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Diffusion (passive transport)
Diffusion is the process by which molecules move from areas of high concentration to areas of low concentration
Diffusion can cause many molecules to move across a cell membrane
but does not require the cell to use any energy
When the concentration of the solute is the same throughout the cell it has reached equilibrium
equilibrium is where there is no net movement of molecules from high to low concentrations
Most biological membranes are selectively permeable
this means some substances are able to pass through them and others are not
Selectively Permeable
Water is small enough that it is able to enter and exit a cell by passing through it’s membrane
Osmosis
Osmosis is the diffusion of water through a selectively permeable membrane
Water moves from areas of high concentration to areas of low concentration
This can effect cells in a few different ways
• Isotonic – cells neither gain nor lose water.
• Hypotonic – water rushes into the cell until equilibrium reached. Animal cells will burst.
• Hypertonic – water leaves the cells; animal cells shrink and plant cells’ vacuoles collapse.
Facilitated Diffusion
Sometimes molecules like glucose are too large to easily diffuse through a membrane
they require a channel protein
Active TransportMovement of a molecule from low concentration to high concentration
Requires Energy from the cell
Transport of large particles (requires
energy)
Endocytosis• Process of taking material INTO the cell by membrane infoldings or in pockets of the cell membrane.
Exocytosis
•Removal of large amounts of materials from the cell.
FIN