Ii active processes cellular energy is used to drive

II. active processes – cellular energy is used to drive the substance “uphill”
against its concentration and electrical gradient. Cellular energy used is
usually ATP. i.e. active transport.
a. Vesicles – tiny, spherical membrane sacs that can be used by other
substance to enter and leave cells.
III. Diffusion – is a passive process in which the random mixing of particles in
a solution occurs because of the particles’ kinetic energy.
a. Solutes – dissolved substance.
b. Solvents – the liquid that does the dissolving.
IV. factors that influence diffusion rate

a. steepness of the concentration gradient – the greater the
difference in concentration between two side of the membrane, the
higher is the rate of diffusion.
b. Temperature – the higher the temperature, the faster the rate of
diffusion. i.e. fever
c. mass of the diffusing substance – the larger the mass of the
diffusing particle, the slower its diffusion rate.
d. surface area – the larger the membrane surface area available for
diffusing, the faster is the diffusion rate. i.e. air sacs of lungs have
large surface area for oxygen diffusion into the blood, but if
affected by lung diseases, it reduce the surface area, slowing the
oxygen diffusion rate which results to difficulty breathing.
e. diffusion distance – the greater the distance over which diffusion
must occur, the longer it takes. i.e. diffusion across plasma
membrane only takes a fraction of a second because the
membrane is so thin.
V. simple diffusion – passive process in which the substances move freely
though the lipid bilayer of the plasma membranes of cells without the help
of membrane transport proteins; important in the movement of oxygen and
carbon dioxide between blood and body cells and between blood and air
within the lungs during breathing.
VI. facilitated diffusion – passive process wherein an integral membrane
assists a specific substance across the membrane. The integral membrane
can either be a membrane channel or a carrier.
a. channel-mediated facilitated diffusion – solute moves down its
concentration gradient across the lipid bilayer through membrane
channel.
i. ion channels – integral transmembrane proteins that allow
passage of small inorganic ions that are too hydrophilic to
penetrate the non-polar interior of the lipid bilayer; most
membranes are these.
ii. gated channels – when part of the channel protein acts as a
plug or gate changing the shape in one way to open the pore
and in another way to close it; can be randomly alternate
between open or closed positions; could be regulated by
chemical or electrical changes inside and outside the cell.
b. carrier-mediated facilitated diffusion – a carrier moves a solute
down its concentration gradient across the plasma membrane; no
cellular energy is required in this passive process.

i. transport maximum – the upper limit on the plasma
membrane placed by the carriers at which the facilitated
diffusion can occur.