1. Tracheids:
* Structure: Long, narrow, dead cells with tapered ends.
* Function: They transport water and minerals through pits (thin areas in the cell wall where cytoplasm connects) and the hollow interior.
2. Vessel Elements:
* Structure: Shorter, wider, dead cells with perforated end walls (called perforation plates).
* Function: Form continuous tubes called vessels, allowing for more efficient water transport than tracheids due to the larger diameter and perforations.
3. Xylem Parenchyma:
* Structure: Living cells that store food and water.
* Function: Provide support and aid in lateral movement of water and minerals between xylem vessels and other tissues.
4. Xylem Fibers:
* Structure: Thick-walled, elongated, dead cells.
* Function: Provide structural support to the xylem and plant as a whole.
How Water and Minerals Move Through Xylem:
* Capillary Action: Water molecules adhere to the walls of xylem cells, creating a continuous column.
* Cohesion: Water molecules are attracted to each other, maintaining the column's integrity.
* Transpiration: Water evaporates from leaves, creating a negative pressure (tension) that pulls the water column upward.
* Root Pressure: Minerals are actively transported into the roots, creating a positive pressure that helps push water upward.
Important Note: Xylem transport is a passive process, meaning it doesn't directly require energy. However, the active transport of minerals into the roots and the transpiration process are essential for the overall movement of water and minerals through the xylem.
