Bacteria, Viruses and Protistans
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- The Biosphere
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Ecosystems (chap 37) Ecosystem – a complex of organisms interacting with each other and with the physical environment Are open systems through which energy flows and materials are cycled Require energy and nutrient input and generate energy (usually as heat) and nutrient output The participants Producers – autotrophs that can capture sunlight energy and incorporate it into organic compounds Consumers – heterotrophs that feed on tissues of other organisms Herbivores – eat plants Carnivores – eat animals Omnivores – eat a variety of organisms Parasites – reside in or on living hosts and extract energy from them Decomposers – heterotrophs (inclu. bacteria and fungi) that extract energy from the remains or products of organisms Detritivores – small invertebrates that feed on partly decomposed particles of organic matter (detritus) Structure of ecosystems Trophic (feeding) levels Level 1 – producers Level 2 – herbivores Level 3 – carnivores Decomposers feed on organisms from all levels Food webs Food chain – sequence of what eats what Food web – interconnected food chains in which the same food resource is often part of more than one food chain Energy flow through ecosystems Primary productivity Def. – The rate of photosynthesis for the ecosystem during a specified interval of time Net primary productivity – the rate of energy storage in plant tissues in excess of the rate of respiration by the plants themselves Major pathways of energy flow Energy flows into ecosystem from the sun Grazing food webs – energy flows from plants to herbivores and then to carnivores Detrital food webs – energy flows from plants through decomposers and detritivores Energy leaves ecosystems through heat losses generated by metabolism Ecological pyramids Trophic (feeding) structure can be diagrammed as a pyramid in which producers form the base for successive tiers of consumers above them Two basic types of pyramids Pyramid of biomass – uses the weight of the members in each trophic level Pyramid of energy – based on energy losses at each level Biogeochemical cycles Overview Biogeochemical cycles influence the availability of essential elements in ecosystems Elements are available to producers as ions The amount of nutrients being recycled Three categories of biogeochemical cycles Hydrologic cycle – oxygen and hydrogen move as water molecules Atmospheric cycles – elements move in the gaseous phase (ex., carbon & nitrogen) Sedimentary cycles – element does not have a gaseous phase (ex., phosphorus) Hydrologic cycle Water is moved or stored by evaporation, precipitation, retention, and transportation Water moves other nutrients in or out of ecosystems Watershed – funnels rain or snow into a single river Nutrients are absorbed by plants and prevent their loss by leaching Carbon cycle Carbon enters the atmosphere (as carbon dioxide) by aerobic respiration, fossil-fuel burning, and volcanic eruptions Carbon is removed from the atmosphere (and bodies of water) by photosynthesis and by shelled organisms Decomposition of buried carbon compounds millions of years ago caused the formation of fossil fuels (ex., coal, oil, natural gas) Burning of fossil fuels puts extra amounts of carbon dioxide into the atmosphere, and may lead to global warming (the greenhouse effect) Nitrogen cycle Nitrogen – needed for production of proteins and nucleic acids (DNA & RNA) Abundant in the atmosphere (80%), but not in the earth’s crust Of all nutrients needed for plant growth, nitrogen is the scarcest Complicated cycle Nitrogen fixation – bacteria convert nitrogen gas to a form that plant roots can use directly Decomposition and ammonification – caused by bacteria and fungi feeding on dead plants and animals (or animal waste products) Nitrification – ammonia (or ammonia compound) is converted into a nitrite and then into a nitrate Denitrification – release of nitrogen gas to the atmosphere by the action of bacteria on nitrites and nitrates Humans affect the cycling of nitrogen compounds Air pollutants (incl. oxides of nitrogen) contribute to soil acidity Heavy nitrogen fertilizer applications are costly and are lost in runoff and harvested crops Phosphorus cycle Long-term geochemical phase – phosphorus moves from land, to sediments in the seas, and back to the land Ecosystem phase – plants take up phosphorus from the soil, transfers