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facilitates diffusion
passive because the solute move down its concentration gradient and the transport requires to energy
active transport
requires energy usually in the form of ATP hydrolysis to move substances against their concentration gradients
describe active transport
requires energy, not spontaneous, +delta G
what proteins are involved in active transport
carrier proteins
why is active transport good for cells
it enables cells to maintain solute concentrations that differ from the environment
example of active transport
the concentration of potassium ions is higher and concentration of sodium ions is lower inside animal cells than their surroundings so sodium is taken out through a pump while potassium is taken in
membrane potential
the voltage across a membrane
how is a voltage created in a membrane
by differences in the distribution of positive and negative ions across the membrane
what is the normal resting membrane potential of a human cell
the inside of the cell is negative relative to the outside
what is the benefit of having a negatively charged cell
it favors passive transport of cations into the cell and anions out of the cel
what two forces make up if electrochemical gradient
a chemical force and an electrical force
what does the electrochemical gradient do
drives the diffusion of ions across a membrane
what is an electrogenic pump
a transport protein that generates voltage across a membrane and stores energy that can be used for cellular work
what electrogenic pumps do animals use
sodium/potassium pump
what electrogenic pump do plants, fungi, and bacteria have
proton pump
why is proton pump important
in the generation of ATP by the mitochondria in cellular respiration and chloroplasts in photosynthesis
cotransport
occurs when active transport of a solute indirectly drives transport of other substances
what do plant cells use proton pumps do to
they use the pumps to generate an H+ gradient across the cell membrane
how does a cotransporter go with a proton pump
a cotransporter couples the movement of H+ that is generated from the pumps back down its concentration gradient to the active transport of sucrose into the cell
how do plants load sucrose to their veins for transport
with a cotransporter
how do cotransporters differ in animal cells
they are used to couple the active transport of glucose to the diffusion of Na+ into cells lining the intestine
what role does sodium play in human bodies
sodium in waste is reabsorbed in the colon to maintain a constant level in the body and a rapid drop in sodium (like after diarrhea) it can be life threatening