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photosynthetic microbes

bacteria which use light as energy source, contain chlorophylls which photophosphorylation happens in. 2 groups purple and green bacteria - anoxygenic phototophs. cyanobacteria - oxygneic phototrophs. cyano - diverse range - simple unicells, rows, filaments, branched filaments. e.g microcystis, cyanothexe, anabaena. planktonic species have a gas vesicle to provide buoyancy. many cyano e.g anabaena contain heterocysts which are sites of nitrogen fixation, they are surrounded by thick wall which helps maintain anaerobic envrio, is best in anoxic enviros e.g where cells dont have photosystem II which releases oxygen. 

purple and green bacteria - anoxygenic, only 1 photosystem, no splitting of water moleucles so no o2 production, instead they use H or sulphur so are generally found in high H2S areas. 

evolution of eu algae - a eu cell engulfed and retained a cyano cell which over time became reduced to an organelle. glaucophyta are important for discovering roots of green/red algal evolution. contain endosymbiotic cyanobacteria rather than chloroplasts but are still considered organelles. They contain cyano pigments and bacterial-type peptidoglycan cell wall. 

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algae

red algae - share common ancestor with glaucophytes and greens. cyanidiales - a unicellular red. chlorophytes - can be referred to as microscopic plants, contain pigments chlorophyll a and b, these went on to evolve into land plants. e.g volvox - 3D sperical colonie of 50,000 cells with daughter colonies inside. e.g microsterias (desmid). e.g spirogyra - filamentous chlorophyte, inner wall cellulose, outer pectin. 

chromalveolates - diatoms either centric or pennate, form huge planktonic blooms, comprise of 2 halves which part when they divide, can be sinlge cells or large filaments. chrysophytes - common in freshwater, single cells or elaborate colonies, consume bacteria as well as being primary consumers e.g dinobryon. haptophytes - form huge oceanic blooms have flagellum and haptophyt. Crytophytes - can photosynthesise at very low light intensites and supplement carbon intake by eating bacteria. Dinoflagellates - e.g gymnodinium, A. catenella responsible for paralytic shellfish poisening. 

Euglenids - probs never had chloroplasts but became photosynthetic through secondary endosymbiosis. have flagella and eye spot close by so can coordinate. chlamydomonas has diploid phase (2N) - resting spore - meiosis - zoospores hapoid phase (1N) - isogametes through fusion - zygote. e.g laminaria. chara - only he cells in the oogonium (contain eggs) are diploid. (antheridium contain sperm).

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algae + mosses

snow algae - C. nivalis. Haematococcus - green algae found in bird baths red pigment protects from UV light. Algae can be pollutent. filamentous can attach to organic matter and clump. red tide algae - alexandinium. algae growing in fungi - lichen. algae can grow in protists and invertebrates - wont get eaten, can go into protochordates, symbiotic algae photosynthesise and produce sugar, host protection and nutrients. some form flagellum when H2o is present. 

early land plants (bryophytes!) - evolved from green algae like chara. distinctive chloroplasts and pigments. oogamous (few large, non-motile eggs; numerious small motile sperm). haploid plants, except for diploid 'resting' oospores (zygotes). general embryophyte life cycle - haploid gametophyte - antheridium with sperm + archegonium with egg - fertilization - zygote - embryo - sporophyte - sporangia - spore mother cells (2N) - meiosis - tetrads of spores - spore - gametophyte. 

challenges of land - fertlization, water loss, water uptake and transport, nutrient uptake and trsnaport, mechanical support and dispersal. opporunities - atmospheric CO2 available, unattenuated light, huge numbers of vacant niches. story of adaptation - spores protected by sporopollenin, multicellular sporophyte (diploid), waxy cuticle, stomata, conducting tissues (phloem, xylem) and roots, leaves (micro and megaphylls), complex vascular systems and wood, gameotphyte retained in sporophyte and seeds. 

