Ch2 Adaptations to the Physcial Environment - Water and Nutrients.pdf

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Spencer Barrett

chapter 2: ADAPTATIONS TO WATER AND NUTRIENTS  challenges for deep-diving mammals  having enough oxygen  keeping warm  sperm whales rely on oxygen stored in hemoglobin in the blood and myoglobin in the muscles (lungs have very little oxygen)  slows metabolism  reduce blood flow to nonvital organs (skin, viscera, lungs, kidneys, muscles)  maintains blood to brain and heart  temp. drops (apart from key organs), heart rate slows, demand for O drops 2  Weddell seal (Antarctic) have thick layer of insulating fat  slows conduction of heat from internal organs to envmt  Adélie penguin (diving bird) insulate by trapping air in their plumage  prob. for diving (buoyancy) – enlarges waistline, increasing drag  water pressure when diving compresses air (decreases volume, buoyancy, drag)  depth of 60 m (pressure 6 times of surface press.) – it has same density as seawater  as it swims up, trapped air expands (positive buoyancy) and propels it up  biotic and abiotic factors exist together  life depends on physical factors: water (basic medium of life), energy  organisms affect physical world: soils, atmosphere, lakes, oceans, rocks gain their properties to activities of orgnms  life functions within physical laws  life exists out of equilibrium w/ the physical world  living orgnms have a purposeful existence  everything is directed toward creating NRG and resources to produce offspring  life exists in a constant state of constant tension w/ its physical envmt Water Has Many Properties Favourable to Life  has capacity to dissolve inorganic compounds (excellent medium for chemical processes of living sys.)  liquid under most conditions on earth  its density needed for rapid chemical reactions Thermal Properties  resists temp. change (mostly stays liquid)  a lot of NRG needed to evaporate and freeze water  keeps large bodies of water from freezing in winter  conducts heat rapidly (thermal NRG spreads evenly)  becomes less dense as it cools below 4°C  freezing water expands and becomes less dense (floats, allowing orgnms to live in bottoms of lake in winter) Density and Viscosity  800 times denser than air, but viscous  some animals are made up of materials denser than fresh water  aquatic orgnm adaptations:  fish have gas-filled swim bladder  size can be adjusted to equalize density of fish’s body with the water  large kelps have gas-filled bulbs that float their leaves to surface to get sunlight  unicellular algae use droplets of oil to float  streamlined shapes (high viscosity of water hampers mvmt)  filamentous appendages (take advantage of water viscosity)  as animals become smaller, the momentum of their mvmt decreases relative to the viscosity of water  a tiny water flea seems to be swimming in molasses  but what impedes swimming also prevents sinking Many Inorganic Nutrients Are Dissolved in Water  orgnms require huge amounts of: H, C, O (the elements in carbs)  also need N, P, S, K, Ca, Mg, Fe  some also need other elements  ex. diatoms construct their glassy shells from silicates  ex. tunicates (sessile marine invertebrates) accumulate vanadium (defense against predators)  animals get nutrients from plants, plants from water The Solvent Capacity of Water  can dissolve many substances (makes them accessible to living sys. and provides a medium within which they can react)  powerful solvent  water molecules are strongly attracted to many solids (these compounds consist of electrically charged atoms or groups of atoms, ionsions  water molecules have both +ve and –ve charges  allows presence of minerals in water bodies  water vapour in atm. condenses to clouds (water is nearly pure, exc. for dissolved atm. gases N, CO )2  rainwater acquires minerals from dust particles and ocean spray in the atm.  picks up more minerals as it flows over the ground  “hard water” has high conc. of dissolved calcium  0.01-0.02% dissolved minerals in lakes, 3.4% in oceans (due to billions of years of accumulation; minerals from streams and rivers, leftovers from evaportation)  in oceans, conc. of some elements (esp. Ca) reach limits set by max. solubility of the compounds they forms 2+  Ca ions readily combine w/ dissolved CO pro2ucing calcium carbonate (soluble only to the extent of 0.014g/L of water – 0.0014%; reached this level eons ago)  excess calcium carbonate precipitates to form limestone sediments  sodium chloride (360g/L) and sodium bicarbonate (69g/L) far exceeds sodium in water  NaCl washing into oceans remains dissolved, thus the conc. in seawater is still increasing Hydrogen Ions in Ecological Systems  H ions are important dissolved substances in water – they are highly reactive  at high conc., affect enzyme activity and create other negative consequences; also crucial in dissolving minerals from rocks and soils  the concentration of hydrogen ions in a solution is referred to as its aciacidityeasured as + pH; the negative of the comment log of H ion conc. mol/L)  in pure water, a small fraction of H O2molecules are dissociated (pH = 7)  strong acids ex. HCl dissociate almost completely when dissolved in water  normal pH of natural waters is 6-9 +  H ions dissolve minerals from rocks and soils enhancing the natural solvent properties of water (making it nutrient-rich) + 2+ -  H +2+aCO  3a + HCO 3  Ca ions are very important to life and high conc. are vital esp. to orgnms who incorporate it into their shells +  H ions are essential for making nutrients available, but it also dissolves highly toxic heavy metals (detrimental to life) Plants Obtain Water and Nutrients from the Soil by Osmotic Potential  plants acquire inorganic nutrients (other than O, C, some N) as ions dissolved in water + -  N in soi3-as NH 4 NO 3  P – PO 4  Ca 2+ +  K  availability varies w/ their chemical form in the soil, temp. acidity, presence of other ions  K often limits plant production even when abundant  its formed compounds don’t dissolve easily Soil Structure and Water-Holding Capacity  soil retains water due to water’s unique properties  H O molecules cling to each other through hydrogen bonding (surface tension) 2  and to the surfaces of soil particles (capillary attraction)  soils consist of particles of clay, silt, sand, and organic materials  sizes: clay < silt < sand  total SA of particles increases as particle size decreases, soils w/ more clay and silt hold more water  clay particles hold water tightly, less water available to plants  plants live better in soil w/ a mixture of particles of diff. sizes (loam)  water potential (MPa megapascals) is the strength of the attractive forces holding water in the soil  most water potential is generated by the attraction of water to the surfaces of soil particles (the soil matrix)  thus, water potential a.k.a matmatric potential  plants must also overcome gravity and diffusion of water from the roots into the soil (due to the presence of dissolved substances in the soil)  pure water: water potential = 0  water moves from higher to lower water potential  soil has –ve water potential b/c it attracts H O f2om a pure soln w/water potential of 0  plants must develop a water potential lower than soil to overcome the matric potential and extract water  matric potential is greatest at surfaces of soil particles and decreases w/ distance from them  water is held by a matric pot. -0.01MPa  drains it out of soil by gravity  drains through large particles as long as the interstices are >0.005mm from their surfaces  field capacity of the soil is the amount of water held against gravity by a matric potential of less than -0.01MPa  represents the max. amount of water available to a plant in well-drained soil  as soils dry, the remaining water is held tighter b/c a greater proportion li
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