Unit 1 Living Systems
1. Ecosystems
Core concept: An ecosystem includes all living (biotic) and nonliving (abiotic) components in an area and the interactions among them.
Key definitions:
Individual = one organism (e.g., an elk)
Population = group of individuals of the same species (elk herd)
Community = all living organisms in an area
Ecosystem = all living & nonliving things in an area (plants, animals, rocks, soil, water, air)
Biome = a large area with similar climate conditions that determine which plant and animal species occur there (e.g., tropical rainforest)
Biosphere: the global region of life; a combination of all ecosystems on Earth.
Ecosystem boundaries and connections:
Some ecosystems (caves, lakes) have distinct boundaries; many lack clear boundaries, making study harder.
One ecosystem can interact with another (e.g., birds migrating), so environmental degradation in one can impact others.
Moving energy and matter through ecosystems:
Energy flows through trophic structures; nutrients cycle via biogeochemical cycles.
Ecosystems rely on interactions among organisms and between organisms and their physical environment.
Producers and autotrophs:
Producers use solar energy to produce usable energy; autotrophs.
Photosynthesis: \text{CO}2 + \text{H}2\text{O} \rightarrow \text{C}6\text{H}{12}\text{O}6 + \text{O}2
Some deep-ocean organisms use chemosynthesis (chemicals from hydrothermal vents) to make energy.
Consumers and heterotrophs:
Consumers eat producers or other consumers; perform cellular respiration.
Aerobic cellular respiration (with oxygen): \text{C}6\text{H}{12}\text{O}6 + 6\,\text{O}2 \rightarrow 6\,\text{CO}2 + 6\,\text{H}2\text{O} + \text{energy}
Anaerobic respiration occurs without oxygen and yields energy with alternative terminal electron acceptors.
Energy transfer and trophic structure:
Trophic levels are successive levels of organisms consuming another.
Primary producers form the base; herbivores are primary consumers; carnivores occupy higher levels; detritivores and decomposers recycle nutrients.
Food webs vs. food chains:
A food chain is a single pathway of energy flow; a food web is an interlocking network of many chains.
Arrows indicate the direction of energy flow from the resource to the consumer.
Symbiosis and interactions:
Mutualism: both parties benefit (e.g., coral and algae in coral reefs).
Commensalism: one benefits, the other is unaffected (e.g., birds nesting in trees).
Parasitism: one benefits at the expense of the other.
Organism interactions (examples):
Mutualism (coral-algae): coral provides reef structure and CO2 to algae; algae provide sugars to coral.
Lichen: composite organism of fungi and algae; algae provide sugars, fungi provide nutrients.
Competition: two species competing for resources reduces population sizes; leading to resource partitioning or decreased coexistence.
Predation: one organism preys on another for energy; examples include predators and parasites on hosts.
Predation types and energy capture:
True predators (carnivores) kill and eat prey for energy (carnivory).
Herbivores eat plants for energy (herbivory).
Parasites live on/within a host organism for energy, often without killing the host (parasitism).
Parasitoids lay eggs in a host; larvae consume the host (parasitism).
Pathogens and coevolution:
Pathogens include viruses, bacteria, fungi, protists, and helminths.
Coevolution: prey/predator adaptations evolve in response to each other.
Exotic/alien vs. native species:
Native species are evolved in the ecosystem; exotic/alien species originate elsewhere.
Invasive exotic species spread rapidly and can harm native ecosystems.
Explanatory frameworks: Exclusion principle, resource partitioning, and ecological niches:
Competition Exclusion Principle: Two species competing for the same resource cannot stably coexist.
Resource partitioning: species use the same resource in different ways or times to reduce competition (temporal, spatial, morphological partitioning).
Examples of partitioning (dietary/niche): woodpeckers and vegetarian finches partition resources; seed size niches can separate competitors.
Biogeographic shifts and climate change:
Biomes shift with climate change (e.g., boreal forest moving north as permafrost melts).
Not all species can track shifting conditions due to sunlight/light requirements and other constraints.
1.1 Terrestrial Biomes
Objectives: Describe global distribution and environmental aspects of terrestrial biomes.
Essential knowledge:
A biome’s characteristics arise from climate; plants and animals adapt accordingly.
Major terrestrial biomes and their properties; global resource distribution varies with climate, geography, latitude, altitude, nutrient availability, soil.
Biome distributions are dynamic and may shift with climate change.
Biome concepts:
Biome = area sharing average yearly temperature and precipitation; examples include tundra, taiga, deserts, tropical rainforest, etc.