it to herbivores and then to carnivores, which excrete it in waste products and decomposing bodies Predicting the impact of change in ecosytems Ecosystem modeling Tries to predict the complex effects of a single change in an ecosystem Computer modeling is valid, if all of the key relationships in the ecosystem have been incorporated into the model Biological magnification – DDT An effective chemical in killing mosquitoes, but accumulated in fatty tissues and causes unexpected nontarget effects DDT now banned in the U.S., and some of the effects have begun to reverse The Biosphere (chap 38) A. Biosphere – earth regions where organisms live 1. Definitions a. Hydrosphere – all water on or near the earth's surface b. Lithosphere – earth's outer, rocky layer c. Atmosphere – gases, particles, and water vapor enveloping the earth 2. Global patterns of climate a. Climate – includes temperature, humidity, wind velocity, cloud cover, and rainfall b. Shaped by four factors 1) Variations in the amount of incoming radiation 2) Earth's daily rotation and annual revolution 3) World distribution of continents and oceans 4) Elevation of land masses
a. Ultraviolet radiation is absorbed by ozone and oxygen in the upper atmosphere b. Clouds, dust, and water vapor absorb and reflect solar radiation c. Radiation warms the earth's surface, generating heat that drives the weather systems 2. Heating from the sun results in air currents a. Sun differentially heats equatorial and polar regions, creating the world's temperature zones b. Warm equatorial air rises, cools, releases it moisture, and spreads N and S where it descends at 30 latitudes as very dry air (results in deserts) c. The air is warmed again and ascends at 60 latitudes d. Amount of solar radiation reaching the earth's surface changes in the N and S hemispheres a. Ocean water covers 71% of the earth's surface b. Latitude and seasonal variations in solar heating cause warming and cooling c. Surface waters move from the equator to the poles, warming the air above d. Immense circular water movements form in the Atlantic and Pacific oceans
a. Topography – physical features of a region (ex., elevation) b. Mountains and valleys influence regional climates 1) Monsoon rains – occur when warm winds pick up ocean moisture and release it over the cooler land masses of Asia and Africa 2) Mountains of the W U.S. cause the winds from the ocean to rise, cool, and lose their moisture a. Biogeography – the study of the global distribution of species b. Biogeographic realms (6 of them) – broad land regions with characteristic types of plants and animals c. Biomes – broad vegetational subdivisions (including all animals and other organisms) 2. Soils of major biomes a. Soil – mixture of rock, mineral ions, and organic matter 1) Size of the mineral component can range from gravel, to sand, silt, and clay 2) The organic matter is called humus b. Soil profiles – defined by the composition of soil from the surface downward 1) Topsoil has the most humus, but is vulnerable to weathering 2) Loam topsoils have the best mix of sand, silt, and clay for agriculture
3. Deserts a. Areas where evaporation exceeds rainfall [30 N and S latitudes] 1) Vegetation is scarce 2) Day/night temperatures fluctuate widely b. More than 1/3 of the world's land area is arid (or semiarid) due to drought and overgrazing, which can lead to desert formation
a. Dry shrublands and dry woodlands – W or S coastal regions of continents between 30 and 40 N and S latitudes 1) Climate is semiarid (rains occur during mild winter months); summers are long, hot, and dry 2) Dry shrublands – rainfall is less than 25-60 cm (ex., California chaparral) 3) Dry woodlands – rainfall 40-100 cm; there are trees but not dense forests b. Grasslands – extend across the interior of continents between deserts and temperate forests 1) Characteristics – flat or rolling land, high rates of evaporation, limited rainfall, grazing and burrowing animals 2) Several types a) Shortgrass prairie, tallgrass prairie (U.S. mW and W) b) Savannas (ex., Africa), monsoon grasslands (S Asia) 5. Tropical rainforests and other broadleaf forests a. Evergreen broadleaf forests (ex., tropical rain forest) – between 20 N and S latitude 1) Temperatures, rainfall, and humidity are all high 2) Plant growth is luxuriant, with incredible animal diversity b. Deciduous broadleaf forests – common at temperate latitudes 1) Tropical deciduous forest, monsoon forests (of SE Asia) 2) Temperate deciduous forests (of North America)
