植物细胞和组织

Plant tissues are categorized as meristematic or permanent. Meristematic tissues are embryonic regions capable of self-renewal and indefinite cell division, enabling continuous growth. Permanent tissues consist of terminally differentiated cells that can no longer divide and perform specialized functions like support, protection, and nutrient transport.

Apical meristems located at root and stem tips enable elongation of these structures, increasing plant length. Lateral meristems in the radial portion of stems and roots increase plant thickness or girth, typically in woody plants. Together, they drive primary and secondary growth in roots and shoots.

Dermal tissue forms the protective outer covering of plants and serves as the first line of defense against pathogens and physical damage. In non-woody plants, it appears as the epidermis, a layer of tightly packed cells. The cuticle, a waxy coating on aerial parts, prevents water loss while allowing gas exchange.

Xylem transports water and minerals from roots to different plant parts through xylem and transpiration driven transport of resources. Phloem conducts sugars produced during photosynthesis from the site of photosynthesis to other plant regions. Together, these vascular tissues form vascular bundles in stems and vascular cylinders in roots.

Ground tissue is responsible for most metabolic functions in plants. It is the primary site of photosynthesis, provides structural support to stems, and offers a supportive matrix surrounding vascular tissue. This simple tissue enables nutrient exchange and storage throughout the plant.

Parenchyma cells are living, metabolically active cells with thin flexible walls that perform photosynthesis, storage, and transport. Collenchyma cells are living with irregular thick walls providing structural support in young stems and leaf veins. Sclerenchyma cells are typically dead at maturity with thickened secondary walls containing lignin, providing protective support.

Parenchyma cells comprise approximately 90 percent of cells in herbaceous seed plants and retain the ability to divide throughout their lives. This capacity makes them essential for wound healing and tissue regeneration. They also perform specialized functions including photosynthesis, storage, and nutrient exchange between xylem and phloem.