Why no cellular respiration without the respiratory chain?

In principle, this is true. No regeneration of NADH from the NADH2 takes place without a respiratory chain. In anaerobic metabolism, there is the possibility to regenerate NADH by using other molecules as oxygen as ekectron acceptor. Here, fermentation reactions serve to regenerate the NADH, for example alcoholic, acetic acid or lactic acid fermentation. However, the anaerobic cell breathing provides much less energy than the aerobic, namely in principle only what arises in glycolysis at ATP. Our body therefore mainly goes the way over aerobic glycolysis. We can’t survive without oxygen. The breathing chain e.g. by cyanide, we suffocate from the inside.

Nevertheless, anaerobic metabolic pathways also take place in our body. If you use your muscles more, they consume more energy. If you continue and continue to use them, they will eventually consume more energy than the aerobic metabolism, because at some point the body cannot absorb even more oxygen. The muscles then also burn glucose via the anaerobic metabolic pathway through lactic acid fermentation. This means that the glucose is formed in glycolysis to give pyruvate and lactic acid is then formed from this. The lactic acid is then transported to the liver, where it is used for glucoseogenesis. The glucose thus constructed is then transported back to the muscle. This glucose-milk acid cycle between muscle and liver is also called Cori cycle. This anaerobic metabolism takes place in addition to aerobic and cannot replace it.