Structure and Function of Plant Root
Anatomically, root of plant is composed of 3 layers or tissue systems; epidermis, cortex and central cylinder (stele).
1. Epidermis
Root epidermal cells are flattened and thin-walled, generally one layer. In the area near to the root tip, the epidermal cells are modified into root hairs. Cuticle layer of the root hair is very thin, because the function is as water absorbent.
2. Cortex
It is the area between epidermis and central cylinder. Cortex is mainly composed of parenchyma cells structured circular. In monocot plants, usually there is sclerenchyma. In some aquatic plants, the parenchyma cells have air space, this parenchyma is called aerenkima. The cortex location in root is outer than in stem.
a. Exodermis
The outermost layer of cortex that is directly adjacent to epidermis can be a hypodermic that the cell wall contains suberin or lignin, called exodermis.
b. Endodermis
The innermost layer of the root cortex develops into endodermis. Endodermis consists of a thick single cell layer, which marks the boundary of the cortex. In young endodermis cells, there are thickened cell walls by suberin or lignin substances. The thickening forms the ribbon-shaped series called Caspary ribbon. Caspary Ribbon prevents water from entering across the cell wall. To get into the central cylinder, water gets into endodermis that the walls are not thickened, called pelalu cells or impregnation cells. Endodermis helps maintaining substance traffic into the root vessels.
3. Central Cylinder (Stele)
Central cylinder is located on the inside of endodermis layer. Root central cylinder is composed by xylem, phloem and perisikel tissues. Perisikel consists of parenchyma cells that are between endodermis and vascular tissue. Perisikel evolves from procambium. Perisikel will evolve to form cambium and pith. In monocot plants, primary xylem is interspersed with primary phloem; with the xylem location is deeper than phloem. While in dicotyledonous plants, xylem is located in center roots and shaped like a star.
Root functions are as follows:
1. Water and minerals entrance, root hairs take water and mineral salts from the soil by osmosis. Water and mineral salts are taken to the leaves for photosynthesis.
2. To embed and sustain the plant body in order to be upright and sturdy.
3. In some plants, root is also a place to store food.
4. Helping breathing, oxygen can enter through the roots by diffusion.
