1 B io F actsheet January 1998 Number 12 Respiration Aerobic respiration can be divided into four stages: 1. Glycolysis (G) 2. The Link reaction (LR) 3. Kreb?s cycle (K) 4. The electron transfer chain (ETC) These take place in different parts of the cell (Table 1) and the detailed biochemistry of these reactions is shown overleaf. Respiratory quotients The respiratory quotient (RQ) is defined as the ratio of carbon dioxide produced to oxygen consumed per unit time by an organism: volume of CO2 produced volume of O2 consumed Different substances give different RQ values Cellular respiration is the process by which the energy contained in organic molecules is made available for all of the active