diffusion Flashcards
diffusion
the NET movement of molecules (particles) down a concentration gradient. Passive transport.
passive transport
no metabolic energy is expended
facilitated diffusion
when large/ hydrophilic particles only able to cross the cell membrane through both transmembrane channel and carrier proteins
when is a carrier protein used
when molecules (e.g. glucose) are too large to diffuse through water filled channel but can bind to a transmembrane carrier protein
what sort of molecules can pass through the membrane normally
lipid soluble molecules/non polar molecules e.g. o2 and co2
what varies for each cell type
the proportion of transmembrane protein channels and carriers
example of specialised cell type for carrier and channel protein
neurone plasma membrane- channels specific to either sodium/potassium which is crucial to conduction of nerve pulses
Ficks law
rate of diffusion is directly proportional to the surface area and concentration difference but inversely proportional to the thickness of membrane
factors effecting rate of diffusion
Temperature, Diffusion distance, Surface area, Size of diffusing molecule, Conc gradient
how does temp affect diffusion rate
as temp increases, molecules have more kinetic energy, so rate increases. As loose energy, rate will slow
how does diffusion distance affect diffusion rate
the thicker the membrane which molecules have to diffuse, the slower rate of diffusion
how does surface area affect diffusion rate
more diffusion can take place across larger membrane = quicker rate
-cells specialised for absorption have extensions to cell surface membrane called microvilli
how does size of diffusing molecule affect diffusion rate
smaller ions/ molecules diffuse more rapidly than larger ones
how does concentration gradient affect diffusion rate
steeper gradient the faster the diffusion to side of fewer moelcules
concentration gradient
the difference in the concentration of a substance between two areas.
equation for water potential
solute potential + pressure potential
what happens when glucose molecules are added to water (in terms of water potential and concentration)
-some solvent molecules cluster around a solute(glucose) when it dissolves, so fewer free molecules which can diffuse to other areas
-lowers water potential and concentration
what happens when salt molecules are added to a solution
-dissociate into charged ions
-number of particles in solution doubles
-lower water potential
solute potential
-contribution that solutes make to the water potential of a solution
-a measure of the tendency of water to move in response to solute concentration
-more solute is more netative
what is pressure potential
-pressure exerted by the contents of the cell against the cell wall
-always a positive value
active transport
-against concentration gradient
-utilises carrier proteins
-requires ATP
Cytolysis
-process in which a cell breaks down and bursts due to the influx of water
Turgid
-state of plant cell when it is full of water, causing cell to swell and press against cell wall
Crenated
-animal cells shrink and develop scalloped/ notched appearance
Plasmolysed
-condition in plant cells when a cell membrane pulls away from cell wall due to loss of water
Flaccid
-soft and lip due to decreased internal pressure
-lost water, no longer turgid
Hypertonic
-solution that has higher concentration of solutes compared to another solution, water moves out of cell
Hypotonic
a solution that has a lower concentration of solutes compared to another solution, water moves into cell
Isotonic
-same concentration of solutes as another soluton, no net movement (equillibrium)
osmotic pressure
pressure on solution side of membrane
edocytosis
-process by which cells engulf external materials to bring them into the cell
-involves the membrane folding inward to form a pocket that pinches off to create a vesicle containing ingested material.
exocytosis
-process by which cells expel materials from within the cell to the outside environment.
-occurs through the fusion of vesicles containing the substances with the cell membrane, releasing their contents outside the cell.
steps of exocytosis
-membrane bound vesicle containing substances to be secreted moved toward cell membrane
-cell surface membrane and membrane of vesicle fuse
-fused site opens, releasing contents
