7.3- Cell Transport Notes
The cell controls what comes in and out by using the cell membrane. The cell membrane helps the cell keep
the right balance between the liquid in the cell and the liquid around the cell.
Passive Transport: The movement of materials across the cell membrane without using cellular energy.
1. Diffusion: The process by which particles move from an area of higher concentration (more) to an
area of lower concentration (less).
- If more of a substance is on one side of the cell membrane than the other side, the particles will
move to the side that has a lower concentration (less).
2. Faciliated Diffusion: The process in which molecules cannot diffuse across the membrane alone and
have to pass through a protein channel.
- The protein channel acts as a helper!
3. Osmosis: The movement of water through a selectively permeable membrane.
- Osmosis involves the movement of water molecules from an area of higher
concentration to an area of lower concentration.
- Many cells contain water channel proteins, known as aquaporins, that allow
water to pass right through them.
- Water will tend to move across the barrier until equilibrium is reached.
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The Effects of Osmosis on Cells:
o Isotonic: The concentration is the same inside and outside the cell.
Water molecules move at the same rate in both directions.
o Hypertonic: the outside solution has a higher concentration than
the solution inside the cell. Movement of water molecules out of the cell causes it to shrink.
o Hypotonic: The outside solution has a lower concentration than the solution inside the cell.
Movement of water molecules into the cell causes it to swell.
Active Transport: Energy from the cell is needed to move molecules from an area of low concentration to high
concentration.
1. Protein Pumps: Chemical energy is used to pump ions across the cell membrane. This works for small molecules
too.
2. Endocytosis: Endocytosis is the process of taking material into the cell by means of infoldings, or pockets, of the
cell membrane. The pocket that results breaks loose from the outer portion of the cell membrane and forms a
vesicle or vacuole within the cytoplasm.
3. Exocytosis: Many cells also release large amounts of material from the cell, a process known as exocytosis.
During exocytosis, the membrane of the vacuole surrounding the material fuses with the cell membrane, forcing
the contents out of the cell.