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