Membranes and osmosis

1. 1. Structure of Plasma membrane
* Two-layered structure:
lipid bilayer
*Made of lipid molecules
with protein molecules in
the lipid layer.
**PROTEINS aid in the
movement of materials
through the membrane

2. hydrophobic
tails
hydrophilic
heads
hydrophilic
heads
extracellular fluid
(watery environment)
cytoplasm
(watery environment)
phospholipid
bilayer

3. tails
(hydrophobic)
head
(hydrophilic)
Polar Head
Non-Polar Tails

4. * Bilayer can be considered a liquidliquid
FLUID MOSAIC MODEL:
plasma membrane : made up of molecules that are
free to flow among one another.
Kinds and arrangements of proteins + lipids vary
from one membrane to another and give each type of
membrane specific permeability properties.

5. Proteins
Membrane
movement
animation
Polar heads
love water &
dissolve.
Non-polar
tails hide
from water.
Carbohydrate cell
markers
Fluid Mosaic Model
of the cell
membrane

6. Outside of cell
Inside of cell
(cytoplasm)
Lipid
Bilayer
Proteins
Transport
Protein
Phospholipids
Carbohydrate
chains
Structure of the Cell Membrane
Go to
Section:
Animations
of membrane
structure

7. 1. Maintaining a BALANCE in a
CELL
Cells Maintain HOMEOSTASIS : internal balance
Selective permeability : allows
some materials to pass through
membrane while rejecting
others.

8. Diffusion
Movement of molecules
high concentration to
lower concentration
Example: skunk,
perfume, night after a
dinner at Taco Bell!

9. 1 A drop of dye is
placed in water.
2 Dye molecules
diffuse into the
water; water
molecules diffuse
into the dye.
drop of dye
pure water
3 Both dye molecules
and water molecules
are evenly dispersed.
Diffusion animation

10. Osmosis
The diffusion of
Water from areas
of high
concentration to
areas of low
concentration
Animation: How Osmosis Works

11. Transport across membranes
Passive transport of water by Osmosis
•a. Isotonic
•b. Hypertonic
•c. Hypotonic

12. Solution concentration of water (solvent) outside
of the cell is the same as concentration inside
the cell (Animal cell normal / plant flaccid)
Isotonic Solution:

13. Hypotonic Solution: concentration of water (solvent)
outside the cell is higher than concentration inside the cell.
Water rushes into the cell!
 Turgor pressure: Pressure that builds in a plant
cell as a result of osmosis. Makes a plant cell firm.
(Turgid) Plant cells are healthiest in a hypotonic
environment.
 Lysed: pressure builds in animal cell (burst)

14. Hypertonic Solution: concentration of water (solvent)
outside cell is lower than concentration inside the cell.
Water rushes out of the cell!
 Plasmolysis: loss of water from within a plant cell,
causing cytoplasm to shrink, pulling inner plasma membrane
away from cell wall. (wilting of plants)
 Crenation: (crenates: shrinks) animal cell loses water
and it shrinks (collapses)

16. What type of solution are these cells in?
A CB
Hypertonic Isotonic Hypotonic

17. (a) isotonic solution (b) hypertonic solution (c) hypotonic solution
10 micrometers
equal movement of water
into and out of cells
net water movement
out of cells
net water movement
into cells

18. Passive transport : movement of substances
across plasma membranes without additional energy
Facilitated diffusion: diffusion of materials across
a plasma membrane by transport (channel) proteins.
5. PASSIVE TRANSPORT : No energy
required for this to happen

19. Active Transport : gradient from low to high.
Energy is required.
Proteins throughout the membrane are “carriers”
used for this purpose.
6. ACTIVE TRANSPORT:
Requires energy in the form of ATP

20. Na+ ions: moved out of cell
 K+ ions: moved by the
same carrier into the cell

(This process is important in nerve and muscle function.)
Sodium-potassium pump
Na  out K  in
ACTIVE TRANSPORT = ATP

21. 7. TRANSPORT of 7. TRANSPORT of LARGELARGE
PARTICLESPARTICLES
· Endocytosis (Endo = In): cell surrounds and takes in
material from environment. Material does not pass through the
membrane; instead, it is engulfed and closed by a portion of
membrane and cytoplasm.
 Pinocytosis: water
 Phagocytosis: food/ minerals/
large particles
 · Exocytosis (Exo = Out):
transport of materials out of cell
across cell membrane.
 

22. Exocytosis

23. (extracellular fluid)
(cytoplasm)
food particle
particle
enclosed in vesicle
phagocytosis
vesicle containing
extracellular
fluid
cell
pseudopod
pinocytosis
(a)
(b)
1
33
2
1 32
Animated Review of Phagocytosis,
Pinocytosis and Receptor Mediated
Endocytosis.
Click on Active Transport, watch the
brief overview of Active Transport and
then click on Endocytosis in the bar below
the animation