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Energy flow and trophic levels

Energy enters ecosystems as sunlight and moves up trophic levels with large losses at each step.
  • Producers (autotrophs) capture energy by photosynthesis or chemosynthesis; consumers and decomposers get energy by eating other organisms or dead matter.
  • Only about 10 percent of energy passes from one trophic level to the next; the rest is lost as heat through respiration and as waste.
  • Food webs show many feeding links; a food chain shows one path. Biomass and numbers usually shrink at higher levels (pyramids).
  • Gross primary productivity (GPP) is total energy captured; net primary productivity (NPP) equals GPP minus the producers' respiration.
  • Decomposers and detritivores recycle nutrients from dead material back into the ecosystem.

Biogeochemical cycles

Matter cycles through living and nonliving pools, and human activity speeds up or alters the flows.
  • Carbon cycle: photosynthesis removes CO2; respiration, decomposition and combustion return it; fossil fuels are a long-term carbon sink being released by burning.
  • Nitrogen cycle: nitrogen fixation, nitrification, assimilation, ammonification and denitrification; fertilizers and fossil-fuel burning add reactive nitrogen.
  • Phosphorus cycle has no significant atmospheric phase; phosphate comes from weathering of rock and often limits growth in freshwater.
  • Water cycle: evaporation, transpiration, condensation, precipitation, runoff and infiltration; groundwater can be stored for thousands of years.
  • Limiting nutrients (often nitrogen on land and phosphorus in lakes) control how much growth an ecosystem supports.

Terrestrial and aquatic biomes

Climate (temperature and precipitation) largely determines the distribution of biomes.
  • Tundra: cold, treeless, permafrost; boreal forest (taiga): cold, conifers; temperate deciduous forest: four seasons, rich soil; grassland: fertile soil, periodic fire.
  • Desert: less than about 25 cm of rain; tropical rainforest: high rain and biodiversity but nutrient-poor soil because nutrients are held in biomass; chaparral: dry summers, fire adapted.
  • Freshwater: lakes (littoral, limnetic, profundal, benthic zones), rivers, wetlands that filter water and buffer floods.
  • Marine: estuaries (mixing of fresh and salt water, high productivity), mangroves, coral reefs (sensitive to temperature and acidity), open ocean (large area, low productivity per area).
  • Lake turnover in spring and fall mixes oxygen and nutrients; thermal stratification forms in summer.

Photosynthesis and respiration

These two processes link energy flow and carbon cycling.
  • Photosynthesis: carbon dioxide plus water plus light energy produces glucose and oxygen.
  • Aerobic cellular respiration: glucose plus oxygen produces carbon dioxide, water and usable energy (ATP); anaerobic respiration and fermentation release less energy.
  • Producers do both processes; consumers and decomposers do respiration only.
  • These reactions keep atmospheric CO2 and O2 roughly balanced until fossil-fuel burning changes the balance.
Energy flows in one direction and is lost as heat; matter cycles. Do not say energy 'cycles' through ecosystems.
Decomposers are not a trophic level that 'eats' the others for energy; they recycle nutrients from all levels.

Levels of biodiversity and ecosystem services

Biodiversity includes genetic, species and ecosystem diversity, and healthy ecosystems provide services to people.
  • Genetic diversity helps populations adapt to disease and change; species diversity includes richness (how many) and evenness (how balanced); ecosystem diversity is the variety of habitats.
  • Ecosystem services: provisioning (food, timber, water), regulating (flood control, climate, pollination, water filtration), supporting (nutrient cycling, soil formation) and cultural (recreation, spiritual value).
  • Higher biodiversity generally makes an ecosystem more resilient to disturbance.

Island biogeography and species roles

Species number depends on island size and distance, and some species have outsized roles.
  • Larger islands and islands closer to the mainland support more species; small, distant islands have fewer.
  • Keystone species have an effect on the community far larger than their abundance (sea otters, wolves, beavers); removing them can restructure the ecosystem.
  • Indicator species signal ecosystem health; umbrella species protect many other species when their habitat is protected.
  • Specialists have narrow niches and are vulnerable to change; generalists adapt to many conditions.

