In Da Club - Membranes &
Transport: Crash Course
Biology #5
(11:14)
The Cell Membrane
• Aka Plasma Membrane
• Controls what enters and leaves the cell
• Phospholipid Bilayer
Passive and Active Transport
• No energy required
• Material moves against the
concentration gradient
• Material is too large to pass
through plasma membrane
• Energy required
• Material moves
down the
concentration
gradient
Diffusion
Diffusion is the
movement of
particles from high
to low
concentration
Osmosis
Osmosis – Diffusion of water across the cell membrane
W
W
S
W
S
W
S
S
W
W
S
S
S
W
W
W
W
W
W
W
S
W
W
W
W
S
W
W
Isotonic – Equilibrium reached
Hypertonic – Less water, more solute
Hypotonic – More water, less solute
W
W
W
W
W
Figure 5.13-2
Hypotonic
solution
Isotonic
solutions
Hypertonic
solution
Osmosis
Sugar
molecule
Selectively
permeable
membrane
Osmosis
Figure 5.14
Animal cell
H2O
H2O
H2O
Normal
Lysing
H2O
Flaccid (wilts)
(a) Isotonic
solution
Shriveled
Plasma
membrane
Plant cell
H2O
H2O
H2O
Turgid (normal)
(b) Hypotonic
solution
Shriveled
(c) Hypertonic
solution
H2O
Facilitated Diffusion
Diffusion through carrier proteins
•
Specialized doors/windows through the plasma
membrane
•
Primarily for molecules like sugar too large to pass
through the plasma membrane
•
Only allow specific material through
Molecular Pump
Pumps material across the plasma membrane
• Moves material “up” the concentration gradient
• Moves material through specific carrier proteins
• Requires energy to “pump”
Lower solute concentration
Solute
ATP
Higher solute concentration
Endo- & Exo- cytosis
Endocytosis accepts material
into the cell via transport
vesicles
Exocytosis discharges
material from the cell
via transport vesicles
Movement of
very large
molecules
http://www.psc.edu/science/2007/bardomain/images/endocytosis.jpg
http://www.college-cram.com/study/biology/files/-1/113/exocytosis.gif
Figure 5.UN03
MEMBRANE TRANSPORT
Passive Transport
(requires no energy)
Diffusion
Facilitated diffusion
Higher solute concentration
Active Transport
(requires energy)
Osmosis
Higher solute
concentration
Higher water concentration
(lower solute concentration)
Solute
Water
Solute
Solute
Solute
ATP
Lower solute concentration
Lower water concentration
(higher solute concentration)
Lower solute
concentration