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Chapter 2: The Physical Environment. News of the week (last semester). One in four.. One in four of the world's 5,487 known mammal species face extinction And about half are declining in population Why?. News of the week (this semester).
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News of the week (last semester) • One in four.. One in four of the world's 5,487 known mammal species face extinction • And about half are declining in population • Why?
News of the week (this semester) • The endorsement for approval of Lebanon's Jabal Moussa as a UNESCO biosphere reserve in early February recognizes the international acclaim for the area's wild and unspoiled habitats, its renowned Adonis Valley with its ancient agricultural terraces and trails, and the strong support expressed among the local communities for the nomination Located in the Lebanon mountain range, Jabal Moussa is situated in the Kesrouan-Jbeil area. • The endorsement raises the number of the Lebanese biosphere reserves to 3, ranking the nation 3rd out of 12 Arab countries with regards to their the number of such reserves.
Cedar Island ? 3,311 square kilometer island off the coast of Lebanon. Divers Union, fishermen and Green Peace are all against the project One question: An example of the mind-boggling problems architects of the project face is where to get the sand from.
Constraints, Solutions, and More • Physical properties of the environment and of biological materials constrain life, but also provide solutions to many of its problems. • Living things have a purposeful existence; their structures, physiology, and behavior are directed toward procuring energy and resources and producing offspring. They: • depend on the physical world for: • energy from sunlight • nutrients from the soil and water • affect and alter the physical world • function within limits set by physical laws
Water has many properties favorable for the maintenance of life. • Water, an ideal life medium: • is abundant over most of earth’s surface • is an excellent solvent and medium for chemical processes • allows for high concentrations of molecules necessary for rapid chemical reactions • enables movements of organisms because of its fluidity
Thermal Properties of Water • liquid over broad range of temperatures • conducts heat rapidly • resists temperature changes because of its heat capacity • resists changes in state: • freezing requires heat removal of 80 cal/g • evaporation requires heat addition of over 500 cal/g • So? Helps to keep large bodies of water from freezing solid during winter
Water has other remarkable thermal properties. • Most substances become denser as they cool. • Water also becomes denser, to a point, but: • reaches maximum density at 4oC, and expands as it cools below that point • expands even further upon freezing • This property is of monumental importance to life on earth: • bottoms of lakes and oceans prevented from freezing • floating layer of ice with covering of snow forms protective, insulating surface
Water: less dense as it freezes, so ice floats. More than 90% of the bulk of this Antarctic iceberg lies below the surface
The Buoyancy and Viscosity of Water • Density of water (800x that of air) means that water is buoyant. • Aquatic organisms achieve neutral density through: • reduction (bony fish) or elimination (sharks) of hard skeletal components • use of gas-filled swim bladder (plants too!) • accumulation of lipids • Water’s viscosity retards the movement of organisms (some organisms are streamlined, others deploy parachutes).
All natural waters contain dissolved substances. • Water is a powerful solvent because of its charge polarity. • Almost all substances dissolve to some extent in water. • Nearly all water contains some dissolved substances: • rainwater acquires dissolved gasses and trace minerals • lakes and rivers contain 0.01-0.02% dissolved minerals • oceans contain 3.4% dissolved minerals
Fresh Versus Salt Water • Noteworthy differences in makeup of solutes: • salt water is rich in (sodium) Na+, (cholorine) Cl- (magnesium) Mg2+, (sulfate) SO42- • fresh water is rich in (calcium) Ca2+, (bicarbonate) HCO3-, and (sulfate ions) SO42- • Solute loads of surface waters reflect bedrock chemistry: • water of limestone areas is “hard” with substantial Ca2+, HCO3- • water of granitic areas contains few mineral elements • Oceanic waters are saturated with respect to Ca2+, but continue to accumulate Na+.
Waters differ in contents of essential nutrients. N and P are among most the important essential elements and are often limiting: • typical fresh water N is 0.40 mg/L, while P is about 0.01 mg/L (N>P). • typical salt water N is less than 0.01 mg/L, while P is about 0.01-0.1 mg/L (P>N). • So?
pH - the Concentration of Hydrogen Ions • Normal pH range of surface waters is 6-9. • Acid rain can lower pH to as low as 4 in some areas. ( [ ] of hydrogen ions in a solution = acidity) • Acidity dissolves minerals • water in limestone areas is “hard” with substantial Ca2+, HCO3- • most organisms regulate pH around neutrality; adaptations to life out of balance with external medium (high or low pH) are costly (it takes energy to be different!)
