Imagine dissolving a spoonful of sugar in a glass of water. Is the sugar-water combination classified as a compound or a mixture? Explain your answer.
BIOL 201 4/11 - straws, the evolution of the plant vasculature: FERNS ) the sporophyte is found on specimens that belong to phylum ___. The structure under the pointer is haploid or diploid A,B, diploid if elaters or sporocyte (hard to tell, bad question!) Xylem: inner layer surrounding the pith Pholoem: outer layer surrounding the xylem; between epidermis and xylem )Character evolution in plants involves... E Bryophytes: flagellated sperm; chlorophyll a and b; starch as storage; cellulose cell walls; hydroids, leptoids; stomata (not closing); no lignin ferns and allies: roots (bryophytes had rhizoids); megaphyllous leaves (branched system of veins); microphyll (single unbranched vein); trichomes (epidermal extensions) General themes: "In ferns it turns..."; dominant sporophyte generation and emergence of heterospory Rise and fall of the roots (rhizomes) vs rhizoids (1 cell); leaves vs flattened blades; megaphyllous vs microphyllous leaves Bryophytes are non-vascular Vascular plants: Seedless vascular plants: ferns, club mosses, horsetails, whiskferns Seeded vascualr plants: gymnosperms (non-flowering), angiosperms(flowering) Vascular tissues: 1) conduct commodities (water: cohesionn and evapotranspirational suction/tension (negative pressure)) (photosynthesis: cytoplasmic transportation in sieve cells) 2) support body (evolution of a lignified support structure-stronger than cellulosic structures) ^These are important for the diversification in the terrestrial environment because there are plants 300' tall and they have to be supported because commodities are not enough cambiam between xylem and phloem and helps with growth in large plants Xylem: 1)tracheids: primitive, found in ferns and gymnosperms, water flows through pits 2)vessel elements: advanced, flowering plants, water flows through sieve plates Xylem cont.: tracheids and vessel elements are elongated calls with thick secondary walls; if something is dead then it has no cytoplasm, cells are dead at maturity but they function chemically Vessel element function: xylem fluid KCI concentraion rapidly and reversibly alters vessel conductivity by a lot; this controls the diameter of the xylem which controls the flow rate much like stomata ) Cells in xylem... A is true, B depends on activity, C is true, so E Phloem: 1) sieve cells 2) sieve tube members: companion cell which regulates carb flow and have sclerenchyma for support; both are long, tapered, and continuous tubes with overlapping ends, alive at maturity but lack nuclei and vacuoles; cytoplasmic transport through continuous cytoplasm of adjacent cells by active transport Evolution of vascular plants: Seedless vascular plants have what many bryophytes don’t: True conducting tissues (not just leptoids, hydroids); True functional stomata (non-functional in mosses, hornworts); Cuticle (in some mosses and liverworts); Lignin biosynthesis - lignin strengthened the secondary cell walls ) Cells in phloem... no A, B seems true, C yes so E Trichomes: epidermal extensions - cotton sees, Drosera, Dionaea Simplest vascular plant: Psilotum (star): seedless vascular plant assumed similar to the ancestral primitive ferns; lacks leaves (but enations) and roots in sporophyte; photosynthetic stems and central star-shaped xylem, surrounded by phloem Earliest vascular plants: Cooksonia: probably appeared during the Silurian (420 mya); no roots, leaves, dichotomous branching, photosynthetic stems, reproduced with spores (sporangia at the terminal branches) ) All seedless vascular plants... A no, B no, C yes up until gymonsperms 4/13 Diversity of ferns: emergence of heterospory bryophytes: hydroids, leptoids; stomata (not closing); no lignin Ferns and allies: Roots, Megaphyllous leaves, trichomes Phylum Psilophyta: whisk ferns: Greek "pilos" = naked because it has no organs; sporphytes dichotomous forking stems arise from rhizomes; no leaves-> enations (tiny, green, superficially leaflike, veinless photosynthetic flaps of tissue) along stems; no roots-> rhizoids (and mycorrhizal fungi) are scattered along rhizomes (belowground stems); primitive Phylum Lycophyta: club mosses (ground pines): sporophyte tissues are differentiated to leaves (microphyll); stems; roots; sporophyll (spore producing, nonphotosynthetic leaf) that are packed in a strobilus (cone); evolution of true roots and root hairs along rhizomes Lycopodium: club mosses: sporophylls packed into a strobilus that produce haploid spores on the 2n sporophyte; homosporous Selaginella: spike mosses: highly branched sporophytes; appear leafy compared to club mosses; heterospory emerges here; produces heteromorphic micro and megaspores Microphyll = leaf with single unbranched vein; no leaf gap Megaphyll = leaf with often branching veins always associated with leaf gap Sporophyll = spore producing leaf Phylum Equisetophyta: horsetails: Equisetum is the only living genus; no true leaves -> microphyll; stem is the photosyntetic organ; sporangia on terminal strobili that form on vegetative or seperate, fertile shoots; asexual reproduction by fragmentation of rhizomes; sexual by the srobili at tips of stems with sporangia connected to sporangiophores, spores green with 4 ribbon-like elaters attached; aid in spore dispersal, gametophytes small (only up to 8 mm in diam.), lobed, green, cushionlike; Stem anatomy: hollow, central cavity from break down