Integrated Study Notes: The Living World, Biomes, and Biogeochemical Cycles (ERT-1 Series)

The Living World (ERT-1.A)

• Learning objective: ERT-1.A — Explain how the availability of resources influences species interactions.
• Suggested skill: 1.A — Concept explanation: Describe environmental concepts and processes.
• Essential knowledge:
  • ERT-1.A.1: In a predator-prey relationship, the predator is an organism that eats another organism (the prey).
  • ERT-1.A.2: Symbiosis is a close and long-term interaction between two species in an ecosystem. Types include mutualism, commensalism, and parasitism.
  • ERT-1.A.3: Competition can occur within or between species where resources are limited. Resource partitioning—using resources in different ways, places, or times—can reduce the negative impact of competition on survival.

Ecosystem Basics (Page 2)

• Key terms:
  • Individual = one organism (e.g., elk)
  • Population = group of individuals of the same species (elk herd)
  • Community = all living organisms in an area
  • Ecosystem = all living and nonliving things in an area (plants, animals, rocks, soil, water, air)
• Biotic vs. Abiotic factors
• Biome = the plants and animals found in a given region (determined by climate); example: tropical rainforest

Organism Interactions (Page 3)

• Mutualism: relationship that benefits both organisms (e.g., coral reef mutualism with algae)
• Competition: organisms competing for a resource (food, shelter); limits population size
• Predation: one organism uses another for energy (predators, parasites)
• Commensalism: one organism benefits; the other is not impacted (e.g., birds nesting in trees)

Predation (+/-) (Page 4)

• True predators: carnivores that kill and eat prey for energy (e.g., leopard and gazelle example)
• Herbivores: eat plants for energy (e.g., giraffe and tree)
• Parasites: use a host for energy, often without killing the host and often living inside the host (e.g., mosquitoes, tapeworms, sea lamprey)

Symbiosis (Page 5)

• Etymology: sym = together, bio = living, osis = condition
• Mutualism (+/+): organisms of different species living close together in a way that benefits both (e.g., coral and algae)
• Symbiotic relationships include mutualism (+/+), commensalism (+/0), and parasitism (+/-)
• Examples:
  • Coral (animals) provide reef structure and CO2 for algae; algae provide sugars for coral energy
  • Lichen = composite organism of fungi living with algae; algae provide sugars and fungi provide nutrients

Competition and Resource Partitioning (Page 6)

• Resource partitioning: different species use the same resource in different ways to reduce competition
• Effects: reduces population size due to limited resources but allows coexistence
• Partitioning types:
  • Temporal partitioning: using resources at different times (e.g., wolves and coyotes hunting at night vs. day)
  • Spatial partitioning: using different areas of a shared habitat (e.g., different root depths)
  • Morphological partitioning: using different resources based on evolved body features

Practice FRQ 1.1 (Page 7)

• Prompt: Identify two organisms that compete for a shared food resource. Describe how resource partitioning could reduce the competition between the two organisms you identified.

Terrestrial Biomes (1.2) (Pages 8-14)

• Learning objective: ERT-1.B — Describe the global distribution and principal environmental aspects of terrestrial biomes.
• Key concepts:
  • A biome contains characteristic communities adapted to its climate (ERT-1.B.1)
  • Major terrestrial biomes include: taiga, temperate rainforests, temperate seasonal forests, tropical rainforests, shrubland, temperate grassland, savanna, desert, tundra (ERT-1.B.2)
  • Global distribution of nonmineral terrestrial natural resources (e.g., water, trees) varies with climate, geography, latitude, altitude, nutrient availability, and soil (ERT-1.B.3)
  • The worldwide biome distribution is dynamic and can shift with climate change (ERT-1.B.4)
• Biome basics:
  • Defined by average annual temperature and precipitation
  • Latitude affects temperature and precipitation: tundra (higher lat, 60° or more), temperate (30°–60°), tropical near the equator
  • Latitude pattern predicts biome locations on Earth
• Nutrient availability in soils:
  • Tropical rainforest: nutrient-poor soil due to rapid decomposition but leaching from high rainfall and acidic soils
  • Temperate forests: nutrient-rich soils with abundant litter and decomposition
  • tundra: frozen soils limit decomposition, resulting in low soil nutrients and low water availability
• Shifting biomes:
  • Climate change can shift biome distributions (e.g., boreal forests moving north as tundra permafrost melts)

Practice FRQ 1.2 (Page 14)

• Prompt: Identify one characteristic of a biome and explain how that characteristic determines the community of organisms found in the biome.

