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Cell Membrane & Transport
Unit 2: The Cell
Types of Outer Cell Boundaries:
CELL WALL
•outer boundary
found in plant cells,
bacteria, fungi,
some protists
•Thick and inflexible
•Function: Provides
support for plant
cell
•Never found in
animal cells
Cell (Plasma) Membrane
• Thin, flexible barrier
between cell &
environment (All cells)
• Selectively permeable
• Functions:
1)Controls movement in
and out of cell
2)Allows cell recognition;
boundary for cell
3)Maintains homeostasis:
balance within the cells
Fluid Mosaic Model
• The fluid mosaic model
states that the cell
membrane is a lipid bilayer
made up of molecules
which are free to move.
• Phospholipids: fatty areas
that attract and repel
water causing the
membrane to behave like
a fluid
• Hydrophilic heads (Polar):
close to water as possible
• Hydrophobic tails (Nonpolar): far away from
water as possible
Animation:
http://www.johnkyrk.co
m/cellmembrane.html
Embedded Proteins
1) Determine which
particles can pass
through
2) Serve as recognition
markers
3) Form channels from
one side of the cell
to the other
4) Used in facilitated
diffusion
Movement Across the
Membrane
1. PASSIVE Transport: requires
no energy, movement
from HIGH to LOW
concentration
* Examples: diffusion,
osmosis
*No Energy required
2. ACTIVE Transport: requires
energy, movement from
LOW to HIGH
concentration
* Examples: endocytosis,
exocytosis
*Energy required! ATP
Types of PASSIVE Transport
• Movement WITH the
concentration gradient
DIFFUSION: movement of
particles from high
concentration to low
concentration
• Causes substances to move
across membrane
• Does not require the cell to
use energy
• Substances move across
membrane until both sides
are equal (EQUILIBRIUM)
•OSMOSIS: diffusion of water through a membrane
•water moves from where there is a lot to where there is a little
until it reaches equilibrium
•exerts pressure (OSMOTIC PRESSURE) which can cause
cell swelling
Higher Concentration
of Water
Water molecules
Lower Concentration
of Water
Sugar molecules
Diffusion may be:
FACILITATED
• Process by which
proteins in the
membrane help
substances enter the
cell
• Protein channels are
SPECIFIC only allowing
some things in/out
• Movement from HIGH
to LOW
Types of ACTIVE Transport
• Movement AGAINST the
concentration gradient
• Energy required
• ENDOCYTOSIS: cells ingest
external fluid,
macromolecules, and large
particles
– Phagocytosis: cell takes in food
– Pinocytosis: cell takes in water
• EXOCYTOSIS: cells remove
fluids, macromolecules and
large particles
TYPES OF
SOLUTIONS
•HYPERTONIC:
concentration is higher
inside the cell than outside
(water)
•HYPER means “above
strength”
•Water moves OUT of cell
causing it to shrivel
•Can result in
PLASMOLYSIS in plants
which causes wilting
• ISOTONIC: solution
where
concentrations of
dissolved
substances outside
the cell is the same
as the inside of the
cell
• ISO- means “equal
to”
• Movement into
cell= movement out
of cell
•HYPOTONIC: concentration
of water is higher outside the
cell than inside
•HYPO means “below
strength”
•Water will move INTO cell
causing it to swell
•Cells could rupture if the cell
takes in too much water
•This increases pressure
inside of cell (TURGOR
PRESSURE)
Animation:
http://www.tvdsb.on.ca/w
estmin/science/sbi3a1/Cell
s/Osmosis.htm
Hippo
Hypo