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bryophytes

liverworts then hornworts then mosses. small and fragile so not many fossils, dont kno haploid stages of early pteridophytes either. main groups - liverworts (marchantiopsida) thalloid or leafy. Mosses (Musci) - leafy. Hornworts (anthocerotopsida) - thalloid. 

thalloid liver wort - marchantia and pellia. leafy - lophocolea. thalloid has rhizoids and young sporophytes on leafs. has antheridia - gametangia where male releases anterozoids to swim in water, has chambers coating photosynthetic cells and pores for gas exchange. archegonia - gametangia, female egg cell protected from drying out by sterile cells of archegonium wall. gemma cups on surface for vegetative reproduction - clumps of photocynthetic cells(germae). leafy liverwort - leaves only 1 cell thick, vestidual leaves (amphijashia). pellia sporophyte has elators to push spores out, hapoloid spores, sporagnium matures before seta (stalk) elongates. 

mosses (bryopsida) e.g polytrichum in acrocarpous habit and hylocomium in pleurocarpous habit. 

hornwort - e.g anthoceros. 

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bryophyte

charactorisitcs - hetermorphic alternation of generations, gametophyte generation dominant, sporophyte short lives, partly or wholly parasitic on gametophyte, complex sex organs have outer layer of sterile cells, water necessary for fertilization (free swimming antherozoids, gamerotphyte consists of flattened thallus or central axis with fragile leaves, no roots only rhizoids, conducting tissue absent. howver dawsonia moss has primitive water conduction cells (hydroids). usually first plants to invade harsh habitats and start process of soil formation as can resist desication. sphagnum has distinctive leaf cellular structure that absorbs water like sponge. 

have chlorophytan plastid pigments and biochemistry like land plants (embryophytes). Hornwort anthoceros has single chloroplast and pyrenoid per cell which is distincitve algal configuration. orther strong algal affinites - e.g mosses hae a juvenile form (protonema) which is like a filamentous green algae. DNa phylogenies also show occurrence of particular introns. 

germinating moss spore-  has rhizoids and protonema. the gametophyte - grows from a spore (via protonema in mosses), usually small and close to ground to ensure water, found in moist places, can survive prolonged desication, produce cellular colloids that retain water, capable of resuming photosynthesis within minnutes of re-wetting, can be thalloid or leafy

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bryophytes

many thalloid hornowrt and liverwort gametophytes have chambered thallus with central pore. with chains of assimilatory cells with numberous chloroplasts inside. parenchymatous tissue separates upper and lower epidermis. mosses and leafy liverworts have central axis with simple leaves. liverworts have four ranks of leaves to give flattened arrangment close to ground. mosses have spiral insertion of leaves up stem.

sex organs - occur embedded in gameotophyte thallus or ends of branches in leafy forms. in marchantia e.g one branch of thallus becomes modified into special gametangiophore - bears either male or female sex organ. male organ - antheridium releases antherozoids to swim in water. female - archegonium, distinticve structure can be traced throughout land plants although reduced. some also oogamy. 

marchntia thallus - antheridial and archegonial receptacles, cupule ith gemmae and rhizoids. bryophyte antherozoid (sperm) - mitochondrion, cytoplasm with plastids and mitochondira, coiled nucleus and flagella. bryophyte archegonium - neck, remains of neck canal cells, ventral canal cell, egg cell (oosphere) and stalk. sporophyte - young differentiates into a foot (organ of parasitism), seta (stalk) and sporangium (containing spore mother cells that produce haploid spores by meiosis). 

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bryophytes + tracheophyta

sporophyte development in mosses - seta elongates early, capsule wall photosynthetic with stomata and cuticle, shed cap then its end, sporangium opens by a special pore - protected by a peristome of hygroscopic teeth, spore shaken out by wind. development in liverworts - sporangium matures before seta elongates, some cells are sterile to form elators. development in hornworts - in anthoceros, sporophytes very long lived almost independent. has stomata and cuticle. 

vascular plants (tracheophyta) - rhyniophytes (early land plants) and lycophytes (clubmosses). pteridophytes (not seed baring- dominant sporophyte and xylem. characteristics of pteridophytes - heteromorphic alternation of generations, sporophyte dominant and persistant, gametophyte reduced, archegonia small and may be embedded in gametophyte tissues, water necessary for fertilization, sporophyte with internal vascular system based on xylem and phloem - the stele, sporophyte shows axial growth - stems, leaves and roots all present but primitve. 

rhyniophyta - only known as fossils. e.g cooksonia. sporophyte aerial axes were smooth, dichotomous branchin and spore bearing with terminal sporangia. some forms had simple strands of water conducting cells (tracheids) and a cuticle. earliest had somata. 

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bryophytes + tracheophyta

sporophyte development in mosses - seta elongates early, capsule wall photosynthetic with stomata and cuticle, shed cap then its end, sporangium opens by a special pore - protected by a peristome of hygroscopic teeth, spore shaken out by wind. development in liverworts - sporangium matures before seta elongates, some cells are sterile to form elators. development in hornworts - in anthoceros, sporophytes very long lived almost independent. has stomata and cuticle. 

vascular plants (tracheophyta) - rhyniophytes (early land plants) and lycophytes (clubmosses). pteridophytes (not seed baring- dominant sporophyte and xylem. characteristics of pteridophytes - heteromorphic alternation of generations, sporophyte dominant and persistant, gametophyte reduced, archegonia small and may be embedded in gametophyte tissues, water necessary for fertilization, sporophyte with internal vascular system based on xylem and phloem - the stele, sporophyte shows axial growth - stems, leaves and roots all present but primitve. 

rhyniophyta - only known as fossils. e.g cooksonia. sporophyte aerial axes were smooth, dichotomous branchin and spore bearing with terminal sporangia. some forms had simple strands of water conducting cells (tracheids) and a cuticle. earliest had somata. 

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pteridophytes

rhynia gwynn-vaughanii - stomata, cuticle with paired guard cells, terminal sporangia, spores in tetrads w/ trilete scare therefore products of meiosis, pseudo-rhizome or creepng stem with no cuticle of stomata, it bore rhizoids but no roots. rhynia stem and stele - protototype vascular cyclinder i.e a protostele. xylem w/ tracheids. phloem of thin walled ill-defined cells, cortex, epidermis with stomata. rhynia sporophyte - some upright axes bore sporangia with tetrads of spores, dichotomous brachnig, aerial shoots w/ cuticle and stomata, terminal sporangia, horizontal stem (pseudo-rhizome) with rhizoids. 

psilotum - whisk fern. most rhnia-like. dichotomously forked axis, small leafy apendages, stem serves as organ of photosynthesis as has stomata, spores in tripods, homospores, terminal sporangia. gametophyte - subterranean and mycorrhizal. 'bumps' are antheridia, bears rhizoids. Y shaped plant behind is deeloping rhizome of very young sporophyte offspring. gametophyte of rhynia not known. 

lycophyta (clubmosses) - most primitive extant group. sporophyte with dichotomously branching axes but differentiate into root and shoot. vascular tissues tracheids and phloem, shoots bear small leaves microphylls. micro - single elaf vein, mega - multiple veins. simple stele and medulla. sporangia borne laterally on modifiied leaves often in whorls packed into cones (strobili). homosporous, rhizopre and roots. 

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lycopodium (clubmosses) + horsetails

photosynthetic free living gametophyte. small sporophyte with shoot and roots is developing as offspring of the gametophyte. heterospory - frist group, selaginella and many fossil forms, produce mega and micro spores. megaspores germinate to give rise to a female only gametophyte. microspores give rise to male only gametophyte. strobilus (cone) has loads of tiny microspores in microsporangium and 4 megaspores is megasproangium on itlycophytes were prominent as trees in the carboniferous; contemportary herbs have leaves, true roots and sporangia arranged in terminal leafy cones. 

sphenophyta (horsetails) - calamites 30m tall. characteristics - hetermorphic alternation of generations, dominant sporophyte with jointed stems and whorls of branches - monopodial growth, leaves microphyls, borne in whorls at nodes, rhizomes bearing adventitious roots, vascilar tissue of tracheids and phloem, sporangiophores aggregated into terminal storibili (cones), homosporous (living forms) but some fossil were hetersporous. xeromophy - reduction of microphyll leaves to papery scales, stems photosynthetic, stomata on sides of deep longitudinal grooves in stem. 

stem - aerial shoot has vigorous branching w/ whorls at each node, inderground rhizome system has sscale leaves and roots, some herbaceous plants w/ hollow stems with pith and a little wood, main strength from outer layer of stem ridges - cells thickened and impregnated with silica. jointed nature of stems w/ nodes separated by internodes. 

