Warm-Up #4
11/1/12
1) What are the 2 other names for the cell
membrane?
2) If a molecule is too big to go through the
membrane alone, what must it use?
3) Label A-D on the Picture below.
4) What is the quiz tomorrow on?
Passive Transport: Diffusion and
Osmosis
Unit 4
Chapter 5
What are we doing?
• Essential Question:
• How do
organisms
maintain
homeostasis?
• Objectives:
• Explain how an
equilibrium is
established as a
result of diffusion.
• Distinguish between
diffusion and
osmosis.
Passive Transport
• Movement of
substances across
the cell membrane
without the use of
ATP (Energy)
Concentration Gradient
• The difference in the concentration of
molecules across a space.
• Diffusion always occurs DOWN the
concentration gradient.
Equilibrium
• Equi--equal
• When the concentration of molecules of
a substance is the SAME throughout a
space
Diffusion
• Simplest type of passive
transport
• NO energy needed
• Always goes from an area
of higher concentration to
lower concentration
• Example:
• Gas exchange in lungs
• Photosynthesis
Rate of Diffusion
• Rate depends on three things:
• 1. Temperature
• Higher the temperature faster the diffusion
• 2. Size
• Smaller the molecule, faster the diffusion
• 3. Type of Molecules
• Bigger molecules will not pass through
without energy input
Osmosis
• Diffusion of water
across a semipermeable
membrane
• Move from high to
low concentration
When does this happen?
• Water moves from areas of LOW solute
concentration to areas of HIGH solute
concentrations
• Will do this until they are evenly
distributed
Hypertonic Solution
• The concentration of solute molecules
outside the cell is higher than the
concentration of solutes inside the cell.
• Water Diffuses OUT of the Cell until
equilibrium occurs
Animal vs. Plants in Hypertonic
Solutions
• Animal Cell:
• Cell shrivels and
shrinks
• Plant Cell:
• Cell membrane pulls
away from the cell
wall
Plasmolysis
• Plants lose water through osmosis.
• It occurs when the cell membrane peels
away from the cell wall.
• The plant shrivels and dies.
Hypotonic
• The concentration of solute molecules
outside the cell is lower than the
concentration of solutes inside the cell
• Water diffuses INTO the cell until
equilibrium is reached
Animal vs. Plant Cells--Hypotonic
• Animal Cell
• Cell will swells and
bursts
• Plant Cell
• DOES NOT burst
because of cell wall
• Called Turgor
Pressure
Isotonic Solution
• The concentration of solutes outside
and inside the cell are equal.
• Water diffuses into and out of the cell
at equal rate
Help…I Need Somebody…
• Facilitated Diffusion
• Use of carrier proteins to help substances move in
or out of the cell
• No Energy Needed
What do the Proteins Do?
• Carry molecules
across the
membrane—carrier
proteins
• Change shape to
help the molecule
pass through
Solution
Isotonic:
The concentration
of solutes is the
same inside and
outside of the cell
Hypertonic:
Solution has a
higher solute
concentration than
the cell
Hypotonic:
Solution has a
lower solute
concentration than
the cell
Animal Cell
Plant Cell
WARM-UP #4
11/3/11
1) What does passive transport not
require?
2) What are 2 types of passive transport?
3) The movement of molecules across a
membrane is called……?
4) Osmosis is the movement of____.