Habitat vs biome: habitat is where a species lives; biome is climate-driven community with dominant plant forms.
Climate diagrams (climatograms): visualize regional temperature and precipitation patterns (double-y axis).
General biome groups: tundra/taiga, temperate, tropical; nine main biomes: tundra, taiga, temperate rainforest, temperate seasonal forest, shrubland, temperate grassland, tropical rainforest, savanna, hot desert.
Latitudinal patterns:
Tundra & boreal at high latitudes; temperate biomes at mid-latitudes; tropical biomes near the equator.
Latitude determines temperature and precipitation, leading to predictable global biome patterns.
Soil nutrients and productivity:
Tropical rainforest: nutrient-poor soils due to rapid uptake by dense vegetation.
Boreal forest: nutrient-poor soils due to cold temperatures and slow decomposition.
Temperate forest: nutrient-rich soils from leaf litter decomposition.
Tundra: nutrient availability limited by frozen soils that slow decomposition.
Examples of key biomes:
Tundra (permafrost), Taiga (boreal forest), Temperate rainforest, Temperate seasonal forest, Shrubland, Woodland/Shrubland, Tropical rainforest, Savanna, Hot desert.
Deforestation and Brazilian Amazon (illustrative drivers):
Annual forest loss measured in hectares; drivers include deforestation, degradation, roads, mining, pasture, soy, and infrastructure.
Data illustrate rates over time and the mix of drivers.
Shifting biomes and climate change:
Warming climate shifts boreal forests northward; some species cannot migrate quickly due to sun/light requirements or slower reproduction.
1.3 Aquatic Biomes
Objectives: Describe global distribution and environmental aspects of aquatic biomes.
Essential knowledge:
Freshwater biomes: streams, ponds, lakes; essential for drinking water.
Marine biomes: coral reefs, marshlands, estuaries; algae in marine biomes supply a large portion of Earth’s oxygen and absorb CO2.
Global distribution of marine resources varies with salinity, depth, turbidity, nutrient availability, and temperature.
Basic water distribution (global): oceans dominate surface water; freshwater makes up ~2.78% of all water, with groundwater and surface water as key sources; most fresh water is locked in ice/glaciers.
Aquatic biome characteristics:
Depth: light penetration affects photosynthesis; deeper waters receive less light.
Temperature: warmer water holds less dissolved O2, supporting fewer organisms.
Salinity: determines which species survive and whether water is drinkable.
Flow: influences plant/animal survival and O2 dissolution.
Freshwater biomes:
Rivers & streams: high O2 due to flow; carry nutrient-rich sediments; deltas and floodplains are fertile.
Lakes & ponds: productivity-based classifications:
Oligotrophic: low productivity
Mesotrophic: moderate productivity
Eutrophic: high productivity; algal blooms can reduce light, cause turbidity.
Wetlands: water-saturated soils for part of the year; plants adapted to submerged roots; ecological services include flood buffering, groundwater recharge, pollutant filtration, and high productivity due to abundant nutrients.
Estuaries and coastal zones:
Estuaries: mix of freshwater and saltwater; high plant productivity due to nutrient-rich sediments; sun exposure supports diverse life; examples include mangrove swamps and salt marshes.
Mangrove swamps: shoreline stabilization, habitat for fish and shellfish; estuary habitats in temperate and tropical climates.
Coral reefs:
Warm, shallow tropical waters; most diverse marine biome; mutualism between corals (animals) and algae (plants);
Corals build calcium carbonate exoskeletons; algae provide sugars via photosynthesis; both depend on each other.
Coral bleaching: heat kills algae inside corals, causing whitening and potential reef collapse.
Intertidal zones:
Narrow band between high and low tide; organisms adapted to waves and heat; examples include barnacles, sea stars, crabs; adaptations to prevent desiccation (desiccation resistance).
Open ocean:
Low productivity per area, but vast; photic zone supports photosynthesis; aphotic zone lacks light and relies on chemosynthesis; ocean algae/phytoplankton contribute a large portion of Earth's O2 and CO2 uptake.
Summary table concept:
Freshwater vs marine: salinity, depth, water flow patterns differ; standing water vs flowing water; depth and light penetration influence productivity and community composition.
1.4 Carbon Cycle
Objective: Explain steps and reservoir interactions in the carbon cycle.
Essential knowledge:
Carbon cycle = movement of carbon-containing atoms/molecules between sources and sinks.
Reservoirs differ in how long carbon stays (short vs long term).