The pH scale of hydrogen ion concentration extends from O (highly acidic) to 15 (highly alkaline).
C and O are intimately involved in energy transformations. • Compounds contain energy in their chemical bonds: • energy is required to create bonds • energy is released when bonds are broken • Energy transformations proceed by oxidation and reduction, often involving C: • oxidation removes electrons, releases energy • reduction adds electrons, requiring energy
Heterotrophs &Autotrophs • Heterotrophs obtain their energy by consuming organic (biological) sources of carbon-rich food, which they oxidize. • Autotrophs obtain their energy from inorganic sources, and use this energy to reduce carbon, which they store for later use: • photoautotrophs obtain energy from light • chemoautotrophs obtain energy from oxidation of inorganic compounds such as H2S, NH4+
Photosynthesis and Respiration • Think of photosynthesis and respiration as complementary reactions which: • reduce carbon (photosynthesis): • energy + 6CO2 + 6H2O C6H12O6 + 6O2 • water is an electron donor (reducing agent) • oxidize carbon (respiration): • C6H12O6 + 6O2 energy + 6CO2 + 6H2O • oxygen is an electron acceptor (oxidizing agent)
The Limited Availability of Inorganic Carbon • Terrestrial plants have a difficult time acquiring inorganic carbon: • carbon (as CO2) diffuses into leaf from atmosphere: • rate of diffusion of a gas is proportional to concentration difference between external and internal media • atmosphere-to-plant difference in [CO2] is small • plant-to-atmosphere difference in [H2O] is great • bottom line: plants lose enormous amounts of water to the atmosphere relative to carbon gained, at a rate of 500 g water for each g of carbon
Tendency of water to leave the leaf far exceeds the tendency of carbon dioxide to enter the leaf. Gas exchange occurs across the surface of a leaf.
Carbon dioxide diffuses slowly through water. • Both CO2 and HCO3- (bicarbonate ions) diffuse slowly through water. • A thin boundary layer (10-500 um) adjacent to the plant surface becomes carbon-depleted, and it forms a diffusion barrier between the plant and C-rich water beyond. • Thus – photosynthesis may still be limited by a diffusion barrier of still water at the surface of the organism
Oxygen is scarce in water. • Oxygen is rather limited in water: • low solubility • limited diffusion • below limit of light penetration and in sediments rich in organic matter, conditions become anaerobic or anoxic
The ‘knees’ of bald cypress trees conduct air from the atmosphere to roots when a swamp is flooded and oxygen is limited
Availability of Inorganic Nutrients • After H, C, and O, elements required in greatest quantity are N, P, S, K, Ca, Mg, and Fe. • Certain organisms require other elements: • diatoms require Si for their glassy cases • nitrogen-fixing bacteria require Molybdenum as part of the key enzyme in N assimilation • Terrestrial plants acquire most elements from water in soil around roots: • availability varies with temperature, pH, presence of other ions • P is particularly limiting in soils
Light is the primary source of energy for the biosphere. • A quick primer on light: • energy reaching earth from the sun covers a broad spectrum of wavelengths: • visible light ranges from 400 nm (violet) to 700 nm (red) • shorter wavelength energy (<400 nm) is ultraviolet (UV) • longer wavelength energy (>700 nm) is infrared (IR) • energy content of light varies inversely with its wavelength • the shorter the wavelength, the more energetic the light
Ozone and Ultraviolet Radiation • UV “light” has a high energy level and can damage exposed cells and tissues. • Ozone in upper atmosphere absorbs strongly in ultraviolet portion of electromagnetic spectrum. • Chlorofluorocarbons (formerly used as propellants and refrigerants) react with and chemically destroy ozone: • ozone “holes” appeared in the atmosphere • concern over this phenomenon led to strict controls on CFCs and other substances depleting ozone
Infrared Light and the Greenhouse Effect • All objects, including the earth’s surface, emit longwave (infrared) radiation (IR). • Atmosphere is transparent to visible light, which warms the earth’s surface. • Infrared light (IR) emitted by earth is absorbed in part by atmosphere, which is only partially transparent to IR. • Substances like carbon dioxide and methane increase the absorptive capacity of the atmosphere to IR, resulting in atmospheric warming.
