Point 2 of 7 — Ecological Balance in Earth Systems, Biogeochemical Cycles and Food WebsQuestion bank: 0 questions (0 with pictures)
02Laws and relations
Lindeman's 10% rule (trophic-dynamic efficiency): only about 10% of the energy of one level appears as biomass in the next; the rest is lost as respiration, heat, movement and unconsumed or undigested matter.
Consequence: food chains rarely exceedfour or five levels, because there is not enough energy left to support another.
Example: if plants fix 10,000 kJ, herbivores store about 1,000 kJ, primary carnivores 100 kJ and top carnivores 10 kJ.
Primary productivity: gross (GPP) minus respiration (R) equals net (NPP) — NPP is what the ecosystem actually offers to consumers; tropical rainforests and coral reefs are the highest, deserts and open ocean the lowest per unit area.
Nitrogen fixation: N₂ + 8H⁺ + 8e⁻ + 16 ATP → 2NH₃ + H₂, catalysed bynitrogenaseinRhizobium in legume root nodules, free-living AzotobacterandClostridium, and cyanobacteria such asAnabaena.
Nitrification: NH₃ → NO₂⁻ (Nitrosomonas) → NO₃⁻ (Nitrobacter); denitrificationbyPseudomonas returns N₂ to the air under anaerobic conditions.
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