Photosynthesis and cellular respiration cycle carbon between living systems and atmosphere.
Plant and animal decomposition stores carbon over long times; burning fossil fuels quickly adds carbon to the atmosphere.
Key concepts:
Movement of carbon compounds among sources and sinks (CO₂, glucose, CH₄).
Atmosphere is a major carbon reservoir; rising atmospheric CO₂ leads to warming.
Carbon sinks store more carbon than they release; examples: oceans (algae, sediments), plants, soil.
Carbon sources add CO₂ to the atmosphere; examples: fossil fuel combustion, animal agriculture (e.g., methane from cattle), deforestation.
Direct exchanges and processes:
Direct exchange: CO₂ dissolves at the air–ocean interface; ocean–atmosphere CO₂ balances quickly, but increased atmospheric CO₂ also increases ocean CO₂, contributing to ocean acidification.
Photosynthesis: algae and phytoplankton remove CO₂ from ocean and atmosphere via photosynthesis.
Carbonates: coral reefs and marine organisms form calcium carbonate shells, removing CO₂ from the ocean.
Sedimentation: dead marine organisms sink to the ocean floor and form carbon-containing sediments.
Burial: long-term storage of carbon in sedimentary rocks (limestone, sandstone) via pressure over geological timescales.
Burial, extraction, and combustion:
Burial stores carbon in underground sinks (sedimentary rock, fossil fuels).
Fossil fuels are formed from ancient organic matter; extraction and combustion release CO₂ into the atmosphere and occur faster than burial creates new fossil fuels, increasing atmospheric CO₂.
Greenhouse effect:
Heat-trapping gases (notably CO₂) trap heat, warming the surface.
Graphical relationships link CO₂ concentration and global temperature.
Steady state concept:
In a steady state inputs equal outputs; fossil fuel extraction is faster than formation, disrupting balance and driving climate change.
Equations and relationships:
Photosynthesis and respiration link biosphere and atmosphere, balancing carbon inputs/outputs in balanced conditions.
Net effect modeled as balancing reservoirs; human actions shift the balance toward increased atmospheric CO₂.
1.5 Nitrogen Cycle
Objective: Explain steps and reservoir interactions in the nitrogen cycle.
Essential knowledge:
Nitrogen cycle moves nitrogen through sources and sinks; most reservoirs hold nitrogen briefly.
Atmosphere is a major reservoir; most atmospheric nitrogen is N₂ and not directly usable by plants/animals.
Nitrogen fixation converts N₂ into forms usable by organisms and can be produced biologically or industrially.
Nitrogen cycle overview:
N is a critical plant and animal nutrient; atmosphere is the main reservoir; movement occurs between sources and sinks.
N2 is 78% of the atmosphere; not directly usable by many organisms.
Reservoirs include plants, soil, atmosphere; turnover is relatively fast compared to carbon cycling.
Fixation and related processes:
Nitrogen fixation: atmospheric N₂ converted into ammonia (NH₃) or nitrate (NO₃⁻), making N usable by plants.
Synthetic fixation: human processes convert N₂ to nitrate via fossil fuel combustion (industrial fixation).
Biological nitrogen fixation: rhizobacteria in root nodules of legumes convert N₂ to NH₃; plants receive amino acids in return.
Nitrification: conversion of NH₄⁺ to nitrite (NO₂⁻) and then nitrate (NO₃⁻) by soil bacteria.
Assimilation: plants take up NO₃⁻ or NH₃ and incorporate nitrogen into tissues; animals obtain N by consumption.
Ammonification: decomposers convert dead biomass to NH₃, returning nitrogen to soil.
Denitrification: NO₃⁻ is reduced to N₂O and N₂, returning nitrogen to the atmosphere.
Mineralization: decomposition converts organic matter back to inorganic nitrogen in soil.
Key shorthand/sequence:
FIX → NH₃ (ammonia) or NO₃⁻ (nitrate) via fixation
Nitrification → NO₂⁻ → NO₃⁻
Assimilation → Proteins/DNA/AA in plants/animals
Ammonification → NH₃
Denitrification → N₂O (and N₂) back to atmosphere
Human impacts on the N cycle:
Leaching and eutrophication from fertilizer use cause NO₃⁻ leaching into water bodies and algal blooms; ammonia volatilization releases NH₃ gas; N₂O is a greenhouse gas produced by denitrification; altered soil N reduces soil N available for crops and increases runoff losses.
