Question

Describe the structure and organization of stem apex.

Answer 1

Hint: Apex is a growing portion of the roots and stem in the plants. The apical portion of stem is generally known as shoot apex.

Complete answer:
The vegetative shoot apex helps to extend growth of the shoot and initiates leaf primordia. The majority shoot apices are indeterminate even if some become determinate. The vegetative shoot apical meristem is generally dome shaped and partitioned by distinct zones of activity). In several species, the outermost two cell layers are maintained principally by anticlinal cell divisions. The corpus in which cell divisions are indiscriminately oriented is the region proximal to the tunica.
The central regions of mutually tunica and corpus are occasionally larger and more highly vacuolated than those on either side. The central region essential for the corpus layer is a rib meristem. This will lead to files of cells that later become the pith. This central region is bounded by a peripheral flank meristem that produces the procambium, cortical region and leaf primordia.
Reproductive shoot apices are the complex examples of determinate growth. Throughout the transition to the flowering phase which is a termed floral transition, the shoot apex generally undergoes profound morphological change, while the tunica or the corpus structure is maintained. Commonly at floral transition there is an overall rise in mitotic activity at the shoot apex, but a proportionally greater increase among the axial apical cells than among the peripheral cells.

Therefore shoot apex is the terminal part of the shoot with leaf primordium. Various theories are generated to explain its structure and organization although the most conventional theory is corpus tunica theory given by Schmidt in 1924.
The structure and organization of shoot apex includes the following: it is convex in shape or they are slightly elongated at the base. It is mainly divided into four regions as tunica, corpus, flank meristem, and rib meristem. Tunica is again divided into two single layers outer and inner tunica which divide from anticlinal division and form epidermis. Corpus layer is a layer which is 3 to 5 layer thick and divides at any plane to give volume growth to the plant. And the cells of the flank meristem are small, narrow and radially elongated. Rib meristem is generally seen below the corpus.

Note: The shoot apex which is a growing tip of the plant shoots and has a major role in the morphogenesis. From this the new leaves and flowers originate.