<span>The answer is C.glycolysis ® Krebs cycle ® electron transport chain. There are 3 stages of cellular respiration: 1. glycolysis when glucose is broken down to pyruvate in the cytoplasm; 2. Krebs cycle when Acetyl CoA and oxaloacetate form a 6 C-atoms compound; 3. Electron transport chain when hydrogen molecules removed through previous stages are pumped to the chain and energy is produced.</span>
The reason why nost scientists thought that the first true cells formed on Earth were anaerobic is being shown in the second option :B. because there was no oxygen on early Earth. Paying attention to this fact scientists discovered that first cells were prokaryotes and greatest part of them created oxygen as a toxic by-product of their own metabolism which make them understand how the planet was provided with oxygen and made a conclusion that first cells were anaerobic.
