All living things are divided into two super-kingdoms: the eukaryotes, which tend to have sexual organs and a nucleus; and the prokaryotes, which tend to have neither. The prokaryotes consist of many different types of bacteria and blue-green algae. Green algae and all other organisms, except viruses, are referred to as eukaryotes. Algae is a type of primitive plant whose color or pigmentation is an important indicator of photosynthetic activity. Blue-green algae is among the oldest and smallest of plant life. This algae lacks a nucleus and normal sexual reproductive organs, but contains chlorophyll. To the naked eye, blue-green algae has a "sea-weed" appearance similar to other algae, but their microscopic internal structure is the same as bacteria. Green algae has a nucleus and reproduces itself. Many believe higher plants evolved from green algae.

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