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BIOL 165 Midterm: BIOL 165 Notes for Midterm 2 - University of Waterloo

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BIOL 165
Marcel Pinheiro

BIOL 165 Notes 2 Plants Introduction to Plants • Traits of Plant (Synapomorphies) o Have chlorophyll a & b (like green algea) o Complex embryo development o Archegonia  contains egg cell ▪ In more evolved plants, the neck and ventor cells are not well differentiated from surrounding tissue o Antheridium  simple spheres that produce sperm via mitosis ▪ In more evolved plants, they are reduced so only few sperm cells develop ▪ Ex. Antheridia of flowering plants consist of only 2 nuclei • General Life Cycle of Plants: Diagram  Pg. 87 o All plant life cycles have a haploid gametophyte (1n) stage that produces egg and sperm cells and diploid sporophyte stage (2n) that produces spores from sporangia through meiosis o Bryophytes: Gametophyte is dioecious and dominant form ▪ Sporophyte is dependent on gametophyte for nutrients so it is not free-living o Tracheophytes: Sporophyte is free-living and dominant form ▪ Exception: very primitive plants ▪ Considerable differences in size, appearance of sporophyte and tissues surrounding sporangia • Differences used to classify plants o Seed plants: Only male gametophyte is free living ▪ Female gametophyte remains inside protective layers of gametophyte and sporophyte tissue • General Trends in Life Cycle of Plants: Diagram  Pg. 88 o Trend 1: Hofmeister noted in 1850s that: Overtime, plants have shifted from a dominant gametophyte stage to a dominant sporophyte stage ▪ Ex. Alga  moss  fern  conifer  flowering plant ▪ Vascular plants: sporophyte stage is dominant ▪ Ferns + allies: Gametophyte is free-living ▪ Seed plants: Gametophyte is very reduced and dependant on sporophyte o Trend 2: Increase independence from the need of free water for fertilization (parallels trend 1) ▪ Seed plants: Have tube through which sperm/nuclei migrate to egg cells; water can be accumulated and stored by sporophytes for later use in fertilization o Trend 3: Increase in number of sporophyte tissue layers surrounding the embryo and gametophyte during development ▪ Evolution of ovary/fruit surrounding seed of flowering plants is the end of this trend Bryophytes • Summary of Bryophytes o Includes 3 phyla of gametophyte-dominant plants that form a phylogenetic clade below vascular plants ▪ Thus, this group is paraphyletic  Why ASK PROF; Diagram  Pg. 90 o Require free water for fertilization; restricted to moist habitats; some gametophytes can be xerophytes BIOL 165 Notes 2 o Includes: Liverworts (Phylum Hepatophyta), Hornworts (Phylum Anthroceratophyta) and Mosses (Phylum Bryophyta) • Liverworts (Phylum Hepatophyta) o Most primitive plants; 9000 species divided into 6 orders o Most have leafy, moss-like gametothalli o About 1000 have flattened, ribbon-like gametothalli that branch dichotomously ▪ Easily recognized as liverworts; occur along streams, swamps and nursery flowerpots o Sporophytes may have elongated stalks that bear sporangium, or sporangium may be sessile? ASK PROF o Some can reproduce asexually: Diagram  Pg. 91 ▪ Marchantia have gemmae cups that produce gemmae (small lens-shaped masses of cells) ▪ Fragmentation of gametothallus is also form of asexual reproduction • Life Cycle of Thallose Liverwort, Marchantia: Diagram  Pg. 92 o Dioicous, gametophyte-dominant, sexual and asexual reproduction o Male gametophyte (1n) has antherideophore (stalk)  contains antheridium that releases sperm  o Which fertilizes egg in archegonium of archegoniophore of female gametophyte (1n)  forms zygote (2n) o  Zygote undergoes mitosis to form  sporophyte containing sporangium (2n)  undergoes meiosis  o Some spores grow into  adult gametothallus  female gametophyte o Some spores grow into  protonema  male gametophyte ▪ Gametophyte also contains gammae cup  disperse gemmae (1n)  which develop into new adult gametophyte though