Course review
Review each learning objective in this topic, then open its concept explanation or question set.
Learning objective
• Ecosystems are open systems exchanging energy and matter with surroundings • Energy flows through ecosystems while matter can enter, leave, and recycle
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Learning objective
• Sunlight is the principal energy source for most ecosystems • Exceptions include caves and deep-ocean vents supported by chemosynthesis
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Learning objective
• Chemical energy flows from producers to consumers through feeding • Energy enters as light or chemical energy and leaves ecosystems as heat
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Learning objective
• Food chains and food webs model feeding relationships in communities • Arrows point in the direction of energy and biomass transfer
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Learning objective
• Decomposers obtain energy from carbon compounds in detritus • Dead organisms, faeces, fallen leaves, and shed tissues supply organic matter
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Learning objective
• Autotrophs synthesize carbon compounds from simple inorganic substances • They use external energy sources to fix carbon and build biomass
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Learning objective
• Photoautotrophs use light captured by photosynthetic pigments • Chemoautotrophs use oxidation of inorganic substances, such as iron or sulfur compounds
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Learning objective
• Heterotrophs obtain carbon compounds from other organisms or organic matter • They use these compounds for respiration and synthesis of their own biomass
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Learning objective
• Both autotrophs and heterotrophs release energy by cell respiration • Oxidation of carbon compounds transfers energy to ATP and heat
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Learning objective
• Trophic levels classify organisms as producers, primary consumers, and higher consumers • Omnivores and decomposers may feed across more than one trophic level
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Learning objective
• Energy pyramids represent energy flow per unit area per unit time • Each bar shows energy available to one trophic level
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Learning objective
• Energy availability decreases at each transfer between trophic levels • Losses occur through respiration, heat, egestion, excretion, and uneaten biomass
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Learning objective
• Cell respiration converts some chemical energy to heat in all trophic levels • Heat dissipates to the environment, so energy cannot be recycled
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Learning objective
• Large energy losses restrict food chains to a few trophic levels • Higher trophic levels usually support less biomass and fewer individuals
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Learning objective
• Primary production is accumulation of carbon compounds in autotroph biomass • Gross production minus respiration gives net primary production
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Learning objective
• Secondary production is biomass accumulation by heterotrophs • It depends on food intake, assimilation, respiration losses, and biomass conversion
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Learning objective
• Carbon cycle diagrams show stores as boxes and fluxes as labelled arrows • Include CO₂, photosynthesis, feeding, respiration, decomposition, fossil fuels, and combustion
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Learning objective
• 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
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Learning objective
• Combustion of biomass, peat, coal, oil, and natural gas releases CO₂ • Draining peat and forest fires increase carbon flux to the atmosphere
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Learning objective
• The Keeling Curve records atmospheric CO₂ at Mauna Loa since the late 1950s • Long-term rise reflects combustion; annual oscillation reflects Northern Hemisphere photosynthesis
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Learning objective
• Photosynthesis supplies atmospheric O₂ used in aerobic respiration • Respiration supplies CO₂ used by photosynthesis, linking autotrophs and heterotrophs
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Learning objective
• All chemical elements required by organisms are recycled in ecosystems • Decomposers convert detritus and waste into inorganic nutrients for producers
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