IB Biology Practice Exam 2025 – Complete Study Resource

The Kingdom classification encompasses the most diverse group of organisms because it represents a broad category in the hierarchy of biological classification. The Kingdom level includes a wide range of life forms across different domains, such as animals, plants, fungi, and protists. Each Kingdom can contain numerous Phyla, which in turn consist of various classes, orders, families, genera, and species. This hierarchical structure means that the Kingdom level includes a vast array of organisms, which are significantly more diverse in terms of evolutionary history, structural characteristics, and ecological roles compared to the other classifications listed.

For instance, while an Order might contain a number of Families, each Family is generally more specialized and contains fewer species. Phylum, though broader than Family and Order, still groups organisms that share more specific characteristics than the broad classifications found in the Kingdom. Hence, the diversity of life represented at the Kingdom level is unmatched by the other taxonomic ranks, making it the most encompassing category.