Single-celled

Single-celled organisms are organisms that are made up of a single cell. They are also known as unicellular organisms. These organisms can be found in all three domains of life: Bacteria, Archaea, and Eukarya.

Characteristics

Single-celled organisms are characterized by their ability to perform all necessary life functions within one cell. These functions include metabolism, reproduction, and response to stimuli.

Metabolism

Single-celled organisms carry out metabolism within their single cell. This includes both anabolism, the synthesis of complex molecules from simpler ones, and catabolism, the breakdown of complex molecules into simpler ones.

Reproduction

Single-celled organisms reproduce through a process known as binary fission, in which the cell divides into two identical cells. Some single-celled organisms, such as certain species of yeast, reproduce through a process known as budding, in which a new cell grows out of the parent cell.

Response to Stimuli

Single-celled organisms are capable of responding to stimuli in their environment. This can include changes in temperature, light levels, and the presence of certain chemicals.

Examples

Examples of single-celled organisms include bacteria, archaea, protozoa, certain algae, and certain fungi.

Bacteria

Bacteria are single-celled organisms that lack a nucleus. They are part of the domain Bacteria.

Archaea

Archaea are single-celled organisms that, like bacteria, lack a nucleus. However, they are part of a separate domain, Archaea.

Protozoa

Protozoa are single-celled organisms that are part of the domain Eukarya. They have a nucleus and are often motile.

Algae

Certain algae are single-celled organisms. These can be found in both freshwater and marine environments.

Fungi

Certain fungi, such as yeasts, are single-celled organisms. They are part of the domain Eukarya.

See Also

• Multicellular organism
• Cell (biology)
• Microorganism