Movement of water in the root

• Water enters through root hair cells and moves into the xylem tissue located in the centre of the root. This movement occurs as a result of a water potential gradient, as the water potential is higher inside the soil than inside the root hair cells, due to the dissolved substances in the cell sap
• Therefore, the purpose of root hair cells it to provide a large surface area for the movement of water to occur
• Minerals are also absorbed through the root hair cells by active transport, as they need to be pumped against the concentration gradient
• There are two ways the water taken up by the root hair cells can move across the cortex of the root into xylem
• It can either occur via the symplast pathway where water enters the cytoplasm through the plasma membrane and passes from one cell to the next through plasmodesmata, the channels which connect the cytoplasm of one cell to the next
• The other pathway is the apoplast pathway where the water moves through the water filled spaces between cellulose molecules in the cell walls
• In the apoplast pathway water doesn’t pass through any plasma membranes therefore it can carry dissolved mineral ions and salts
• The final step in the apoplast pathway is when the water reaches a part of the root called the endodermis, it encounters a layer of suberin which is known as the Casparian strip, which cannot be penetrated by water
• Therefore, in order for the water to cross the endodermis, the water that has been moving through the cell walls must now enter the symplast pathway
• Once it has moved across the endodermis, the water continues down the water potential gradient from cell to cell until it reaches a pit in the xylem vessel which is the entry point of water