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Ramsey Samy
AP BIO
Mrs. Ahlert
4 November 2009
Cell Transport
Active transport is the transport of substances from a low
concentration to a high
concentration, against the rules of the chemical concentration
gradient.
This method of transport must use carrier-mediated transport and
is broken down into
primary and secondary transport. Active transport has 3
potassium and 2 sodium ions
entering and exiting the cell respectively.
Primary uses Potassium Sodium Pumps where Sodium is transported
from
intracellular fluid to extracellular fluid and Potassium from
extracellular fluid
to intracellular fluid. In order to achieve such movement, must
use metabolic
energy, generally ATP. In addition, Sodium Potassium Pumps can
be used as
inhibitors.
Uses Proton Pump which can be used Transport Hydrogen ions, with
the direct
use of ATP, into lumen against the chemical gradient.
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Secondary Primary Transport
Cotransport
Countertransport
Cotransport- solute move in same direction, and is coupled.
Energy derived from transport of Sodium, maintained by Potassium
Sodium Pump inside
of the membrane, is used to transport actively transport
potassium.
Example, Sodium-glucose transport in small intestine.
Countertransport- Calcium from a low intracellular fluid to high
extracellular fluid,
and the opposite for sodium generating ATP.
Sodium increases muscle contraction such as in the heart, an
increase in sodium
forces the heart to contract more which makes increases
metabolic energy
production.
Unlike Active transport Passive transport does not use
energy.
Passive transport is the transport of substances following the
concentration gradient
(High to low).
Examples of passive transport
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Simple diffusion-Unlike active transport this method of
transport does not
need carrier mediated transport occurs down an electro chemical
gradient
and does not require metabolic energy.
Channel diffusion- unlike active transport does not use energy
for transport (for
hydrophilic substances).
Facilitated diffusion- Though this method of transport does use
carrier mediated
transport, it is just a faster use of diffusion, since it does
not use energy for
transport.
Glucose and Galactose- Glucose in muscle and adipose cells
travels to an area of low concentration and is inhibited by
Galactose, because they have generally the same structure,
this
usually happens in the small intestine. Such a competition
between two substances is a factor of carrier-mediated
transport.
Other Factors that affect transport are in the cell membrane of
the
organism.
Fat solubility- the oil/water partition of a solute, increases
solubility in
the lipid membrane.
J=-PA (C1-C2)
Flow= Permeability X Area X (Concentration 1- Concentration
2), break down of solute increases solubility of the
membrane.
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Hydrophobic substances have the highest solubility through
the
membrane.
Phospholipid Bilayer
The smaller the solute the faster it diffuses through the
membrane
The smaller the membrane thickness decreases diffusion
distance
Hydrophilic substances must cross through pores or channels.
If an ion is charged than the flow or flux would be determined
by the
concentration difference and potential difference across the
membrane.
Therefore, the cell has many methods of transport. Without the
use of energy, the
cell could you passive transport to bring in or exit out
substances. Though, active transport
requires energy, it is very similar to passive transport in that
it directs substances in following a
specific direction, and is carrier-mediated. Both methods of
transport are carrier-mediated and
have to go through specific transmembrane proteins in order to
enter and exit the cell, except for
simple diffusion, which does not need to use such channels. The
main differences between the
two methods of transport are what they bring in, i.e. ions, and
variations in the use of energy.
With these methods of transport and the properties of the cell
membrane, substances are
governed and determined upon entering and exiting.
