CELL BOUNDARIES &
SPECIALIZED CELLS
CELL MEMBRANE
• Function: Regulates what enters and leaves the cell;
provides protection and support
• Structure: Phospholipid Bilayer
• Proteins are embedded in the bilayer
• Act as pumps/ passageways
• Carbohydrates may connect to the proteins
• Chemical “I.D. cards”
CONCENTRATION
• Concentration:The mass of a solute in a given
solution.
[C]= m/v (mass (g)/ volume (L))
• Ex: 12 grams of salt in 3 Liters of water
(solute)
(solvent)
• 12 grams divided by 3 Liters= 4 g/L
• What is the concentration if you double the amount of salt in
the same amount of solvent?
DIFFUSION
• Particles in a solution move constantly
and collide into each other, spreading out randomly
• Because of this, the particles tend to move from
areas of high concentration to areas of low
concentration
• This process is Diffusion
• Process continues until equilibrium is reached
OSMOSIS
• Osmosis- Diffusion through a selectively permeable
membrane (like a cell membrane)
• Isotonic- concentration on both sides of the
membrane is equal
• Hypotonic- “below strength” fewer molecules in
solution
• Hypertonic- “above strength” more molecules in
solution
OSMOSIS CONT.
ELODEA IN SALT WATER
FACILITATED DIFFUSION
• Facilitated diffusion: Process by which large
molecules (like glucose) can pass through cell
membrane easily through protein channels
• Each protein channel allows a specific molecule to
pass
• Still considered diffusion meaning it depends on
concentration gradients between cell and
environment
ACTIVE TRANSPORT
• Requires energy
• Movement of molecules like ions across cell
membrane by transport proteins called pumps
MOLECULAR TRANSPORT
• REQUIRES ENERGY!!!
• Some proteins work as pumps to allow small
molecules and ions into and out of the cell
• Molecules include: calcium, potassium, and sodium
ions
• Allows cell to concentrate materials even against
forces of diffusion
ENDOCYTOSIS
• Endocytosis: Process of taking material into the cell
by means of infolding (pockets) of the cell
membrane
• Large molecules and clumps of food taken up this
way
• 2 types: Phagocytosis and Pinocytosis
ENDOCYTOSIS (CONT.)
• Phagocytosis: extensions of cytoplasm surround a
particle and package it in a vacuole
• = CELL EATING
• Pinocytosis: taking up liquid from environment.
Pockets form along cell membrane and pinch to
form vacuoles in the cell
• = CELL DRINKING
EXOCYTOSIS
• Release large amounts of material from cell
• Vacuole fuses to cell membrane and forces
materials out of cell
• Water can be removed from a contractile vacuole
in this way