asexual reproduction • Mosses (Phylum Bryophyta) o 12,000-15,000 divided into 3-5 clasess o Small non-vascular plants with gametophyte-dominant life cycle ▪ Have simple dependant sporophyte that produces one meiosporangium ▪ Sporangia have a central sterile column o Show little tissue differentiation compared to tracheophytes o Occupy wide range of habitats: moist swamps to dry rocks o Some are ecologically and economically valuable o Show range of stem and leaf traits; some grow vertically, some horizontally; none grow more than a few cm • Life Cycle of a True Moss o Monoicous, gametophyte-dominant, sexual reproduction only o Adult gametophyte (1n) has antheridium (& paraphysis) releases sperm to fertilize egg in archegonium o  Zygote (2n) forms inside achegonium  forms a stalk (seta) which carries calyptra (old archegonium)  o This is the sporophyte (2n)  sporangium undergoes meiosis  releases spores (1n)  grow into adults gametophyte • Peat Mosses: Sphagnum o Dominant plants in some bog habitats o Moss biomass accumulates at pH of 4.5 or lower; results in low rates of decay ▪ Low pH limits number of other plants that can grow which tend to be xerophytic (drought tolerant) ▪ Low pH bogs also preserve remains of dead plants, animals and even humans BIOL 165 Notes 2 o Have leaves that are one cell layer thick and composed of many cell types ▪ Photosynthesis occurs in smaller cells ▪ Larger dead cells serve as water storage tissue o Peat bogs are harvested commercially for dried peat which is used in horticulture/landscape trade ▪ Valuable for water retention properties of leaves ▪ Used to improve garden soil by lowering pH and improving water absorption Tracheophytes: Vascular Plants • Summary of Tracheophytes o Have dominant sporophytes and either free-living or dependent gametophytes ▪ Recall trend is of increasing dependency of gametophyte on sporophyte and decreasing complexity of gametophyte o All members have same basic life cycle but big difference in stem and leaf traits and number of protective tissues surrounding the sporangia and gametophytes o Anatomy of VP ▪ Tracheids and vessels are the primary water conducting cells of the vascular bundles • Vascular bundles consist of xylem and phloem tissue ▪ Number and type of cells that compose vascular tissue differ among clades • Primitive VP have only a few cell types • Evolved VP have many different types of cells reflecting division of labour/cell function o Three main groups: Ferns, Fern Allies and Seed Plants ▪ This textbook recognizes all VP under one phylum, Tracheophytes ▪ Other books recognize 15 phyla of living and extinct tracheophytes • DNA and Cladistic Studies on Tracheophytes o DNA studies are leading to significant revisions for relationships btw VP ▪ Old Rhyniophyyta is polyphyleic with different order basal to: • All vascular plants • Lycophyte clade • Euphyllophyte clade ▪ Euphyllophytes are split into two main groups based on stem anatomy and development • Moniliforms (ferns and most fern allies) lack secondary growth and woody stems • Lignophytes have secondary growth and woody stems o Protogymnosperms, gymnosperms, flowering plants • Basic Morphology of Tracheophytes o All members have same basic body plan o Primary axis is a stem; most VPs also have roots and leaves o Spores are produced in (meio-)sporangia which occur singly at the ends of branches ▪ Can also occur in a specialized terminal cluster called a strobilus (pine cone, flower) ▪ In ferns: sporangia are grouped into clusters called sori on underside of leaves ▪ In fern allies: sporangia are borne singly: at the ends of branches, on leaves (sporophylls) or grouped into stroili o See Diagram  Pg. 99 BIOL 165 Notes 2 • Basic Stem Anatomy: Diagram  Pg. 100 o VP stems have a number of basic tissue types ▪ Primitive VP had simple stems ▪ Seed plants have the most complex in terms of # and specialized type of cells o Primary tissue: laid down by the shoot meristem o Secondary tissue: laid down