CHAPTER 7:
Cell Structure and
Function
7-3: Cell Boundaries
BIOLOGY
Vocabulary
• Cell
membrane
• Lipid bilayer
• Concentration
• Diffusion
• Equilibrium
• Osmosis
• Isotonic
• Hypotonic
• Facilitated
diffusion
• Active
transport
• Endocytosis
• Phagocytosis
• Exocytosis
Cell Membrane
Cell membrane:
regulates what
enters and
leaves the cell
 maintains
homeostasis
inside the cell.
-Also protects and supports the cell.
- Made of a lipid bi-layer: a double layered
sheet of lipids (=fatty acids)
Lipid
• Hydrophilic head
= “water loving”
 attracted to
water
• Hydrophobic tail
= “water hating”
 stays away
from water
Lipid bi-layer
●When mixed with water (such as cytoplasm
inside the cell or plasma outside the cell), the
hydrophobic tails cluster together away from
the cytoplasm, and the hydrophilic heads are
attracted to the water in the cytoplasm-----this
forms the lipid bi-layer.
Cell Membrane
• Selectively
permeable
(Semipermeable)=
only some
molecules can
cross through
the membrane
and not others.
Centrioles
• Centrioles = are
located near the
nucleus and help
organize cell division.
- In animal cells, but
NOT in plant cells.
Passive Transport
• Passive
Transport:
DOES NOT
TAKE UP
ENERGY FROM
THE CELL
= (Energy NOT required)
Passive Transport
Passive transport:
diffusion of
molecules
across the cell
membrane
without using
energy from the
cell
Diffusion
• Diffusion:
movement of
molecules from
area of higher
concentration
to an area of
lower
concentration
Diffusion
• Diffusion:
movement of
molecules from
area of higher
concentration
to an area of
lower
concentration
Diffusion Through Cell
Boundaries
• Concentration: the
amount of solute in
a certain amount of
solution
• Solute: dissolved
particle in a solution
(for example, if I mix sugar
into water, sugar is the
solute)
Diffusion Through Cell
Boundaries
These beakers contain
tea.
Which beaker of tea is
more concentrated
(has more solute)?
Diffusion
• When the concentration of the solute is
the same throughout a system, the
system has reached equilibrium.
Diffusion
• Even after equilibrium is reached,
movement will still happen in both
directions in equal amounts (to
maintain equilibrium)
Facilitated Diffusion
• Facilitated
diffusion: certain
molecules pass
through the cell
membrane
through “channel
proteins”
– From areas of high
to low concentration
Requires NO energy from the cell
Active Transport
• Active Transport:
Movement of
molecules against
a concentration
gradient (from low
to high
concentration)
–REQUIRES
ENERGY FROM
THE CELL
Active Transport
• Transport
Proteins (or
Protein Pumps) –
proteins in cell
membranes that
change shape to
help transport
(move) molecules
across cell
membranes
Active Transport of Large Molecules
• Endocytosis: Large
molecules moving
into the cell (such as
food, nutrients).
- cell membrane 1engulfs the molecules
into a small 2pouch which pinches off
and forms a 3vesicle which carries the
molecules through the cell
Endocytosis
Phagocytosis
• Phagocytosis: the
cytoplasm extends
around something and
engulfs it into the cell, or
“eats” it.
- (Ex: amoebas engulf
food, white blood cells
engulf damaged cells or
bacteria)
Exocytosis
• Exocytosis: the
reverse of
endocytosis,
releasing material
out of the cell, like
wastes or proteins
going to other parts
of the body.
Exocytosis
• vesicle (holding
waste or protein)
fuses with cell
membrane and
then pushes the
material out of the
cell.
Osmosis
• Osmosis:
diffusion of
water across
a cell
membrane
from higher
to lower
concentration
Osmosis
• Hypotonic: solute
concentration
outside the cell is
lower than inside
• Hypertonic: solute
concentration
outside cell is
higher than inside
Isotonic
• Isotonic:
solute
concentration
inside and
outside the
cell is equal
Osmotic Pressure
• Turgor
pressure:
pressure
on plant
cell walls
by water
Review of transports across cell
membrane
Cell Membrane
• Protein molecules:
– proteins in cell membrane-stick out,
used for recognition
– proteins in cell membrane-inside,
used for transporting molecules
inside
• Fluid mosaic model: theory that
membrane acts more like a liquid
than a solid, made of many parts
Cell Wall
• Protects cell,
gives support,
prevents
drying out
– Found
outside the
cell
membrane
– Made of
cellulose
Don’t Forget:
• Egg Lab-Day 2
– Carefully remove egg from
cup and dry it off.
– Pour vinegar out of the
cup
– Find the new mass of your
egg
– Put the egg back in the
empty cup
– Fill cup with distilled water