- There are two main ways in which dissolved substances are moved into and out of cells.
- Substances move by diffusion along a concentration gradient which MUST be in the right direction to be useful to the cells.
- Osmosis depends on a concentration gradient of water and a partially permeable membrane.
ONLY WATER MOVES IN OSMOSIS
- Sometimes substances needed by the body have to be moved againsst a concentration gradient or across a partially permeable membrane. The process is known as ACTIVE TRANSPORT
- Active transport allows cells to move substances from an area of low concentration to an area of high concentration. So substances move against the concentration gradient. This means cells can absorb ions from very dilute solutions. It is also possible for them to move substances like sugars and ions from one place to another through the cell membrane.
- It takes energy for the active transport system to carry a molecule across the membrane and then return to its original position. The energy comes from…