Organism Classification: Identifying Single-Celled Life

The question asks to identify an example of a single-celled organism from the provided list. A single-celled organism, also known as a unicellular organism, consists of only one cell. This single cell performs all essential life functions.

Option Analysis: Evaluating Organism Types

• Protozoa: These are typically single-celled eukaryotic organisms. They exhibit characteristics of animals and are found in various environments. Examples include amoebas and paramecia. This fits the definition of a single-celled organism.
• Arthropods: This is a large phylum of invertebrate animals that includes insects, arachnids, myriapods, and crustaceans. They are characterized by their exoskeleton, segmented body, and jointed appendages. Arthropods are complex multicellular organisms.
• Echinoderms: This phylum includes marine animals like starfish, sea urchins, and sea cucumbers. They possess radial symmetry and are exclusively marine. Echinoderms are multicellular organisms.
• Annelids: This phylum consists of segmented worms, such as earthworms and leeches. They have bilateral symmetry and a true coelom. Annelids are multicellular organisms.

Conclusion: Single-Celled Example

Based on the analysis, Protozoa are the only group listed that exclusively comprises single-celled organisms. The other options (Arthropods, Echinoderms, Annelids) are all categories of complex multicellular animals.

Therefore, Protozoa is the correct example of a single-celled organism.