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Life Science: Session 2

Classifying Living Things: The Domain Bacteria

What features distinguish bacteria from other life forms?

Representing potentially the largest group of organisms on this planet, the domain Bacteria is composed of a remarkably diverse group. From deadly diseases to “helper” bacteria in our bodies, bacteria inhabit almost every ecological niche known. Colonizing spaces in other organisms, in the deep-sea, and even in toxic waste sites, bacteria are single-celled organisms known for their striking diversity.

cyanobacteria
Cyanobacteria, image courtesy of Cyanosite

Even though these prokaryotic organisms lack a nucleus and organelles, they are able to exploit a wide range of substances for food sources. Bacteria do have a cell wall, which includes the compound peptidoglycan, also found in fungal cell walls. There are two common shapes among bacterial cells: rods and spheres.

Unlike animals, bacteria do not ingest their food. Many bacteria are like fungi in that they secrete digestive chemicals into the local environment to break down complex molecules, which they then absorb. Some bacteria are like plants and are able to make their own food through photosynthesis. In fact, most of the photosynthesis on Earth occurs in the open ocean and is carried out by a group of bacteria called cyanobacteria, or blue-green algae. However, many bacteria use reactions completely different from plants to make their own food from an array of chemicals. And, there are bacteria that are able to switch between making their own food and absorbing food from an external source.

How are bacteria important to people?

Bacteria are important to humans in many ways. Did you know that bacterial cells outnumber human cells in our bodies? Many times they are portrayed as germs and agents of disease but there are also many beneficial and practical applications of bacteria in our everyday lives. Some bacteria serve to ward off infection in our bodies as well as to facilitate digestion. Wine, cheese, and yogurt are produced with bacterial cultures. Furthermore, certain bacteria produce important compounds used in industrial and pharmaceutical industries.

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