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Cell membrane &
Cellular Transport
Biology
Why do cells need cellular
transport?
 Homeostasis (maintain stable internal
environment for cell survival)
 Substances need to move in and out of
the cell as they are needed
Cell Membrane AKA
Plasma Membrane
 Cell boundary that helps controls what
enters the cell and what leaves the cell
 Permeable-being able to pass through
 Semi-permeable—some materials freely
move through; some cannot
 Selective permeable-selects what may
move in or out of the cell
Cell Membrane Diagram
Permeability-Which one is
permeable, semi-permeable, not
permeable at all?
Passive Transport
 DOES NOT REQUIRE ENERGY
 Like riding a bike downhill; its easy, you
coast, and not much energy is required
Types of Passive
Transport
 Diffusion
 Facilitated Diffusion
 Osmosis
Diffusion
 Causes substances
to move across the
cell membrane (high
concentration (a lot
of particles to low
concentration (few
particles)
 Does NOT
require energy
Diffusion Demo
 Example: Perfume smell, Cookie smell
 Example: Making Kool-Aid
 http://highered.mcgrawhill.com/sites/0072495855/student_view0
/chapter2/animation__how_diffusion_wor
ks.html
 http://www.youtube.com/watch?v=jinJNe
Hvowo&feature=related
Facilitated Diffusion
 Also called passive transport
 DOES NOT REQUIRE ENERGY
 Protein channels allow certain substances to
pass through
 Example: HOV lanes in Atlanta
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapt
er2/animation__how_facilitated_diffusion_work
s.html
Osmosis
 Diffusion of water
through a selectively
permeable
membrane
 DOES NOT
REQUIRE ENERGY
Active Transport
 REQUIRES ENERGY
 Movement of substances from lower
concentration to higher
 Like you trying to move through crowded
halls or ride a bike uphill; it takes a large
amount of energy
Types of Active Transport
 Endocytosis—Movement INTO the cell
 Exocytosis—Movement OUT of the cell
Tonicity
 Remember, water flows from an area of high
concentration to an area of low concentration
through diffusion and osmosis
 Solution—mixture made of two substances
mixed and evenly distributed
 Ex: Salt water
 Solvent—substance that does the dissolving
 Ex. Water
 Solute—substance being dissolved
 Ex. Salt
Tonicity
 The solution outside the cell may have a
different concentration of solute inside
the cell
 Equilibrium-when water molecules are
evenly distributed on both sides of the
membrane
Isotonic
 The concentration of solutes is the same
on either side of the membrane
 Water enters and leaves the cell at the
same rate.
 Diagram:
Hypotonic
 Hypo-means LESS
 Less solute outside the
cell; more water outside
the cell
 Water pressure outside
the cell pushes water
into the cell
 Causes cells to swell
or burst
 Animal cells may burst!
 Hypo—”Oh no! It’s
going to burst!”
 Diagram:
Hypertonic
 Hyper-mean MORE
 More solute molecules
outside the cell; less
water outside the cell
 Water pressure pushes
water outside the cell
 CELL WILL SHRINK
OR CONTRACT
 Plant cells can wilt
 Diagram:
Three Types of Diffusion
Types of Diffusion
Review
 http://highered.mcgrawhill.com/sites/0072495855/student_view0
/chapter2/animation__how_osmosis_wor
ks.html
ADD TO NOTES
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BIO---means “life”
ENDO—means “inside”
EXO-– means “outside”
LOGY—means “study of”
CYTO---means “cell”
OSIS– means “process or action”