Biochemical cycles & ecosysemss dynamics

1. Ecosystem Roles

  • Producers (autotrophs): make organic molecules via photosynthesis

  • Consumers (heterotrophs): obtain energy by feeding on others

  • Decomposers: break down dead matter → recycle nutrients

2. Energy vs Matter

  • Energy:

    • Enters as sunlight

    • Flows one-way through ecosystem

    • Lost as heat (not recycled)

  • Matter:

    • Finite on Earth

    • Recycled continuously through biogeochemical cycles

Key elements: C, H, O, N, P

3. Nutrient Limitation

  • A limiting nutrient restricts ecosystem growth

  • Example:

    • ↓ plankton → ↓ fish → ↓ predators

  • Controls primary productivity

4. Biogeochemical Cycles

  • Movement of elements through:

    • Biological (living organisms)

    • Geological (soil, rock)

    • Chemical (molecular transformations)

5. Water Cycle

  • Processes:

    • Evaporation: water → vapor

    • Transpiration: water loss from plants

    • Condensation: vapor → clouds

    • Precipitation: rain/snow

    • Runoff + infiltration: water returns to bodies/soil

Function:

  • Regulates temperature

  • Transports nutrients

6. Carbon Cycle

  • CO₂ in atmosphere = main reservoir

Processes:

  • Photosynthesis: CO₂ → organic molecules

  • Respiration: organic → CO₂

  • Decomposition: releases CO₂

  • Combustion (fossil fuels): increases CO₂

Storage:

  • Fossil fuels

  • Oceans (dissolved CO₂, CaCO₃ shells)

7. Nitrogen Cycle

  • Atmosphere: N₂ (79%), unusable directly

Steps:

  1. Nitrogen fixation: N₂ → NH₃ (by bacteria)

  2. Nitrification: NH₃ → NO₂⁻ → NO₃⁻

  3. Assimilation: plants absorb nitrates

  4. Consumption: animals obtain nitrogen

  5. Denitrification: NO₃⁻ → N₂ (back to atmosphere)

Importance:

  • Required for proteins and nucleic acids

8. Phosphorus Cycle

  • No gaseous phase (sedimentary cycle)

Steps:

  • Weathering of rocks → phosphates

  • Plants absorb phosphates

  • Animals consume plants

  • Decomposition returns phosphorus to soil/water

Key role:

  • DNA, ATP, bones

9. Ecosystem Stability

  • Balance depends on:

    • Nutrient availability

    • Recycling efficiency

  • Disruption → trophic cascade effects

10. Human Impact

  • Burning fossil fuels → ↑ CO₂

  • Fertilizer runoff → algal blooms

  • Alters natural cycles → affects climate and ecosystems

Core Takeaways

  • Energy flows, matter cycles

  • Ecosystems depend on continuous nutrient recycling

  • Limiting nutrients control productivity

  • Biogeochemical cycles maintain ecosystem equilibrium