Everything Life Sciences Grade 10

Figure 6.7: Dicotyledonous root profile showing the major tissues found in the root system which

also aid in transport.

The epidermisis a single layer of cells on the outside that protects the inner tissues. The

epidermal layer of the root has no waterproof cuticle as this would prevent the absorption of

water. Structurally, the cells of the root hair (shown in Figure 6.8) have large central vacuoles

and cover a large surface area which allows water to enter these cells readily via osmosis.

Figure 6.8: Diagram of a root hair cell

The cortexconsists ofparenchymacells. These cells are large which enables them to store

water and food. They also facilitate the movement of water from the root hair cells on the

outside of the plant to the xylem on the inside of the plant.

The endodermisforms the innermost layer of the cortex. It is a layer of tightly-packed,

modified parenchyma cells. The radial and transverse cell walls are thickened with a water-

impermeable, waxy suberin layer, known as the Casparian strip. This layer helps to regulate

the flow of water from the cortex into the stele, rather than allowing the water to spread to

all the root cells.

The stele, orvascular cylinder(responsible for transporting water and minerals), consists

of the pericycle, phloem, cambium and xylem. Thepericycleis the outermost layer of the

stele, and consists of one or more rows of thin-walled parenchyma cells. It is in close contact

162 6.2. Anatomy of dicotyledonous plants