Plant Tissue Growth
Key Concepts Overview of Plant Tissues Seed-bearing vascular plants have a shoot system with stems, leaves, and reproductive parts Most also have a root system These systems consist of ground, vascular, and dermal tissues Plants lengthen or thicken at meristems
Introducing Meristems Plant tissues originate at meristems, which are regions of undifferentiated cells that retain their ability to divide Primary growth (or lengthening) arises from apical meristems Secondary growth (or thickening) arises from lateral meristems
Key Terms meristem Zone of undifferentiated plant cells Cells of meristem tissue can divide rapidly primary growth Plant growth from apical meristems in root and shoot tips secondary growth Thickening of older stems and roots In woody plants, secondary growth occurs when cells of a thin cylindrical layer of meristem divide
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25.3 Components of Plant Tissues Simple tissues consist primarily of one type of cell Examples: Parenchyma, collenchyma, and sclerenchyma Complex tissues have two or more cell types Examples: Xylem, phloem, and epidermis
Simple Tissues Parenchyma cells are typically thin-walled, flexible, and are alive in mature tissue Function in storage, secretion, wound repair, photosynthesis, and other specialized tasks Mesophyll is photosynthetic parenchyma parenchyma Simple plant tissue made up of living cells Main component of ground tissue
Simple Tissues Collenchyma cells have thick, flexible walls that support fastgrowing plant parts, and are alive in mature tissue collenchyma Simple plant tissue composed of living cells with unevenly thickened walls Provides flexible support
Simple Tissues Cells in sclerenchyma die at maturity, but their ligninreinforced walls remain and support the plant sclerenchyma Simple plant tissue that is dead at maturity Its lignin-reinforced cell walls structurally support plant parts
Complex Tissues Complex tissues consist of simple tissues in varying arrangements and proportions Complex tissues: Dermal Ground Vascular
Dermal Tissues The first dermal tissue to form on a plant is epidermis, which is usually a single layer of cells on the plant s outer surface Epidermal secretions form a cuticle that helps the plant conserve water and repel pathogens epidermis Outermost tissue layer of a plant
Some Dermal Tissues Dermal tissues include specialized cells, hairs, and other epidermal cell outgrowths Pairs of specialized epidermal cells form stomata, which control diffusion of water vapor, oxygen, and carbon dioxide gases across the epidermis Periderm replaces epidermis in woody stems and roots
Vascular Tissues Xylem and phloem are vascular tissues composed of elongated conducting tubes often surrounded by sclerenchyma fibers and parenchyma Xylem conducts water and dissolved mineral ions Consists of dead tracheids and vessel members with perforated, interconnected walls Phloem conducts sugars and other organic solutes Consists of live sieve-tube members interconnected to form sieve tubes Companion cells load sugars into sieve tubes
Vascular Tissues one cell s wall pit in wall sieve plate of sievetube cell companion cell A B C parenchyma vessel of xylem phloem fibers of sclerenchyma Fig. 25.7, p. 401
Simple Graphic
Ground Tissues Ground tissue (everything other than dermal and vascular tissue) makes up the bulk of a plant Consists mostly of parenchyma, but can also include other simple tissues mesophyll Photosynthetic parenchyma
Overview
Key Terms xylem Complex vascular tissue of plants; its tracheids and vessel members distribute water and mineral ions tracheid Tapered cell that forms water-conducting tubes in xylem Dead at maturity vessel member Cell that forms water-conducting tubes in xylem Dead at maturity
Key Terms phloem Complex vascular tissue of plants; distributes sugars through its sieve tubes sieve tube Conducting tube of phloem companion cell In phloem, parenchyma cell that loads sugars into sieve tubes
Complex Tissues in a Sunflower
verview of Flowering Plant Tissues