Practice question

Fungi and bacteria initiate biochemical decomposition by colonizing dead material and secreting extracellular enzymes. These enzymes depolymerize proteins, polysaccharides, lipids, and, in specialized taxa, lignin into compounds small enough for cellular uptake. Fungal hyphae penetrate litter and transport resources across microsites, while bacteria exploit soluble products and newly exposed surfaces. Detritivores and scavengers accelerate the process through fragmentation, but they do not replace microbial mineralization; their feeding increases surface area and redistributes inoculum. Carbon and mineral nutrients follow different accounting paths: energy is dissipated, whereas atoms may be retained, exported, or recycled into new biomass. Decomposition rate therefore emerges from interactions among substrate chemistry, decomposer traits, temperature, water, oxygen, and nutrient balance rather than from a single universal control. At ecosystem scale, these reactions regulate soil fertility, atmospheric carbon exchange, detrital food webs, and the residence time of organic matter. Mass loss alone cannot identify mechanism, because leaching, fragmentation, respiration, assimilation, and stabilization can produce different fates for carbon and nutrients.