Threats to biodiversity

Human activities are driving species loss at rates far above background extinction.
  • HIPPCO: habitat destruction, invasive species, pollution, human population growth, climate change, overexploitation.
  • Habitat fragmentation isolates populations and creates edge effects; corridors can reconnect habitat.
  • Invasive species often lack natural predators and can outcompete native species (zebra mussels, kudzu).
  • The Endangered Species Act, CITES and protected areas are major conservation tools.

Ecological succession and adaptation

Communities change over time after disturbance, and species adapt through natural selection.
  • Primary succession starts on bare rock or new land with no soil; pioneer species such as lichens build soil.
  • Secondary succession follows a disturbance, such as fire or farming, where soil remains, and proceeds faster.
  • Early successional species are fast-growing r-selected plants; later stages shift toward slower-growing, shade-tolerant species.
  • Natural selection acts on heritable variation; adaptations suit organisms to their environment.
Keystone species are defined by their effect, not their size or numbers.
Primary succession needs soil formation; secondary succession starts with soil already present.

Population growth and regulation

Populations grow exponentially until limits slow them.
  • Exponential growth produces a J-shaped curve; logistic growth levels off at carrying capacity (K), producing an S-shaped curve.
  • Density-dependent factors (disease, competition, predation) intensify as density rises; density-independent factors (storms, fires) act regardless of density.
  • r-selected species have many offspring and little parental care; K-selected species have few offspring with extensive care and are more vulnerable to extinction.
  • Survivorship curves: Type I (most live long, die old), Type II (constant death rate), Type III (most die young).

Human population dynamics

Demographers use rates and age structure to understand and project human populations.
  • Total fertility rate (TFR) is the average number of children per woman; replacement level is about 2.1 in developed countries.
  • Age-structure diagrams: a wide base means rapid growth, a straight-sided shape means slow or stable growth, a narrow base means decline.
  • Rule of 70: doubling time in years is about 70 divided by the percent growth rate.
  • Demographic transition: high birth and death rates, then falling death rates (rapid growth), then falling birth rates, then low and stable.
  • Growth rate = (birth rate - death rate) plus net migration, expressed as a percent.

Human impacts and carrying capacity

Resource use per person, as well as population, determines human impact.
  • IPAT: impact equals population times affluence times technology; wealthy countries have a much larger footprint per person.
  • Ecological footprint measures the land and water needed to supply a person's resources and absorb their waste.
  • Education and economic opportunity for women, access to family planning and lower infant mortality reduce fertility rates.
Replacement-level fertility is above 2.0 because some children die before reproducing.
Do not confuse growth rate (a percent) with doubling time (years); use 70 divided by the rate.

Plate tectonics and soil

Geologic processes shape landscapes and soil forms over long periods.
  • Divergent, convergent and transform plate boundaries explain earthquakes, volcanoes and mountain building.
  • Soil horizons from the top: O (organic), A (topsoil), E (eluviation), B (subsoil), C (parent material), then bedrock.
  • Soil texture depends on sand, silt and clay; loam balances them. Sandy soil drains fast; clay holds water but drains slowly.
  • Soil fertility depends on organic matter, nutrients, pH and the ability to hold water and nutrients.

Atmosphere and global wind patterns

Uneven solar heating and Earth's rotation drive weather and climate.
  • Layers: troposphere (weather), stratosphere (ozone layer), mesosphere, thermosphere.
  • More solar energy reaches the equator than the poles; warm air rises at the equator and sinks near 30 degrees, creating Hadley cells and deserts there.
  • The Coriolis effect deflects winds right in the Northern Hemisphere and left in the Southern; trade winds, westerlies and polar easterlies result.
  • A rain shadow forms on the leeward side of a mountain as air loses moisture while rising.

