BIOLOGY 12 - Cell Membrane and Cell Wall Function: Chapter Notes
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The cell membrane is the gateway into the cell, and must allow needed things such as nutrients into the cell without
letting them escape. In the same way, it must allow wastes to leave the cell. A wide variety of molecules and
substances must pass through the cell membrane -- large, small, hydrophobic, hydrophilic. Molecules of the same
size must sorted out, and the cell must also be able to get large amounts of molecules in and out when necessary. How
can the cell membrane accomplish this?
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The answer lies in its structure. We already know about the FLUID MOSAIC MODEL of membrane structure. Why is it given that
name?
Review of FLUID MOSAIC MODEL:
double layer of
_______________
molecules (“X” on diagram)
 consistency of
__________________
(~fluid)
 ____________ wholly or
partly embedded in
phospholipid bilayer 
forms mosaic pattern
 ________________ strung
together in chains are
attached to proteins
Please Label the Parts of the Cell Membrane
("____________") or lipids
("____________") of membrane. Function as ____________ ____________for cell recognition (helps
immune system identify which cells belong to body and which are invaders).
is ________________________: some molecules enter the cell, while other molecules (which can be the
same size) are not allowed to enter. The cell membrane can discriminate between different molecules that
are the same size!
all living cells, whether plant, animal, fungal, protozoan, or bacterial, are surrounded by cell membranes
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Plant Cell Wall
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Primary Cell Wall
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Secondary Cell Wall
plants have ____________in addition to cell membranes.
The cell wall lies ____________ the cell membrane.
(bacteria have cell walls too, but bacterial cell walls are NOT the
same in composition as plant cell walls).
____________ of cell wall varies with cell function
________________________ is
outermost layer, composed of threadlike
cellulose microfibrils.
sticky substance called middle lamella binds cells together
woody plants also have a ____________cell wall which forms inside the primary wall. Composed of
alternating layers of cellulose microfibrils reinforced with lignin (which adds strength). Function is support of
Cellulose Microfibrils
large plants. Wood is made largely of secondary cell wall material.
Cellulose of plant cell walls used by humans: cotton, rayon, flax, hemp, paper, wood, paper (paper has lignin removed to prevent
yellowing). Lignin used in manufacture of rubber, plastics, pigments, adhesives.
plant cell wall is FREELY PERMEABLE (anything small enough to fit through openings in cellulose microfibrils will get through).
plant cell therefore relies instead on its cell membrane to regulate what gets in and out.
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THERE ARE THREE GENERAL MEANS BY WHICH SUBSTANCE CAN ENTER AND EXIT CELLS:
Name
Examples
1.
2.
3.
Diffusion
BEFORE
AFTER
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diffusion is a physical process that can be
observed with any type of particle. A
__________________________________
__
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Law of Diffusion: particles MOVE FROM THE
AREA OF ______________________TO THE
AREA OF
______________________
UNTIL EQUALLY DISTRIBUTED.
for instance: opening a perfume bottle in corner of a room. The smell of perfume soon permeates the room because the molecules
that make up the perfume have drifted to all parts of the room. e.g. dropping dye into water.
 movement by diffusion ________________________to be added (although adding energy (i.e. heat) will speed it up).
 diffusion is a ____________ process. The rate of diffusion is affected by the ____________ ____________ (the
difference in concentration of the diffusing molecules between the two regions), the __________ ______ ________of the
molecules, and the ____________. Diffusion in liquid is slower than in gas. However, distribution of molecules in cytoplasm is
speeded up by an ever-constant flow of the cytoplasm that is called cytoplasmic streaming.
Three Ways of increasing the rate of diffusion:
1. ________________________
2. ________________________
3. ________________________
 The properties of the cell membrane allow ____________ of molecules to pass by diffusion: Lipid-soluble molecules like
steroids and alcohols can diffuse directly across because the membrane itself is made of lipids.
 ____________ moves readily across membrane, probably through charged, protein-lined pores called ____________ in the
membrane (remember, water is not lipid-soluble) that will not allow anything else but water through.
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Osmosis
 the movement of water across a selectively permeable membrane is a ________________________called ____________
Definitions:
Osmosis:
Solute:
Solvent:
Solution:
Osmotic Pressure:
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Explain what would
happen to the
concentrations of
water, glucose, and
copper sulphate on
side A of this
experiment.
.
