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Chapter 2 Lecture Outline Tissues Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Outline Organs and Tissues Meristematic Tissues Apical Meristems Lateral Meristems Intercalary Meristems Tissues Produced by Meristems Simple Tissues Complex Tissues
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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.
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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).
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Meristematic Tissues Apical Meristems Primary meristems develop from apical meristems. – Protoderm – Ground Meristem – Procambium Primary meristems produce primary tissues.
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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
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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
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Tissues Produced By Meristems Simple Tissues 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 Simple Tissues - Consist of only one kind of cell
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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
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Tissues Produced By Meristems Simple Tissues Collenchyma tissue - Contains collenchyma cells Collenchyma cells: – Living cytoplasm – May remain alive a long time – Cell walls thick, with uneven thickness – Pliable and strong, thus providing flexible support Collenchyma cells
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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: o sclereids o fibers
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Tissues Produced By Meristems Simple Tissues o Sclereids – Stone Cells – Scattered in tissue – Cells as long as wide
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Tissues Produced By Meristems Simple Tissues o Fibers o Much longer that wide and contain lumen (tiny cavity) Fibers in cross section and longitudinal section
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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
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Tissues Produced By Meristems Complex Tissues Vessels – Long tubes made of vessel elements – Vessel elements: o Thick secondary cell walls o Open at both ends o Secondary walls develop irregularly o Perforation plate between end walls Vessels elements Spiral thickenings on vessel walls
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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 Rays - Function in lateral conduction and food storage – Composed of long-lived parenchyma cells Tracheids
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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
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Tissues Produced By Meristems Complex Tissues 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 Phloem Companion cells - Aid in conduction of food
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Tissues Produced By Meristems Complex Tissues Epidermis- Protective layer that is one cell- layer thick covering all plant organs Composed mostly of parenchyma cells, guard cells of stomata, secretory glands and hairs Leaf cross section
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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.
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Tissues Produced By Meristems Complex Tissues 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 - Replaces epidermis when cork cambium begins producing new tissue – Lenticels - Loosely arranged pockets of parenchyma cells formed by cork cambium that protrude through the surface of periderm. Allows for gaseous exchange.
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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
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Review Organs and Tissues Meristematic Tissues Apical Meristems Lateral Meristems Intercalary Meristems Tissues Produced by Meristems Simple Tissues Complex Tissues
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