Aquatic Biomes (1.3) (Pages 15-25)

• Objective: ERT-1.C — Describe the global distribution and principal environmental aspects of aquatic biomes.
• Key points:
  • Freshwater biomes include streams, rivers, ponds, lakes; vital for drinking water
  • Marine biomes include oceans, coral reefs, marshlands, estuaries; algae in marine biomes provide a large portion of Earth's oxygen and absorb CO2
  • Global distribution of nonmineral marine resources (e.g., fish) depends on salinity, depth, turbidity, nutrients, and temperature
• Characteristics of aquatic biomes depend on:
  • Depth: light penetration for photosynthesis
  • Temperature: oxygen solubility; warmer water holds less dissolved O2
  • Salinity: determines species composition and drinking suitability
  • Flow: affects species survival and oxygen availability
• Freshwater: Rivers & lakes
  • Rivers have high O2 due to flow; carry nutrient-rich sediments; deltas/flood plains yield fertile soils
  • Lakes: littoral (shallow, emergent plants), limnetic (open water with phytoplankton; no rooted plants), profundal (deep, no sunlight), benthic (bottom with inverts and nutrient-rich sediments)
• Wetlands: submerged or saturated soil part of the year; plants adapted to submerged roots (cattails, lily pads, reeds); ecosystem services include flood mitigation, groundwater recharge, pollutant filtration, high productivity
• Wetland types and examples: Swamps, Marshes, Reeds & cattails, Cypress wetlands, Bog, Spruce & sphagnum moss
• Estuaries: rivers meeting the ocean; mix of fresh and salt water; high productivity due to nutrient-rich sediments; habitat examples: mangroves, salt marshes, mangrove swamps
• Coral Reefs: warm, shallow waters; most diverse marine biome; mutualism between coral and algae; coral provide CO2 and structure; algae provide sugars; mutually dependent
• Intertidal Zones: narrow band along coast between high and low tides; organisms adapted to waves and exposure; examples: barnacles, sea stars, crabs; adaptations include desiccation resistance
• Open Ocean: low productivity per m² outside photic zone; photic zone supports photosynthesis; aphotic zone relies on detritus or chemosynthesis near hydrothermal vents; vast contributor to Earth's O2 and CO2 balance

Practice FRQ 1.3 (Page 25)

• Prompt: Identify an organism found in an aquatic biome and explain how that organism is uniquely adapted to live in that biome.

Carbon Cycle (1.4) (Pages 26-33)

• Learning objective: ERT-1.D — Explain the steps and reservoir interactions in the carbon cycle.
• Key concepts:
  • The carbon cycle moves atoms/molecules containing carbon between sources and sinks
  • Some reservoirs hold carbon for long periods (long-term storage); others hold it for short periods
  • Carbon cycles between photosynthesis and cellular respiration in living things
  • Plant and animal decomposition stores carbon over millions of years; burning fossil fuels quickly moves stored carbon into the atmosphere as CO₂
• Core terminology:
  • Carbon sink: reservoir that takes in more carbon than it releases (e.g., oceans, plants, soils)
  • Carbon source: reservoir that releases more carbon than it takes in (e.g., burning fossil fuels, deforestation, certain agricultural practices)
• Key processes and equations:
  • Photosynthesis: ext{CO}2 + ext{H}2 ext{O}
    ightarrow ( ext{CH}2 ext{O}) + ext{O}2
  • Respiration: reverse of photosynthesis, releasing CO₂
  • Direct exchange: CO₂ moves between the atmosphere and the ocean by dissolving at the surface; rapid and roughly balanced
  • Algae and phytoplankton remove CO₂ from the ocean/atmosphere via photosynthesis
  • Calcium carbonate formation: reef-building organisms use CO₂ to form CaCO₃ exoskeletons; sedimentation/burial moves carbon to deep ocean sediments over long timescales
  • Sedimentation and burial: long-term storage of carbon in sediments/rock (limestone, sandstone)
  • Burial and fossil fuels: Formation of fossil fuels from buried organic matter; extraction and combustion release CO₂ back to the atmosphere; burial forms FFs much more slowly than extraction/combustion
• Reservoirs and flows:
  • Atmosphere is a key carbon reservoir; rising atmospheric CO₂ is linked to global warming
  • A CO₂ sink includes oceans, plants, and soils; CO₂ sources include fossil fuel combustion, certain agricultural practices, and deforestation
• Important distinctions:
  • CO₂ sink vs CO₂ source; fast vs slow processes; human influence accelerates transfer of carbon to the atmosphere via combustion of FFs

