●The cell membrane is “semi-permeable”,
which means that it regulates the passage
of materials into and out of the cell.
●Cells maintain a balance between themselves
and their environment.
●This balance is called equilibrium.
●The cells can adjust to changes in their
environment, but there is a limit to the amount of
change.
●Molecules are in constant motion. As they move,
they tend to go to areas that are less crowded
or “less concentrated”.
●Molecules always spread from an area of higher
concentration to an area of lower concentration.
High concentration
of sugar

Low concentration
of sugar

Equal concentration
of sugar all over

●Two examples of diffusion & passive
transport (no energy required).
1.Perfume / scent around a room
2.Food coloring in water
●In diffusion and osmosis, the molecules move
“downhill” or with the concentration gradient.
●Notice how no energy is required to move in
passive transport.
High
Concentration
Diffusion
Low
Concentration
●How long will molecules continue to move in
diffusion and osmosis?
o Until they are evenly distributed.
●This is known as equilibrium.
●(They will continue moving forever, but you will
not notice the motion once they are evenly
mixed).
●Molecules don’t only move in liquid or gas as
we demonstrated.
o They can also diffuse across the cell membrane
(which is semi-permeable).
Particles (circles)
will move from
inside to outside
until there is an
equal amount of
particles on either
side of the
membrane
INSIDE CELL
OUTSIDE CELL
●The ability of a molecule to pass through a
membrane depends on two things:
1.The size of the molecule
2.The structure of the membrane it is trying to pass
through
●“Semi-permeable” membranes
regulate which molecules enter and
which molecules exit the cell.
Other Terms
•
PERMEABLE – lets anything in/out
•
SEMI – PERMEABLE – lets some thing in/out
•
IMPERMEABLE – lets nothing in/out
●In facilitated diffusion, molecules too big to fit
through the membrane directly will instead pass
through special protein “channels” or “carrier
proteins” in the cell just for these molecules.
●Like diffusion, it does not require energy.
●When molecules move across a cell membrane
to establish equilibrium, it is called diffusion.
●When water moves across a cell membrane, it is
called osmosis.
●Water will enter a cell or leave a cell depending
on the concentration of water inside the cell
and in the surrounding environment.
●Isotonic Environment
oThe concentration of water is equal inside and
outside of the cell.
oWater enters and leaves equally.
●Hypotonic Environment
o The concentration of water is higher outside of the cell.
o More water enters than leaves.
 “hypo-” means “below” or “under”
o What are some other words that start with “hypo-”?
 Hypodermic, hypothermia, hypoallergenic, hypoxia,
hypoglycemic
●Hypertonic Environment
o The concentration of water is lower outside of the cell.
o More water leaves than enters.
 “hyper-” means “above” or “higher”
o What are some other words that start with “hyper-”?
 Hyperactive, hyperextend, hypertension, hyperbaric,
hyperbole, hyperglycemic, hypersensitive, hypersonic,
hyperventilate
Draw this cell in far left column under “Draw and label the environments below as
isotonic, hypotonic, or hypertonic”.
______Isotonic______
Label below what might happen to the cells as nothing, swell, shrink, or burst.
______nothing______
Label below what is this called as: turgor pressure, cytolysis, plasmolysis, or equilibrium.
______equilibrium______
What will the cell look like in a little while? (Draw below)
Draw this cell in far left column under “Draw and label the environments below as
isotonic, hypotonic, or hypertonic”.
______Hypotonic______
Label below what might happen to the cells as nothing, swell, shrink, or burst.
_____swell & burst_____
Label below what is this called as: turgor pressure, cytolysis, plasmolysis, or equilibrium.
______cytolysis______
What will the cell look like in a little while? (Draw below)
Draw this cell in far left column under “Draw and label the environments below as
isotonic, hypotonic, or hypertonic”.
______Hypotonic______
Label below what might happen to the cells as nothing, swell, shrink, or burst.
______swell______
Label below what is this called as: turgor pressure, cytolysis, plasmolysis, or equilibrium.
______turgor pressure______
What will the cell look like in a little while? (Draw below)
Draw this cell in far left column under “Draw and label the environments below as
isotonic, hypotonic, or hypertonic”.
______Hypertonic______
Label below what might happen to the cells as nothing, swell, shrink, or burst.
______shrink______
Label below what is this called as: turgor pressure, cytolysis, plasmolysis, or equilibrium.
______plasmolysis______
What will the cell look like in a little while? (Draw below)
Nothing Shrink Burst (animal), Swell (plant)
Equilibrium Plasmolysis Cytolysis – animal cell bursts
Turgor Pressure – plant cell swells
●Sometimes molecules
the cell needs are too
big to diffuse into or
out of the cell.
●The cell must use
energy to move these
molecules in or out of
the cell.
●When the cell must use
energy to bring things
in, it is called active
●Active transport moves molecules from an area of
LOW concentration to an area of HIGH
concentration.
o In other words, they are moving AGAINST the
concentration gradient.
o Notice how energy is required in active transport.
High
Concentration
Active
Transport
Low
Active Transport Video
● There are four types of active transport, all of which
require energy.
1.Endocytosis
o Cell brings in material
2.Pinocytosis
o Cell “drinking”
3.Phagocytosis
o Cell “eating”
4.Exocytosis
o Cell releases waste
● Each of these involves bringing materials into the
cell except for exocytosis.