transport Flashcards
what is diffusion defined as?
the net movement of molecules (simple) or ions (facilitated) from a region where they are highly concentrated to one where their concentration is lower until evenly distributed
which molecules pass across the membrane via simple diffusion?
small, non-polar (lipid soluble) molecules such as oxygen and carbon dioxide
what does the ‘passive’ part mean in diffusion?
energy comes from the natural, inbuilt motion of particles, rather than an external source such as ATP.
what is simple diffusion?
the net movement of small, uncharged (non-polar) molecules from a region where they are highly concentrated to a region where their concentration is lower until they are evenly distributed
what is facilitated diffusion?
the net movement of larger, charged ions and polar molecules from a region where they are more highly concentrated to a region where their concentration is lower until they are evenly distributed, by using channel and carrier proteins that span the membrane.
how are simple and facilitated diffusion similar?
-both passive process so relies only on the inbuilt KE of the diffusing molecules (NO ATP)
describe what is meant by facilitated diffusion?
larger, polar molecules are transported along their conc gradient (from high to low) e.g. glucose, ions. It is a passive process that doesn’t require energy from ATP
what is required for facilitated diffusion ?
carriers or channels (intrinsic proteins) in the cell membrane
these allow molecules that are large and insoluble in lipids (polar) to be transported across membranes
what must a carrier/channel protein have?
a complementary shaped receptor site to the molecule
what happens when a molecule binds to a carrier protein?
it causes a shape change to the carrier that means that the molecule is transported across the membrane
what affects the rate of facilitated diffusion?
the number of complementary carriers/ channels; greater number of carriers means greater rate
also steepness of conc gradient, SA (greater capacity for carriers) and temperature
what is the rate of facilitated diffusion and active transport limited by?
the number of carriers- they reach a point of saturation (every carrier is occupied by a molecule)
describe what is meant by active transport?
molecules are transported against their concentration gradient (low to high) which requires energy (ATP) from respiration
how may cells carrying out high rates of active transport be adapted?
high number of mitochondria to provide the ATP
if resp is inhibited eg by cyanide, then active transport will cease
what is required for active transport?
carriers in the cell membrane
carriers must have a complementary shapes receptor site to the molecule being transported