Cellular Transport Unit
Passive Transport = movement of substances across the cell membrane without any
input of energy by the cell
Types
1) Diffusion = movement of molecules from high to low [ ](concentration)
- driven by the concentration gradient
- spreads out evenly till dynamic equilibrium is reached
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
Direction of Osmosis
Outside the Cell
Hypotonic
Inside the Cell
Hypertonic
Net Movement of Water
Inside the Cell
Hypertonic
Hypotonic
Outside the Cell
Isotonic
Isotonic
None
** 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
Active Transport = substances can cross the cell membrane with an input of energy from
the cell
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
2) Exocytosis = the process by which cells release “stuff”
- is essentially the reverse of endocytosis