Carbon dioxide concentrations in the atmosphere – measured at Hawaii
The Absorption Spectra of Plants • Various substances (pigments) in plants have different absorption spectra: • chlorophyll in plants absorbs red and violet light, reflects green and blue • water absorbs strongly in red and IR, scatters violet and blue, leaving green at depth • Absorption of light by water limits depth at which aquatic photosynthetic organisms can exist. Euphotic zone…
Algae and Light Quality • The quality of light is related to photosynthetic adaptations in the ocean: • algae growing near the surface have pigments like those in terrestrial plants (absorb blue and red, reflect green) • algae growing at depth have specialized pigments that enable them to use green light more effectively
Light Intensity • Ecologists measure PAR (photosynthetically active radiation). • Total radiation is measured as radiant flux = 1,400 W/m2 above the atmosphere (solar constant). • Radiant flux at earth’s surface is reduced by: • nighttime periods • low angle of incidence • atmospheric absorption and scattering • reflection from the surfaces of clouds
The Thermal Environment • Energy is gained and lost through various pathways: • radiation - all objects emit electromagnetic radiation and receive this from sunlight and from other objects in the environment • conduction - direct transfer of kinetic energy of heat to/from objects in direct contact with one another • convection - direct transfer of kinetic energy of heat to/from moving air and water • evaporation - heat loss as water is evaporated from organism’s surface (2.43 kJ/g at 30oC) change in heat content = metabolism - evaporation + radiation + conduction + convection
Staying cool • ?: Tern Island nests on the bare sand on small coral atolls in the Tropics – face high sunlight. They nest on the surface of the sand in full sunlight • Wedge-tailed shearwater – similar size and coloration – builds its nests in deep burrows beneath the surface of the sand. • Why?
Hatching success of wedge-tailed shearwaters is highly dependent on the thermal environment
Why? • Diets and feeding regimes • -- sooty terns feed on fish and squid – close to the nesting sites; male and female cooperation • Shearwaters feed hundreds of km from ther nesting sites • So: • Sooty terns have stomach full of water-laden food water for evaporative heat loss • Shearwaters plenty of fat for fast but little water
Organisms must cope with temperature extremes. • Unlike birds and mammals, most organisms do not regulate their body temperatures. • All organisms, regardless of ability to thermoregulate, are subject to thermal constraints: • most life processes occur within the temperature range of liquid water, 0o-100oC • few living things survive temperatures in excess of 45oC • freezing is generally harmful to cells and tissues
Tolerance of Heat • Most life processes are dependent on water in its liquid state (0-100oC). • Typical upper limit for plants and animals is 45oC (some cyanobacteria survive to 75oC and some archaebacteria survive to 110oC). • Good: high temp -> organisms develop quicker • The bad: High temperatures: • denature proteins • accelerate chemical processes • affect properties of lipids (including membranes)
Tolerance of Freezing • Freezing disrupts life processes and ice crystals can damage delicate cell structures. • Adaptations among organisms vary: • maintain internal temperature well above freezing • activate mechanisms that resist freezing • glycerol or glycoproteins lower freezing point effectively (the “antifreeze” solution) • glycoproteins can also impede the development of ice crystals, permitting “supercooling” • activate mechanisms that tolerate freezing
Glycoproteins act as a biological antifreeze in the antarctic cod
Organisms use physical stimuli to sense the environment. • To function in complex and changing environments, organisms must: • sense and detect environmental change (plants must sense changing seasons) • detect and locate objects (predators must find food) • navigate the landscape (salmon must recognize their home river to spawn)
Sensing Electromagnetic Radiation • Many organisms rely on vision (detection of visible light and other wavelengths): • light has high energy • light permits accurate location and resolution of targets • Many variations in capabilities exist: • hawks have extreme visual acuity • insects and birds can perceive UV • insects can detect rapid movements • Animals operating in dark surroundings may sense IR (e.g., pit vipers utilize pit organs to sense prey).
Many organisms use signals that are ‘visible’ only in UV light The human eye sees this Yellow Daily in reflected light in the range of 400-700 nm Bees see a different pattern in the same flower in the range of 300-400 nm. The light flecks are pollen grains