a. Typical tree is some variety of evergreen cone-bearer with needlelike leaves b. Found in widely divergent geographic areas 1) Boreal forests (taiga) – found in cool to cold N regions of North America, Europe, & Asia (spruce & balsam fir) 2) Montane coniferous forests – extend S through the great mountain ranges (fir & pine) 3) Temperate rain forest – W coast of North America (sequoias & redwoods) 4) Pine barrens – in sandy soil of several E coast states
a. Arctic tundra 1) A vast treeless plain N of the boreal forests 2) Very cold, with low moisture; characterized by permafrost b. Alpine tundra – occurs at high elevations in mountain throughout the world
1) Body of freshwater with three zones a) Littoral zone – extends from the shore to where rooted plants stop growing b) Limnetic zone – open, sunlit waters beyond the littoral zone to a depth where photosynthesis is no longer significant; plankton life is abundant c) Profundal zone – deep, open water below the depth of light penetration 2) In temperate regions, lakes undergo a) Winter – ice (less dense) forms on the surface over water that is warmer (4C) and denser b) Spring overturn – warming and winds cause oxygen to be carried downward and nutrients to the surface c) Midsummer – a thermocline between the upper warmer layers and lower cooler layers prevents vertical warming d) Fall overturn – upper layers cool and sink 3) Lakes and nutrients a) Oligotrophic lakes – deep, nutrient-poor, and low in primary productivity b) Eutrophic lakes – shallow and nutrient-rich (often due to agricultural and urban runoff wastes) b. Stream ecosystems 1) Start out as freshwater springs or seeps 2) Three kinds of habitats from head waters to river's end a) Riffles – shallow, turbulent stretches b) Runs – fast-flowing waters with a smooth surface c) Pools – slow-moving deep waters 2. Ocean provinces a. The ocean consists of two vast provinces 1) Benthic province – includes all of the ocean bottoms 2) Pelagic province – includes the entire volume of ocean water a) Neritic zone – the relatively shallow water overlying the continental shelves b) Oceanic zone – the water over the ocean basins; photosynthesis is restricted to the surface b. Primary productivity 1) Phytoplankton are at the bottom of food chains; organic remains and wastes enter the detrital webs 2) About 70% of the productivity comes from microscopic phytoplankton c. Hydrothermal vents 1) In fissures between the earth's plates; water becomes heated and laden with minerals 2) Elaborate food webs based on mineral-feeding bacteria 3. Coral reefs and banks a. Coral reefs are the accumulated remains of countless corals, etc. 1) Most are located in clear, warm sea waters of the tropics 2) Human activities are destroying the reefs with pollution and physical damage b. Coral banks are located farther N and S at the edges of the continental shelves near Japan, California, Norway, England, and New Zealand
a. Estuaries 1) Partially enclosed regions where fresh and salt water meet 2) Incredibly productive feeding and breeding grounds b. Intertidal zone 1) Alternately exposed and submerged; existence is difficult 2) Rocky shores – have three vertically arranged zones a) Upper littoral – submerged only during the highest tides; it is sparsely populated b) Mid-littoral – submerged during the regular high tide and exposed at low tide c) Lower littoral – exposed only during the lowest tides 3) Sandy and muddy shores a) Unstable stretches of loose sediments b) Detrital food webs occur; invertebrates are plentiful c. Upwelling along coasts 1) Upwelling – upward movement of deep, nutrient-rich water along margins of continents a) Under the influence of N winds and the earth's rotation, water along the W coast of the N Hemisphere moves W where cold, deep water moves in vertically to replace it b) Nutrients circulate and primary productivity increases 2) Ever 3-7 years, the warm surface waters of the W equatorial Pacific move E to the coasts of C & S America, causing a downwelling (El Nino) Human Impact on the Biosphere (chap 39) A. Human indifference – population growth and individual demands are stressing the environment (Fig. 39.1) B. Air pollution 1. Pollutants – substances with which ecosystems have no prior experience and therefore cannot deal with them a. Include carbon dioxide, oxides of nitrogen and sulfur, and chlorofluorocarbons b. Each day 700,000 metric tons of pollutants are dumped into the atmosphere in the U.S.
