Unformatted text preview: • • • • • • • The frog heart has three chambers: two atria and one ventricle Birds and mammals have (independently evolved) four chambered hearts: two atria and two ventricles Turtles, like frogs, have three chambers – but there is an par?al septum (wall) apparent in the ventricle The four chambered heart is crucial for homeothermy (warm‐bloodedness) – much more oxygen needed than for ectothermy (cold‐ bloodedness) The paBern of expression of a gene called Tbx5 correlates with the diﬀerence between three and four chambered hearts recent work in turtles shows that the Tbx5 expression paBern also predicts its transi?onal morphology between three and four chambers Tbx5 is a "transcrip?on factor" ‐ a protein that controls the transcrip?onal expression of other genes – The evolving Tbx5 expression paBern likely contributed strongly to the evolu?on of four chambered from three chambered hearts today’s factoid hBp:// news_images.jsp? cntn_id=115520&org=NSF ‘Tbx5 and Heart Evolu?on’ posted in Biology in the News on BB mid term 1 sta?s?cs • average: 71.47% • standard devia?on: 17.68 Bio 201 Spring 2010 mid term 1 35 30 number of students 25 20 15 10 5 0 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91 94 97 100 score (%) Soil • provides: – mineral nutrients – water – oxygen for roots soil horizons • A: crucial for growing crops; leeching by water movement removes nutrients to B horizon, where they are o`en not available to plant roots; also contains decaying organic maBer • can be lost by erosion [1930s Dust Bowl in Midwest, Great Plains] • sand: air space plen?ful but doesn't hold much water • clay: doesn't have much air space but binds minerals well • loam: contains adequate amounts of sand, silt (ﬁne par?cles), and clay ‐ best for growing plants • B: contains leeched minerals but liBle or no decaying organic maBer; some plant roots can reach B • C: bedrocks; plant roots typically do not reach C • o`en essen?al for mineral availability to plant roots – many crucial ions posi?vely charged (K+. Mg2+. Ca2+, NH4+); clay is nega?vely charged CO2 + H20 <‐> H2CO3 <‐> H+ + HCO3‐ clay • • •
• H+ from this aqueous reac?on in soil bind to clay strongly and displace weaker binding mineral ca?ons (posi?vely charged ions) This is called ion exchange • – The displaced mineral ions are thus more available for plant uptake However, crucial nega?ve ions (anions): Nitrate (NO3‐) and Sulfate (SO42‐) cannot be maintained in the A soil horizon in the same way; leach very easily => most A horizon N is in the form of decaying organic maBer (slowly breaks down and releases NH4+, plants uptake this) fer?lizers in agriculture • agricultural plant growth rapidly depletes nutrients • most common elements in fer?lizers N P K • "N‐P‐K" "5‐15‐5" = % by weight of Nitrogen, Phosphorous, and Potassium • Ammonium Sulfate also common in fer?lizers • Inorganic fer?lizers ‐ provide nutrients in readily available form (ions); formulas can be precisely controlled for speciﬁc crops • Organic fer?lizers ‐ e.g. manure, compost; beBer for soil composi?on (less leaching) but minerals not immediately available for plants • op?mal for plant growth ~6.5 • but some crops (e.g. blueberries) grow best at more acidic pH (~4.0) • rainfall; organic maBer decomposi?on ‐ decrease soil pH (acidiﬁca?on) • applica?on of calcium carbonate, calcium hydroxide, or magnesium carbonate increases soil pH – (used to reverse acidiﬁca?on) – e.g. lime [insert pic of lime bag]; removes H+ ions and increases concentra?on of available calcium • if a crop needs a more acidic soil ‐ Sulfur can be added – soil bacteria convert this to sulfuric acid soil pH • leaves take up some nutrients beBer than roots • copper, iron, manganese • these are s?ll commonly in soil fer?lizers but solu?ons can be sprayed directly onto leaves hBp:// hBp:// hBp://hubpages.com/hub/soil‐ph‐level hBp:// ‐6/Environments/ac?vi?es/ delgap/images_sized/phﬁeld2001.GIF plants and soil • soil forma?on depends on local condi?ons: – plants growing there – mechanical weathering of rock – what type of parent rock hBp:// soil%20photo.jpg • plant liBer becomes humus ‐ dark material with ﬁne par?cles, by the ac?on of fungi and bacteria in the soil; rich in minerals; traps water and oxygen that plant roots can then absorb • plants aﬀect local soil pH by either exre?ng H+ or excre?ng OH‐ or HCO3‐ ions – plant roots can also excrete organic acids (e.g. citric acid, malic acid) to decrease the pH of soil immediately surrounding them (makes it easier to uptake Fe3+ and other ions) How do plants get Nitrogen? • N2 in atmosphere extremely stable – (triple bond; hard to break) • Nitrogen