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horsetails and ferns

stem - calamites had seconadary thickening that developed from cambium between xylem and phloem. vascular systen - stele is ring of vascular bundles, located in circles on the inside of the stem, each one corresponding w/ a co-radial stem ridge. stem bundles one ring at each node. 

has vegetative branching. sporophyte has strobilus with sporangium and sporangiophore. spores have elaters. gametophyte development in equisetum - is homosporous but spores can produce 2 types of gametophyte. male gametophyte is small and short lived and only produces antheridia. female lives 2 yrs of longer and becomes large and produces crop of archegonia if not fertilized then produces crop of antheridia and then a further crop of archegonia. density dependant sex determination; under crowded onditions growth is restricted and they are more likely to me male. 

ferns (pterophytes) - tree ferns and plant ferns. D.antarctica - trunks of tree ferns have very little wood, lignified secondary xylem. most of mechanical support comes from the persistent cylinder of lignified leaf bases ensheathing the stem. highly developed leaf or 'frond' which is megaphyll. so large that leaves gap in stele above where its pushed out, gives rise to a sequence of complex types of stele. siphonostele, solenostele and dictyostele. 

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ferns

fern sporophyte - central axis (stem) usually short and subby often buried, bears wholrs of megaphylls that unroll as develop. massive increase in photosynthetic capacity represented by megaphylls was important development. depends on improved vascular system.

sporophyte of polypodium - sori on undersurface of leaf. has indusia - little umbrealla to protect young sporophytes, ribs of thickened cells rupture at one end and sends spores catapulting. most ferns homosporous. sporangia - sporangium (2N) and spores (n) w/ vascular tissue. sorus of dryopteris - vascular bundle, palisade mesophyll spongey tissue, indusium protecting sporangia. 

gametophyte: small heart shaped prothallus with sex organs embedded on underside. has archegonia, antheridia (produce motile antherozoids) and rhizoids. 

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heterospory

heterospory - differentiation in spore size into micro and mega spores. separation of the sexes. micro - male mega - female. early stages seen in selaginella (a lycophyte). microgametophyte of selaginella - microsporangium contain large numbers of microspores. when ruptured they are carried by wind some become trapped in part of cones containging leafy megasporophylls. spores germinate to produce one somative cell and an antheridium with 128 or 256 antherozoids. 

megagametophyte of selaginella - has single tetrad of 4 megaspores. ruptures and megaspores may disperse of be retained. within each megaspore, cell division and differentiation occur to form a female prothallus, with archegonia, that is retained within the spore wall - an endosporic megagametophyte. the megaspore wall ruptures to allow fertilization by free swimming antherozoids. depends on close proximity of mega nd microspores. at fertilization egg cell in archegonium, after young embryo of sporophyte (2n) grows inside archegonium from endosporic gametophyte. 

evolution of seed habit - habitats limited by need for water, hetersporty evolved as offered partial solution as at least female gametophyte no longer had to assimilate own food and was protected. in fossil lepidocarpon 3 megaspores aborted, 1 stayed protected by sporophyll - seed like, but not true as still had to rupture to allow fert by swimming antherozoids. true seeds first appeared in the gymnosperms. 