Limiting nutrients (macronutrients):
Nitrogen, Phosphorus, Potassium, Calcium, Magnesium, Sulfur; limiting nutrients restrict growth when scarce; nitrogen and phosphorus often limiting in many ecosystems.
1.6 Phosphorus Cycle
Objective: Explain steps and reservoir interactions in the phosphorus cycle.
Essential knowledge:
Phosphorus cycle moves phosphorus through sources and sinks; major reservoir is rocks.
There is no atmospheric phase for phosphorus; global P levels are mostly cycle through land and water.
In undisturbed ecosystems, phosphorus is often the limiting nutrient.
Phosphorus cycle basics:
Rocks and minerals contain phosphorus; weathering releases phosphate (PO₄³⁻) into soils and waters.
Phosphorus moves from rocks to water/soil, is taken up by organisms, and returns via decomposition.
Weathering is slow; phosphorus cycling is slow relative to C and N cycles, making it a limiting nutrient.
No gas-phase phosphorus cycle; no atmospheric transport.
Phosphorus sources (abiotic):
Weathering of phosphate-containing rocks is the natural source.
Wind and rain release PO₄³⁻ into water/soil.
Human sources:
Mining phosphate minerals and adding to fertilizers; detergents contribute phosphates via wastewater.
Runoff carries phosphates to water bodies, contributing to eutrophication.
Assimilation and decomposition:
Plants assimilate phosphate via roots; animals obtain phosphate by consuming plants/other animals.
Decomposers return phosphate to soil; phosphate tends to precipitate as solids and settle into sediments.
Sedimentation and uplift:
Phosphates in sediments can be compressed into sedimentary rocks over long timescales; geological uplift can expose rocks to weathering again, restarting the cycle.
1.7 Hydrologic (Water) Cycle
Objective: Explain steps and reservoir interactions in the hydrologic cycle.
Essential knowledge:
The hydrologic cycle is powered by the sun; it moves water through its various states between sources and sinks.
The ocean is the primary surface reservoir; ice caps and groundwater are smaller but important fresh water sources.
Water cycle overview:
Evaporation: liquid water becomes water vapor; driven by solar energy.
Evapotranspiration: combined water loss from evaporation and plant transpiration; plants pull groundwater up through roots and release water from leaves via stomata.
Precipitation: return of water to land/ocean as rain, snow, etc.
Runoff: surface flow of water into rivers, lakes, or oceans.
Infiltration: water seeping into soil to refill groundwater aquifers; dependent on soil permeability.
Human impacts on the water cycle:
Deforestation reduces evapotranspiration rates.
Impermeable surfaces (concrete, roads) prevent water from entering the ground, increasing runoff.
Artificial reservoirs alter river flow and distribution.
Eutrophication and pollution degrade waterways.
Climate change melts ice caps and can alter cycle intensity.
Overuse of freshwater can dry up aquifers.
1.8 Primary Productivity
Objective: Explain how solar energy is acquired and transferred by living organisms.
Key concepts:
Primary productivity (PP) is the rate at which solar energy is converted into organic compounds via photosynthesis.
Gross primary productivity (GPP): total rate of photosynthesis in an area.
Net primary productivity (NPP): energy stored after subtracting plant respiration; NPP = GPP − RL, where RL is respiration losses.
Productivity units: kcal m⁻² yr⁻¹.
Light penetration in aquatic systems: red light absorbed near the surface; blue light penetrates further (up to ~100 m in clear water); this constrains photosynthesis at depth.
Measurements and relationships:
Photosynthesis rate can be measured as CO₂ uptake during photosynthesis (total CO₂ uptake in light and dark conditions).
GPP increases with vegetation amount; tropical rainforests have high GPP; polar regions have low GPP.
NPP typically ranges from 25% to 50% of GPP in many ecosystems.
Biomass concepts:
Biomass = total mass of living matter in an area.
Standing crop = biomass present at a given time (seasonal variation).
Ecological efficiency and trophic pyramids:
Ecological efficiency is the proportion of energy transferred from one trophic level to the next; typically 5–20%, averaging about 10%.
Trophic pyramid represents the distribution of biomass, numbers, and energy among trophic levels.
Energy accounting:
GPP − RL = NPP; RL accounts for plant respiration and energy lost to maintenance activities.
Implications:
Ecosystems with higher PP tend to be more biodiverse due to greater energy availability for higher trophic levels.
1.9 & 1.10 Trophic Levels and the 10% Rule
Objective: Explain how energy flows, decreases, and cycles through trophic levels.
Core ideas:
The 10% rule approximates energy transfer efficiency between trophic levels.