Oceans, seasons and climate patterns

Ocean circulation and Earth's tilt move heat around the planet.
  • Seasons result from the 23.5 degree axial tilt, not distance from the Sun.
  • Surface currents are driven by winds; thermohaline circulation is driven by differences in temperature and salinity (density).
  • El Nino brings warm surface water to the eastern Pacific, reduces upwelling and shifts weather; La Nina is the cool phase.
  • Upwelling brings nutrient-rich water to the surface and supports productive fisheries.
Seasons come from Earth's tilt, not its distance from the Sun.
Clay has tiny particles and high water-holding capacity, so it drains slowly; sand drains quickly.

Agriculture

Food production relies on land, water, energy and chemicals, each with environmental trade-offs.
  • Monocultures are efficient but vulnerable to pests; crop rotation, cover crops and polyculture improve soil and reduce pests.
  • Tilling causes erosion; no-till, contour plowing and terracing reduce soil loss.
  • Irrigation: flood irrigation wastes water and can cause salinization; drip irrigation is more efficient.
  • Fertilizer runoff causes eutrophication; integrated pest management (IPM) combines biological, cultural and limited chemical controls.
  • Concentrated animal feeding operations (CAFOs) produce large volumes of waste and use antibiotics; overgrazing can lead to desertification.

Fishing, forestry and mining

Harvesting natural resources can exceed sustainable yield.
  • Overfishing, bycatch and bottom trawling harm marine populations; aquaculture can ease pressure but pollutes and spreads disease.
  • Clear-cutting is cheap but causes erosion and habitat loss; selective cutting and certified forestry are more sustainable.
  • Surface mining includes strip and mountaintop removal; acid mine drainage lowers stream pH and mobilizes metals.
  • Sustainable yield is the harvest that does not reduce the resource's ability to renew.

Urbanization and water use

Cities concentrate people and change land and water systems.
  • Urban sprawl increases car use and consumes farmland; impervious surfaces raise runoff and flooding.
  • The urban heat island effect makes cities warmer than surrounding areas.
  • Dams provide water and power but alter flow, trap sediment and displace people.
  • Groundwater overdraft, as with the Ogallala Aquifer, drops water tables and causes land subsidence.
  • Tragedy of the commons: shared resources are overused when individuals act in their own interest.
Salinization comes from irrigation water evaporating and leaving salts behind.
Bycatch is the unintended catch of non-target species, not a type of aquaculture.

Fossil fuels

Fossil fuels supply most energy but cause pollution and carbon emissions.
  • Coal rank by carbon content: peat, lignite, bituminous, anthracite; coal releases the most CO2 and sulfur and mercury pollutants per unit of energy.
  • Oil and natural gas are formed from buried marine organisms; natural gas burns cleaner than coal and oil but methane leaks are a potent greenhouse gas.
  • Fracking injects fluid to release oil and gas but can contaminate groundwater and trigger small earthquakes.
  • Fossil fuels are nonrenewable on human timescales.

Nuclear and renewable energy

Low-carbon sources each have advantages and limits.
  • Nuclear fission splits uranium-235; it produces no CO2 during operation but creates long-lived radioactive waste and risk of accidents (Three Mile Island, Chernobyl, Fukushima).
  • Solar photovoltaics convert light to electricity; wind turbines convert wind's kinetic energy; both are intermittent and need storage or backup.
  • Hydroelectric power is reliable but affects rivers and fish; geothermal taps Earth's heat in suitable locations.
  • Biomass and biofuels can be carbon neutral if replanted but compete with food and land; hydrogen fuel cells emit only water if the hydrogen is produced cleanly.

Energy conversion and conservation

Efficiency and conservation reduce demand.
  • Energy conversions lose usable energy as heat; a power plant converts heat to electricity at about 35 to 40 percent efficiency.
  • Cogeneration uses waste heat from electricity production for heating, raising overall efficiency.
  • Conservation: insulation, efficient appliances, public transportation, smart grids and green building standards (LEED).
  • Units: a kilowatt-hour is the energy of one kilowatt used for one hour.
Nuclear power plants do not emit CO2 when operating, but the full life cycle and waste storage still have impacts.
Natural gas is cleaner than coal in CO2 per energy but leaked methane is a much stronger greenhouse gas than CO2.

