Answer:
They have helical thickening of lignin in their walls to prevent collapse
Explanation:
the primary function of Xylem and its conducting vessels tracheids is to provide support and tranport water and minerals in plants.
Xylem vessels have layers of dead materials in the walls called LIGNIN. Lignin is a polymer; a very strong, hard materials that stop water passage through it,because it contains dead cells,
Therefore the presence of deposit of these strong impermeable, ligified walls in its walls prevent its collapse during mass flow of water of transpiration pull.
form cell membrane
Explanation:
It provides barriers in cellular membranes to protect the cell , and they make barriers for the organelles with in those cells. It work to provide pathways for various substance across membranes
A contusion occurs when a strong blow or repeated blows from an object struck the body, crushing the underlying muscle fibres and connective tissues without breaking the skin.
A contusion can vary in severity depending on the object and location of the injury. For example a contusion to the brain may cause a concussion that can cause serious symptoms that require immediate medical attention
