transport across cell membranes Flashcards
what is the cell membrane described as?
fluid-mosaic model
what does ‘phospholipid bilayer’ mean?
two layers of phospholipids
why is the membrane described as a ‘fluid-mosaic’ model?
fluid - phospholipid molecules are constantly moving
mosaic - proteins scattered through phospholipid bilayer
what is the function of the cholestrol in the membrane?
to stabilise the membrane
stability and support
what are the 3 methods of transport across cell membranes?
simple diffusion
facilitated diffusion
active transport
what methods of transport are passive?
simple and facilitated diffusion
what does it mean for one of the methods to be ‘active’?
requiring energy in the form of ATP
what type of molecules are moved in simple diffusion?
small
uncharged
lipid solublew
what molecules are moved in facilitated diffusion?
larger
charged
water soluble
what molecules are transported in active transport?
larger
charged
water soluble
ions
what factors will increase the rate of active transport?
increase in temperature
increase in respiration
respiratory inhibitors (cyanide) will inhibit respiration so will stop active transport
what factors will increase the rate of simple diffusion?
increase in temperature
increase in surface area
increase in concentration gradient
thinner exchange surface
what factors will increase the rate of facilitated diffusion?
increase in temperature
increase in concentration gradient
increase in number of channel or carrier proteins
what is co-transport used to absorb?
used to absorb glucose and amino acids into the small intestine
what is the definition of osmosis?
the movement of water particles from an area high water potential to an area of low water potential through a partially permeable membrane
how does co-transport work?
- sodium ions actively transported out of the cell by the sodium-potassium pump
- this decreases the sodium ion concentration, so there is a concentration gradient
- this means sodium ions are diffused into the cell, via the sodium-glucose transporter proteins
- carries in glucose aswell, so the glucose concentration increases
- glucose diffuses out of the cell and into the blood by diffusion
what factors affect the rate of osmosis?
the water potential gradient
the thickness of the exchange surface
the surface area of the exchange esurfacew
how does the water potential gradient affect the rate of osmosis?
the higher the water potential gradient, the faster the rate of osmosish
how does the thickness of the exchange surface affect the rate of osmosis?
the thinner the exchange surafce, the faster the rate of osmosis