Air pollutants and regulation

Air pollutants harm health and ecosystems and are regulated under the Clean Air Act.
  • Primary pollutants are emitted directly (CO, SO2, NOx, particulates, lead); secondary pollutants form in the atmosphere (ground-level ozone, sulfuric and nitric acids).
  • Criteria pollutants regulated by the EPA: carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter and sulfur dioxide.
  • Catalytic converters reduce CO, NOx and hydrocarbons from cars; scrubbers remove SO2 from power plant exhaust.
  • Particulate matter (PM2.5) penetrates deep into lungs and is linked to heart and lung disease.

Smog, acid deposition and inversions

Weather and chemistry combine to create pollution events.
  • Photochemical smog forms when nitrogen oxides and volatile organic compounds react in sunlight to produce ground-level ozone.
  • Industrial (gray) smog comes from burning coal and releases sulfur dioxide and particulates.
  • A temperature inversion traps cooler air under a layer of warm air and holds pollution near the ground.
  • Acid deposition forms from SO2 and NOx converting to sulfuric and nitric acid; it acidifies lakes, damages forests and corrodes buildings.

Indoor air and the ozone layer

Pollution occurs inside buildings and high in the atmosphere.
  • Indoor pollutants include radon (a radioactive gas from soil), asbestos, carbon monoxide, mold and volatile organic compounds.
  • Stratospheric ozone absorbs ultraviolet radiation; CFCs release chlorine that destroys ozone.
  • The Montreal Protocol phased out CFCs and is a model for international environmental agreements.
  • Ground-level ozone is harmful pollution, while stratospheric ozone is protective.
Ozone is 'good up high, bad nearby': stratospheric ozone protects us, ground-level ozone is a pollutant.
Acid deposition includes dry deposition as well as acid rain.

Water pollution

Pollutants enter water from point and nonpoint sources.
  • Point sources have a single identifiable discharge (a pipe); nonpoint sources are diffuse (fertilizer and urban runoff).
  • Eutrophication: excess nitrogen and phosphorus cause algal blooms; decomposition of dead algae lowers dissolved oxygen and can create dead zones.
  • Biochemical oxygen demand (BOD) measures the oxygen microorganisms need to break down organic waste.
  • Thermal pollution from power plants lowers oxygen solubility and stresses aquatic life.
  • Bioaccumulation builds up a toxin in an organism over time; biomagnification increases its concentration up the food chain (mercury, DDT).

Waste and hazardous materials

Waste management reduces harm and recovers resources.
  • Landfills produce leachate and methane; modern landfills have liners, leachate collection and gas capture.
  • Incineration reduces volume and can generate energy but emits pollutants and leaves toxic ash.
  • Reduce, reuse, recycle, and composting keep material out of landfills; reducing is the most effective step.
  • Superfund (CERCLA) funds cleanup of contaminated sites; RCRA regulates hazardous waste from creation to disposal.
  • Plastics persist for centuries and break into microplastics that enter food webs.

Wastewater, laws and human health

Treatment and regulation protect water and public health.
  • Wastewater treatment: primary (physical removal of solids), secondary (biological breakdown), tertiary (chemical removal of nutrients, disinfection).
  • The Clean Water Act regulates discharges into surface waters; the Safe Drinking Water Act sets standards for drinking water.
  • Dose-response curves and LD50 describe toxicity; infectious diseases such as cholera spread through contaminated water.
Biomagnification is concentration increasing up trophic levels; bioaccumulation is buildup within one organism.
The dead zone is caused by oxygen depletion after algae die and decompose, not by the algae directly using oxygen to bloom.

