Plants have two separate transport systems. A network of xylem vessels transports water and mineral ions from the roots to all other parts of the plant. Phloem tubes transport food made in the leaves to all other parts of the plant. Neither of these systems has a pump, this is because they are not as active as animals and do not need such rapid supplies of food. Neither xylem nor phloem transports oxygen as oxygen …showed first 75 words of 1496 total…

…showed last 75 words of 1496 total…sealed by clotting. Phloem sap has a high turgor pressure because of its high solute content, and would leak out rapidly if the holes in the sieve plate were not quickly sealed. Moreover, phloem sap contains valuable substances such as sucrose, which the plant cannot afford to lose in large quantity. The "clotting" of phloem sap may also help to prevent the entry of micro-organisms which might feed on the nutritious sap or cause disease.