are essential plant organs. They anchor the plant in thejround, absorb water and minerals from the soil, and transport

materials to other parts of the plant body. Roots may alsoict as storage organs, storing excess carbohydrate reserves until

are required by the plant. Roots are covered in an epidermis>ut, unlike the epidermis of leaves, the root epidermis has only[thin cuticle that presents no barrier to water entry. Young roots

are also covered with root hairs (see below). Much of a rootcomprises a cortex of parenchyma cells. The air spaces betweenthe cells are essential for aeration of the root tissue. Mineralsand water must move from the soil into the xylem before theycan be transported around the plant. Compared with stems, rootsare relatively simple and uniform in structure. The structure ofmonocot and dicot roots is compared in the photographs below.

The Structure of a Dicot Root :These photographs (left and below) show crosssections through a young dicot root (i.e. primarytissues). In the photograph to the left, note thelarge area of the root occupied by the cortex.The parenchyma (packing) cells of the cortexstore starch and other substances. The airspaces between the cells are essential foraeration of the root tissue, which is non-

Cortex ofparenchymacelts

Airspace

Vascular tissue(vascular cylinderor stele) isenlarged in thephoto on the right.

Root hairs are located behind the region ofcell elongation in the root tip. They are singlecelled extensions of the epidermal cells thatincrease the surface area for absorption.Individual root hairs are short lived, but theyare produced continually. The root tip iscovered by a slimy'root cap. This protectsthe dividing cells of the tip and aids theroot's movement through the soil.

Monocot roots (right) vary from dicotroots in several ways. As in dicots, thereis a large cortex but the endodermis isvery prominent and heavily thickened.The stele (ring of vascular tissue) islarge compared with the size of the rootand there are many xylem points. Thereis a central pith inside the vasculartissue that is absent in dicot roots.

photbsynthetic. The vascular tissue; xylem (X)and phloem (P) forms a central cylinder throughthe root and is surrounded by the pericycle, aring of cells from which lateral roots arise. The

^primary xylem of dicot roots forms a star shapein the center of the yascuiar cylinder with usually3 or 4 points, Unlike monqcots, thercjs'; no,,.central pjthof parenchyrna cells. ; V :'"r'- • - : • : .>-•

Cortex

iBericycie/:

Endodermis

The Structure of a Monocot Root

Cross section through an old root of corn(Zea mays), a typical monocot.

an •

K

1. Explain the purpose of the root hairs:

2. Explain why the root tip is covered by a cap of cells:

3. Describe two features of internal anatomy that distinguish monocot and dicot roots:

(a)

(b)

4. Describe one feature that monocot and dicot roots have in common: