⚡ How humans change energy & matter in ecosystems
Big idea: Ecosystems depend on energy input (photosynthesis) and recycling of matter (nutrients). Human actions can reduce productivity, remove biomass, and disrupt cycles.
When producers are removed (deforestation/urbanisation) or conditions change (pollution/climate), less energy becomes biomass — so food webs weaken.
Key activities
- Fossil fuels: more CO₂ + pollution → climate change and stress on productivity
- Deforestation: fewer producers + less carbon storage → reduced biomass and higher CO₂
- Urbanisation: habitat removal + fragmentation → lower biodiversity and productivity
- Agriculture: simplified ecosystems; biomass exported by harvest → less nutrient recycling
Strong exam link: deforestation reduces energy input (fewer producers) AND matter storage (less carbon in biomass/soil).
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How human activities change energy and matter
Big idea: Human activities can alter how energy flows and how matter is stored and transferred in ecosystems, often reducing biomass and disrupting food webs.
Ecosystems rely on a balance of energy inputs and the recycling of matter. When humans change land use or release pollutants, this balance can be disturbed.
Burning fossil fuels
The burning of fossil fuels releases large amounts of carbon dioxide (CO₂) into the atmosphere. This strengthens the greenhouse effect and leads to global warming.
Changes in temperature and air quality can reduce primary productivity, limiting the energy available to food webs.
- Air pollutants damage plant tissues and reduce photosynthesis
- Climate change alters rainfall and temperature patterns
- Ocean warming and acidification disrupt marine food webs
Although plants need CO₂ for photosynthesis, excessive CO₂ causes environmental changes that reduce ecosystem stability.
Deforestation
Deforestation reduces the number of producers in an ecosystem.
Trees store carbon, produce biomass, and influence the water cycle. When forests are removed, less energy enters food webs and stored carbon is released into the atmosphere.
- Lower primary productivity
- Loss of habitats and biodiversity
- Increased atmospheric CO₂
- Disrupted nutrient and water cycles
Deforestation reduces both energy input and matter storage in ecosystems.
Urbanisation
Urbanisation replaces natural ecosystems with buildings, roads, and infrastructure.
This process removes producers and fragments habitats, reducing energy flow at the base of food webs.
- Reduced biomass production
- Habitat fragmentation
- Disrupted food webs
- Increased energy demand and pollution
Agriculture
Modern agriculture often involves clearing natural vegetation to grow a single crop species. This simplifies ecosystems and reduces biodiversity.
Although crops carry out photosynthesis, much of the biomass is removed from the system during harvest, limiting the recycling of nutrients.
- Less energy available for natural food webs
- Reduced nutrient cycling in soils
- Greater reliance on fertilisers and irrigation
- Lower ecosystem resilience
International perspective
Global trade moves food and nutrients far from where they are produced. Consuming local and seasonal food can help keep energy and nutrients within local ecosystems.
Big exam takeaways
- Human activities alter energy flow and matter storage
- Fossil fuels affect productivity and climate
- Deforestation reduces producers and biomass
- Urbanisation removes habitats and fragments food webs
- Agriculture exports biomass from ecosystems