Electrons generally move from a more negative (lower) or less positive redox potential to less negative or a more positive (higher) redox potential, reflecting a downhill energy flow. However, in the Z-scheme of photosynthesis, there are two key points where light energy is used to excite electrons, allowing them to move uphill to a more positive redox potential.

During replication and transcription a nucleic acid was copied to form another nucleic acid. Hence, these processes are easy to conceptualise on the basis of complementarity. The process of translation requires transfer of genetic information from a polymer of nucleotides to synthesise a polymer of amino acids. Neither does any complementarity exist between nucleotides and amino acids, nor could any be drawn theoretically. There existed ample evidences, though, to support the notion that change in nucleic acids (genetic material) were responsible for change in amino acidsin proteins. This led to the proposition of a genetic code that could directthe sequence of amino acids during synthesis of proteins.