Transcript osmosis & cell transport notes preAP

9.30.13

Which cellular
structure separates
the cytoplasm from
the external
environment in all
cells?
Why do you think a snail shrivels up and dies when you add salt to
it??
•
You should be able to give me a scientific explanation after these notes
Cell transport = the movement of
molecules in, out, and throughout
cells
 To
stay alive, a CELL MUST
EXCHANGE Materials such as Food
and Waste With Its ENVIRONMENT
and these materials must cross the
Cell Membrane
 Transporting materials across the
cell membrane helps the cell keep a
balance of water, pH, and nutrients
homeostasis
(________)
Solutions
 A solution
is a mixture of a solute and
a solvent.
 A solute is dissolved in the solvent.
 For example: Salt is dissolved in
water.
○ Salt is the solute
○ Water is the solvent
Cell Membrane
• Cell membranes separate cells from extracellular
fluid, from other cells, and from the environment
• The main parts of membranes are the phospholipid
bilayer with membrane proteins embedded
throughout it
Permeability
•
A material is permeable if it allows molecules to
pass through.
• The cell membrane is semi-permeable. (Only
some molecules can freely cross the membrane)
Is the membrane permeable to
Is the membrane permeable to
? No
? Yes
Passive Transport


Passive transport is the movement of molecules
across the membrane that requires no energy.
Both Osmosis and Diffusion are types of passive
transport because both are movement of
molecules from high concentration to low
concentration.
Weeee!!!
high
low
Diffusion

The passive movement of molecules from an
area of high concentration to an area of low
concentration is called diffusion.
 Ex. Perfume diffusing through the air
 Food coloring diffusing in water
Diffusion
•
Molecules are
never stationary but
are in constant
motion.
• Collisions cause the
molecules to spread
apart until the
molecules are
evenly distributed
throughout the
available space.
Which direction will
?
?
flow?
Which direction will
?
?
flow?
Osmosis
 Osmosis
is the diffusion of water
molecules across a permeable
membrane.
 In osmosis, like diffusion, water
molecules move from an area of
high concentration to low
concentration.
Where is the
greatest
concentration of
salt?
in the beaker?
in the bag? 
70% water
30% salt
Semi-permeable membrane
Where is the
greatest
concentration of
water?
in the beaker?
in the bag?

70% water
30% salt
Semi-permeable membrane
Which arrow
indicates the
correct direction
of water flow?
from the bag
into the beaker?
OR
from the beaker
into the bag?
70% water
30% salt
Semi-permeable membrane
Water flows from
the beaker into
the bag.
Salt does not flow
through the
selectively permeable
membrane.
70% water
30% salt
Semi-permeable membrane
What happens to
the bag?
The bag swells.
Semi-permeable membrane
Osmosis
Hypotonic Solution: (less solute)
Cell:
90% water
10% solute
Solution:
100% water
0 % solute
Where will the water go?
What happens to the cell?
Osmosis


Red blood cell
placed in distilled
water
Hypotonic solutions
contain a lower
concentration of solute,
and therefore a higher
concentration of water
than a solution to which
it is being compared.
If a cell is in a
hypotonic solution,
water will diffuse into
the cell
Osmosis
Hypertonic Solution: (more solute)
Cell:
90% water
10% solute
Solution:
50% water
50% solute
Where will the water go?
What happens to the cell?
Osmosis
Hypertonic solutions
contain a higher
concentration of solute,
and therefore a lower
concentration of water
than the solution to
which it is being
compared
 If a cell is in a
hypertonic solution
than water will diffuse
out of the cell

Red blood
cell placed
in salt water
solution
Osmosis
Isotonic Solution: (same solute)
Cell:
90% water
10% solute
Solution:
90% water
10% solute
Where will the water go?
What happens to the cell?
Osmosis
•
Isotonic solutions
– When the
Red blood cell
in an isotonic
solution
concentrations of
solute inside the
membrane and out
are equal.
– An isotonic solution
is at equilibrium
– In an isotonic
solution there is no
net change in the
cell, water flows in
and out of cell
Osmosis
A
B
C
1. Which is the most hypertonic solution?
2. Which is the most hypotonic solution?
3. Which solution is isotonic?
D
E
Cellular Transport
When molecules cannot move
through hydrophobic membrane
Some molecules must undergo passive
transport by traveling across the membrane
through a transport protein.
 This is called: FACILITATED DIFFUSION
and still requires NO ENERGY because
the molecule still moves from high to low
concentration.

Water moves
through special
transport proteins
called aquaporins
Transport Proteins
There
are two types of
transport proteins:
1. channel proteins
2. carrier proteins
Channel Proteins
 Channel
proteins
are tubelike and
provide openings
through which
particles can
diffuse.
Carrier Proteins


Carrier proteins have
a specific shape that
fits a specific
molecule.
When the proper
molecule combines
with the protein, it
changes shape and
moves the molecule
across the membrane.
Active Transport


Can a cell ever move particles from a region of
lesser concentration to a region of greater
concentration?
Yes, but it requires an input of cellular energy
(ATP)!
This is
gonna be
hard work!!
high
low
Membrane Pump

The transport of materials against a
concentration gradient requires energy
(ATP) and is called ACTIVE
TRANSPORT.
Active Transport uses ATP
Endocytosis

Some cells can
take in large
molecules, groups
of molecules, or
even whole cells
through
ENDOCYTOSIS.
requires an input of
ATP
Exocytosis

The reverse
process of
endocytosis is
EXOCYTOSIS.
Cells use this to
expel wastes, and
secrete cellular
products. Requires
an input of ATP
Review

Passive Transport

Active Transport
 No energy
 Requires energy
 Molecules move from
 Examples:
○ Membrane pump
an area of high
concentration to an
area of low
concentration
 Examples:
 Molecules move from
an area of low
concentration to an
area of high
concentration
○ Osmosis
○ Endocytosis
○ Diffusion
○ Exocytosis
○ Facilitated Diffusion
Back to the snail….

Why does a snail shrivel up and die when
you pour salt on it?
 Draw a diagram
 Use content vocabulary