Question

Explain why it is important that xylem cells (vessels and tracheids) are dead at maturity. Additionally, describe what property of water allows for xylem to be an efficient water transportation tissue from the roots to the leaves?

Answer 1

Xylem is a vascular tissue of a plant that is used for transporting water and sugar from bottom to top of the tree that is xylem helps in the transport of water and sugar from roots to stems and leaves and also transports other dissolved compounds. Basically xylem has three types of cells that are xylem parenchyma cells, xylem cells, tracheary elements (Tracheid). Tracheids are completely dead at maturity and then it behaves like a pipe that helps to transport water and minerals through them. Although tracheids and vessels both are important but vessels are more advanced in terms of transport but tracheid is the only part of xylem which helps to water transport in most gymnosperms and seedless vascular plants. The vessel also works as a water transporter but in angiosperms. xylem cells (vessels and tracheids) are dead because both tracheids and the vessel's central vacuole burst due to the autolytic hydrolysis of the cell and then the worst thing happens that is cell death. After death, these two (Tracheids and vessels )lose their transporting ability so the remaining skeleton part of Tracheids and vessels give support in water and minerals transportation.

Basically xylem has an internal hydrophobic surface which helps in water transportation. At first, the water and nutrients come from semi root(secondary root) to the primary root, and then with the help of cohesion and adhesion force of xylem, it comes to the stem and then to leaves part. This means the cohesion property of water is created as a result intermolecular hydrogen bond helps to the upward movement of water then water molecules become evaporated from the leaves surface. This whole process is called Cohesion Theory of Sap Ascent in plants

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