Every living organism is constructed from cells. For cells to be able to work properly they share resources by passing essential things the body needs between them such as water and nutrients. To regulate this trade between cells the cell walls are constructed of a ‘semipermeable’ membrane, meaning certain materials can pass through into other cells, while others cannot, controlling and regulating the cells of the organism.
Material moves between cells via one of two methods; ‘Passive Transport’, which doesn’t require energy, is used to move essentials such as oxygen and water. Most other chemicals use ‘Active Transport’ to achieve this, this is more common in cells that require a lot of energy such as muscle cells and brain cells.