Download 3.4 Diffusion and Osmosis

DIFFUSION AND
OSMOSIS
3.4
KEY CONCEPT
• Materials move across membranes because of
concentration differences.
Diffusion and Osmosis
• Molecules can move across the cell membrane
through passive transport.
• Passive transport does not require energy input
from a cell
• There are two types of passive transport
1. Diffusion
2. Osmosis
Diffusion
• Diffusion is the movement of
molecules in a fluid or gas from high
concentration to low concentration
• Molecules diffuse down a
concentration gradient.
• “Move downhill” or from
high to low
Diffusion
• Diffusion stops when dynamic equilibrium (spread
evenly, but molecules still moving) is reached
Diffusion
• Concentration
• Number of molecules in a substance in a given
volume
• Concentration gradient
• Difference in concentration from one area to another
Diffusion
• Diffusion plays a key role in cells ability to
move substances into and out of the cell
• Small lipids and nonpolar molecules like O2 and
CO2 diffuse easily
• Cells continually consume O2
• Therefore the concentration of O2 is almost always
higher outside the cell
• Result O2 diffuses into cell without the need of energy
Osmosis
• Osmosis is the diffusion of water molecules across a
semipermeable membrane from high water molecule
concentration to low H20 concentration.
• Continues until dynamic equilibrium is reached
Osmosis
• Homeostasis
• Biological Balance
• Key concept of selectively permeable membrane and
osmosis is to maintain homeostasis!
Osmosis
• Tonicity
• A measure of water
pressure against a
semipermeable
membrane
• Three types of Tonicity
1. Isotonic
• Concentration of
solute is equal inside
and outside of cell
Cell in Isotonic Solution
10% NaCl
90% H2O
ENVIRONMENT
CELL
10% NaCl
90% H2O
What is the direction of water movement?
The cell is at _______________.
equilibrium
NO NET
MOVEMENT
Osmosis
2. Hypertonic
• The concentration of
solute is greater outside
the cell
• Plasmolysis – The
process by which the
cell shrinks from losing
water
Cell in Hypertonic Solution
15% NaCl
85% H2O
ENVIRONMENT
CELL
5% NaCL
95% H2O
What is the direction of water movement?
Osmosis
3.
Hypotonic
• The concentration of
solute is greater inside
the cell
• Cytolysis – The process
by which a cell bursts
from water entering
• Turgor pressure –
Pressure exerted on the
cell wall of plants due to
water pushing out
Cell in Hypotonic Solution
10% NaCl
90% H2O
CELL
20% NaCl
80% H2O
What is the direction of water movement?
Osmosis
• Some single celled
organisms and animals
are adapted to survive
hypotonic solutions
• They have structures
(cell wall and vacuole)
to store or remove
(contractile vacuole)
excess water
Practice
• Draw arrows to indicate the direction of water movement
into cell, out of cell, or both!
• The 10% solution represents a cell
Video
• Tonicity and osmosis
Some Molecules diffuse through transport
proteins
• Facilitated Diffusion
• Some molecules cannot easily diffuse across the
cell membrane.
• A transport or carrier protein provides a door for
a substance to enter the cell. Square peg in a
round hole idea!
• Still No energy is used