cell membrane + transport Flashcards
what is diffusion
the net movement of particles from an area of higher concentration to an area of lower concentration
molecules will diffuse both ways, but the net movement will be to the area of low concentration - this continues until even distribution
passive process - no energy is needed for it to happen
particles can diffuse across cell membranes, as long as they can move freely through the membrane
what is simple diffusion
when molecules diffuse directly through a cell membrane
what is facilitated diffusion
when particles diffuse through carrier proteins or channel proteins in the membrane
down a concentration gradient (higher to lower)
passive process
what particles use facilitated diffusion
larger molecules (amino acids, glucose) would diffuse extremely slow through the phospholipid bilayer because they’re so big
charger particles (ions and polar molecules) would diffuse slowly because they’re water soluble and the centre of the bilayer is hydrophobic
what are carrier proteins
move large molecules across membranes, down their concentration gradient
different carrier proteins facilitate the diffusion of different molecules
carrier protein stages
a large molecule attaches to a carrier protein in the membrane
the carrier protein will then change shape
this releases the molecule on the opposite side of the membrane
what are channel proteins
they form pores in the cell membrane for charged particles to diffuse through (down the concentration gradient)
different channel proteins facilitate the diffusion of different charged particles
factors that effect simple diffusion
concentration gradient - the higher it is, the faster the rate of diffusion - as diffusion takes place, the difference in the concentration between the two sides of the membrane decreases until it reaches an equilibrium
thickness of exchange surface - the thinner the exchange surface, the shorter the distances the particles have to travel, the faster the rate of diffusion
the surface area - the large the surface area of the cell-surface membrane - the faster the rate of diffusion
factors that affect facilitated diffusion
concentration gradient - the higher the concentration gradient, the faster the rate of facilitated diffusion - as equilibrium is reached, the rate of facilitated diffusion will level off
the number of channel or carrier proteins - once all the proteins in the membrane are in use, facilitated diffusion can’t happen any faster
differences between active transport and facilitated diffusion
active transport usually moves solutes from a low to a high concentration - in facilitated diffusion, they always move from a high to a low concentration
active transport requires energy - facilitated diffusion does not
ATP supplies energy from hydrolysis reaction, splitting it into ADP and Pi which releases energy
what are co-transporters
a type of carrier protein
they bind two molecules at a time
the concentration gradient of one of the molecules is used to move the other molecule against its own concentration gradient
