AP Environmental Science - Hard Analysis

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Explain the discrepancy between Gross Primary Productivity (GPP) and Net Primary Productivity (NPP) in mature forests.

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In mature forests, NPP is significantly lower than GPP because a large proportion of the energy fixed via photosynthesis is utilized for cellular respiration (R) to maintain the massive biomass of the existing trees. NPP = GPP - R. While GPP is high, the metabolic maintenance costs (R) of the woody tissue are substantial, leaving little energy for new growth (NPP). This results in a steady-state or climax community.

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Law of Tolerance regarding species distribution vs. Liebig's Law of the Minimum.

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Liebig's Law of the Minimum states that growth is controlled not by the total amount of resources available, but by the scarcest resource (limiting factor). The Law of Tolerance expands on this, stating that a species' existence depends on a complex set of conditions, and a species can exist within a range of tolerance for each factor; too little or too much of an abiotic factor (like temperature or pH) limits a species' presence, not just scarcity.

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Isoelectric point (pI) implications in wetland soils for metal retention.

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The isoelectric point is the pH at which a molecule carries no net electrical charge. In wetland soils, if the soil pH is below the pI of soil particles (like clay or organic matter), they tend to be positively charged and repel metal cations. If the pH is above the pI, particles become negatively charged and bind/retain metal cations, improving remediation. Peat wetlands are acidic (often below pI), affecting their ability to immobilize certain metals compared to alkaline wetlands.

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Derive the LD50 calculation from toxicity data.

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LD50 (Lethal Dose 50%) is the dose of a substance required to kill 50% of a test population. To calculate: 1. Convert dose data to logarithmic scale (log). 2. Plot mortality (probit or %) against log dose. 3. Identify the dose corresponding to 50% mortality. Formula logic: Dose = (Mass of Substance / Body Weight). Units are typically mg/kg. A lower LD50 indicates higher toxicity (less substance needed to kill).

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SLOSS Debate (Single Large vs. Several Small) in conservation biology.

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The SLOSS debate concerns whether it is better to have a Single Large or Several Small reserves to protect biodiversity. Arguments for Single Large: supports larger populations, reduces edge effects, preserves wider habitat gradients, better for large carnivores. Arguments for Several Small: spreads risk (catastrophes won't wipe out everything), covers more habitat types/heterogeneity, creates more edge habitat for generalist species. Current consensus favors a mix but emphasizes connectivity (corridors).