ﬁxing bacteria – (170 million metric tons N ﬁxed per year; human industry ﬁxes 80 million per year) • ocean: cyanobacteria plus others • fresh water: mainly cyanobacteria • land: various soil bacteria (small amounts); N‐ﬁxing bacteria living in associa?on with plant roots (MUTUALISM) – the majority of soil N • most well known: Rhizobium, mutualist of legumes (beans, alfalfa, clover, etc.); infec?ons form nodules in plant roots – used in crop rota?on • other associa?ons for N ﬁxa?on – lichens: fungi + N‐ﬁxing cyanobacteria (these bacteria also ﬁx N in fems, cycads, nonvascular plants] – rice: can be grown in ﬂooded ﬁelds with the water fern Azolla, mutualist with a N‐ﬁxing cyanobacteria – woody plants (alder, lilac) associate with N‐ﬁxing ﬁlamentous ac?nobacteria • plants get ﬁxed N (ammonium); bacteria get high energy carbon compounds (plant photosynthe?c products) nitrogen ﬁxing reac?ons • three requirements: – strong reducing agent ‐> transfers H to N2 and intermediate products • (can be provided by photosynthesis or respira?on, depending on species) – energy: ATP – nitrogenase enzyme (catalyst of the reac?on) • inhibited by oxygen; many nitrogen ﬁxing bacteria are anaerobic • root nodules maintain a low O2 environment (respira?on s?ll possible; nitrogenase is not inhibited) • in nodules, plants use leghemoglobin (pink color visible if high enough concentra?on) to transport O2 (molecule is an evolu?onary rela?ve of hemoglobin) ‐ contains iron heme component plant‐bacteria symbiosis: absolutely necessary for N ﬁxa?on to take place in nature • need communica?onfor nodule to form (ﬂavinoids from root cause bacteria to transcribe nod genes) • need O2‐free interior of nodule ‐ depends on leghemoglobin transport of O2 • need bacteria to form bacteroids (highly specialized morphology for N ﬁxa?on) • analogous to (and may involve some of the same genes as) mycorrhizal fungal associa?ons with plant roots global nitrogen cycle • usually found in N deﬁcient habitats (e.g. bogs) • evolved to gain nutri?on (N) from animal ?ssues • venus ﬂy traps (dicot) – – specialized leaves triggered to close by hairs carnivorous plants • pitcher plants (dicot) – • sundews (dicot) – – aBract insects by colors and scents; downward poin?ng hairs on steep sides prevent insects from escaping – hairs secrete s?cky sugar solu?on; insects are aBracted and get stuck • these plants don't absolutely need to eat insects, but grow faster and perform more photosynthesis when hBp:// they do gallery2/v/Tropicalia/lady_s
+slipper+orchid.jpg.html? g2_GALLERYSID=85bdf00ed9398 484c34cﬀdb21a22e7a parasi?c plants • most are autotrophs but some are no longer capable of adequate photosynthesis and are heterotrophs • most famous example: mistletoe • parasi?zes other plants (trees) using haustoria organs that insert into host plant ?ssues and absorb nutrients • dwarf mistletoe (Arceuthobium americanum) ‐ pest to lumber industry in US hBp:// u.edu/Viscaceae/ images/AME.JPEG plants and dry habitats/climates • some plants (cac?) – adapta?ons of structure – e.g. barrel stem modiﬁca?ons for water storage • other plants – no special structures – complete en?re life cycle during brief wet periods structural adapta?ons for dry climates = “xerophy?c” adapta?ons • thick epiderms • dense, hairy covering • stomatal crypts • eucalytpus: leaves hang ver?cally to avoid direct sunlight • succulence • spines – recessed stomata – photosynthesis is stems, not leaves – may deﬂect solar radia?on or func?on in heat dissipa?on but there is a cost to being a xerophyte • typically slow growth • why? – keeping stomates closed to reduce water loss also reduces CO2 intake – also can only grow in brief ?mes of the year adapta?on of most xerophytes: higher water use eﬃciency than other plants root adapta?ons of desert plants • very deep taproots or • very fast growing roots ac?ve during brief wet seasons – die back during dry seasons • also: accumula?on of proline in vacuoles – creates more nega?ve "solute poten?al" and "water poten?al" inside cells – forces a greater rate of water intake by cells; more extrac?on of water from environment • plants in salt‐rich environments also have this adapta?on how to test rela?onship between root growth and drought tolerance? • • • hypothesis: plants with high survival ability in dry environments have fast growing roots need: a species with varia?on in root growth rate – perhaps occurs in variety of environments experiment: grow individual strains with diﬀerent growth rates each in several environments varying in water availability – measure root size and survival over ?me Which result would be consistent with your hypothesis?
