8.2.B—Explain how energy flows and matter cycles through trophic levels

Explain how energy flows and matter cycles through trophic levels.

• Ecological levels of organization include populations, communities, ecosystems, and biomes.
• Energy flows through ecosystems, while matter and nutrients cycle between the environment and organisms via biogeochemical cycles. The cycles are essential for life, and each cycle demonstrates the conservation of matter. The cycles are interdependent.
• Biogeochemical cycles include abiotic and biotic reservoirs, as well as processes that cycle matter between reservoirs.
• The hydrologic (water) cycle involves water movement and storage within the hydrosphere. Reservoirs include oceans, surface water, the atmosphere, and living organisms. Processes include evaporation, condensation, precipitation, and transpiration.
• The carbon cycle involves recycling carbon atoms through Earth’s biosphere into organisms as carbohydrates and back into the atmosphere as carbon dioxide ()CO At the highest levels of organization, 2 . the carbon cycle can be simplified into four parts: photosynthesis, cellular respiration, decomposition, and combustion.
• The nitrogen cycle involves several steps, including nitrogen fixation, assimilation, ammonification, nitrification, and denitrification. These steps are performed by microorganisms in the soil. The largest reservoir of nitrogen is the atmosphere. In nitrogen fixation, nitrogen gas ()N2 is fixed into ammonia ()NH3 , which ionizes to ammonium (NH + 4 ) by acquiring hydrogen ions from the soil solution.
• The phosphorus cycle involves weathering rocks releasing phosphate ()PO 3− 4 into soil and groundwater. Producers take in phosphate, which is incorporated into biological molecules; consumers eat producers, transferring phosphate to animals. Phosphorus returns to the soil via decomposition of biomass, or excretion. Phosphate can also be incorporated back into the environment via decomposition of decaying organic matter.