Concept 35.2 Different meristems generate cells for primary and secondary growth. Meristem Plant growth is not limited to embryonic period, it occurs throughout the plant’s life (indeterminate growth). Meristems: unspecialized tissues that divide continuously when conditions permit allowing the plant to elongate and become specialized , there exist two types of meristems ( apical and lateral)
Apical meristems: located at the tips of roots and shoots and in axillary buds of shoot responsible for primary growth (enables root to elongate). Lateral meristems: adds thickness to woody plants in roots and stems, this is secondary growth, there are two types: vascular cambium and cork cambium. Vascular cambium adds layers of vascular tissue called secondary xylem(wood) and secondary phloem The cork cambium: replaces the epidermis with thicker tougher periderm Meristems give rise to initials (stem cells) that remain in the meristem, and derivatives they become specialized in mature tissues. Flowering plants are categorized based on their life cycle (annual, biennials, perennials) Concept 35.3 Primary growth lengthens roots and shoots; product of the apical meristems. Primary growth of roots The tip of the root is covered by the root cap, it protects the apical meristem as the root pushes through the soil. Growth happen behind the tip in three zones (cell division, elongation, and differentiation). - zone of cell division: includes the root apical meristem and its derivatives. - Zone of elongation: roots cells elongate - Zone of differentiation: cells specialize and are mature. Responsible for the production of the epidermis, ground tissues and vascular tissues. Angiosperm tissue root organization: The stele (vascular tissue of roots) is a cylinder . - Eudicots the xylem is a star and phloem between - Monocots the vascular tissue has central core of parenchyma cells surround by a ring of xylem and phloem tissues The ground tissue of roots (parenchyma cells) - Present in the cortex, the region between the vascular cylinder and epidermis; stores carbs and transports water and salts from the root hairs to the center of the root , also allows for the extracellular diffusion of water and minerals and oxygen from the root hairs inward. - The endodermis is the innermost layer of the cortex, it is a cylinder one cell thick that forms the boundary with the vascular cylinder; regulates passage of substances from the soil into the vascular cylinder - Lateral roots arise from the pericycle, the outermost cell layer in the vascular cylinder (inside the endodermis), pushes through the cortex and epidermis until it emerges from the established root
Primary Growth of Shoots Shoot apical meristem: dome-shaped mass of dividing cells at the shoot tip.
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- Spring '17
- Plants, phloem, Plant anatomy, Secondary Vascular Tissue