diffusion Flashcards
diffusion definition
the net movement, as a result of the random motion of its molecules or ions, of a substance from a region of its higher concentration to a region of lower concentration
how to particles move on a concentration gradient
down the concentration gradient
what is the movement caused by
natural kinetic energy if the molecules or ions
what do particles reach due to diffusion
an equilibrium where they are evenly spread within a volume of space
what factors affect the rate of diffusion
-steepness of the concentration gradient
-temperature
-surface area
-properties of molecules or ions
how does steepness of concentration gradient affect rate of diffusion
faster rate of diffusion
what does steepness of the concentration gradient mean
difference in concentration of the substance on the two sides of the surface
how does temperature affect the rate of diffusion
higher rate
why does steepness of concentration gradient increase rate of diffusion
the greater the difference in concentration means a greater difference in the number of molecules passing in the two directions and therefore a faster rate of diffusion
why does higher temperature increase rate of diffusion
molecules and ions have more kinetic energy at higher temperatures
how does surface area affect rate of diffusion
the greater the surface area, the faster the rate of diffusion
why does increase in surface area affect the rate of diffusion
the greater the number of molecules that can cross in any one moment. However, as cell size increases surface area to volume ration increases which slows down rate of diffusion as distance required becomes too great
how does properties of molecules and ions affect rate of diffusion
-larger molecules diffuse more slowly as require more energy to move
-uncharged and non-polar ions diffuse directly across the phospholipid bilayer
-non-polar molecules diffuse faster than polar ones as the are soluble in the non-polar phospholipid bilayer
facilitated diffusion definition
transport of substances across a biological membrane from an area of higher concentration to an area of lower concentration with the help of a transport molecule
examples of substances which cannot diffuse through phospholipid bilayer
-large polar molecules such as glucose and amino acids
-ions such as Na+ and Cl-
two types of proteins enabling facilitated diffusion
-channel proteins
carrier proteins
what are channel proteins
water-filled pores
what do channel proteins allow
charged substances to diffuse through the cell membrane
how do channel proteins facilitate diffusion
they are gated meaning the channel protein on the inside surface of the cell membrane can move in order to close or open the pore
carrier protein shapes
can switch between two shapes
how do carrier proteins work
the binding site of the carrier protein is open on the side of the membrane first and open to the other side when carrier protein switches shape. the direction of movement of molecules diffusing across the membrane depends on concentration on each side of the membrane
when does net diffusion occur
down the concentration gradient
carrier and channel proteins specifity
both highly specific
