Primary Growth: Root Growth and Development
• Primary growth occurs in the apical meristem of a plant.
• The apical meristem is embryonic tissue found in the tips of stems and roots that allows the plant to grow in length.
• Three primary meristems derive from the apical meristem of the root:
· Procambium gives rise to vascular tissue.
· Ground meristem gives rise to storage and structural cells.
· Protoderm gives rise to the epidermis.
• The roots of monocots and dicots have several structural differences.
primary meristems, zone of cell division
- The diagram to the left depicts the longitudinal section of a root. The root cap at the tip of the root covers and protects the apical meristem as the root grows.
- The apical meristem of the root forms three
primary meristems. The central primary meristem is the procambium. Procambium gives rise to the water- and
nutrient-conducting vascular tissues. Surrounding the
procambium is ground meristem, which gives rise to storage and structural tissue known as ground tissue. The protoderm is the outermost primary meristem that gives rise to epidermis. - The zone of cell division includes the apical meristem and the three primary meristems. As the root grows, the cells in the zone of cell division gradually enter the
zone of elongation. Here, cells elongate, causing the tip of the root to push further into the ground. Finally, the cells complete their development and become fully differentiated in the zone of maturation
monocot
- A monocot root is shown in the diagram to the left. The epidermis is the single layer of cells that covers the root. Beneath the epidermis is the cortex. The cortex consists of ground tissues that function in the storage of nutrients. The endodermisis a layer of cells that form the boundary between the cortex and the stele (not labeled in the diagram). The stele is the central cylinder of vascular tissues that arise from the procambium. Xylem and phloem are arranged in a ring within the stele of a monocot root. Within the ring of vascular tissue is the pith, a region of cells that function in the storage of nutrients.
dicot
- Like the monocot root, the dicot root has an outer epidermis and a cortex that surrounds the central stele. Inside of the stele, however, the vascular tissue is arranged differently. The cells of the xylem radiate out from the center of the stele, creating an x-like shape. The phloem of the stele is arranged in between the arms of the xylem.
pericycle
- Just inside of the endodermis of both monocots and dicots is the pericycle. The pericycle gives rise to lateral roots, which can sprout out from an established root.
Label _______ points to the xylem.
- D
Starting from the tip of the root, the four major regions of a plant root occur in the following order:
- root cap, zone of cell division, zone of elongation, zone of maturation
The length of a root is largely the result of:
- the elongation of cells
Label ________ points to the endodermis.
- C
True or false?
The vascular tissue in a monocot root is arranged in a ring around a central core of parenchyma cells called the pith.
- true
The following diagram depicts a __________ root.
- dicot