Membrane Transport
Guided Notes
Let’s review…
Structure of the Plasma Membrane
• Phospholipid Molecules
– Description:
• Lipid polymer
• Has two distinct ends
– Hydrophilic Head End:
• Water-loving
• Polar
• Glycerol and phosphate group
– Hydrophobic Tail End:
• Water-fearing
• Nonpolar
• Fatty acid chains
Fluid Mosaic Model
1.
2.
3.
4.
Phospholipids form a bilayer (2 rows)
Polar heads on the outside
Nonpolar tails on the inside
Large proteins between layers, act as
channels
5. Cholesterol helps stabilize the structure
6. Surface proteins and carbohydrate chains for
recognition
So… Just how does a plasma
membrane regulate what goes in
and out – and WHY?
Let’s start with the “WHY?”…
• Plasma Membrane (PM) and Homeostasis:
• Homeostasis is the regulation of internal
conditions to maintain functions.
1.
2.
3.
4.
PM is responsible for maintaining homeostasis
PM keeps the cell in balance
PM regulates products and wastes
PM regulates intake and output substances
Now…Let’s get to the “How?”
Diffusion
• Movement of particles from an area of higher
concentration to an area of lower concentration
• Passive – no energy needed!
Concentration Gradient
• Measure of how concentration changes from
one place to another
Osmosis
• Diffusion of water across semi-permeable
membrane
• Depends on concentration of solute on either
side of a membrane
Solute
• Part of a solution
• The substance dissolved by or into the solvent
• Example: Kool-Aid powder
Solvent
• Part of a solution
• The substance that does the dissolving
• Example: Water
Dynamic Equilibrium
• Result of diffusion
where particles move
in and out of the cell
but overall
concentrations stay
the same
Isotonic Solution
• Solution where the concentration of solute
OUTSIDE the cell is the same as the concentration
of solute INSIDE the cell
• Water flows both ways
Hypertonic Solution
• Solution where the concentration of solute
OUTSIDE the cell is HIGHER than the
concentration of solute INSIDE the cell
• Water flows OUT OF the cell
Hypotonic Solution
• Solution where the concentration of solute
OUTSIDE the cell is LOWER than the
concentration INSIDE the cell
• Water flows INTO the cell
Passive Transport
• Movement of particles across a membrane by
diffusion or osmosis
• No energy used
Facilitated Diffusion
• Passive transport across cell membrane that
uses transport or carrier proteins to help
move particles
Think: Does
this require
energy?
Active Transport
• Transport of materials across a cell membrane
against a concentration gradient
• Requires energy (ATP)
• Like swimming upstream!
Endocytosis
• Active transport process where a cell engulfs
(“eats”) materials using the plasma membrane
• Releases materials into the cell
Exocytosis
• Active transport process where materials are
excreted or expelled out of the cell through
the membrane.
What is happening in each image?