Greenhouse effect and climate change

Greenhouse gases trap heat, and human emissions have increased their concentrations.
  • The natural greenhouse effect keeps Earth warm; the enhanced greenhouse effect results from added CO2, methane, nitrous oxide and CFCs.
  • Global warming potential compares gases: methane and nitrous oxide trap more heat per molecule than CO2 but are less abundant.
  • Feedback loops: melting ice lowers albedo and amplifies warming (positive); increased cloud cover or plant growth can dampen it (negative).
  • Evidence includes rising temperatures, ice-core records, shrinking glaciers and sea-level rise.

Impacts of global change

Warming and related changes affect ecosystems and people.
  • Sea-level rise from thermal expansion and melting land ice threatens coastal communities and aquifers.
  • Ocean acidification: CO2 dissolves to form carbonic acid, lowering pH and harming corals and shellfish.
  • Species ranges shift, coral bleaching increases, and extreme weather events become more frequent.
  • Invasive species and habitat loss add to biodiversity decline.

Responses and solutions

Mitigation reduces emissions; adaptation prepares for change.
  • Mitigation: renewable energy, efficiency, carbon taxes, cap-and-trade, reforestation and carbon capture.
  • Adaptation: sea walls, drought-resistant crops, relocating communities.
  • International agreements include the Montreal Protocol, the Kyoto Protocol and the Paris Agreement.
  • Individual choices (transportation, diet, energy use) and policy both matter.
Weather is short-term; climate is the long-term average (about 30 years).
The ozone hole and global warming are different problems with different causes (CFCs versus CO2 and other greenhouse gases).
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Unit 1: The Living World: Ecosystems

Trophic level
A feeding position in a food chain, such as producer, primary consumer or secondary consumer.
Gross primary productivity (GPP)
The total rate at which producers capture energy through photosynthesis.
Net primary productivity (NPP)
GPP minus the energy producers use in respiration; the energy available to consumers.
10 percent rule
Only about 10 percent of the energy at one trophic level is passed on to the next.
Nitrogen fixation
Conversion of atmospheric nitrogen (N2) into ammonia by bacteria or lightning.
Denitrification
Conversion of nitrate into nitrogen gas by anaerobic bacteria, returning nitrogen to the atmosphere.
Limiting nutrient
The nutrient in shortest supply, which restricts growth in an ecosystem.
Estuary
A coastal area where fresh water from rivers mixes with salt water; highly productive.
Biome
A large region defined by its climate and characteristic plant and animal communities.
Detritivore
An organism, such as an earthworm, that feeds on dead organic matter.

Unit 2: The Living World: Biodiversity

Biodiversity
The variety of life, including genetic, species and ecosystem diversity.
Ecosystem services
Benefits that ecosystems provide to people, such as food, water filtration, pollination and recreation.
Keystone species
A species with a disproportionately large effect on its ecosystem relative to its abundance.
Indicator species
A species whose presence or condition reflects the health of an ecosystem.
Island biogeography
A theory that larger islands closer to a mainland have more species.
Habitat fragmentation
The breaking of a large habitat into smaller isolated patches.
Invasive species
A non-native species that spreads and harms ecosystems, often without natural predators.
Primary succession
Ecological change that begins on bare rock or new land without soil.
Secondary succession
Ecological change that follows a disturbance in an area where soil remains.
Pioneer species
The first species to colonize a barren or disturbed area, such as lichens.

Unit 3: Populations

Carrying capacity (K)
The maximum population size an environment can sustain over time.
Exponential growth
Growth at a constant percentage rate that produces a J-shaped curve.
Logistic growth
Growth that slows and levels off at carrying capacity, producing an S-shaped curve.
r-selected species
Species with many offspring, little parental care and rapid reproduction.
K-selected species
Species with few offspring, long lives and extensive parental care.
Density-dependent factor
A limiting factor whose effect grows with population density, such as disease.
Total fertility rate (TFR)
The average number of children a woman is expected to have in her lifetime.
Rule of 70
Doubling time in years is about 70 divided by the percent growth rate.
Demographic transition
The shift from high birth and death rates to low birth and death rates as a society develops.
Ecological footprint
The area of land and water needed to supply a person's resources and absorb their waste.

