TOPIC 1. CLASSIFICATION KINGDOM FUNGI

Monocotyledonous stem

The arrangement of vascular bundles is random. See Figure below

Dicotyledonous stem

The vascular bundles are arranged around the central pith, See Figure below

Absorption and movement of water and mineral salts

Plants absorb water and mineral salts from the soil through root hairs.

Structure and functions of root hairs

Root hairs are extensions of the epidermal cells of the root. Figure below shows the structure of a root hair.

 

Structure of root hair

Root hairs are long and slender to provide a large surface area for the absorption of water and mineral salts from the soil. The large number of root hairs also increases the total surface area of the roots.

The root hair cell sap is usually hypertonic to the surrounding. Hence, water enters the cell by osmosis.

Root hair cells have a higher concentration of minerals than the surrounding. Mineral salts are therefore absorbed by active transport.

The root hairs are very thin in order to provide a short distance over which absorption of water and mineral salts takes place.

Movement of water and dissolved mineral salts

When water is absorbed by the root hair, it dilutes the contents of the cell sap vacuole. As a result, the cells of the cortex, which are adjacent to the epidermis, have less water than the root hair cells. Water moves from the root hair cells to the cortex cells by osmosis. It moves the same way into the cells of the endodermis, then into the pericycle and then into the xylem.