Practice question

Biological magnification describes increasing concentrations of persistent, biologically available toxins at higher trophic levels. Producers take up a contaminant from water or soil; herbivores consume many producers, and predators consume many contaminated prey. When assimilation exceeds metabolism and excretion, tissue concentration rises at each transfer. Dilution is the opposite pattern, while fertiliser runoff is a pollution source rather than the trophic process itself. 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. Climate, nutrients, disturbance, species traits, and food-web structure interact, so broad ecological generalisations describe tendencies rather than universal rules. 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.