Unit 4: Earth Systems and Resources

Soil horizon
A distinct layer of soil, such as O, A, E, B or C.
Permeability
How easily water flows through soil.
Troposphere
The lowest layer of the atmosphere, where weather occurs.
Stratosphere
The atmospheric layer above the troposphere that contains the ozone layer.
Coriolis effect
The deflection of moving air and water caused by Earth's rotation.
Hadley cell
A large air circulation near the equator in which warm air rises and sinks near 30 degrees latitude.
Rain shadow
A dry region on the leeward side of a mountain range.
El Nino
A climate pattern with warm eastern Pacific surface water and reduced upwelling.
Upwelling
The rise of cold, nutrient-rich deep water to the ocean surface.
Thermohaline circulation
Deep ocean circulation driven by differences in water temperature and salinity.

Unit 5: Land and Water Use

Monoculture
Growing a single crop over a large area.
Crop rotation
Planting different crops in sequence on the same land to maintain soil fertility and reduce pests.
No-till farming
Planting crops without plowing to reduce erosion and retain moisture.
Salinization
Buildup of salts in soil, often caused by irrigation in dry regions.
Integrated pest management (IPM)
A strategy combining biological, cultural and limited chemical pest controls.
Bycatch
Unintended catch of non-target species in fishing.
Sustainable yield
The amount of a resource that can be harvested without reducing its ability to renew.
Acid mine drainage
Acidic water formed when water reacts with exposed sulfide minerals at mines.
Urban heat island
A city that is warmer than surrounding areas because of heat-absorbing surfaces.
Tragedy of the commons
Overuse and depletion of a shared resource by individuals acting in their own interest.

Unit 6: Energy Resources and Consumption

Anthracite
The highest rank of coal, with the greatest carbon and energy content.
Fracking
Hydraulic fracturing: injecting fluid underground to release trapped oil or natural gas.
Nuclear fission
Splitting of heavy atomic nuclei, such as uranium-235, to release energy.
Photovoltaic cell
A device that converts sunlight directly into electricity.
Biomass
Organic material, such as wood or crop waste, used as fuel.
Geothermal energy
Energy obtained from Earth's internal heat.
Hydrogen fuel cell
A device that combines hydrogen and oxygen to produce electricity and water.
Cogeneration
Using waste heat from electricity production for another purpose, increasing efficiency.
Kilowatt-hour
A unit of energy equal to one kilowatt used for one hour.
Intermittent energy source
A source, like solar or wind, whose output varies with weather and time.

Unit 7: Atmospheric Pollution

Primary pollutant
A pollutant emitted directly from a source, such as carbon monoxide.
Secondary pollutant
A pollutant formed by reactions among other pollutants in the atmosphere, such as ozone.
Photochemical smog
Air pollution formed when nitrogen oxides and VOCs react in sunlight to create ozone.
Temperature inversion
A layer of warm air over cooler air that traps pollutants near the ground.
Acid deposition
Wet or dry deposition of sulfuric and nitric acids formed from SO2 and NOx.
Catalytic converter
A car device that converts CO, NOx and hydrocarbons into less harmful gases.
Scrubber
A device that removes pollutants, such as sulfur dioxide, from exhaust gases.
Radon
A radioactive gas from soil and rock that can accumulate in buildings.
Chlorofluorocarbons (CFCs)
Chemicals that release chlorine in the stratosphere and destroy ozone.
Montreal Protocol
International agreement that phased out ozone-depleting substances.

