Transcript Homeostasis and Transport

Across Biological Membranes
Review for Transport
1. What are the two parts of a solution?
2. In cells, what is normally the solvent?
3. When would water need to move across
the cell membrane?
4. When would solutes move across the cell
membrane?
Diffusion


Movement of molecules from an area
of high concentration to an area of low
concentration.
Concentration Gradient
• Difference in concentrations across a
space
CONCENTRATION
GRADIENT
Diffusion
 Equilibrium
• A balance between environments
• No more NET movement of
materials
Review Questions
1. What is it called when a difference in
concentrations exists across a space?
2. What types of particles have the
easiest time moving across a lipid bilayer?
3. Name some molecules that may have
difficulty entering or leaving a cell.
4. What organelles (aside from the cell
membrane) have one or more lipid bilayers?
Diffusion
Mainly small, nonpolar

Particles diffuse through lipid bi-layers
to reach equilibrium
Conc.
Gradient
Egg in solutions

Fill beaker 2/3 with
vinegar

Place egg in solution
What will happen to
the egg?

Egg in solutions



Fill a NEW beaker 2/3
with Corn syrup
Transfer egg from
Vinegar solution
What will happen to
the egg?
Osmosis

Diffusion of water
• When solute cannot cross membranes to
•
reach equilibrium, the solvent (water) does
Water moves from where it is purest (hi
conc.) to where it is least pure (lo conc.)
H 2O
H2O
H 2O
H 2O
H 2O
H2O
H 2O
H 2O
H 2O
H 2O
H 2O
H 2O
H 2O
H 2O
H 2O
H 2O
Osmotic Solution Types

Isotonic Solution
• Conc of solute is
same outside cell
as it is inside
• No net movement
of water
Osmotic Solution Types

Hypertonic
Solution
• Conc. of solute is
higher outside
cell
• Net movement of
water out of cell
• Plasmolysis
occurs
Osmotic Solution Types

Hypotonic Solution
• Conc of solute is lower
outside cell
• Net movement of water
into cell
• W/ cell wall:
turgor pressure
• W/out cell wall:
cytolysis
How do fish in Hyper/Hypo tonic
solutions adapt?
What if they move
from hyper to hypo
tonic environments?
Osmotic Solution Types
Passive Transport
NO ENERGY
Active Transport
YES Energy
Facilitated Diffusion

Membrane proteins carry materials through
the lipid bilayer.
• Molecule binds to membrane protein.
• The membrane protein changes shape.
• The molecule is released on the other side.
Ion Channel Proteins

Membrane proteins open passage for
materials through the lipid bilayer.
• Ions crosse membranes through channels
Passive Transport



Materials move from high  low
concentration.
No energy is required
Includes…
• Diffusion
• Osmosis
• Facilitated Diffusion
• Channels
Active Transport



Often low  high concentration
E is required
Pump
• Similar to facilitated diffusion except it’s AT
ADP + P
ATP
Active Transport

Endocytosis
• Cells engulf large materials (nutrients,
enemies) with cell membrane.
Active Transport

Exocytosis
• Pre-packaged materials are released from
the cell.
Review Questions
1. What’s the difference between active
and passive transport?
2. In what direction will particles always
diffuse?
3. What happens to a wall-less cell in a
hypotonic solution?
4. Osmosis is a specialized form of
diffusion. Create a Venn diagram
comparing osmosis and diffusion.