TOPIC 1.CLASSIFICATION KINGDOM FUNGI

Movement of water from root hair xylem

Once in the xylem, the water and the mineral salts dissolved in it move up the xylem vessel by transpirational pull, capillarity and root pressure.

Transpirational pull

Transpiration occurs when water evaporates from the plant through the stomata in the leaves. As the water is lost, the mesophyll cells draw water from the xylem in the leaf which hi turn draws water from the xylem in the stem. This creates a tension called transpirational pull which draws water from the roots.

This results in a continuous column of water from the roots, through the xylem to the leaves. This column of water is called transpirational stream

Transpirational stream

Capillarity

Capillarity is the action that causes water to rise in narrow tubes. Xylem vessels have a narrow lumen which makes it possible for water to rise in them by capillarity.

Capillarity is made possible by cohesion and adhesion forces. Cohesion is the attraction between like molecules. It makes the water molecules Stick to each other. Adhesion is attraction between different molecules. It causes water molecules to adhere to the xylem vessels.

Root pressure

Root   pressure   pushes   water   and   dissolved mineral salts upwards from the root. This happens because the cells of the endodermis push mineral It’s into the xylem. This increases osmotic pressure in the xylem thereby creating a force that moves the water and dissolved minerals up the xylem vessel. When a plant is cut, fluid oozes out the remaining stem (Stump). This is proof of root pressure in plant.