Unit 8: Aquatic and Terrestrial Pollution

Point source
A single, identifiable source of pollution, such as a discharge pipe.
Nonpoint source
A diffuse source of pollution, such as agricultural or urban runoff.
Eutrophication
Nutrient enrichment that causes algal blooms and oxygen depletion in water.
Dead zone
An area of water with too little dissolved oxygen to support most life.
Biochemical oxygen demand (BOD)
The amount of oxygen microorganisms use to decompose organic matter in water.
Bioaccumulation
The buildup of a substance in an organism over time.
Biomagnification
The increase in concentration of a toxin at higher trophic levels.
Leachate
Liquid that has passed through waste and picked up contaminants.
Superfund (CERCLA)
U.S. law that funds and enforces cleanup of hazardous waste sites.
LD50
The dose of a substance that kills 50 percent of a test population.

Unit 9: Global Change

Greenhouse effect
Warming caused by gases in the atmosphere that trap outgoing heat.
Global warming potential
A measure of how much heat a gas traps compared with carbon dioxide.
Albedo
The fraction of sunlight reflected by a surface.
Positive feedback loop
A process in which a change causes further change in the same direction.
Ocean acidification
Lowering of ocean pH as seawater absorbs carbon dioxide.
Coral bleaching
Loss of color when stressed corals expel their symbiotic algae.
Mitigation
Actions that reduce greenhouse gas emissions or remove them from the atmosphere.
Adaptation
Actions that help people and ecosystems cope with the effects of climate change.
Carbon tax
A fee on carbon emissions meant to encourage reductions.
Cap-and-trade
A system that limits total emissions and lets participants trade emission permits.
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Unit 1: The Living World: Ecosystems

Energy transfer up a food chain
A grassland has 20,000 kcal of energy in producers. How much reaches secondary consumers using the 10 percent rule?

Unit 3: Populations

Doubling time with the rule of 70
A population grows 2.5 percent per year. About how long until it doubles?
Population growth rate
A country has 15 births and 7 deaths per 1000 people each year and no migration. What is the annual growth rate as a percent?

Unit 6: Energy Resources and Consumption

Energy use in kilowatt-hours
A 1500 W space heater runs 4 hours a day for 30 days. How many kWh does it use, and what does it cost at $0.12 per kWh?
Power plant efficiency
A power plant burns fuel containing 500 MJ and produces 150 MJ of electricity. What is its efficiency and how much energy is lost?

Unit 8: Aquatic and Terrestrial Pollution

Biomagnification calculation
A toxin is 0.5 ppm in algae. Each trophic level increases concentration tenfold. What is the concentration in a fish that is a tertiary consumer (algae to zooplankton to small fish to large fish)?
Dissolved oxygen and temperature
Why does a warm discharge from a power plant lower dissolved oxygen downstream?

Unit 9: Global Change

Carbon emissions from driving
A car gets 25 miles per gallon and burning one gallon of gasoline releases about 20 pounds of CO2. How much CO2 is released driving 500 miles?
Explaining a positive feedback loop
Explain how melting Arctic sea ice is a positive feedback loop.

Unit 1: The Living World: Ecosystems

Energy flow and trophic levels
Energy enters ecosystems as sunlight and moves up trophic levels with large losses at each step.
Biogeochemical cycles
Matter cycles through living and nonliving pools, and human activity speeds up or alters the flows.
Terrestrial and aquatic biomes
Climate (temperature and precipitation) largely determines the distribution of biomes.
Photosynthesis and respiration
These two processes link energy flow and carbon cycling.

Unit 2: The Living World: Biodiversity

Levels of biodiversity and ecosystem services
Biodiversity includes genetic, species and ecosystem diversity, and healthy ecosystems provide services to people.
Island biogeography and species roles
Species number depends on island size and distance, and some species have outsized roles.
Threats to biodiversity
Human activities are driving species loss at rates far above background extinction.
Ecological succession and adaptation
Communities change over time after disturbance, and species adapt through natural selection.

Unit 3: Populations

Population growth and regulation
Populations grow exponentially until limits slow them.
Human population dynamics
Demographers use rates and age structure to understand and project human populations.
Human impacts and carrying capacity
Resource use per person, as well as population, determines human impact.

