Transcript How does stuff get in and out of cells?

How does stuff get in and out
of cells?
Active and passive transport across the
Plasma Membrane (PM)
Diffusion and Osmosis
2 categories of transport
across PM
1. passive transport: no cell energy
required. Moves along a concentration
gradient from areas of high concentration
to areas of lower concentration.
• diffusion
• osmosis
2. active transport: requires cell energy
because molecules are transported
against a concentration gradient
Passive Transport
1. Diffusion: net movement of particles
from an area of high concentration
(overcrowding) to an area of lesser
concentration.
2. Osmosis: the diffusion of H2O
molecules through the PM.
Diffusion (in detail)
• All objects in motion have
kinetic energy & move in
straight line until they
collide w/ something else.
• 1827: Robert Brown
(Scotland)
– Studied pollen under
microscope
– Observed random
movements of grains
– Called it “Brownian
motion”
•What happens when you
put a drop of food coloring in
water?
Diffusion (cont.)
• The goal is to get as far
away from other molecules
as possible
– From area of “high
concentration” to area of
“low concentration.”
– Eventually the particles
will be as far apart from
each other as possible
Fig 2
• Key terms
– Concentration gradient: diffusion
cannot occur unless there’s an area of
high concentration (overcrowding).
– Selective permeability: The
phospholipid bilayer of the PM is
selective about what passes through by
diffusion.
OSMOSIS
WHAT: Diffusion of H2O molecules from higher
concentration to lower concentration. PM lets water
pass through.
concentration of
H2O is higher
OUTSIDE the cell
than inside the cell
so H2O molecules
move IN
concentration of
H2O is higher INSIDE
the cell than outside
so H2O molecules
move OUT
increases pressure
in the cell and cell
may burst
Turgor pressure
decreases and cell
may shrivel up
concentration of
H2Ois THE SAME
inside & outside the
cell so there is No
Gain or Loss of H2O
molecules
Turgor pressure stays
the same & cell
maintains
homeostasis
Passive Transport (in detail)
• Substances can pass through PM because it is permeable.
• They move WITH a concentration gradient
• They do this via diffusion, osmosis, etc
Facilitated Diffusion
Membrane protein
Carrier (Transport) Proteins