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Cell transport
Cell transport
is the movement of substances across the cell membrane. There are two basic types of
cell transport.
Passive transport does not require energy.
Materials move from an area higher concentration
to lower concentration down their concentration gradient.
Active transport requires energy from ATP.
Materials move from and area of lower concentration
to higher concentration up their concentration gradient.
In passive transport
substances move from an area of higher concentration
to an area of lower concentration without the use of energy.
Diffusion is the passive movement of a solute from an area of
higher concentration to an area of lower concentration.
Diffusion will continue until equilibrium is reached
such that the concentration of solutes is equal in both areas.
In cells it is mostly small
lipid soluble molecules that are capable of simple diffusion across the cell
membrane.
Here we can see that the small lipid soluble solute
in yellow is able to move freeley from the area of
high concentration to the area of low concentration
thus equalizing the concentration between the two sides.
Osmosis is a
special type of diffusion in which water, which are the solvent molecules,
move from an area of higher concentration to an area of
lower concentration through membrane proteins called aquaporins.
Facilitated diffusion is the path of moment of solutes from an area
higher concentration to an area lower concentration through a membrane channel protein
protein
or with the aid of a transport protein but without the use of energy.
Here we can see that the channel protein in green
spans the entire width of the membrane whereas the carrier protein is a smaller
protein
only found on one side of the membrane. Solute molecules can easily
travel through the channel protein but
must attach themselves to the carrier protein in order to be carried across.
Filtration involves a fluid called the filtrate being forced across the cell
membrane
due to fluid pressure. The filtrate contains both solute and solvent
and only large molecules and cells that are not contained in the filtrate.
Filtration does not depend on the concentration of substances.
Active transport involves the movement of solutes from an area
lower concentration to an area of higher concentration
with the use of ATP energy. ATP energy
is used by either a vesicle or carrier protein to move substances across the cell
membrane.
In this example a carrier protein
is used to move a molecule from an area low concentration
to an area of high concentration with the aid of ATP energy.