Active transport

All organisms use ATP as an immediate energy source for processes such as active transport. In plants, the roots are an organ system whose purpose is the uptake of mineral ions and water, and its movement though to the endodermis and xylem via the apoplast and symplast pathways. The root hair cells have specific channels for ions such as nitrate and potassium. These channels have the enzyme ATPase which hydrolyses ATP and releases energy to absorb the ions against a concentration gradient into the cell. This movement into the cell from the soil lowers the water potential of the roots hair cells allowing water to enter by osmosis. Movement of this water then takes place via the symplast pathways (through cell cytoplasm) and apoplast pathways (via gaps in the cell walls. Water crosses the junctions of adjacent cells through plasmodesmata, smallgaps that allow its smooth passage to the endodermis. Active transport of the mineral ions into the xylem allows the water to enter the xylem by osmosis generating a hydrostatic pressure called the root pressure. This creates a push, which together with the cohesion-tension pulls water up the xylem in a column through the hollow lignified xylem vessels.