AP Environmental Science - Ecosystem Dynamics & Biogeochemical Cycles

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Gross Primary Productivity (GPP) vs. Net Primary Productivity (NPP)

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GPP is the total amount of solar energy converted into chemical energy by photosynthesis. NPP is GPP minus the energy used by plants for cellular respiration (R). Formula: NPP = GPP - R. NPP represents the biomass available for consumers.

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The 10% Rule of Energy Transfer

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Only about 10% of the energy stored in biomass at one trophic level is transferred to the next level. The remaining 90% is lost primarily as heat ( Second Law of Thermodynamics) or used for metabolic processes. This limits the number of trophic levels in a food chain.

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Nitrogen Fixation

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The process of converting atmospheric nitrogen gas (N2) into forms usable by plants, such as ammonia (NH3) or nitrate (NO3-). It is performed primarily by symbiotic bacteria (e.g., Rhizobium in legume root nodules) and lightning.

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Eutrophication

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The process by which a body of water becomes overly enriched with minerals and nutrients (usually nitrogen and phosphorus), leading to excessive growth of algae (algal blooms). When the algae die and decompose, oxygen is depleted, killing aquatic life (hypoxia).

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Generalist vs. Specialist Species

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Generalists (e.g., raccoons, rats) have broad niches, can eat a variety of foods, and adapt easily to changing environments. Specialists (e.g., koalas, pandas) have narrow niches, rely on specific food sources, and are vulnerable to habitat change.