Cyanide is a potent inhibitor of the electron transport chain in mitochondria, primarily affecting cytochrome oxidase, which is crucial for oxygen consumption. A concentration of 1 mM KCN can reduce oxygen consumption by over 98%, effectively halting the Krebs cycle, similar to suffocation. This mechanism is akin to carbon monoxide poisoning, where both substances competitively inhibit oxygen binding, but cyanide specifically targets mitochondrial enzymes. The discussion suggests that the effects of cyanide on organisms capable of fermentation could provide further insights into its impact on respiration without oxygen.