by cambium tissue which consists of cells derived from the shoot meristem ▪ Cambium tissue develops in several locations in stem and produces different kinds of 2° tissue • Xylem and Phloem: Diagram  Pg. 101 o Are conducting tissue in vascular bundles ▪ Xylem carries water and dissolved nutrients from roots to shoots ▪ Phloem carries photosynthate, hormones and other material to all parts of the plant o Three kinds of tacheid vessles: helical, scalariform and wither bordered pits • Secondary Growth and Wood: Diagram  Pg. 102 o Secondary Growth: If a stem has cambium as one of its primary tissues, it can add additional cells to increase stem thickness o Bark: Includes the cambium and all cells to the outside (non-functional epidermis, cortex, cork, cork cambium, primary and secondary phloem) o Wood: Includes primary and secondary xylem and ray of parenchyma ▪ Growth rings form if there is cyclic seasonal differences in the sizes, numbers and types of secondary xylem cells produced by the cambium • Ex. Spring wood has bigger cells • Wood Anatomy and Traits: Diagram  Pg. 104 o Wood is made up of tracheidss, vessels, ray parenchyma (relatively undifferentiated cells) and thick-walled fibres in various combinations o Thus different kinds of wood have a distinctive appearance at micro and macroscopic levels ▪ Appearance differs depending on the way wood is cut ▪ Pattern of wood will differ btw cross, radial and tangential sections o Wood is used by 6B people for heat, cooking, housing, construction etc ▪ Very economically valuable ▪ Also provides habitat for many organisms • Leaves of Vascular Plants: Diagram  Pg. 106 o Leaves are plants organs adapted for photosynthesis ; two basic types ▪ Microphylls: simples out-growths of stem with simple vasculature ▪ Megaphylls: very modified branching systems that usually have complex vasculature • Vary in size, shape, colour, texture, blade patterns, margin morphology and surface features • Describing leaves requires many technical terms o Do we need to know all terms? ASK PROF • The Earliest Vascular Plants o VP appear in fossil records about 450M y/a in Silurian Period but underwent real divergence in Devonian Period (405-350M y/a) BIOL 165 Notes 2 o Rich fossil record for Devonian Period; most major plant groups evolved at this point ▪ Exception: flowering plants o First vascular plants are called Rhyniophytes; paraphyletic group which are now placed in 3 clades: ▪ Rhyniopsida, Trimerophytes, Zosterophyllosida  Are these the 3? ASK PROF Ferns and Fern Allies • Summary of Ferns and Fern Allies o Classification of these groups has been radically revised based on DNA studies; clear that groups are intermixed phylogenetically and require further revision o Include primitive kinds of extant VP that first appeared in the mid-upper Devonian Period o Gametophytes are small and free-living ▪ Spores are typically produced in large thick-walled sporangia (eusporangiate) except in some orders o Lycopsid fern allies are microphyllous where all others are megaphyllous o All living species are small except for a few kinds of tree ferns o Certain genera from the Carboniferous Period acted as the main vegetation in forest ecosystems ▪ They also formed vast coal deposits that are mined today • Subphylum Lycophytina: Lycophytes o Fern allies with bean shaped sporangia; includes two classes ▪ Class Lycopsida: ground pines, ground cedars, club mosses, spike mosses, quillworts ▪ Class Zosterophyllopsida: A rhyniophyte group; microphyllous plants, but some had leaves 1m long • Most are now extinct o Class Lycopsida ▪ All extant (not extinct)members are small herbaceous perennial plants; some members from Carboniferous Period were large, tree-sized plants with secondary growth but simple stele anatomy ▪ Characteristics that define group: • Sporangia that are eusporangiate (bean shaped, large thick-walled, produce many spores) • Sporangia are borne on leaves (sporophylls) and usually grouped into strobili (cones) • Can be homosporous (one size spore) or heterosporous (two kinds of spores, gametophytes develop inside spore wall)  ASK PROF • Gametophytes are cylindrical, subterranean and live in symbiotic relationship with fungi • Life Cycle of Lycopodium: Diagram  Pg. 112 o Monoicous, sporophyte-dominant, sexual reproduction only o Adultsporophyte (2n) has strobilus that holds sporangium  sporangium undergoes meiosis to release  o Tetrad of spores (1n) (homosporous)  spores land on earth and grow into bisexual gametophyte (1n)  o Antheridia releases sperm to fertilize egg in achegonium  sporophyte embryo (2n) attached to gametophyte  grows into adult sporophyte • Life Cycle of Selaginella: Diagram  Pg. 112 o Monoicous (in sporophyte), sporophyte-dominant, sexual reproduction only o Adultsporophyte (2n) has strobilus that holds bisexual sporangium releases 2 spore types (hetersporous) ▪ Microsporangium (2n) undergoes meiosis to release  microspore (1n)  grows into mature male gametophyte (1n) (antheridium)  releases sperm to fertilize egg BIOL 165 Notes 2 ▪ Megasporangium (2n) undergoes meiosis to release  megaspore (1n)  grows into mature endosporal female gametophyte (1n)  sperm fertilizes egg in archegonium o Zygote (2n)  grows into sporophyte embryo inside female gametophyte  grows through embryo and becomes adult sporophyte • Subphylum Euphyllophyta: Megaphyllous Plants o Largest group of vascular plants; includes two clades ▪ Moniliforms: Without woody stems of with limited areas of secondary xylem ▪ Lignophytes: With woody stems of with well-developed secondary xylem • Moniliforms I: Class Equisetopsida: Horsetails o Only about 25 living species; but have many extinct fossil genera o Includes plants known as horsetails and scouring rushes o Characteristics that define group: Diagram  Pg. 117 ▪ Have leaves and branches arranged in whorls ▪ Branches arise between leaves rather than above them ▪ Stems are distinctly jointed with a strong node vs. internode difference; mostly hollow ▪ Living members are small herbaceous plants with reduced leaves fused into a leaf sheath ▪ Have no secondary growth ▪ Sporangia are borne in strobili with homosporous spores ▪ Gametophytes are free-living and leafy-lobed o Fossils range from small woody stemmed plants to large tree-sized plants with secondary growth and whorls of unfused leaves (common in Carboniferous Period) • Life Cycle of Equisetum: Diagram  Pg. 116 o Monoicous, sporophyte-dominant, sexual reproduction only o Adultsporophyte (2n) holds strobilus in 2° stem that is morphologically distinct from other stems ▪ Note: Other species in this class have only one type of shoot that can also be fertile o Strobilus in 2° stem holds sporangium  sporangium undergoes meiosis to release  o Spores (1n) (homosporous)  spores land on earth and grow into bisexual gametophyte (1n)  o Antheridia releases sperm to fertilize egg in achegonium  sporophyte embryo (2n) grows through archegonium  into adult sporophyte • Moniliforms II: Class Psilopsida: Whisk Ferns o Includes two genera and five species o Genus Psilotum is basically a green stick in the mud with no roots (strange fern ally) ▪ In life cycle: 3 sporangia fuse to form synangium at the end of a short lateral branch ▪ Gametophytes are subterranean, non-chlorophyllous and symbionts with fungi • Life Cycle of Psilotum Diagram  Pg. 118 o Monoicous, sporophyte-dominant, sexual reproduction only o Adultsporophyte (2n) has synangium (3 fused sporangia)  sporangium undergoes meiosis to release  o Spores (1n) (homosporous)  spores land on earth and grow into bisexual gametophyte (1n)  o Antheridia releases sperm to fertilize egg in achegonium  sporophyte embryo (2n) attached to gametophyte  grows into adult sporophyte BIOL 165 Notes 2 • Moniliforms III: Ferns o All ferns were traditionally placed in a single phylum, Pteridophyta (Polypodiophyta) but are now placed in 3 classes based on differences in
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