Osmosis is the process by which cells exchange water with their environment.
It can be defined as: 'The net movement of freely moving water molecules from a region of their higher concentration to a region of their lower concentration through a partially permeable membrane'.
The water potential of a solution falls when solutes are added because water molecules cluster around the solute molecules. This is called the SOLUTE POLTENTIAL. This is always negative because it always lowers water potential. Becomes more negative as more solutes are added to the system.
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Active transport
Active transport is the movement of substances against a concentration gradient (from a lower to higher) across a cell membrane.
The energy for Active Transport comes from ATP.
Cells that carry out a lot of active transport have a high level of mitochondria to produce ATP.
Active transport ceases if ATP production is prevented. This can happen if there is a lack of oxygen.
Carriers may move a single subtance in a single direction (uniport), two substances in the same direction (symport) or two substances in opposite directions (antiport)
It has been suggested that protein molecules change shape to transport solutes from one side of the membrane to the other by hydrolysing ATP to ADP.
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