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Cell or Plasma Membrane

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Plasma Membrane
What is special about a membrane?
Helper
protein
HYDROPHILIC
HEAD
Cell or Plasma Membrane

Cell membranes are
bilayered, dynamic
structures that:

Regulate cells

Form boundaries between
cells and environments

Regulate movement of
molecules into and out of
cells

Maintain HOMEOSTASIS!

Selectively
permeable
phospholipid
bilayer
•Each has a hydrophilic
region, where the
phosphate groups are
located, and a
hydrophobic region, the
fatty acid “tails.”
Diffusion

Molecules move from an area of high
concentration to an area of low concentration
Tendency to reach equilibrium
 Does not require cell energy

Osmosis

The passage of WATER through a
selectively permeable biological membrane

Substance travels from area of high
concentration to an area of low concentration
Permeability
If a substance is able to diffuse across a
membrane = Permeable
 If a substance is unable to diffuse across a
membrane = Impermeable
 If only certain substances can diffuse across
a membrane = Selectively Permeable

Concentration Gradients

Isotonic=



Hypertonic=



Solution containing equal concentration of solute
No net movement of water
Solution containing high concentration of solute
Water moves into solution
Hypotonic=


Solution containing low concentration of solute
Water moves out of solution
Sugar and Water
Types of movement through a
membrane
Passive
Transport
Active Transport
Facilitated Diffusion
Passive Transport
“Going with the flow” or “with the concentration
gradient”
Does not require cell
energy to occur



Particles move from an
area of high
concentration to low
concentration
Includes osmosis and
diffusion
Particles move with the
concentration gradient
Facilitated Diffusion
Molecules that cannot diffuse across a
membrane on their own need “helper
molecules”
 Carrier proteins are used to get needed
molecules into the cell
 Does not require energy; just proteins
 Examples: Sugars and salts

Active Transport
“Going against the flow” or “against the
concentration gradient”
Requires ENERGY from
the cell to accomplish


Movement from area of
low concentration to
area of high
concentration
Particles move against
the concentration
gradient
Active Transport

Types of active transport
Endocytosis- cells fold in their cell membrane
and take in materials
 Exocytosis- cells removing materials
 Phagocytosis - cell eating/engulfing large
particles
 Pinocytosis – cell drinking
 Na+/K+ Pumps – maintains an electrochemical
gradient in cells; pumps 3 Na+ ions out of the
cell and 2 K+ ions into the cell

Essential Functions of
Membranes in Cells
Barrier for the cell and organelles from the
external environment
 Provides region for concentration gradients
to form in cells. This allows for osmosis and
diffusion to occur.
 Formation of vesicles for the transportation of
materials in and out of the cell.

Auteur
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