a. Industrial smog – gray air found in industrial cities that burn fossil fuels b. Photochemical smog – brown air (ex., auto exhaust) found in large cities in warm climates
a. Burning coal produces sulfur dioxides; fertilizers and burning fossil fuels produce nitrogen oxides b. Tiny particles of these oxides fall to Earth as dry acid deposition or acid rain (Fig. 39.3)
a. Ozone in the lower stratosphere absorbs most of the ultraviolet radiation from the sun 1) Thinning of the ozone layer has produced an ozone hole over Antarctica 2) In response, skin cancer has increased, cataracts may increase, and phytoplankton may be affected b. Chlorofluorocarbons (CFCs) seem to be the cause 1) One chlorine atom can convert 10,000 ozone molecules to oxygen 2) Other ozone "eaters" include methyl bromide, jet vapor trails, and methane
a. Paper products and nonreturnable bottles and cans are our biggest problems b. Need to move from a "throwaway" society to one of conservation and reuse
a. 21% of land is used for agriculture; another 28% is available but may not be worth the cost b. The "Green Revolution" has increased crop yields, but uses many times more energy and mineral resources c. Growing human population is moving into marginal lands to meet its increasing needs 3. Deforestation (Fig. 39.7) a. Forests are watersheds that control erosion, flooding, and sediment buildup in rivers and lakes 1) Deforestation can reduce fertility, change rainfall patterns, increase temperatures, and increase carbon dioxide 2) Clearing large tracts of tropical forests may have global repercussions (inclu. alteration of rates of evaporation, transpiration, runoff, and rainfall as well as photosynthetic activity rates b. In "slash-and-burn" agriculture, trees are cut, the land used for a few growing seasons, and then abandoned as fertility plummets
a. Desertification – conversion of grasslands and croplands to desertlike conditions 1) The term also applies when agricultural productivity drops by 10% or more 2) At least 200,000 square kilometers are being converted annually b. Large-scale desertification is caused by overgrazing of cattle on marginal lands
a. Large-scale agriculture accounts for nearly 2/3s of the human population's use of fresh water b. Salt buildup (salination) of the soil and waterlogging can result c. Withdrawal of underground water causes water tables to drop 3. Water pollution a. Caused by human waste, insecticides, herbicides, chemicals, radioactive materials, and heat b. Wastewater treatment 1) Primary treatment – removes and burns sludge before it is dumped in landfills; chlorine is added to water 2) Secondary treatment – uses microbes to degrade organic matter; but nitrates, viruses, and toxic substances remain 3) Tertiary treatment – uses experimental methods to remove solids, phosphates, organics, etc.; used on about 5% of the nation's wastewater c. The coming "Water Wars" 1) In the past decade, 33 nations have engaged in conflicts over reductions in water flow, pollution, and silt buildup 2) By restricting water flow, countries upstream may attempt to influence political behavior in countries downstream
a. Are a limited b. Extraction and use of abundant reserves of oil shale and coal are not "environmentally attractive"
a. The net energy produced is low and the cost high compared with coal-burning plants b. Meltdowns may release large amounts of radioactivity to the environment c. Nuclear waste is so radioactive that it must be isolated for 10,000 years 4. Alternative energy sources a. Solar-hydrogen energy 1) An attractive technology because it depends on a "limitless" energy source -- the sun 2) Photovoltaic cells produce an electric current that splits water into oxygen and hydrogen gas which can be used directly as fuel or to produce electricity b. Wind energy 1) Where winds travel faster than 7.5 meters/second, wind turbines are cost-effective producers of electricity 2) Because winds do not blow on a regular schedule, wind turbines cannot be the exclusive source of energy c. Fusion power 1) Temperature like those on the sun cause atomic nuclei to fuse and release energy 2) Fusion power is possible, but many obstacles make the technology a distant possibility Download 227.21 Kb. Share with your friends:
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