Branch of biology that describes patterns of organismal variation.

• A. Systematics
• B. Cladistics
• C. Speciation
• D. Species

Answer: (A)

Systematics is the branch of biology that describes patterns of organismal variation and organizes life's diversity. It brings together naming, description, and classification (taxonomy) with the reconstruction of evolutionary relationships (phylogenetics) to explain how organisms vary and are related across all groups. The question points to describing and organizing variation, which systematics does best because it encompasses the broad patterns of diversity and the framework used to classify them.

Cladistics is a method within systematics focused on inferring evolutionary relationships based on shared derived traits, emphasizing branching patterns rather than describing all patterns of variation. Speciation describes how new species arise, a process rather than a field. Species refers to a taxonomic unit, not the discipline that studies variation.