Ecosystems: Energy Flow & Biogeochemical Cycles

Earth's Spheres and Cycles

• Earth's biological, geological, and chemical processes involve the recycling of matter in four spheres: biosphere (organisms), hydrosphere (water), atmosphere (air), and lithosphere/geosphere (soil and rocks).
• Matter is conserved and cycled in both biotic and abiotic parts of an ecosystem through four major cycles: carbon (C), water (H2O), nitrogen (N), and phosphorus (P).

Biogeochemical Cycles

• The nitrogen cycle involves anaerobic bacteria, nitrogen-fixing bacteria, and denitrifying bacteria to convert nitrogen gas (N2) into nitrate (NO3-) for plant growth.
• Anaerobic bacteria also play a role in the carbon cycle through methanogenesis, converting CO2 to methane (CH4) and producing ATP.

Energy Flow in Ecosystems

• Energy is transferred from one trophic level to the next in a food chain, but not all consumed biomass is transformed into digested energy.
• Approximately 10% of energy is transferred between trophic levels, with a range of 25%.
• Energy transfer varies depending on environmental factors like aquatic vs terrestrial ecosystems, temperature, and complexity of the food web.

Biogeochemical Nutrient Cycles

• Five chemical elements are essential nutrients in organic matter: C, H, N, O, and P.

Energy and Biomass

• Energy flow and cycles of matter occur within organisms through anaerobic and aerobic respiration.
• Energy flow and cycles of matter also occur in ecosystems through interactions between organisms and their physical environment, including food chains and webs and biogeochemical cycles.
• Solar energy is converted into chemical energy through photosynthesis, with primary productivity measured as Gross Primary Productivity (GPP) and Net Primary Productivity (NPP).
• Energy is conserved and transformed from one form to another, but cannot be created or destroyed, according to the Law of the Conservation of Energy.