100 90 80 70 % survival 60 50 40 30 20 10 0 0 5 10 15 20 25 root growth rate (cm/day) 100 90 80 70 % survival 60 50 40 30 20 10 0 % survival root growth rate (cm/ day) 16 root growth rate (cm/day) 14 12 10 8 6 4 2 0 what about environments with too much water? • • • hard for roots to get enough oxygen most plants cannot live long in ﬂooded/ saturated soils some have adapta?ons – slow root growth, very shallow soil penetra?on – anaerobic metabolism (fermenta?on) instead of aerobic respira?on in roots – less eﬃcient than aerobic respira?on =>slow growth • pneumatophores ‐ extensions of roots that grow out of the water into air – spongy ?ssue allows diﬀusion of oxygen for en?re root – e.g. cypress, mangrove • aerenchyma in leaves and pe?oles – have large air spaces for storage of Oxygen – also increase buoyancy plants in hot environments • transpira?on can cool – but also can dehydrate • similar adapta?ons to some dry environments – e.g. hairs and spines increase heat radia?on • expression of heat shock proteins – help stabilize the folding of other proteins ? v=0 plants and cold • low temps above freezing – membranes lose ﬂuidity – ?ssue damage can occur • freezing temps – ice crystals damage ?ssues • adapta?on: cold hardening – takes several days – increases unsaturated faBy acid content in membranes • preserves ﬂuidity • see next slide • an?freeze proteins – prevent ice crystals from forming fat • Lipid ‐ general term for fats, fat‐like molecules • Fat ‐ a class of lipids, produced by plants and animals, density lower than water, insoluble in water – Fats that are liquid at room temperature = “oils” O • Triglycerides ‐ a main component of natural fats • FaBy acid ‐ a carboxylic acid || – with a long hydrocarbon chain -C-O-H • Saturated ‐ no C‐C double bonds in chain • Unsaturated ‐ has C=C double bonds in chain • Polyunsaturated ‐ has >1 C=C double bonds in chain – –
R2 \ / Cis ‐ most common in unprocessed food C = C / \ H H R1 H \ / Trans ‐ common in processed food C = C / \ H R2 R1 • the most restric?ve substance to plant growth • saline (=salty) environments salt – oceans – river estuaries going into ocean – soil near estuary, river delta areas ricebreedingcourse/image46.jpg also: textbook mentions genetically modified tomatoes that express high levels of a gene whose product causes salt to be stored in vacuoles – greatly increasing salt tolerance • saliniza?on of soil = growing problem in salty environments •
halophytes = plants adapted to salty environments high nega?ve water salt glands – excrete salt to outside poten?al in environment and excreted salt in bladders in some plantscan help leaves get water from roots and – water moves toward prevent water loss due to transpiration nega?ve poten?al • plant cells need even more nega?ve water poten?al to preserve water – otherwise, wil?ng due to water loss • also: Na+ and Cl‐ ions can be toxic to plants halophytes and xerophytes share: • • • succulence ‐ thick, watery ?ssue – conserves water; stored water can vary in daily cycles in salt marshes • succulents o`en use: Crassulacean Acid Metabolism (CAM) store CO2 at night (incarboxyl groups on organic acids) ‐ release for photosynthesis during the day stomate opening‐closing cycles are reversed in these plants ("reversed stomatal cycles") – stomata stay closed during the day to conserve water • other adapta?ons: high ra?o of root to shoot ?ssue, sunken stomata, thick cu?cles (already discussed for xerophytes) Crassulacean acid metabolism • refers to metabolism in succulent plant family Crassulaceae (e.g. jade plant) – not a kind of acid – orchids, bromeliads, cac?, pineapple, many others – occurs in unrelated plant lineages – ‐thought to have evolved independently mul?ple ?mes – ~7% of plants (~16,000); most are angiosperms 20050831/0207_red_bromeliad.JPG heavy metal contaminated environments • toxic to most plants • but some popula?ons of some plants have adapted – various mechanisms, many not well studied • tolerance usually speciﬁc to one or two metals • strains, mechanisms may be useful for bioremedia?on of polluted sites all of these environments are becoming more common • understanding how plants adapt (or not) is interes?ng and crucial for the future • crop of the future? Salicornia bigelovii (and related species; samphires; family Amaranthaceae) • halophy?c succulent herb – steamed; tastes like young spinach; salty • plants very edible • seeds produce edible oil – but have saponins • complex with cholesterol • may pose hazard in some forms File:Glasswort.jpg ...
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- Fall '08
- Midwest, Leach, Condi, halophytes, essen