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Tissues Chapter 4 Outline Organs and Tissues Meristematic Tissues • Apical Meristems • Lateral Meristems • Intercalary Meristems Tissues Produced by Meristems • Simple Tissues • Complex Tissues Organs and Tissues Plants have 3 or 4 major groups of organs: • • • • Roots Stems Leaves Flowers Each organ composed of tissues • Tissue - group of cells performing similar function • May be more than one tissue per organ Meristematic Tissues Apical Meristems Meristems - permanent regions of growth and active cell division Apical Meristems - found at tips of roots and shoots • Roots and shoots increase in length as apical meristems produce new cells (= 1° growth) Meristematic Tissues Apical Meristems Primary (1°) meristems develop from apical meristems • Protoderm • Ground Meristem • Procambium 1° meristems produce primary tissues Diagram of longitudinal axis of a plant Meristematic Tissues Lateral Meristems Lateral Meristems - produce 2° tissues that increase girth of roots and stems (= 2° growth) • Vascular Cambium - produces tissues functioning primarily in support and conduction −Composed of thin cylinder of brick-shaped cells that extends length of stems and roots • Cork Cambium - lies outside vascular cambium just inside outer bark −Produces bark Meristematic Tissues Intercalary Meristems Grasses and related plants do not have vascular cambium nor cork cambium • Intercalary Meristems −In vicinity of nodes (leaf attachment area) −Add to stem length Tissues Produced By Meristems Simple Tissues Simple Tissues - consist of only one kind of cell Parenchyma - composed of parenchyma cells • Parenchyma cells −Thin, pliable walls −Usually 14-sided at maturity −Living cytoplasm, often containing large vacuoles and various secretions −May remain alive long time −Have spaces between them Parenchyma cells Tissues Produced By Meristems Simple Tissues Types of parenchyma tissue and cells • Aerenchyma - parenchyma tissue with extensive connected air spaces, usually in aquatic plants • Chlorenchyma - parenchyma cells containing chloroplasts (photosynthesis) • Transfer Cells - develop irregular extensions of inner wall that greatly increase surface area of plasma membrane – Nectaries of flowers Tissues Produced By Meristems Simple Tissues Collenchyma Tissue contains collenchyma cells • Collenchyma cells −Living cytoplasm −May remain alive long time −Cell walls thick, and with uneven thickness due to extra 1° wall in cell corners −Pliable and strong, thus providing flexible support Collenchyma cells Tissues Produced By Meristems Simple Tissues Sclerenchyma Tissue - contains sclerenchyma cells • Sclerenchyma cells −Thick, tough, 2° walls, normally impregnated with lignin −Dead at maturity −Function in support −Two types: sclereids and fibers −Sclereids – stone cells –Scattered in tissue –Cells long as wide Sclereids Tissues Produced By Meristems Simple Tissues − Fibers – Much longer than wide and contain lumen (tiny cavity) Fibers in cross section and longitudinal section Tissues Produced By Meristems Complex Tissues Complex Tissues - composed of 2 or more kinds of cells • Vascular tissues include xylem and phloem Xylem - chief conducting tissue for water and minerals absorbed by roots • Composed of parenchyma cells, fibers, vessels, tracheids and ray cells Tissues Produced By Meristems Complex Tissues Vessels - made of vessel elements • Vessel elements – Open at each end, but may have perforation plate – Dead at maturity – Thick 2° cell walls – Many have spiral thickenings on cell walls Vessels elements Spiral thickenings on vessel walls Tissues Produced By Meristems Complex Tissues Tracheids • Tapered at ends with pairs of pits that allow water to pass from cell to cell – Pits - areas without 2° cell wall • Dead at maturity • Thick 2° cell walls • May have spiral thickenings Tracheids Pit pairs Rays - function in lateral conduction and food storage – Composed of long-lived parenchyma cells Tissues Produced By Meristems Complex Tissues Phloem - conducts dissolved food materials produced by photosynthesis throughout plant • Composed of sieve tube members, companion cells, fibers, parenchyma cells and ray cells Sieve Tube Members • Lack 2° cell walls and nuclei • Lay end to end to form sieve tubes • Walls have sieve plates with small pores • Callose forms callus plug - prevents leaking of contents when cell injured Companion Cells - aid in conduction of food Phloem Tissues Produced By Meristems Complex Tissues Epidermis - one cell-layer thick protective layer covering all plant organs • Composed mostly of parenchyma cells, guard cells of stomata, secretory glands, and hairs Leaf cross section Tissues Produced By Meristems Complex Tissues Cutin - fatty substance on surface of outer walls of epidermis forming cuticle • Wax secreted on cuticle • Cuticle and wax prevent water loss by evaporation – Resistant to bacteria and other disease organisms Root epidermal cells produce root hairs • Increase absorptive area of root surface Leaves have stomata bordered by pairs of guard cells Tissues Produced By Meristems Complex Tissues Periderm - replaces epidermis when cork cambium begins producing new tissue • Constitutes outer bark • Primarily composed of cork cells − Dead at maturity − While still alive, cytoplasm secretes suberin (fatty substance) into walls – Makes cork cells waterproof and helps protect phloem Periderm with lenticel • Lenticels - loosely arranged pockets of parenchyma cells formed by cork cambium that protrude through surface of periderm Tissues Produced By Meristems Complex Tissues Secretory Cells and Tissue • Secretory cells may function individually or as part of secretory tissue −Flower nectar −Citrus oils −Glandular hair mucilage −Latex −Resins Review Organs and Tissues Meristematic Tissues • Apical Meristems • Lateral Meristems • Intercalary Meristems Tissues Produced by Meristems • Simple Tissues • Complex Tissues