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gymnosperms

characteristics - seed bearing. the megasporangium is enclosed within a distincitve new sporophyte structure, the integument, forming and ovule. gametophyte no longer autotrophic entirely dependent on the sporophyte. archegonium very reduced, male gametes not free-swimming but retained in pollen tube, they may or may not be motile, water unecessary for fertilization, heterosport general, sporophyte with well-developed vascular system; xylem composde mainly of tracheids (many trees). 

gymnopsperm form 2 groups. cycadoids and coniferoids. cycadoids - with pinnate leaves include pteridospermales 'seed ferns', cycadales and bennettitales. coniferoids - with entire of needle shaped leaves - cordatitales 'cordaites', coniferales, ginkgoales and gnetales. 

cycadoids: pteridosperms (seed ferns): fossily group. early form was lyginopteris a sort of tree fern that bore seeds (lagenostoma) protected by a cup-like whorl of glandular leaves. heterosporous. highly reduced megagametophyte retained within megaspore. only one megaspore develops and is retained within megasporangium which is fleshy and called the nucellus. megasporangium of seed plants is enveloped by one or 2 additional layers of tissue (integuments). the ovule comprises the nucellus containing the embryo sac or mature female gametophyte and the integument. the seed is the produc of the ovule after fert; the integument forms the seed coat (testa)

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gymnosperms

characteristics - seed bearing. the megasporangium is enclosed within a distincitve new sporophyte structure, the integument, forming and ovule. gametophyte no longer autotrophic entirely dependent on the sporophyte. archegonium very reduced, male gametes not free-swimming but retained in pollen tube, they may or may not be motile, water unecessary for fertilization, heterosport general, sporophyte with well-developed vascular system; xylem composde mainly of tracheids (many trees). 

gymnopsperm form 2 groups. cycadoids and coniferoids. cycadoids - with pinnate leaves include pteridospermales 'seed ferns', cycadales and bennettitales. coniferoids - with entire of needle shaped leaves - cordatitales 'cordaites', coniferales, ginkgoales and gnetales. 

cycadoids: pteridosperms (seed ferns): fossily group. early form was lyginopteris a sort of tree fern that bore seeds (lagenostoma) protected by a cup-like whorl of glandular leaves. heterosporous. highly reduced megagametophyte retained within megaspore. only one megaspore develops and is retained within megasporangium which is fleshy and called the nucellus. megasporangium of seed plants is enveloped by one or 2 additional layers of tissue (integuments). the ovule comprises the nucellus containing the embryo sac or mature female gametophyte and the integument. the seed is the produc of the ovule after fert; the integument forms the seed coat (testa)

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gymnosperms

pteridosperm ovule - pollen chamber, cupule, archegonium, glands, megaspore membrane, nucellus (megasporangium), female gametophyte (megagametophyte). 

cycadoids: the cycads. only modern representatives, only in tropical and subtropical part, 9 genera. E.woodii of africa represented only by male plants. modern have unbranched thick stem with apical rosettte of pinnate leaves. they are slow growing, stem has slender ring of 2ndary xylem (wood), massive taproot and then branching roots. cycad cones (strobili) - mega and microsporangiophores are aggregated into separate strobili borne on different plants. e.g in cycas circinalis the ale cone is compact with large numbers of microsporangia in underside of each microsporangiophore. female cone is a loose aggregation of whorls of leaf like megagporangiophores each with several paris of ovules and a distal sterile portion. 

megasporangiophylls of cycas with naked ovules - female cone larger than male. cycas male cone and microsporangiophore - is attached to axis of cone and has hundreds of microsporangium and sporangiophores. cycad ovule - micropyle, pollen chamber, outer and inner integument, archegonium, megaspore membrane, female gametophyte. cycad archegonium - neck cells, ventral canal cell and egg cell. cycad male gametophyte - stalk call, prothallial cell, pollen grain, tube cell, tube nucleus, body cell. 

