<span>endocrine system.............</span>
Spore production is the answer
The answer is; prokaryotes are the earliest life forms
Glycolysis was the earliest energy harvesting pathway in early living organisms. Glycolysis does not require oxygen attribute to the early condition of the earth where its atmosphere was majorly comprised of carbon dioxide. It is only after the great oxygenation event that life evolved the oxidative phosphorylation process.
