Glossary for an Invisible World

Return to main article:

Feature Article: The Undiscovered Planet

Archaea: One of three major domains, or classifications, of life, archaea are morphologically similar to bacteria, but have a different molecular transcription machinery, indicating an ancient evolutionary divergence.

Bacteria: One of three major domains of life. Bacteria are single-celled microorganisms with neither a nucleus nor organelles (specialized intracellular structures; see below).

Cyanobacteria: A division of bacteria that produce their energy through photosynthesis. Formerly called blue-green algae (hence the name “cyano,” or blue, bacteria), they are not “true” algae. Algae are eukaryotes, while the cyanobacteria are prokaryotes.

Eukarya: One of three major domains of life, the eukarya include all single and multicellular organisms in which the cells have a distinct nucleus. Examples are plants, animals, and fungi. The classification includes everything that is not a bacterium or an archaean.

Microbe: Generally considered to include all life that cannot be seen with the unaided eye, microbes are found in all three major divisions of life and include all the bacteria, all the archaea, and some of the eukarya. Some scientists say that only prokaryotes (see below) should be considered microbes, thereby excluding even single-celled fungi. Others argue that even multicellular organisms can be considered microbes. Mushrooms, for example, are the multicellular fruiting bodies of fungi that may start as unicellular organisms in the soil. Furthermore, both unicellular bacteria and archaea form aggregates (“colonies”) on surfaces, often referred to as biofilms, that exhibit distinctive multicellular patterning.

Organelles: Structures within a cell that perform specialized functions, such as energy production. Mitochondria and chloroplasts are examples of energy-producing organelles that are thought to have evolved from autonomous bacteria. Eventually they became dependent on their hosts—and vice versa.

Primary production: Production is the creation of new organic matter. Primary production refers to the creation of new organic matter by photosynthetic microbes.

Prokaryotes: An inclusive term that refers to the bacteria and archaea, single-celled organisms that, as distinct from eukaryotes, lack a nucleus.

You might also like

The Roman Empire’s Cosmopolitan Frontier

Genetic analysis reveals a culture enriched from both sides of the Danube.

Tobacco Smoke and Tuberculosis

Harvard researchers illuminate a longstanding epidemiological connection. 

Discourse and Discipline

Harvard’s Faculty of Arts and Sciences broaches two tough topics.

Most popular

Yesterday’s News

Headlines from Harvard’s history

Chiara String Quartet

The Chiara String Quartet are Harvard's current Blodgett Artists-in-Residence.

Storytelling Scholar

Marie Rutkoski blends sixteenth-century history with fantasy in The Cabinet of Wonders, a new novel for young adults.

More to explore

Illustration of a box containing a laid-off fossil fuel worker's office belongings

Preparing for the Energy Transition

Expect massive job losses in industries associated with fossil fuels. The time to get ready is now.

Apollonia Poilâne standing in front of rows of fresh-baked loaves at her family's flagship bakery

Her Bread and Butter

A third-generation French baker on legacy loaves and the "magic" of baking

Illustration that plays on the grade A+ and the term Ai

AI in the Academy

Generative AI can enhance teaching and learning but augurs a shift to oral forms of student assessment.