tissues chapter 4. outline organs and tissues meristematic tissues apical meristems lateral...

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 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


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


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


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


− 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


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


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


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


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


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


• 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


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

tissues chapter 4. outline organs and tissues meristematic tissues apical meristems lateral...

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