Roots are vital to the plant in a variety of ways: they provide stability,
store nutrients, and act as the primary source of water and nutrient
acquisition. In general, the root comprises all parts of the plat that lie
beneath the soil, even though most of the tissues of the plant, including the
vascular tissues, are continuous throughout the root and shoot (stem,
leaves, flowers, etc.).
There are three different types of root structure. A taproot,
characteristic of dicots, is a single dominant root from which smaller,
secondary roots extend. In a fibrous root system, composed of many small
roots, no single root dominates. Taproots stretch deep into the soil, while
fibrous roots spread out close to the surface. Adventitious roots develop
on vines after embryonic development and help plants cling to substrates other
than the soil, such as a tree trunks.
Typical roots contain three different sections, or zones: the meristematic zone, the zone of elongation,
and the zone of differentiation. In the meristematic zone, named after the apical meristem, the plant cells
undergo rapid mitotic division, creating new cells for root growth. These new cells, once they enter the zone
of elongation, begin,unsurprisingly, to elongate, furnishing the root with added length. The zone of
differentiation containsmature, specialized cells, such as phloem, xylem, and
root hairs.
Figure %: A Root
Root Hairs
Root hairs are extensions of the epidermal cells on the surface of the root,
and are continually being sloughed off by the soil and regrown. The tiny root
hairs, which have a huge total absorptive surface area, have evolved in order to
allow the plant to take in as much water from the soil as possible. Not
surprisingly, most of the water and minerals taken in by the plant are absorbed
by the root hairs. Water and dissolved minerals from the soil move into the
root hairs by osmosis and travel into the xylem found in the root, where they
are transported to the rest of the plant. The movement of fluids from the root
hairs to the xylem can occur through one of two conductive pathways--
apoplast or symplast. With the apoplast, water travels along cell walls
and through intercellular spaces from the root surface to the core. The
symplast route, on the other hand, moves fluids through the cells, via
channels that connect their contents.