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cycads + coniferoids

fertilization in cycads - microspore is caught in sugary dropley at mouth of micropyle and the droplet is withdrawn into pollen chamber. pollen tube germinates, mainly haustorical in function - anchors male gametophyte and forces into nucellus and absorbs nutrients. 2 multiflagellate antherzoids released into fluid of degenerating nucellus above archegonia and swim to them for fert. Fert egg cell becomes zygote and develops into sporophyte embryo. growth sustained by food reserves of megaspore and nucellus. outer integument forms sarcotesta (fleshy and edible) and sclerotesta (hard and protective).

coniferoids (with entire or needle shaped leaves). gnetales - oddball group, have broad or strap-shaped leaves with naked ovules. 3 distinct genera - gnetum , ephedra and welwitschia. 

ginkgoales: ginkgo biloba, 'living fossil', distinctive fan-shaped leaves with dichtomously bracnhed venation. forms large trees with separate sexes. branches with long and short shoot. microspotandiate male cones and pairs of nakes ovules formed at tips of short shoots. pollination assisted by pollination drop and pollen tube is haustorial like cycas.

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cycads + coniferoids

fertilization in cycads - microspore is caught in sugary dropley at mouth of micropyle and the droplet is withdrawn into pollen chamber. pollen tube germinates, mainly haustorical in function - anchors male gametophyte and forces into nucellus and absorbs nutrients. 2 multiflagellate antherzoids released into fluid of degenerating nucellus above archegonia and swim to them for fert. Fert egg cell becomes zygote and develops into sporophyte embryo. growth sustained by food reserves of megaspore and nucellus. outer integument forms sarcotesta (fleshy and edible) and sclerotesta (hard and protective).

coniferoids (with entire or needle shaped leaves). gnetales - oddball group, have broad or strap-shaped leaves with naked ovules. 3 distinct genera - gnetum , ephedra and welwitschia. 

ginkgoales: ginkgo biloba, 'living fossil', distinctive fan-shaped leaves with dichtomously bracnhed venation. forms large trees with separate sexes. branches with long and short shoot. microspotandiate male cones and pairs of nakes ovules formed at tips of short shoots. pollination assisted by pollination drop and pollen tube is haustorial like cycas.

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coniferoids

cordaitales - extict group. large strap shaped leaves with parallel leaves. cordaites coexisted with e.g lepidodendron. appeared in late devonian/early carboniferous. wood structure very similar to araucaria. fossil group of substantial trees with vascular cambium producing secondary xylem and phloem. dense wood (secondary xylem) composed of typical coniferoid tracheids - heavily lignified, elongated cells that are very efficient in water transport. coniferoid tracheids - tall trees have water columns in the xylem due to great tension becuase of evaporation: bordered pits allow isolation of embolisms. 

conifers - most widespread and important gymnosperms. very big trees.oldest : bristlecone pine (pinus aristata). much dense wood formation (secondary xylem) composed of annual rings of lignified tracheids. Reproductive structure generally borne in male and demale cones on diff branches of same tree. 

conifer leaves - megaphyll usually reduced. possibly xeromorphic response to water shortage. needles sveral cm long often in groups on short shoots as in pinus. scale like leaves reaching only few mm. mostly evergreen, the leaves persisting for several seasons. often contain resin canals containing fragrant terpenoids and oils for defense? pinus sylvestris - large tree typical indeterminate and determinate leaf frowth respectively. 

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coniferoids

cordaitales - extict group. large strap shaped leaves with parallel leaves. cordaites coexisted with e.g lepidodendron. appeared in late devonian/early carboniferous. wood structure very similar to araucaria. fossil group of substantial trees with vascular cambium producing secondary xylem and phloem. dense wood (secondary xylem) composed of typical coniferoid tracheids - heavily lignified, elongated cells that are very efficient in water transport. coniferoid tracheids - tall trees have water columns in the xylem due to great tension becuase of evaporation: bordered pits allow isolation of embolisms. 

conifers - most widespread and important gymnosperms. very big trees.oldest : bristlecone pine (pinus aristata). much dense wood formation (secondary xylem) composed of annual rings of lignified tracheids. Reproductive structure generally borne in male and demale cones on diff branches of same tree. 

conifer leaves - megaphyll usually reduced. possibly xeromorphic response to water shortage. needles sveral cm long often in groups on short shoots as in pinus. scale like leaves reaching only few mm. mostly evergreen, the leaves persisting for several seasons. often contain resin canals containing fragrant terpenoids and oils for defense? pinus sylvestris - large tree typical indeterminate and determinate leaf frowth respectively. 

