UMD BSCI 124 - Lecture 8: Plant Systematic and Darwinism Evolution

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Lecture 11: Algae, Bryophytes, and FernsAlgae: Kingdom protista – eukaryotesMostly photosynthetic* (4 photosynthetic pigments and many accessory pigments)Require most environments because they lack waxy cuticle (prevents water loss) or vascular (tissue) cambium – need water readily availableCan be microscopicReproduce sexually and asexuallyDiversity – Four divisionsHeterokontophyta: diatoms & kelpsDinophyta: dingoflagellatesRhodophyta: red algaeChlorophyta: green algae1. Diatoms: division heterokontophyta – mostly unicellular, have silicia in cell wallsa. Large group (many unidentified), relatively recently evolved groupb. Habitat: cool oceans – very important in aquatic food chains, provide phytoplankton (bottom of food chain)c. Reproduce asexually for many generations and then reproduce sexually2. Kelps or Brown algae: division heterokontophyta – multicellulara. Habitat: rocky coasts in temperate zones or open seas (cold water)b. Holdfast, stipe, blade, air bladder/float3. Dingoflagellates: division dinophyta – mainly unicellular, green or colorless, biflagellate (2 flagellate)a. Unusual nucleus: chromosomes always visibleb. Some are bioluminescentc. Mostly asexual reproduction – important in food chains in warm tropical oceans4. Red algae: division rhodophyta – oldest eukaryote’s on eartha. Abound in tropical warm waters – act as food and habitat for many marine speciesb. Range from thin films to complex filament membranesc. Red because accessory pigments, phycoblins mask chlorophyll a – can photosynthesis in warm water at different wavelengthsd. Commercial uses: carrageenan-> ice cream, jellies, syrups, breads also lotions, toothpastes AND agar-> growing bacteria and fungi for research5. Green algae: division chlorophyta – largest and most diverse –a. Habitat: fresh waters, land, or floating in rivers, lakes, reservoirs and creeks. Also rocks, trees soilb. Ex. Sea lettuce, Single cell (micrasterias), filaments (spiragyra), colonies (volox), thalli (leaf shaped)c. Terrestrial plants arose from green algae ancestors! – same photosynthetic pigments (chlorophyll a and b)d. Some have cell wall made of cellulose – divide similarlye. Commercial value: important source of oxygen and good for aquatic organismsf. Litchens: green algae and fungi symbiosis (mutualism)*Q: Why do photosynthetic pigments vary in algae and not land plants?*A: Algae grows at different depths and needs to capture light at different wavelengthsBenefits of algaeBase of aquatic food chain – photosynthetic organismsProvide oxygen 50%Lichens – fungi need algae photosynthesis to stay aliveServe as good and shelter under waterHarmful algaeAlgae blooms: sudden population explosion – excessive growth causes clogged waterways – water taste badCan produce toxins harmful to animals“Red tides” caused by dingoflagellatesCommercial uses of algaeAlgin (thickening agent), Carrageenan (foods, creamy texture), Iodine, Algar, Food (sushi), Fertilizers, Pharmaceuticals, biofuelsKingdom PlantaeAlgae cannot survive on land (unless moist) -> plants had to evolve characteristics that would allow them to survive and live on dry land (Cooksonia is the earliest known land plant)The ancestor of land plants is green algaeHave the same photosynthetic pigmentsUse starch to store photosynthetic productsHave cellulose in their wall‘Alternation of generations’Form a cell plate during cell divisionFrom primitive to advanced traits…Living on land -> Environmental challenges & adaptationsObtaining enough water: evolved roots to absorb mineralsPreventing water loss: evolved waxy cuticle, multicellular gametangia (sex organs) helped protect gametes from drying out & resistant coat on spores that prevents drying outGetting enough energy (light): growing taller, evolve support cells, adapt to lower light intensitiesPhotosynthesis/water dilemmaProblem: pores are need for gas exchange but open pores (stomata) allow water to leaveSolution: Stomata open during the day and close at nightMulticellularity plant evolved vascular tissueAdvantages: root better, protect gamates & grow to obtain lightDisadvantage: getting water to all cellsSexual reproduction:Algae have motile gamates and single sex organsLand plants developed multicellular sex organs – genetic variability enables adaptationsLife cycle:Algae: water dependant life cyclePlants: water independent life cycle - developed dryness-resistant gametophytes (spores) or zygotes (seeds).Dominant gametophyte stage (n) algae dominant sporophyte stage (2n)Plants vs. Humans:Humans live in 2n dominate stage – single celled gametes are 1nPlants Alternation of generation: spend part of their life cycle in the haploid (1n) and part in the diploid (2n) both stages are multicellularBryophytes: Mosses, LiverwortsNon vascular plants – do not have xylem or phloemAdvancements over algae: waxy cuticle, multicellular gametangia, & stomataHabitat: require moist environment for growth and sexual reproductionLife cycle: gametophyte and sporophyte generation – ReproductionGametophyte (1n) is dominantGreen leafy stems/root like structures called rhizoids for anchoringHave stomata and cuticle but lack root, stem and leavesLack of vascular tissue limits size and environment (must be moist)Sporophyte (2n) occur after egg is fertilized by spermGrows in archegonium of gametophyte – dependant on itConsists of food (attachment), seta (stalk), and capsule (spore case)Seed—matured ovule containing:A plant embryoA food supplyCovered by a seed coatEmbryoThe seed contains a well-formed multicellular young plant embryo (germ)Embryo is diploid (2n)It will become a whole plantNutritive TissueSeed contains a food supplyStored food contains enough energy for the embryo to grow through the soil when seedling is unable to photosynthesizeFood source can be the endosperm which is triploid (3n) as a result of double fertilizationSeed CoatA thick protective coat-outer layer of the seedFormed from he megasporangiumGymnosperm SeedsSingle fertilization produces the diploid embryo (2n)Food source is the haploid megagametophyteBSCI EXAM #2 REVIEW UNIT: PLANT DIVERSITYLecture 8: Plant Systematic and Darwinism EvolutionPlant Systematics- Common Names: evolved over centuries in many different languages->problem: diff name diff region- Scientific Names: Kingdom-Division-Class-Order-Family-Genus-Species- First name genus, second name species ex. Humans homo (genus) sapiens (species)-


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UMD BSCI 124 - Lecture 8: Plant Systematic and Darwinism Evolution

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