Thermodynamics explain why energy decreases at higher trophic levels (energy used for movement, growth, reproduction, heat).
All ecosystems depend on energy flow and biogeochemical cycles; matter is conserved (per the first law of thermodynamics) while energy quality degrades (second law).
10% rule details:
Roughly 10% of energy from one trophic level is transferred to the next; about 90% is lost as heat or used for metabolism.
Ecological efficiency typically ranges from 5% to 20% with an average around 10%.
Implications for human diets and farming:
Because energy transfer is inefficient, feeding humans at lower trophic levels can reduce land and resource use (e.g., meat vs. plant-based foods).
Biomass and energy transfer visuals:
Producers → Primary consumers → Secondary consumers → Tertiary consumers form a pyramid of biomass and energy.
Example numbers (illustrative): producers 8000 kg, primary consumers 800 kg, secondary consumers 80 kg, tertiary consumers 8 kg (illustrative not from the data).
Calculating transfers:
To estimate energy or biomass at the next level, move the decimal point one place to the left (divide by 10): e.g., 950.00 J → 95.0 J at the next level.
1.11 Food Chains and Food Webs
Objective: Describe food chains and webs and their trophic-level members.
Key concepts:
A food web is an interlocking pattern of two or more food chains; it represents energy and nutrient flow in an ecosystem.
Positive and negative feedback loops occur in webs; removing or adding a species can ripple through the web.
Food chain vs food web:
Food chains show linear energy transfer; food webs show multiple, interconnected chains.
Examples illustrate how one species can occupy multiple trophic levels (e.g., a grass → hare → owl chain; or grass → grasshopper → robin → owl chain).
Trophic cascades:
Changes at the top of the food web ripple to lower trophic levels (e.g., decline of a top predator can increase prey like deer, leading to overgrazing and tree decline).
Disturbance and ecosystem responses (brief overview):
Disturbance is an event altering population size or community composition (physical, chemical, or biological).
Resistance measures how much a disturbance can affect energy and matter flow; resilience measures how quickly a system returns to its pre-disturbance state.
Restoration ecology aims to restore damaged ecosystems.
1.12 Watersheds, Disturbance, and Intermediate Disturbance Hypothesis
Watershed: all land in a given area that drains into a particular stream, lake, river, or wetland.
Intermediate Disturbance Hypothesis: ecosystems experiencing intermediate levels of disturbance tend to be more diverse than those with high or low disturbance levels.
Too little disturbance: system may miss the competition necessary for speciation.
Too much disturbance: high species turnover and die-offs.
Practical implications:
Management aimed at maintaining biodiversity should consider disturbance regimes and watershed dynamics.
The sections above align with the exam objectives and standards:
Use mathematical representations to support explanations about biodiversity and ecosystem factors.
Design and refine solutions to reduce human impacts on biodiversity and ecosystems.
Evaluate solutions considering cost, safety, reliability, aesthetics, and social/cultural/environmental impacts.
Mathematical and symbolic references (recap):
Photosynthesis: \text{CO}2 + \text{H}2\text{O} \rightarrow \text{C}6\text{H}{12}\text{O}6 + \text{O}2
Cellular respiration (general): \text{C}6\text{H}{12}\text{O}6 + 6\,\text{O}2 \rightarrow 6\,\text{CO}2 + 6\,\text{H}2\text{O} + \text{energy}
Net Primary Productivity: \text{NPP} = \text{GPP} - \text{RL}
Gross Primary Productivity (definition) and Energy units: kcal m^{-2} yr^{-1}
Ecological efficiency: typically between 5% and 20%, averaging around 10% (energy transfer between trophic levels)
Carbon cycle balance: steady-state concepts and human perturbations (CO₂ as a reservoir and atmospheric warming)
Nitrogen fixation: \text{N}2 \rightarrow \text{NH}3 \text{ or } \text{NO}_3^-
Phosphorus form: phosphate PO₄^{3-}
Phosphorus cycle lacks an atmospheric phase; no gas-phase transport
Hydrologic cycle processes: evaporation, evapotranspiration, precipitation, runoff, infiltration, groundwater
Connections to real-world relevance:
Climate change shifts biomes; resource availability and nutrient cycles (N, P, C, S) drive ecosystem responses.
Human activities (deforestation, fossil fuel combustion, fertilizer use, water management) disrupt cycles and ecosystem services (food, drinking water, climate regulation).
Restoration and sustainability require balancing energy flow, nutrient cycling, and biodiversity preservation within socio-economic constraints.