrane function. I.e. the ______________________ of animals like
a moose have a lot of cholesterol to prevent freezing when exposed to snow.
Q: Number the components to the cell membrane below.
1. ECM
2. Integral / Transport Protein
3. Cholesterol
4. Peripheral Protein
5. Cytoplasm / Cytosol
6. Phospholipids
7. Glycoprotein
8. Glycolipid
•Integral / Transport proteins span _______________________ the phospholipid bilayer.
In actuality, they are ___________________________________________ (2° structure).
They allow _______________________________ molecules to enter or exit the cell.
•Peripheral proteins are usually found on the ___________________________ of the cell
membrane. Their role is to give ____________________________________ to the cell.
•The _____________________/ ____________________ tails are what bring about the
“selectively permeable” nature to the cell membrane.
Q: What molecules would not be able to get past the non-polar tails?
________________________________________________________________________
Q: What molecules would easily get past the non-polar tails?
________________________________________________________________________
•The molecules that cannot get past the non-polar tails, will use specific ______________
proteins that have a ___________________________ interior.
•_________________________________ is the tendency for molecules (i.e. a gas or a
solute) to spread out in an open space. A gas for example will diffuse from a ______ to a
______ concentration. In other words, the gas molecules go _______________________
their concentration gradient (a gradient = higher on one side versus the other). Diffusion
is spontaneous, therefore no _____________________________ is required. This is
called ________________________________ transport.
•Osmosis is the __________________________ transport of _________________ from a
_______ to a _________ concentration across a ________________________ permeable
membrane.
Q: In the U-Tube above, what is moving across the selectively permeable membrane (the
dashed line)? How is it moving?
________________________________________________________________________
Q: Draw lines between the correct term and definition.
A) Hypertonic Solution
Same concentration of solutes on both sides
B) Hypotonic Solution
High concentration of solutes in the solution
C) Isotonic Solution
Low concentration of solutes in the solution
•Water always moves from a _________________________________ solution towards a
_____________________________________ solution. If 2 solutions are isotonic, water
___________________ to still move between the 2 solutions at equal ______________.
Q: Name the solutions the plant and animal cells are in below.
Q: Which solution above do terrestrial animal cells want? ________________________
Q: Which solution above do terrestrial plant cells want? _________________________
Animal cells placed in a ___ solution
Hypotonic
Isotonic
Hypertonic
Plant cells placed in a ____ solution
Hypotonic
Isotonic
Hypertonic
The cell will…
The cell will…
•Many terrestrial animal’s cells are in ______________________________ solutions.
Protists however are in ________tonic environments and must _____________________
/ control their water balance and do so with the aide of ___________________________
vacuoles.
•Plant cells respond differently than animal cells in a solution due to the presence of a
________________________________.
•______________________________ diffusion is the ______________________
transport of a substance across the cell membrane from a ______ to a _______
concentration, but it requires a _________________________ protein.
•__________________________ transport differs from diffusion because it requires
___________________________. Active transport is opposite of diffusion, it goes from
a ________ to a _________ concentration. While diffusion occurs spontaneously, active
transport is an _______________ reaction that goes __________________ the
concentration gradient.
•The _________________________ is a good example of active transport.
Q: How many and in which direction are the sodiums and potassiums going?
________________________________________________________________________
•A membrane ___________________________/ electrochemical gradient is the idea that
all cells have voltage on each side of the plasma membrane. The insides of cells are
______________________ in charge, while the outside of cells are _________________.
This favors ______________________ with a positive charge to come into a cell and
_______________________ with a negative charge to exit a cell. __________________
main pump in the body is the __________________ pump, while __________________
main pump is a ______________________ pump. Proton pumps __________________
pump H+ ions __________ of cells from a ___________ to ___________ concentration.
•Potential energy generated by transmembrane solute gradients can be _______________
by the cell and used to transport ____________________________ substances across the
membrane. In other words, a substance that is ________________________ transported
across a membrane can do ____________________ as it ___________________ back by
_____________________________ diffusion (_____ to _____ concentration, no energy
required, through a __________________________________ protein). For example, a
plant cell actively pumps _______ out of a cell. H+ then leaks back into the cell passively
by facilitated diffusion through a transport protein. In doing so it can bring back with it
__________, ________________, or nutrients. This is called _____________________.
Q: How do large molecules enter or exit a cell?
________________________________________________________________________
•Large molecules such as ______________________ or polysaccharides enter cells by
___________cytosis and exit cells by _____________cytosis. If a cell takes in food it is
called __________cytosis. If a cell takes in fluids/ drinks it is called __________cytosis.
•__________________________________ endocytosis is very ____________________
in terms of what a cell takes in. ___________________ on the outside of a cell bind to a
specific molecule. In biology, a general term for any molecule that binds is called a
_____________________. Receptor-mediated endocytosis allows a cell to take in
___________ substances than it normally would, even if the substance is in ________
concentrations outside of the cell. For example, ________________________ (a steroid/
lipid) is acquired this way.
•Transport proteins can also___________________________________ to changes in the
extracellular environment with __________________ transport only! For example, if a
cell has enough Na+, a transport protein can ______________________ down the active
pumping of the molecule up the concentration gradient. However, __________________
or passive transport occurs regardless if a cell has enough of a substance.