• Also known as the “Plasma Membrane”
• Made of lipids & proteins
• Called the Fluid Mosaic Model and/or
the Phoso-Lipid Bilayer
• Comes in contact w/the internal &
external environment
• Semi-permeable (shows selective
permeability)
characteristic of
cell membranes
that allows some
chemicals to pass
through them
more easily than
others
The chemicals that a
membrane allows to
pass through it
depends on several
of the chemicals'
characteristics
including size, shape
and electrical charge.
Composed of
two layers of
lipids with
proteins
scattered
throughout
:
The Cell Membrane
•Composed of a lipid bi-layer and
transport proteins embedded in the bilayer.
•
+
•Has receptors on its surface which allows
the cell to recognize hormones and
communicate with cells.
Why do we need proteins in a
cell membrane?
1. Transport: Move materials within,
and in and out the cell.
2. Enzymes: Speed up reactions to
complete life functions.
3. Receptors: Binds with other
substances for cell communication.
Aim: How do materials move
through the cell membrane?
Do Now: Draw and Identify the lipid bi-layer,
proteins and receptors.
Role of the Cell Membrane
1. The cell (plasma) membrane provides
the following for the cell :
A. Protection
B. Shape
C. Strength
D. A structure that helps regulate the flow of
materials going into and out of the cell
E. All of the above
Process by which a
substance moves from an
area of high
concentration to an area
of low concentration.
Movement of molecules
with the concentration
gradient.
No energy is necessary.
DIFFUSION
LOW
HIGH
HIGH
Why we can smell
things
Why the whole spoon
gets hot when it's only
half in the tea
LOW
Why smoke spreads to
fill a whole room
The movement of molecules from an area of high
concentration to an area of low concentration across
the cell membrane.
When there is NO net movement of molecules
into or out of the cell, it is said to be in
Equilibrium
DIFFUSION
OF SOLUTE
ACROSS A
MEMBRANE
What about Water?
• Water crosses the cell membrane by a
process of Osmosis.
• Osmosis: is a type of passive transport in
which water flows from high to low
concentration
• A process in which molecules
are moved from an area of
low concentration to an area
of high concentration.
• Movement of molecules
against the concentration
gradient
• Energy is required.
Energy needed for active
transport would come
from ………
Aim: How important is active transport
to cell function?
Do Now:
1. Explain the difference
active and passive
transport and
osmosis.
1. Materials must transport through the
cell membrane in order to:
•Maintain homeostasis
• Achieve equilibrium
•Eliminate cellular wastes
•Provide other “body” parts with need
molecules
2. Substances that may enter a cell include:
Oxygen, water, nutrients
Substances that may leave a cell
include:
Carbon dioxide, water, urea
2 types of Active Transport:
a)Endocytosis
b)Exocytosis
ENDOCYTOSIS
 Process of transporting
materials into a cell
 2 types of Endocytosis:
a) Phagocytosis (solid)
b) Pinocytosis (liquid)
video
ENDOCYTOSIS: Phagocytosis
ENDOCYTOSIS: Pinocytosis
EXOCYTOSIS
 Process of releasing materials from
inside the cell by discharging it
from organelles
 What organelle might have
materials waiting for elimination?
video
ENDOCYTOSIS & EXOCYTOSIS
PASSIVE vs ACTIVE
TRANSPORT
A
B
C
The life function of transport in
an organism directly involves
those activities used to
1.
2.
3.
4.
absorb and distribute materials
obtain and hydrolyze materials
release energy from food
produce cellular waste
products
The diagram represents a white
blood cell engulfing some
bacteria. The structure labeled
X is most likely a
1.
2.
3.
4.
nucleus
centriole
ribosome
vacuole
What about Water?
• Water crosses the cell membrane by a
process of Osmosis.
• Osmosis: is a type of passive transport in
which water flows from high to low
concentration
Is energy needed for OSMOSIS?
Making Observations
Notice the number of water molecules
Aim: How is water balance achieved in living
things?
Do Now: Predict the movement of
molecules in the diagram below.
Hypotonic Solutions: contains a lower
concentration of solute outside the cell. The
water diffuses into the cell, causing the cell to
swell and possibly explode.
w
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Hypertonic Solutions: contain a higher
concentration of solute outside the cell. The
water diffuses out of the cell, causing the cell
to shrivel.
w
w
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w
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Isotonic Solutions: contains the same
concentration of solute as the cell. The water
diffuses into and out of the cell at the same
rate, no change occurs in the cell.
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Video
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the movement of WATER molecules
from an area of high concentration to
an area of low concentration.
Cell membranes are completely permeable
to water, therefore, the environment the cell
is exposed to can have a dramatic effect on
the cell.
• Movement of
WATER from a
higher
concentration
to
a lower
concentration
WATER BALANCE OF LIVING
THINGS
C
E
L
L
Outside of cell
M
E
M
B
R
A
N
E
Inside of Cell
Type of cell:
Plant cell
Type of solution added:
Saltwater
Answer the following:
A
Hypothesize
State
Identify
B
If a human cheek cell is placed in
distilled water, what changes
would occur to the cell?
EXPLAIN why these changes
would occur.
Less than 100% water
100% water
If a human cheek cell is placed in
98% saltwater, what changes would
occur to the cell? EXPLAIN why
these changes would occur.
Less that 98% salt
More than 2% water
98% salt
2% water
What materials diffuse into the
cell? Why?
• Materials needed for life functions
diffuse into the cell.
• These materials include: OXYGEN,
GLUCOSE and AMINO ACIDS.
• The size and charge of the materials
usually determines if the materials will
be allowed across the membrane using
diffusion.
A swollen
Red Blood
cell
A shriveled
Red Blood A normal
cell
Red Blood
cell
Answer the following questions:
1. Why must materials be able to
complete transport through the cell
membrane?
2. List 3 things which must enter a cell?
List 2 things that must exit a cell?
What type of molecules enter and
leave the cell?
Materials needed for homeostasis enter the cell.
These include:
1. OXYGEN
2. GLUCOSE
3. Digested nutrients (amino acids, fatty acids)
Waste materials from the life functions that
leave the cell.
These include:
1. Carbon dioxide (CO2)
2. Urea
Key points!
• The cell membrane controls what enters and
leaves the cell membrane.
• Passive transport is the movement of
materials into and out of the cell which does
not require energy (ATP)
• Diffusion is one type of passive transport in
which material move from high concentration
to low concentration.
• Only small material diffuse easily across the
cell membrane.