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Exam 2: Life Cycles, Vascularization, Roots, and Secondary Tissues -…
Exam 2: Life Cycles, Vascularization, Roots, and Secondary Tissues
Vascularization
Tracheids 
Early Tracheids - Facilitated water transport; lignified, long and wide; in ferns and lycophytes; possess pit membranes
True Tracheids - Lignified; function in water transport and structural support; narrow and tapered at both ends; evolved likely only once, in tracheophytes
Pine Tracheids - Water movement and structural support; Torus-margo pit membrane which moves to prevent cavitation
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Xylem
Hyroids - Water conducting cells which do not have plasmodesmata (imperforate); assist in refilling from cavitation; possess no lignin; apomorphic trait to true vascular tissue
Tracheary Elements - Cells with thickened cell walls for waterproofing and structural support which die at maturity
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Vessel Elements - Large in diameter, dead at maturity, open, digested cell walls
Differences in Vessel Elements of Angiosperms v. Gymnosperms - Different diameters, lengths; permits more fiber with more vessel element; larger vessel elements increases capacity for transport but also cavitation
Vessel Element Differentiation - Apical meristem to vacuolization to elongation to development of secondary cell wall to death at maturity
Phloem
Special Features
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Longitudinal Arrays of Endoplasmic Microtubules - Plastids, mitochondria, ER vesicles
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Cell Types
Sieve Cells and Albuminous Cells - Transport photosynthate, hormones, electric signals; gymnosperms only have these; sieve elements possessed by earlier lineages; sieve area pores narrow; uniform areas mostly on ends; lacks sieve plate
Sieve Tube Element - Found only in angiosperms; has sieve plate with many holes on end wall; sieve tube elements together = sieve tube; primary cell wall; mostly ER and some protoplasts at maturity; callose and callose plugs
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Plasmodesmatal Connectivity - Sieve tube elements and companion cells are connected by many plasmodesmata, given that they originate from the same mother cell; one pore on element side can branch into many on companion side
Sieve Tube Contents
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Plastids, Very Few Mitochondria
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Wood
Selective Advantages - Allows plant to grow taller to access more light; higher rates of transpiration due to more xylem, wider xylem, larger conduits; evidence shows 5 possible separate instances of evolution of wood
Monocotyledonae - Not true wood; arborescent, no secondary growth
Secondary Growth - Complex plant development; growth in girth; secondary xylem (wood), secondary phloem (inner bark), ground tissue (rays) ; continuous ring growth
Vascular Cambium
Fusiform Initials - Stem cells; xylem and phloem; fascicular cambiumb (longitudinal)
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Annular Rings - Xylem secondary cell walls robust; phloem compressed, ring width determined by environment and changing conditions; early to late wood, larger vessel elements to smaller vessel elements
Sapwood vs. Heartwood - Sapwood = water transport, heartwood = storage, no water transport; softwood = tracheids only with little room for fibers, gymnosperms; hardwood = space for fibers, angiosperms
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Bark
Periderm - Composed of (from exterior) phellem (cork), phellogen (cork cambium), phelloderm
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Life Cycle Evolution
Alternation of Generations - Life cycle scheme which includes a haploid gametophyte and a diploid sporophyte; common to current land plants
Antithetic Theory - Most likely explanation for the emergence of Alternation of Generations; suggests that mitotic division interjected into meiosis resulting in a diploid embryo on gametophyte
Marchantiophyta
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Sporophyte - Parasitic structure on gametophyte; contains sporangium, in which sporocytes (2n) produce spores (1n)
Bryophyta
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Lycophyte - Heterosporous; spore contained within spore walls
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Monilophyta - Independent gametophyte and sporocyte
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Sporophyte - Large, persistent, diploid structure
Gymnosperm - Microgametophyte not restricted to aqueous environment; megagametophyte protected by integuments
Sporophyte - Dominant, diploid structure; large
Gametophyte - Micro produces pollen, megagametophyte serves as nutritive tissue, protected by integuments, within ovule
Angiosperm - Sporophyte dominant; gametophytes microscopic as with gymnosperms
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Gametophyte
Microgametophyte - Multicellular haploid stage; produces pollen grain which is immature until germination
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Roots
Rhizoid - Proto-root structure which provides anchorage and possesses some mineral absorption capabilities
Rhizomorphs - Dichotomous rooting system; no chloroplasts or stomata as with other roots; branched with no root cap; some examples possess root hairs
Root Types
Primary Roots - Main root; derived from radicle, dominant in eudicots, ancillary in monocots
Lateral Roots - Adventitious; derived from leaves and stems, dominant in monocots
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Organizational Diversity
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Monocot - Pith in center; endodermis evident, surrounded by cortex
Eudicot - No pith; endodermis, surrounded by cortex
Leaves
Evolutionary Conditions - Environmental conditions on Earth were unfavorable for extensive leaf development until roots came about and more moisture was available
Independent Leaf Development - Leaves convergently evolved in liverworts, mosses, lycophytes, monilophytes, and spermatophytes
Indeterminate Growth - Preceded leaf development; allows for leaves to grow in configuration that maximizes sunlight exposure
Enation Theory - Describes evolution of leaves in lycophytes; epidermal outgrowths give rise to leaves, with vascular strands emerging later
Zimmerman Telome Theory - Euphyll evolution; unequal branching, flattening into 2 dimensions; webbing resulting in thin tissue between axes, branches become veins, webbing becomes mesophyll; by Devonian, euphylls widespread
Development of Leaves
Liverwort and Moss - Mitosis of a single cell produces leaves; moss produce them from the midvein cell layer
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Euphylls (Seed Plants) - Pool of recruited cells produce leaves from multicellular shoot apical meristem
Chlorenchyma - Ground tissue; specialized parenchyma which has many chloroplasts; main function is photosynthetic
Aerenchyma - Ground tissue; specialized parenchyma which contains large air spaces; permits gas exchange and buoyancy
Collenchyma - Ground tissue with thickened cell walls; main function in flexible support
Vascular Tissue
Xylem, Tracheids - Water transport #
Phloem - Sieve tube elements/sieve tube cells, companion cells/albuminous cells; serve to transport photosynthate #
Epidermis - Epidermal cells, guard cells; often cuteinized
Organization
Lycophylls - Microphyllic; single, central vascular trace, vascular strand connects to stem # #
Monocots - Adaxial (outer) and abaxial (stemward) epidermis; cuteinized, has bulliform cells for rolling up; veins are surrounded by bundle sheathes
Eudicot Leaf - Upper and lower epidermis, polarized by sunlight; palisade cells of mesophyll for photosynthetic activity, spongy cells for gas exchange; xylem on top and phloem on bottom in veins; bundle sheathes