Diffusion and Osmosis Flashcards
- Explain diffusion across a membrane in terms of a generalised Force-Flow relationship - Relate the diffusion coefficient to permeability (considering Fick's Kaw applied to membranes) - Interpret likely effects of size, shape and charge of molecules on their permeation through a membrane - Appreciate the concept of water potential in relation to oasmotic water movement
Explain the permeability of particles with high diffusion coefficients
Particles with higher diffusion coefficients have higher permeability
Describe ways of increasing rate of diffusion according to Fick’s Law
- increase of concentration/pressure
- increased area
- diffusion constant
- thickness of wall
What is passive diffusion
- process by which molecules diffuse from a region of higher concentration to a region of lower concentration
- refers to lipophilic molecules
What is facilitated diffusion
- molecule passes through membrane via carrier/channel
Ways in which small molecules can cross cell membranes
- passive diffusion
- aqueous diffusion
- facilitated diffusion
- active transport
- endocytosis (pinocytosis)
What is aqueous diffusion
- diffusion via a channel that transverses the plasma membrane
- does not require energy
- requires concentration gradient
What is active transport
- diffusion via specialised carrier proteins
- requires energy
- can move molecules against concentration gradient
What is endocytosis
- invagination of a part of the membrane
- molecule is encased in small vesicle and released inside cell
Impact of saturation on rate of diffusion
high saturation = slower diffusion rate
Define simple diffusion
random movement of solute molecules in solvent tending towards an evenly-distributed state
Rate of diffusion equation
Rate of diffusion (J) is proportional to concentration gradient over distance (dc/dx)
What is rate of diffusion related to
- physical properties of solute and solvent molecules (e.g. size, electric charge)
- temperature
- electric field
Diffusion of solute across membrane is dependant on…
- membrane (selective barrier properties)
- concentration gradient across membrane barrier
- permeability of solute (diffusion + partitioning)
Diffusion is vital for …
- gas exchange
- lipophilic drug actions
Fick’s Law states that…
Rate of diffusion (J) of a solute (S) across a medium is proportional to the thickness of the medium, the cross-sectional area, and the concentration gradeint across the medium
