Diffusion, osmosis, active transport Flashcards
diffusion definition
the net movement of particles from a region of higher concentration to a region of lower concentration
is diffusion an active or passive process
passive
what two factors affect the rate of diffusion and how?
temperature - increases rate of diffusion as higher temperatures have more kinetic energy and move at higher speeds
concentration difference - greater diff in conc increases rate of diffusion as overall movement from higher to lower concentration will be larger
what does diffusion across membranes involve
particles passing through the phospholipid bilayer- however this can only happen if the membrane is permeable to the particles
what kind of molecules tend to move across a membrane via diffusion
small molecules
lipid soluble molecules
non-polar molecules
what 4 factors affect rate of diffusion across a membrane
temperature
concentration gradient
surface area - larger the area of an exchange surface the higher the rate of diffusion
thickness of membrane - thinner the exchange surface the higher the rate of diffusion
what type of membranes are selectively permeable and why
membranes containing protein channels because most channel proteins are specific to one molecule or ion therefore only these molecules/ions are able to move across the membrane
facilitated diffusion definition
the diffusion across a membrane through protein channels
are polar molecules able to pass through membranes in facilitated diffusion
yes
membranes with protein channels are __________ _________
selectively permeable as most protein channels are specific to one molecule or ion
is facilitated diffusion an active or passive process
passive as it doesn’t require energy from respiration
what 5 factors affect the rate of facilitated diffusion
temperature
concentration gradient
membrane surface area
membrane thickness
number of channel proteins present - the more channel proteins present the higher the rates of diffusion overall
what can facilitated diffusion also involve
carrier proteins which change shape when a specific molecule binds
active transport definition
the movement of particles from a region of low concentration to a region of high concentration across a cell membrane using ATP and carrier proteins
what does active transport require
energy because the particles are being moved against the concentration gradient
process of active transport
- molecule/ion binds to receptors in channel of carrier protein on the outside of the cell
- on inside of cell, ATP binds to the carrier protein and is hydrolyses into ADP and phosphate
- binding of phosphate molecule to carrier protein causes protein to change shape opening up to the inside of the cell
- molecule/ion is released into the cell
5.phophate molecule is released from carrier protein and recombines with ADP to form ATP - the carrier protein return to its original shape
why is active transport a selective process
specific substances are transported by specific carrier proteins
what is bulk transport
another form of active transport. large molecules (enzymes, hormones, whole cells) are too big to move through channel or carrier proteins so are moved in and out of the cell by bulk transport
endocytosis
bulk transport of material into cells. there are two types of endocytosis : phagocytosis for solids and pinocytosis for liquids
process of endocytosis
cell surface membrane invaginates when comes into contact with material to be transported.
membrane enfolds material until membrane fuses, forming a vesicle.
vesicle pinches off and moves into the cytoplasm to transfer material for further processing within the cell
invaginates definition
bends inwards
exocytosis
bulk transport of material out of cells
exocytosis process
vesicles move towards and fuse with cell surface membrane. contents of vesicles then released outside of the cell
osmosis definition
the movement of water from an area of higher water potential to an area of lower water potential across a partially permeable membrane
is osmosis an active or passive process
passive
what is water potential
the pressure exerted by water molecules as they collide with the membrane or contained.
measured in Pa or kPa.
symbol of water potential is Ψ
the more concentrated the solution, the more negative the water potential
effect of osmosis on animal cell - higher Ψ than cytoplasm
net movement of water into the cell.
cause cell to swell and burst
in a red blood cell, cell contents lost and haemoglobin released
effect of osmosis on animal cell - equal Ψ of cytoplasm
water constantly and enters and leaves cell but at equal rates so state of cell won’t change
effect of osmosis on animal cell - lower Ψ than cytoplasm
net movement of water out of the cell. cause cell to shrink resulting in a crenation.
in a red blood cell - haemoglobin is more concentrated giving cell darker appearance, cell shrunken and shrivelled
effect of osmosis on plant cell - higher Ψ than cytoplasm
net movement of water into the cell.
cause protoplast to swell and become turgid. protoplast will be pushed up against cell wall
effect of osmosis on plant cell - equal Ψ to cytoplasm
water constantly enters and leaves cell so the state of the cell won’t change
effect of osmosis on plant cell - lower Ψ than cytoplasm
net movement of water out of the cell.
will cause plasmolysis and the contents will shrink
protoplast will be completely pulled away from cell wall, the space will be filled with external solution of lower water potential
concentration definition
the amount of solute in a certain volume of aqueous solution
