Final answer:
The best explanation for the difference in ATP production from glucose is that energy is lost as heat during cellular respiration. Different species and different electron sources can result in varying ATP yields. Additionally, intermediate compounds in glucose catabolism can be used for other purposes, affecting the extraction of energy from glucose.
Step-by-step explanation:
The best explanation for the difference between the approximately 30 ATP produced per glucose molecule and the theoretical maximum of 90 ATP is that energy is lost as heat during cellular respiration.
During aerobic respiration, the electron transport system complexes pump hydrogen ions through the membrane to generate enough proton motive force to make ATP. However, the actual number of hydrogen ions pumped and ATP molecules generated can vary between different species and depending on whether the electrons come from NADH or FADH₂. Overall, the maximum ATP yield during aerobic respiration is approximately 38 molecules, but in reality, the total ATP yield is usually less than that.
Furthermore, intermediate compounds in glucose catabolism can be used for other purposes in the cell, which affects the extraction of energy from glucose. Other molecules may be formed or broken down, and energy may be used for the synthesis of nucleic acids, amino acids, lipids, and other compounds. Therefore, even under ideal conditions, only about 34% of the energy contained in glucose is extracted.