2.13 understand that movement of substances into and out of cells can be by diffusion, osmosis and active transport

Diffusion:

Particles in a liquid or a gas move continuously and randomly. Particles change direction when they bump together. Particles collide more often when they are close together (more concentrated) so they diffuse or spreads out, until they are spaced evenly. When diffusion happens in living cells, the cells do not have to use energy for it to take place:

Diffusion is:

-        the net movement (overall direction of flow) of molecules within a gas or liquid

-        from a region of high concentration to a region of lower concentration (down a concentration gradient)

-        as a result of their random movement until an equilibrium is reached (balanced)

Osmosis:

When 2 solutions do not have the same concentrations of a substance, molecules may move from one to another by diffusion, if the membrane is permeable to the substance.

<-- a diagram of 2 glucose solutions of different concentrations separated by a partially permeable membrane 

This diagram shows 2 glucose solutions separated by a partially permeable membrane. This will allow the water molecules to pass through but not the glucose molecules. As a result, water can move from where there is a high concentration of molecules to where there is a lower concentration by the process of diffusion  (osmosis) which will continue until equilibrium has been reached.

Osmosis is:

- the diffusion of water molecules

- from a region of higher concentration of water molecules to a region of lower concentration of water molecules

- down a water potential gradient

- through a partially permeable membrane

If a cell is placed in a solution of lower water potential, water leaves the cell by osmosis. If the cell is placed in a solution of higher water potential, water enters by osmosis.

Active transport:

Active transport requires energy to move materials, molecules can move from one place to another by diffusions but only until an equilibrium has been reached. If no concentration gradient exists between 2 places, no diffusion can occur. Active transport is a method by which particles can cross membranes even against a concentration gradient. In active transport, protein molecules (carriers) pick up and carry particles across the membrane. Protein carriers use energy supplied by the cell.

Active transport:

-        can move molecules against a concentration gradient but

-        requires energy and

-        involves protein carriers in membranes