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In cellular systems, ______________________, but other molecules can't. Therefore, it is often ______________________that
can move and follow the law of diffusion. According to the law of diffusion, water will move from where there is more of it (i.e.
solution that has less solute in it) to where there is less of it (i.e. solution that has more solute in it). This has important
consequences on living systems.
TONICITY: Comparison of the concentration inside a cell to the concentration of the surrounding solution.
Summary of what happens to ANIMAL CELLS placed in different tonicities of solution:
Tonicity of Solution Cell is Put Into
Net Movement of Water
Effect on Cell
H2O
“lysis”
H2O
“crenation”
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Significance of Tonicity to PLANT CELLS
Summary of what happens to PLANT CELLS placed in different tonicities of solution:
Tonicity of Solution Cell is Put Into
Net Movement of Water
Effect on Cell
H2O
“turgor pressure”
H2O
“plasmolysis”
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TRANSPORT BY CARRIERS
FACILITATED TRANSPORT
FACILITATED TRANSPORT
BEFORE
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OUTSIDE CELL
INSIDE CELL
OUTSIDE CELL
utilizes ______________________in cell membrane to control
passage of molecules in and out of cell.
are ______________________- each carrier passes only one
type molecule
molecules only pass along concentration gradient.
______________________- is like diffusion in this sense
explains how ______________________like ______________________ and ______________________cross the cell membrane.
INSIDE CELL
ACTIVE TRANSPORT
 also performed ______________________
 ______________________ (ATP)
 moves molecules ______________________ ______________________ ______________________ (i.e. in the opposite direction
of diffusion).
ACTIVE TRANSPORT
BEFORE
 molecules move from _____________
_________ to ____________________________________________.
 Active Transport vitally important to organisms:
e.g. Iodine & Thyroid Gland. [I+] is low in blood, high in Thyroid
Gland. Active Transport moves I+ from blood to thyroid.
e.g. Na+ actively transported out of urine by kidney tubule cells
e.g. sodium/potassium pump in nerve/muscle cells (see text).
Moves Na+ from inside to outside of cell, and K+ from outside to
inside.
OUTSIDE CELL
OUTSIDE
CELL
INSIDE CELL
INSIDE CELL
e.g. Na+ Cl- and cystic fibrosis - a genetic disease, usually
fatal, caused by blockage of Cl- transport.
ENDOCYTOSIS AND EXOCYTOSIS
 another way to get molecules, ____________________________________________, in and out of cell.
 ______________________: cell membrane forms a ______________________ around the substance to be taken in.
 ______________________: what you call endocytosis if particles taken in really large (like other cells - e.g. human
macrophages). Can be see with light microscope.
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______________________: (= cell drinking) - same idea as phagocytosis, except smaller particles taken in (requires electron
microscope to see).
______________________: Reverse of endocytosis. Vacuole within cell fuses with cell membrane and the vacuole contents are
deposited on the outside. Important in secretion and excretion in cells.
REVIEW QUESTIONS
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1.
A drop of ink is placed on the surface of the water. Eventually the ink is evenly distributed throughout the entire beaker. Explain
how this happens using what you know about molecules and their motions.
2.
A blood cell is placed in a solution. The concentration of salt is higher in the solution than inside the cell. The cell membrane
allows water to go through but not the salt ions.
a. Draw a series of three pictures showing what happens to the cell over time with the last
picture showing the equilibrium stage.
Change in time
b. Explain, as the blood cell changes volume, what happens to the concentration of salt
inside and outside the cell.
3. The kidneys remove small molecules of waste from the blood, leaving behind large molecules,
such as proteins, and blood cells. When kidneys do not work well, an artificial kidney is needed.
Inside the artificial kidney, blood goes to a container separated by a
cellophane membrane from another container that holds fluid.
a. The membrane must have channels that are (check all that apply):
__Larger than salt ions
__Smaller than salt ions
__Larger than waste molecules
__Smaller than waste molecules
__Larger than blood cells
__Smaller than blood cells
b. Suppose the liquid coming out of the wastes tube is pumped directly back to the
washing fluid tube. Describe what would happen.
4. A lab technician needs to remove salt ions from a protein solution in
order to restore the protein’s structure. To do so, she needs to place the
sample containing proteins and salt in a dialysis bag and then place the
bag in beaker of water so the salt can be removed.
She needs to choose the size of the beaker. She has a choice of the
following three beakers.
a. Circle the one she should choose to remove the most salt.
b.
Explain why you circled the beaker you did.
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