Plants 5 Transport in Vascular Plants

Root Transport  Hairs absorb essential nutrients by active transport  Water enters by osmosis  This accumulation of water and minerals creates a pressure that pushes the sap up the xylem: called root pressure.  Root pressure cannot account for all the movement of water.

Stem Transport  Water sticks to surfaces: known as adhesion. It sticks to the inside walls of the xylem and creates a pulling force.  Water can also stick to itself: cohesion. Because of the small diameter of the xylem tube, the cohesion of water can result in the water column holding together continuously.  There is a leaf pull or a transpiration pull from the leaves on the chain of water molecules, that keep the chain moving up.

Leaf Transport  Most water that comes into the leaf, is lost due to transpiration.  Water evaporates from the leaf: the hotter it is, the more water is brought up.

Vascular Tissue  Xylem has two types of cells:  Vessel elements are only in angiosperms and consists of many vessel elements connected end-to-end. The ends are absent or perforated. They can be next to other vessels and connect through a pit.  Tracheids are much narrower and their ends are sharply angled, and looked a bit pointed.  Cellulose and lignin are deposited on the outside surface of xylem cells to form rigid walls.

 Most phloem cells are called sieve tube cells because they have sieve plates at each end. They are smaller than vessel elements and have no nuclei when mature. The cytoplasm in the sieve tube cells are connected by pores to a small nucleated companion cell next to it.