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Chapter 4 Lecture Outline Tissues Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 three or four major groups of organs: • Roots • Stems • Leaves • Flowers Each organ is composed of tissues. • A tissue is a group of cells performing a similar function. • There 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 the tips of roots and shoots • Roots and shoots increase in length as the apical meristems produce new cells (= primary growth). Meristematic Tissues Apical Meristems • Primary meristems develop from apical meristems. – Protoderm – Ground Meristem – Procambium • Primary meristems produce primary tissues. Diagram of longitudinal axis of a plant Meristematic Tissues Lateral Meristems Lateral Meristems - Produce secondary tissues that increase the girth of roots and stems (= secondary growth) • Vascular Cambium - Produces tissues that function primarily in support and conduction. – Composed of a thin cylinder of brick-shaped cells that extends the length of stems and roots • Cork Cambium - Lies outside vascular cambium just inside the outer bark – Produces bark Meristematic Tissues Intercalary Meristems Grasses and related plants do not have vascular cambium nor cork cambium. • They have intercalary meristems. • 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 a 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 that function in photosynthesis – Transfer cells - Develop irregular extensions of inner wall that greatly increase surface area of plasma membrane o Nectaries of flowers Tissues Produced By Meristems Simple Tissues Collenchyma tissue Contains collenchyma cells • Collenchyma cells: – Living cytoplasm – May remain alive a long time – Cell walls thick, and with uneven thickness due to extra primary 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, secondary walls, normally impregnated with lignin – Dead at maturity – Function in support – Two types: sclereids and fibers – Sclereids - Stone Cells o Scattered in tissue o Cells as long as wide Sclereids Tissues Produced By Meristems Simple Tissues – Fibers o Much longer that wide and contain lumen (tiny cavity) Fibers in cross section and longitudinal section Tissues Produced By Meristems Complex Tissues Complex tissues - Composed of two or more kinds of cells • Vascular tissues include xylem and phloem. Xylem - Chief conducting tissue for water and minerals that are absorbed by the roots • Composed of parenchyma cells, fibers, vessels, tracheids and ray cells Tissues Produced By Meristems Complex Tissues • Vessels - Made of vessel elements – Vessel elements: o Open at each end, but may have perforation plate o Dead at maturity o Thick secondary cell walls o Many have spiral thickenings on cell walls Vessels elements Spiral thickenings on vessel walls Tissues Produced By Meristems Complex Tissues • Tracheids – Tapered at the ends with pairs of pits that allow water to pass from cell to cell o Pits - Areas without secondary cell – Dead at maturity – Thick secondary cell walls – May have spiral thickenings on cell walls Tracheids • Rays - Function in lateral conduction and food storage – Composed of long-lived parenchyma cells Pit pairs 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 secondary 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 sieve tube contents when cell injured • Companion cells - Aid in conduction of food Phloem Tissues Produced By Meristems Complex Tissues Epidermis- Protective layer that is one celllayer thick 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 the surface of outer walls of epidermis that forms cuticle – Wax secreted on cuticle – Cuticle and wax prevent water loss by evaporation o 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. o – 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 the surface of periderm Tissues Produced By Meristems Complex Tissues Secretory Cells and Tissue • Secretory cells may function individually or as part of a 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