diffusion Flashcards
why do cells need to receive raw material
for the biochemical reactions and processes that go on in cells to sustain life
what do cells make when they respire
ATP
what does ATP provide
cellular energy to drive biochemical reactions
what do cells need to respire
they need oxygen and glucose and need to remove the toxic metabolic ewaste products such as carbon dioxide.
what else do cells need to do apart from respiring
to export some of the molecules they make, such as enzymes, hormones or other signalling molecules
what does active and passive transport refer to
the exchange of substances between cells and their environment, or between membrane bound compartments within cells and the cell cytosol
what does all movement require
energy usually in the form of ATP
what does passive movement utilise
passive transport utilises energy from the natural motion of particles rather than the energy from another source. they do not use ATP
what is diffusion
the net movement of particles (atoms, molecules or ions) from a region of high concentration to a region of low concentration
what kind of process is diffusion
a passive process
at what point does diffusion continue to occur
until there is a concentration equilibrium between the two areas
why does diffusion happen
the particles in a gas or liquid have kinetic energy. this movement is random and an unequal distribution of particles eventually becomes an equal distribution.
what does equilibrium actually mean
it doesnt mean the particles stop moving, the movement is just equal in both directions
why is diffusion fast over short distances
particles move at high speeds which are constantly colliding which slows down their overall movement. so diffusion is faster when the pathway is shorter. as diffusion distance increases, the rate of diffusion slows down because more collisions take place
what is a concentration gradient
a difference in concentration. it goes from high to a low concentration
where does diffusion take place along the concentration gradient
DOWN the concentration gradient
what acts as a barrier in the membrane
the non polar, hydrophobic tails of phospholipid molecules.
if a molecule is small and less polar what does this mean
it will diffuse across the membrane easier and faster
when does simple diffusion take place
for small non polar molecules.
what types of molecules can easily pass through the lipid bilayer
small non polar molecules in a high concentration on one side of the membrane can easily pass through the bilayer. lipid soluble molecules and very small molecules can diffuse directly through the bilayer
give examples of molecules can pass through cell membranes in simple diffusion
oxygen and carbon dioxide
how do fat soluble molecules such as steroid hormones diffuse through cell membrane
even if they are larger, they diffuse through cell membranes as they dissolve in the lipid bilayer. they still move down their concentration gradient.
