C4.2 Transfers of energy and matter

• Ecosystems are open systems exchanging energy and matter with surroundings

• Energy flows through ecosystems while matter can enter, leave, and recycle

• Sunlight is the principal energy source for most ecosystems

• Exceptions include caves and deep-ocean vents supported by chemosynthesis

• Chemical energy flows from producers to consumers through feeding

• Energy enters as light or chemical energy and leaves ecosystems as heat

• Food chains and food webs model feeding relationships in communities

• Arrows point in the direction of energy and biomass transfer

• Decomposers obtain energy from carbon compounds in detritus

• Dead organisms, faeces, fallen leaves, and shed tissues supply organic matter

• Autotrophs synthesize carbon compounds from simple inorganic substances

• They use external energy sources to fix carbon and build biomass

• Photoautotrophs use light captured by photosynthetic pigments

• Chemoautotrophs use oxidation of inorganic substances, such as iron or sulfur compounds

• Heterotrophs obtain carbon compounds from other organisms or organic matter

• They use these compounds for respiration and synthesis of their own biomass

• Both autotrophs and heterotrophs release energy by cell respiration

• Oxidation of carbon compounds transfers energy to ATP and heat

• Trophic levels classify organisms as producers, primary consumers, and higher consumers

• Omnivores and decomposers may feed across more than one trophic level

• Energy pyramids represent energy flow per unit area per unit time

• Each bar shows energy available to one trophic level

• Energy availability decreases at each transfer between trophic levels

• Losses occur through respiration, heat, egestion, excretion, and uneaten biomass

• Cell respiration converts some chemical energy to heat in all trophic levels

• Heat dissipates to the environment, so energy cannot be recycled

• Large energy losses restrict food chains to a few trophic levels

• Higher trophic levels usually support less biomass and fewer individuals

• Primary production is accumulation of carbon compounds in autotroph biomass

• Gross production minus respiration gives net primary production

• Secondary production is biomass accumulation by heterotrophs

• It depends on food intake, assimilation, respiration losses, and biomass conversion

• Carbon cycle diagrams show stores as boxes and fluxes as labelled arrows

• Include CO₂, photosynthesis, feeding, respiration, decomposition, fossil fuels, and combustion

• Carbon sinks absorb more carbon than they release, such as forests, soils, and oceans

• Carbon sources release more carbon than they absorb, such as fossil fuel combustion

• Combustion of biomass, peat, coal, oil, and natural gas releases CO₂

• Draining peat and forest fires increase carbon flux to the atmosphere

• The Keeling Curve records atmospheric CO₂ at Mauna Loa since the late 1950s

• Long-term rise reflects combustion; annual oscillation reflects Northern Hemisphere photosynthesis

• Photosynthesis supplies atmospheric O₂ used in aerobic respiration

• Respiration supplies CO₂ used by photosynthesis, linking autotrophs and heterotrophs

• All chemical elements required by organisms are recycled in ecosystems

• Decomposers convert detritus and waste into inorganic nutrients for producers