 Boundary that separates the living cell from its’
non-living surroundings.
 Controls what enters and leaves the cell and
provides protection and support.
 Selectively permeable- only allows certain things
to enter and leave the cell
 Maintains homeostasis
 Permeable – anything can cross.
 Impermeable –nothing can cross
 Selectively permeable-(cell
membrane)allows some substances
to cross more easily than others.
 The amount of solute (what is dissolving) per
amount of solution.
 The cytoplasm of the cell is one concentration
 The outside of the cell is another concentration
 They work to have the same concentration
 Concentration gradient – occurs when there are
differences in concentration.
 When the concentration of the outside of the cell is
the same as the concentration of the cytoplasm, the
cell has reached equilibrium.
 Osmosis occurs when water molecules
move across a membrane from an area of
high concentration to an area of low
concentration. (with a concentration
gradient). This occurs until equilibrium
occurs.
 Diffusion is the movement of particles from
an area of high concentration to an area of
low concentration.
 Does not require energy.
 The diffusion of water.
 Hypertonic solution – a solution with a greater
concentration of solute outside the cell than inside.
What direction will water flow??
 The diffusion of water.
 Hypotonic solution – a solution with a lower
concentration of solute outside the cell than inside the
cell.
What direction will water flow??
 The diffusion of water.
 Isotonic solution – a solution with a concentration
of solute outside the cell equal to the concentration
inside the cell.
What direction will water flow??
 Diffusion of larger or highly charged molecules with
the “help” of protein channels.
 Does not require
energy.
 Movement of particles across a
membrane from an area of lower
concentration to an area of higher
concentration. (against the
concentration gradient)
 Requires energy!!
 Small particles use protein pumps.
 Larger particles require movement of the cell
membrane.
 Endocytosis – taking in material.
 Phagocytosis – cell eating (taking in food)
 Pinocytosis – cell drinking (taking in liquid)
 Exocytosis – getting rid of waste.
* Membrane
is composed of Phospholipids,
Proteins, and Carbohydrates
a. Phospholipids- an amphipathic
molecule, which means it has both a
hydrophilic region (attracts water) and
a hydrophobic region (repels water).
b. Proteins- embedded and dispersed
throughout the membrane
c. Carbohydrates
2 major types:
1.
2.
3.
4.
5.
Peripheral- lies on the surface of the
membrane. Transmits stimuli from
outside the cell to inside the cell and
inf luences cell shape
Integral- extends through the membrane
A. marker protein-(name tags) identifies
cells
B. Transport protein(shipping/receiving)
C. Receptor protein- (communication)
interacts with other cells
•Look like helium balloons
•They are not connected together
•They have a hydrophilic region (polar) which
attracts water
•They have a hydrophobic region (non-polar)
which repels water
•A bi-layer system
•Called a Fluid Mosaic Model- because it
f lows and has many parts that intermingle.