Examples of monerans include bacteria and blue-green algae. Bacteria are the most populous of all living organisms and critical to life on this planet. As decomposers, they break down organic matter and return the nutrients to the soil for plants to absorb.
Both bacteria and blue-green algae of the Monera kingdom are prokaryotic single-celled organisms. Most bacteria get their energy from carbon, while others, including blue-green algae, require sunlight. Carbon-feeding bacteria are called chemotrophic, and those that need sunlight are photosynthetic. Bacteria are also classified as aerobic or anaerobic. Aerobic bacteria need oxygen while anaerobic do not.
Thiobacteria require sulfur, acidophilic bacteria require acid and methanobacteria require methane. Thiobacteria are often found in hot springs where the sulfur they require is abundant. Methanobacteria often live in the digestive tracts of organisms. Acidophilic bacteria are used to make yogurt and cheese. There are also iron-oxidizing bacteria that attach to the hulls of ships.
One type of organism formerly classified in the Monera kingdom are the Archaea, which thrive in extreme conditions, such as extremely hot temperatures. Although they are also single-celled, they are more closely related to eukaryotic organisms than to bacteria and have been placed in the Archaea kingdom. Experts believe that these single-celled organisms are the oldest life forms on the planet.