Unit 4: Earth Systems and Resources

Plate tectonics and soil
Geologic processes shape landscapes and soil forms over long periods.
Atmosphere and global wind patterns
Uneven solar heating and Earth's rotation drive weather and climate.
Oceans, seasons and climate patterns
Ocean circulation and Earth's tilt move heat around the planet.

Unit 5: Land and Water Use

Agriculture
Food production relies on land, water, energy and chemicals, each with environmental trade-offs.
Fishing, forestry and mining
Harvesting natural resources can exceed sustainable yield.
Urbanization and water use
Cities concentrate people and change land and water systems.

Unit 6: Energy Resources and Consumption

Fossil fuels
Fossil fuels supply most energy but cause pollution and carbon emissions.
Nuclear and renewable energy
Low-carbon sources each have advantages and limits.
Energy conversion and conservation
Efficiency and conservation reduce demand.

Unit 7: Atmospheric Pollution

Air pollutants and regulation
Air pollutants harm health and ecosystems and are regulated under the Clean Air Act.
Smog, acid deposition and inversions
Weather and chemistry combine to create pollution events.
Indoor air and the ozone layer
Pollution occurs inside buildings and high in the atmosphere.

Unit 8: Aquatic and Terrestrial Pollution

Water pollution
Pollutants enter water from point and nonpoint sources.
Waste and hazardous materials
Waste management reduces harm and recovers resources.
Wastewater, laws and human health
Treatment and regulation protect water and public health.

Unit 9: Global Change

Greenhouse effect and climate change
Greenhouse gases trap heat, and human emissions have increased their concentrations.
Impacts of global change
Warming and related changes affect ecosystems and people.
Responses and solutions
Mitigation reduces emissions; adaptation prepares for change.
Common mistakes for each unit — read the mistake, then make sure you know why it's wrong.

Unit 1: The Living World: Ecosystems

Watch out
Energy flows in one direction and is lost as heat; matter cycles. Do not say energy 'cycles' through ecosystems.
Watch out
Decomposers are not a trophic level that 'eats' the others for energy; they recycle nutrients from all levels.

Unit 2: The Living World: Biodiversity

Watch out
Keystone species are defined by their effect, not their size or numbers.
Watch out
Primary succession needs soil formation; secondary succession starts with soil already present.

Unit 3: Populations

Watch out
Replacement-level fertility is above 2.0 because some children die before reproducing.
Watch out
Do not confuse growth rate (a percent) with doubling time (years); use 70 divided by the rate.

Unit 4: Earth Systems and Resources

Watch out
Seasons come from Earth's tilt, not its distance from the Sun.
Watch out
Clay has tiny particles and high water-holding capacity, so it drains slowly; sand drains quickly.

Unit 5: Land and Water Use

Watch out
Salinization comes from irrigation water evaporating and leaving salts behind.
Watch out
Bycatch is the unintended catch of non-target species, not a type of aquaculture.

Unit 6: Energy Resources and Consumption

Watch out
Nuclear power plants do not emit CO2 when operating, but the full life cycle and waste storage still have impacts.
Watch out
Natural gas is cleaner than coal in CO2 per energy but leaked methane is a much stronger greenhouse gas than CO2.

Unit 7: Atmospheric Pollution

Watch out
Ozone is 'good up high, bad nearby': stratospheric ozone protects us, ground-level ozone is a pollutant.
Watch out
Acid deposition includes dry deposition as well as acid rain.

Unit 8: Aquatic and Terrestrial Pollution

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Biomagnification is concentration increasing up trophic levels; bioaccumulation is buildup within one organism.
Watch out
The dead zone is caused by oxygen depletion after algae die and decompose, not by the algae directly using oxygen to bloom.

Unit 9: Global Change

Watch out
Weather is short-term; climate is the long-term average (about 30 years).
Watch out
The ozone hole and global warming are different problems with different causes (CFCs versus CO2 and other greenhouse gases).