of pith; 2 cylinders of smaller canals outside pith; carnial canals with xylem and phloem; vallecular canals outside carnial canals contain air; silica deposits on walls of stem epidermal cells; why vallecular canals protection agsinst predators cause they chew on silica Phylum Polypodiophyta: ferns: 1 cm tall to 25 m tall; leaves are megaphylls (called fronds); require external water for reproduction; fern leaves usually fertile (dont form strobili) and underneath side have clusters of sporangia (called sori); penny- sized gametophyte; folding of the fiddlehead unroles and is similar to angiosperms ) evolutionary discoveries in ferns include... A not first lignin syntesis, B not first rhizoids, C not the first stomata, D not the first cuticle, E first seed (extinct though) Why are seedless, vascular plants important conifers provide a lot of coal () Why are non-flowering, vascular plants important aquatic fern that overtakes waterways; salvinia molest ) Microsporangia contain… E microsporocytes and microspores, not microphylls 4/15 Gymnosperms ) All gymnosperms...E no monoecious D no dioecious C (deciduous: leaves fall every year) no B no evergreen; A! produce lignin Seeds: gametophyte don't need water for fertilization; can delay growth until favorable conditions; not likely ferns will evolve for certain environments such as dry; food supply with embryo which allows it to move just about anywhere 4 steps in the origin of seeds: Heterospory (Lycopodium vs. Selaginella) Retention of the female gametophyte on the sporophyte (note dispersal though) Development of the seed coat or testa Adaptations to deliver the male gametophyte to a receptive female gametophyte (pollination) Time periods emphasized: Devonian: adaptive radiation; aquatic vertebrates (no terrestrial); Pangea is 2 supercontinents; wet, warm (no glaciers) Carboniferous: Lignocellulosic plants that make coal; hot, humid; amphibians and herbivores; rainforest collapse lead to reptile evolution and increased herbivory; climate went to cold and dry Permian: dry, highly varied climate; cycling climate conditions; plants need to adapt -> SEEDS! from this point on (gymnosperms and higher plants): all have roots, true leaves (megaphyllous), seeds Gnetophytes share most recent common ancestor with angiosperms because they attempt double fertilization and they are the only gymnosperms with vessel elements (not just tracheids in xylem) Heterosporous: ALL SEED PLANTS; most seedless were homosporous (Selaginella was the exception); all of the following are because of heterospory: Male and female sporangia, male and female spores, microspores and megaspores, microgametophytes and megagametophytes A single plant individual may have male and female sporangia, they are rarely (if ever) in the same cones Seed ferns: 1st seed plants; trees with fern like foliage and secondary wood; these are now extinct... Glossopteris: common pteridosperm in southerm hemisphere Archaeopteris: heterosporous trees (some homosporous); closest to early seed plants; modern secondary wood; did NOT produce seed; 1st real tree; progymnosperm; easily 300' tall; lignin present; modern developmental characteristics: lateral buds and branches, bidirectional (bifacial) cambium (feature found in all seed plants) makes a ring of growing tissue that produce xylem towards the center and phloem away from center; dominated for 15 million yrs Talking through the life cycle (directly from slides): Male/female (micro- and megagametophyte) gametophytes in separate male/female cones (strobili) Micro-/megaspore mother cell (2n) goes through meiosis resulting in 4 micro-/megaspores (1n) The 4 micro-/megaspores develop into the micro-/megagametophytes Megasporocyte is retained within the megasporangium, enclosed in an integument (future seed coat) Megasporangium is called nucellus, encloses the megasporocyte, resultant megaspore(s) and the future megagametophyte Together, megasporangium and integuments form the ovule In the megasporangium, after meiosis, three megaspore nuclei are aborted; only one develops into the megagametophyte This remaining functional megaspore undergoes mitotic divisions, which are not immediately followed by cytokinesis - free-nuclear gametophyte, i.e., multinucleate megagametophyte that is not divided into cells by cell walls. In the megasporangium, cell walls form later around each 1n nucleus: resulting megagametophyte is multicellular After this, 2 or more archegonia develop in the micropyle end of the ovule Each archegonium contains an egg, which may be fertilized + develop into an embryo Microgametophyte sticks to the pollination droplet and is sucked into contact with the nucellus; directly to ovule, not to stigma (Angiosperms) Pollen tube digests the nucellus tissue to reach the egg One of the two sperms fertilizes each egg; diploid zygote (compare the sperm with Angiosperms), another sperm disintegrates Zygote develops into a seed with seed coat (former integuments), embryo with apical meristems, cotyledons, and hypocotyl gymnosperms dont really need 2 sperm but in angiosperms, they both have functions All gynosperm phyla have similar life cycles that produce seeds from exposed ovules Some gymnosperm sperm is flagellated: Ginko, Cycad; non-flagellated: gneto, pino "pregnancy time": Almost 2 years to produce a mature pine seed Meiosis occurs in late winter, and pollination and the developement of the female gametophyte takes 9 months; fertilization in pines can take longer than that to reach maturity