The five main groups of single-celled organisms are protozoa, archaea, bacteria, unicellular fungi and unicellular algae. While single-celled organisms can be either eukaryotic or prokaryotic, most are prokaryotes. The t... More »

An organism is a living entity composed of many interrelated components that work together to achieve a common goal. Organisms come in a wide variety of sizes, shapes and lifestyles, but they all share some similar trait... More »

Photosynthesis is completed by many different organisms, ranging from plants to bacteria. Organisms that carry out photosynthesis are called photosynthetic. More »

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Although members of the kingdom Animalia are almost exclusively multicellular, there are several unicellular organisms classified as animals, including species of bacteria, protozoa, fungi, algae and archaea. Bacteria ar... More »

Even a single drop of pond water may contain thousands of organisms, including different types of bacteria, protozoa, algae, rotifers, hydras and worms. Although most of the organisms that live in water are microscopic, ... More »

Humans cannot see, smell, or taste individual micro-organisms such as bacteria, protozoa and certain fungi and algae. Such living organisms are microscopic and too small to be seen without magnification instruments (they... More »

The types or groups of human pathogens include bacteria, viruses, fungi, protozoa, worms and prions. All of these pathogens are responsible for causing disease in human hosts, but some are more common than others. More »