Practice FRQ 1.4 (Page 32)

• Prompt: Identify one process in the diagram that happens quickly and one that happens slowly. Explain how the rate at which fossil fuels are transferred into the atmosphere, as shown in the diagram, has altered the carbon cycle during the past 250 years.
• Additional Carbon Cycle Resource: NASA (reference given in the material)

Nitrogen Cycle (1.5) (Pages 33-39)

• Learning objective: ERT-1.E — Explain the steps and reservoir interactions in the nitrogen cycle.
• Key concepts:
  • The nitrogen cycle moves nitrogen between sources and sinks; most reservoirs hold nitrogen for relatively short periods (short vs long timescales)
  • Atmospheric nitrogen (N₂) is the major reservoir and is largely unusable by most organisms unless fixed
• Nitrogen fixation:
  • Abiotic: lightning converts N₂ to nitrate NO₃⁻ and fossil fuel combustion converts N₂ to ammonia NH₃
  • Biotic: certain bacteria (in soil or in plant root nodules) convert N₂ into NH₃ (ammonia); rhizobacteria in legume nodules form a mutualism with plants
  • NH₃ can be further processed into NO₃⁻ via nitrification and taken up by plants
• Other steps:
  • Nitrification: NH₄⁺ → NO₂⁻ → NO₃⁻ by soil bacteria
  • Ammonification: decomposers convert waste into NH₃, returning nitrogen to soil
  • Assimilation: plants uptake NO₃⁻ or NH₃ and incorporate N into biomass; animals acquire N by eating plants or other animals
  • Denitrification: NO₃⁻ is reduced to N₂O and N₂, returning N to the atmosphere
• Human impacts:
  • Leaching and eutrophication: synthetic fertilizers increase nitrate leaching, causing nutrient loading in water bodies; excessive N₂O emission contributes to greenhouse warming
  • Nitrates runoff leads to algal blooms and oxygen depletion in aquatic systems
• Practice FRQ 1.5:
  • Describe one chemical transformation in the natural nitrogen cycle and explain its importance to an ecosystem.

Phosphorus Cycle (1.6) (Pages 40-47)

• Learning objective: ERT-1.F — Explain the steps and reservoir interactions in the phosphorus cycle.
• Key concepts:
  • Phosphorus cycle involves movement of phosphorus between sources and sinks; major reservoirs are rock and sediment containing phosphate minerals
  • There is no atmospheric component in the phosphorus cycle; phosphorus is naturally scarce due to the absence of atmospheric cycling
  • Phosphorus is a limiting nutrient in undisturbed ecosystems
• Cycle basics:
  • Weathering of P-bearing rocks releases phosphate (PO₄³⁻) into soils and water; natural weathering is a slow process
  • Biotic uptake: plants and animals assimilate phosphate into tissues
  • Decomposition and excretion return phosphate to soil
  • Phosphate tends to precipitate as solid forms and settle to the bottom; sedimentation slowly cycles phosphate into sediments
  • Over long timescales, sedimentary rock formation can bury phosphate; uplift can re-expose rocks to weathering
• Human impacts and eutrophication:
  • Mining of phosphate minerals and use in synthetic fertilizers increases phosphate runoff into water bodies
  • Phosphates from detergents and wastewater contribute to eutrophication when discharged into waterways
• Eutrophication cascade (N & P):
  • Excess nutrients fuel algal blooms; sunlight is blocked; plants die; decomposition consumes oxygen, potentially creating hypoxic or anoxic conditions
  • Positive feedback loop: less O₂ → more dead matter → more decomposition → further O₂ depletion
• Practice FRQ 1.6:
  • Choose two reservoirs in the diagram and describe how phosphorus moves from one to the other

Hydrologic Cycle (1.7) (Pages 48-53)

