Cellular Transport Unit
Passive Transport = movement of
substances across the cell
membrane without any input of
energy by the cell
Passive Transport
Types
1) Diffusion = movement of
molecules from high to low [ ]
(concentration)
- driven by the concentration
gradient
- spreads out evenly till dynamic
equilibrium is reached
Diffusion
2) Osmosis = diffusion of water
A solution may be one of the following:
(compared to a cell)
- isotonic solution: same [ ] of water
and solute
- hypotonic solution: lower [ ] of
solute, a lot of water
- hypertonic solution: higher [ ] of
solute, less water
Isotonic Solution (Red Blood Cells)
A solution is
isotonic to a cell if
it has the same
concentration of
solutes as the cell.
Equal amounts of
water enter and
exit the cell, so its
size stays constant.
Hypotonic Solution (Red Blood Cells)
A hypotonic
solution has fewer
solutes than a cell.
Overall, more
water enters a cell
in a hypotonic
solution, causing
the cell to expand
and even burst.
Hypertonic Solution (Red Blood Cells)
A hypertonic
solution has more
solutes than a cell.
Overall, more
water exits a cell
in a hypertonic
solution, causing
the cell to shrivel
and even die
Direction of Osmosis
Outside the Cell
Inside the Cell
Net Movement of Water
Isotonic
Hypotonic
Hypertonic
Isotonic
Hypertonic
Hypotonic
None
Inside the Cell
Outside the Cell
** If the solution outside the cell is hypotonic,
then inside the cell is hypertonic and vice versa
** Water tends to diffuse from hypotonic to
hypertonic
- Plasmolysis = cells shrink when
turgor pressure is lost
- the reason plants wilt
- Cytolysis = cell bursts due to water
entering the cell
3) Facilitated Diffusion
= move molecules across the cell
membrane through
carrier/transport proteins
- are specific for the type of
molecule they help diffuse
Facilitated Diffusion (Open Channels)
Facilitated Diffusion
(Proteins Change Shape)
Diffusion vs. Facilitated Diffusion
Diffusion
Facilitated Diffusion
Active Transport = substances
can cross the cell membrane
with an input of energy from
the cell
Active Transport
1) Endocytosis = the process by which
cells ingest “stuff”
- vesicle holds the “stuff”
- two types:
1) pinocytosis - solutes and fluids
2) phagocytosis - large particles or
whole cells
Endocytosis
2) Exocytosis = the process by
which cells release “stuff”
- is essentially the reverse of
endocytosis
Exocytosis