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coniferales

male cones of pinus - siparally inserted male cones each relpacing a pair of needles on a short shoot. has cone axis with microsporangiophore (bears 2 microsporangia), microsporangium (2N) contains microspore mother cells which undergo meiosis to produce tetrads of hapoloid microspores (pollen). 

female ovulate or megasporangiate cones of pinus - has ovule and ovuliferous scale, integument nucellus. develop over 2 years. pollen grain in, megaspore mother cell undergoes meiosis, 4 megaspores, 1 develops into female gametophyte with archegonium. fertilization about a year after pollination and mature seed after another year. pollen tube delivers non-motile male gametes via the micropyle to the egg cell. 

pinus sylvestris - evolution from horsetail ferns. female cones on tip of long shoot. proper cones are female as males onees produce spores and drop off. has paired needles. each blob on males cone is a male cone and are on short shoots. 

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angiosperms

flowering plants - developed early cretaceous. characteristics - seed bearing and heterosporous. ovule is enclosed within and protected by the carpel. the carpel constitutes the ovary. the fruit is the mature ovary. gametophytes endosporic and very reduces (female on is an embryo sac). 3 phases of life cycle with double fertilization: sporophyte (dominant, diploid), gametophyte (reduced, haploid), endosperm (triploid). male gametes non-motile. sporophyte with well developed vascular system - xylem with tracheids and vessels and phloem of sieve tubes and distinctive companion cells.

the carpel - angiosperms are distinguised from gymnosperms by the carpel which protects ovule and seed. part of new whorled arrangement of reproductive structures (the flower). thought to have arisen from modification of megasporophyll such that it wraps around the ovule borne upon it. in primitve forms the edges of carpel probs acted as stigmatic surface on which pollen grains could germinate and grow towards ovules. e.g degeneria - stigmatic surface, interlocked hairs, folded carpel, suture not joined but has interlocking hairs where the edges of the in-folded megasporangiophyll meet. 

wood possesses conducting cells called vessels in secondary xylem (wood). wider than tracheids and offer less resistance to water flow. more susceptible to emolism so replaced annually. 

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angiosperms

2 types of vessel element. typa A - long with oblique end walls that have pits - scalariform pitting. in fossils. type B - short and wide and end in transverse wall with single large pit results in chain of cells arranged ina single storey. 

flower characters - plant families whose pollen occured in early deposits have a tendancy to a syndrome of charactors called magnolioid e.g magnolia - flower with petals removed showing gynaecium of sperarate carpels, androecium of undifferentiated stamen and petal scars. single stamen with 2 pollen sacs (microsporandia) showing later dehiscence. each carpel contain 2 ovules, stamenand carpels scars have spiral arrangment. carpels end in short, curved stigmas. petals free, flower parts numerous, flowers regular i,e radially symmetrical, woody plants  - magnolioid flowers correlate well with type A wood vessels. suggests evolution from a cycadoid gymnosperm - probs from pteridosperms.

dicotyledons - 2 seed leaves, limited flower parts 4/5, flower parts fused into more complex structure, bilateraly symmetrical, flowers grouped in clusterss called inflorescecences, mainly insect pollination, herbaceous. 

monocotyledons - single leaf on embryo, no real secondary thickening, parallel venation in leaves, orchids show most highly sophisticated co-evolution w/ insects, wind pollination and a loss of flower parts. 

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mono and dicot

mono - grasses, small herbaceous plants, highly reduced flower structure, pattern of leaf growth from meristems at bases of leaves is adapted to herbivory by vertebrates. orchids - small herbaceous plants, highly specialised flower structure. cp-evolution w/ insects. 

lilium casablance - stigma where pollen grains land, female gymnecium 6 long style orange stamen. ovary in chamber, stalk with whorls of 3 outer leaves and 3 inner petals. 6 stamen, 3 stigma. 

the flower  - reproductive organs typically in a whorled structure (flower) and arranged concentrically on the receptacle. components of each whrol are derived from a modified leaves and may be fused. from centre outwards the whorls are : female part (gynaecium) comprising a whorl or cerpels with ovary, style and stigma (receptive surface for pollen), ovary contains the ovule each of which contains a megasporagium. male part (androecium) comprising a whorl of stamens, each consisting of an anther (fused microsporagnia) and filament. the petals often attract insect pollinators. the sepals are protecive structure that surround flower bud before it opens. 

haploid generation - both gametophytes are even more reduced, male is just pollen grains (microspores) that develop from pollen mother cells by meiosis in the anthers of stamen. anthers usually have 4 chambers lined with nutritive tapetum. 