• Learning objective: ERT-1.G — Explain the steps and reservoir interactions in the hydrologic cycle.
• Key concepts:
  • The hydrologic cycle is powered by the sun and involves the movement of water among solid, liquid, and gaseous phases between sources and sinks
  • Oceans are the primary surface water reservoir; ice caps and groundwater are smaller but essential reservoirs
• Main processes:
  • Evaporation: liquid water becomes water vapor, driven by solar energy
  • Evapotranspiration: combined evaporation and plant transpiration
  • Transpiration: plants draw groundwater from roots to leaves; stomata release water vapor
  • Runoff: surface water flow to bodies of water
  • Infiltration: water enters soil and groundwater through permeable soils
  • Groundwater flow and recharge: refill of aquifers by infiltration
• Practical implications:
  • Precipitation recharges groundwater and surface waters; runoff can carry pollutants into water sources

Primary Productivity (1.8) (Pages 54-60)

• Learning objective: ENG-1.A — Explain how solar energy is acquired and transferred by living organisms.
• Key definitions:
  • Primary productivity (PP): rate at which solar energy is converted into organic compounds via photosynthesis per unit time
  • Gross primary productivity (GPP): total rate of photosynthesis in an area
  • Net primary productivity (NPP): energy stored as biomass after subtracting plant respiration (RL)
  • Productivity units: ext{kcal}/ ext{m}^2/ ext{yr} (energy per unit area per unit time)
• Light penetration in aquatic systems:
  • Most red light absorbed in the upper 1 m; blue light penetrates deeper than 100 m in clear water; this affects photosynthesis in aquatic environments
• Common relationships:
  • NPP = GPP − RL
  • Higher PP leads to greater biomass and typically higher biodiversity
• Ecological efficiency:
  • Only about 1% of incoming solar energy is captured and converted into GPP; approximately 40% of that (≈0.4% of total) becomes biomass as NPP
  • Efficiency varies among ecosystems
• Factors affecting productivity:
  • Water availability, temperature, and nutrient availability are major drivers of NPP
  • Predictions: deserts and tundra have low PP due to water/temperature limitations; open ocean productivity is limited by nutrient supply
• Trends and applications:
  • More productive biomes support greater biodiversity
  • Ecologists predict most productive terrestrial and aquatic biomes by considering water, temperature, and nutrients
• Practice FRQ 1.8:
  • Describe the process of net primary productivity (NPP) and the relationship between primary productivity and biodiversity

Trophic Levels and the 10% Rule (1.9 & 1.10) (Pages 61-68)

• Learning objective: ENG-1.B — Explain how energy flows and matter cycles through trophic levels.
• Key concepts:
  • All ecosystems require a continuous input of high-quality energy to support matter transfer via biogeochemical cycles
  • Biogeochemical cycles conserve matter; energy is conserved in the sense of transfer through trophic levels though some is lost as heat
  • In terrestrial and near-surface marine communities, energy flows from the sun to producers (lowest trophic level) and upward to higher trophic levels
• The 10% rule (ENG-1.C):
  • Approximately 10% of energy is transferred from one trophic level to the next
  • The rest is lost as heat or used for respiration and metabolic processes (law of thermodynamics)
  • Equation perspective: if
  • E{ ext{producer}} = E0 then
  • E{ ext{primary}} oughly = 0.1 E0,
  • E{ ext{secondary}} oughly = 0.01 E0,
  • and so on
• Thermodynamics and conservation:
  • 1st law: energy cannot be created or destroyed; it only changes form
  • 2nd law: energy transfer is inefficient; energy becomes less usable at higher levels
• Biomass and energy transfer:
  • Biomass transfer also follows the 10% rule: only about 10% of biomass at one level supports biomass at the next
  • Example progression (illustrative): Producers 8,000 kg → Primary consumers 800 kg → Secondary consumers 80 kg → Tertiary consumers 8 kg (illustrative numbers from notes)
• Calculations:
  • To estimate biomass at the next level, move the decimal point one place to the left: e.g., 8,000 kg → 800 kg
• Practice FRQ 1.9 & 1.10:
  • Explain why a relatively large forest can support only a small number of wolves
  • Calculate energy available to a tertiary consumer given energy produced by plants (e.g., 100,000 J of energy produced by plants after respiration)

