Practice question

DDT exposure caused eggshell thinning in many predatory birds through its metabolite DDE. DDE interferes with calcium metabolism and inhibits processes involved in shell deposition within the shell gland, so females lay fragile eggs that crack during incubation. Biomagnification made raptors and fish-eating birds particularly vulnerable. Population recovery after restrictions on DDT provided strong evidence linking the contaminant to reproductive failure. Energy is lost as metabolic heat at every trophic transfer, while elements such as nitrogen and phosphorus are recycled through organisms and the physical environment. Mechanistic interpretation connects individual physiology and species interactions to population change, community composition, and ecosystem-level fluxes. Reliable inference requires the complete experimental design, definitions, units, and statistical evidence; missing labels cannot be reconstructed from an answer key alone. Net primary production equals gross primary production minus plant respiration and represents biomass or energy made available for growth and consumers. Rates must be compared on the same area, biomass, leaf-area, and time basis because changing the denominator can reverse an apparent ecosystem ranking.