L 7b Transport through the
membrane
Week W4
Main
Conditions inside every cell must remain nearly constant for it to continue
its functions
Homeostasis
condition where cells/organisms maintain a constant internal
environment despite changes in the external environment
cell membrane plays a key role in maintaining homeostasis
Cells exchange nutrients and stuff through a thin layer of fluid
surrounding
extracellular fluid
materials from blood vessels go to extracellular fluid first then into the
cells
waste leaves cells in the opposite direction and end up in the blood stream
nutrient path: blood vessels → extracellular fluid → cells
nutrient path: cells → extracellular fluid → blood vessels
Passive Transport
no energy used by the cell to transport; requires a concentration gradient
Two main types
diffusion (& Facilitated diffusion)
a substance moving a high concentration area to a low
concentration area
L 7b Transport through the membrane 1
, bouncing into each other so they’re gonna move to a space
where they bump less
concentration gradient
a difference in concentration between two regions
small molecules such as O2 & CO2 diffuse easily through
membranes
Facilitated Diffusion
where special membrane proteins assist in diffusion of larger
substances through the membrane
carrier proteins
binds to specific, non-charged molecules due to their
shape and they change their own shape to drop the
molecule in the cell
channel proteins
have tunnel-like shapes that allow ions (charged particles)
go through
the proteins have CHARGED R GROUPS exposed in
their structure that push the CHARGED IONS through
(like a magnet, they won’t go through if they have the
L 7b Transport through the membrane 2
membrane
Week W4
Main
Conditions inside every cell must remain nearly constant for it to continue
its functions
Homeostasis
condition where cells/organisms maintain a constant internal
environment despite changes in the external environment
cell membrane plays a key role in maintaining homeostasis
Cells exchange nutrients and stuff through a thin layer of fluid
surrounding
extracellular fluid
materials from blood vessels go to extracellular fluid first then into the
cells
waste leaves cells in the opposite direction and end up in the blood stream
nutrient path: blood vessels → extracellular fluid → cells
nutrient path: cells → extracellular fluid → blood vessels
Passive Transport
no energy used by the cell to transport; requires a concentration gradient
Two main types
diffusion (& Facilitated diffusion)
a substance moving a high concentration area to a low
concentration area
L 7b Transport through the membrane 1
, bouncing into each other so they’re gonna move to a space
where they bump less
concentration gradient
a difference in concentration between two regions
small molecules such as O2 & CO2 diffuse easily through
membranes
Facilitated Diffusion
where special membrane proteins assist in diffusion of larger
substances through the membrane
carrier proteins
binds to specific, non-charged molecules due to their
shape and they change their own shape to drop the
molecule in the cell
channel proteins
have tunnel-like shapes that allow ions (charged particles)
go through
the proteins have CHARGED R GROUPS exposed in
their structure that push the CHARGED IONS through
(like a magnet, they won’t go through if they have the
L 7b Transport through the membrane 2