Food Chains, Food Webs, and Trophic Cascades (1.11) (Pages 69-74)

• Food web concept:

  • A food web is an interlocking pattern of two or more food chains; it depicts the flow of energy and nutrients across multiple species

• Food chains vs. food webs:

  • Food chains are linear paths of energy transfer, while food webs show multiple interconnected chains

• Arrows in food webs indicate direction of energy flow

• Trophic cascades and feedbacks:

  • Changes in population size of one species can impact many others in the web
  • A top predator decline can cause a cascade: e.g., wolves decline → deer increase → overgrazing → tree decline; this is a trophic cascade

• Practice FRQ 1.11:

  • Describe one direct effect of a decline in frog population on the food web
  • Identify an organism that serves as both a secondary and a tertiary consumer

• Connections across sections and real-world relevance:

  • Resource availability and niche differentiation influence competition, predation, and symbiosis in communities
  • Biome distribution is shaped by climate and nutrient dynamics, and is shifting with climate change
  • Aquatic systems illustrate how nutrients cycle through water bodies, with human activities (fertilizers, wastewater) driving eutrophication
  • Biogeochemical cycles (C, N, P, H2O) show conservation principles and how human actions perturb these cycles, with implications for climate, fertility, and water quality
  • Primary productivity links solar energy capture to energy transfer through trophic levels, affecting biodiversity and ecosystem services

• Key equations and concepts to memorize:

  • Net primary productivity: ext{NPP} = ext{GPP} - ext{RL}
  • Energy transfer between trophic levels: E{ ext{next}} oughly= 0.1 imes E{ ext{current}}
  • Open vs closed cycles; reservoirs, sinks, and sources in C, N, P cycles
  • Photosynthesis and respiration as complementary processes for carbon exchange
  • Eutrophication sequence: nutrient load → algal blooms → reduced light → plant die-off → decomposition consumes oxygen → hypoxia; potential positive feedback

• Real-world relevance and ethics:

  • Managing nutrient runoff (agriculture, wastewater) to prevent eutrophication
  • Conservation of keystone predators to balance ecosystems and prevent trophic cascades
  • Climate policy implications tied to carbon cycle dynamics and ocean acidification

Quick reference: Key terms and definitions

• Abiotic vs. biotic: nonliving vs. living components of an ecosystem

• Biome: large ecological unit defined by climate and the communities it supports

• Symbiosis: close, long-term interaction between two different species; includes mutualism, commensalism, parasitism

• Competition: interaction where organisms contend for limited resources

• Predator, prey, herbivore, parasite: different consumer roles in food webs

• Carbon cycle reservoirs: atmosphere, oceans, vegetation, soils, sediments; processes include photosynthesis, respiration, decomposition, burial, combustion

• Nitrogen cycle reservoirs: atmosphere (N₂), soil, plants, animals; processes include fixation, nitrification, ammonification, assimilation, denitrification

• Phosphorus cycle reservoirs: rocks and sediments; no atmospheric component; processes include weathering, assimilation, sedimentation, uplift

• Hydrologic cycle reservoirs: ocean, atmosphere, groundwater, rivers, lakes, glaciers; processes include evaporation, transpiration, precipitation, infiltration, runoff

• Primary productivity metrics: GPP, NPP; units kcal/m²/yr; productivity depends on light, nutrients, and temperature

• Trophic levels and 10% rule: energy transfer between levels is about 10% efficient; biomass transfer similarly limited

• Food chain vs. food web: linear vs. network representations of energy transfer

• Essential equations to remember:

  • Photosynthesis (simplified): ext{CO}2 + ext{H}2 ext{O}
    ightarrow ( ext{CH}2 ext{O}) + ext{O}2
  • Net primary productivity: ext{NPP} = ext{GPP} - ext{RL}
  • Trophic energy transfer: E{ ext{next}} oughly= 0.1 imes E{ ext{current}}

• Notable numerical anchors:

  • Biome latitudinal tendencies: tundra at higher latitudes (approximately ≥ 60°), temperate regions at mid-latitudes (≈ 30°–60°), tropical biomes near the equator
  • Productivity units: ext{kcal}/ ext{m}^2/ ext{yr}
  • Nutrient-poor soils in tropical rainforest vs. nutrient-rich soils in temperate forests; tundra with frozen soils limiting decomposition