tissues chapter 4. outline organs and tissues meristematic tissues apical meristems lateral...
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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 TissuesApical 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 TissuesApical 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 TissuesLateral 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 TissuesIntercalary 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 MeristemsSimple 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 long time−Have spaces between them
Parenchyma cells
Simple Tissues - consist of only one kind of cell
Tissues Produced By MeristemsSimple 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 MeristemsSimple 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 MeristemsSimple 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 MeristemsSimple Tissues
− Fibers– Much longer than wide and contain lumen (tiny
cavity)
Fibers in cross section and longitudinal section
Tissues Produced By MeristemsComplex 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 MeristemsComplex 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
Vesselselements
Spiral thickenings on vessel
walls
Tissues Produced By MeristemsComplex 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
Rays - function in lateral conduction and food storage– Composed of long-lived parenchyma cells
Tracheids
Pit pairs
Tissues Produced By MeristemsComplex Tissues
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 Phloem
Phloem - conducts dissolved food materials produced by photosynthesis throughout plant • Composed of sieve tube members, companion cells,
fibers, parenchyma cells and ray cells
Companion Cells - aid in conduction of food
Tissues Produced By MeristemsComplex 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 MeristemsComplex 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 MeristemsComplex Tissues
• 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 - replaces epidermis when cork cambium begins producing new tissue
Periderm with lenticel
• Lenticels - loosely arranged pockets of parenchyma cells formed by cork cambium that protrude through surface of periderm
Tissues Produced By MeristemsComplex 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