All living organisms found on Earth, and this includes both eukaryotes as well as prokaryotes, need three different things to actually survive and grow. And these three things are energy, carbon, as well as electrons. Now, why exactly do our organisms need these three different things? Well, basically, they need energy to power the different types of processes that take place within that organism. They need carbon to create the biomolecules used by those organisms, and they need electrons to basically undergo oxidation reduction reactions that are used to create different types of molecules. For example, if we examine the human body, humans need energy to basically power different types of processes.