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angiosperm fertilization

at dispersal pollen contain 2 cells - vegetative and generative cells - divides to give 2 non-motile male gametes. After pollen arrives on the stigmatic surface of carpel , the pollen tube germinates through a pore. the pollen tube grows through maternal tissues towards embryo sac, at expense of material s from stigma.

pollen development - male gametes produced by division of generative cell. pollen tube deliver the 2 gamete to female gametophyte, allows evolution of chemical mechainsms to direct pollen tube forwth and exclude growth of unwanted pollen. 

female gametophyte - young ovule of the sporophyte flower is largely nucellus. withing this, a large spore mother cell arises and undergoes meiosis to form 4 haploid megaspores; 3 degenerate. remaining megaspore develops into female gametophyte by 3 successive divisions to give 8 nuclei within embryo sac.

plant embryo sac has polar nuclei (located in central cell) and an egg cell at micropylar end. pollen tube grows into ovule and 2 male gametes are released. one fuses with egg cell to form the zygote. other fuses with 2 polar nuclei to form a triploid endosperm nucleus. this is double fertilization. 

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fertilization

endosperm - develops by divisions of triple-fusion nucleus. precedes zygote. nuclear division may outstrip cell-wall formation. coconut has liquid endosperm. rapid growth at expense of nucellus which usually disappears. endosperm cells ebgin to organise first at end of embryo sac adjasent to fertilized egg cell. the function is to nurutre the developing embryo, it becomes paced with food materials and contains growth refulating substances e.g cytokinins as well as vitamins amino acids and nitrogenous bases. 

sporophyte generation - first division gives 2 cells: one gives rise to embryo, other the suspensor. suspensor is device for pushing embryo depper into expanding embryo sac. embryo differentiates into root, shoot and cotyledons, growth at expense of endosperm. eventually growth stops and the seed becomes dormant for dispersal. 

embryos -1) linear not folded embryo. very small extreme in orchids. 2) plate like embryo with leaves expanded but endosperm still dominant food store. 3) folded, relatively large with cotyledons packed with food reserves and endosperm completely absorbed. most advanced.

the seed - sucks materials from phloem. builds own nutrient sore - proteins, main energy from starch or lipid oils. at maturity loses most of water and remians dormant. integuments dry to form testa. 

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angiosperms

endosperm reserves - starch e.g cereals. lipids e.g castor bean. cotyledon reserves: starch e.g pea (folded embryo) and lipid e.g sunflower (plate-like embryo). 

the fruit - growing ovule producs hormones that stimulate carpel to keep pace. some species replace need for pollination and fertlization before fruit development by application of an auxin e.g tomato. Carpel can grow into a dry protective pericarp, closely associated with the testa. In other plants pericarp becomes fleshy and palatable to animals. aided by synchronous ripening many ripening fruits produce gas ethylene which acts as a hormone in promoting ripening of other fruits. 

seedless fruits - bananas - sterile triploid varietes that develop parthenocarpically without fert or embryo. seedless grapes - pollinated but embryos abort at early stage and fruit continues to develop. complex fruits - apples and strawbs - fleshy edible part not strictly the fruit wall but includes swollen receptacle or stem outgrowth. pips 'achenes' are the botanical fruits. aggregate fruits - raspberries (from single flowers with multiple carpels) and pinapples (multiple flowers in an inflorescence)

mature seed is enclosed within a fruit (developed from the carpel), dries and may remain dormant before dispersal and germination. 

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