In biological taxonomy, which of the following best describes how organisms are classified within a phylum?

• A. Based on shared fundamental body plans and major structural features
• B. Based solely on their habitat and ecological role
• C. According to their ability to interbreed and produce fertile offspring
• D. By similarities in their DNA sequences only

Answer: (A)

Verified step by step guidance

1. Understand the concept of biological taxonomy: Biological taxonomy is the scientific system used to classify and organize living organisms into hierarchical categories based on shared characteristics.
2. Recognize the role of a phylum in taxonomy: A phylum is a high-level taxonomic rank that groups organisms based on shared fundamental body plans and major structural features. This is broader than classifications based on DNA or reproductive compatibility.
3. Eliminate incorrect options: Consider why 'Based solely on their habitat and ecological role' is incorrect, as taxonomy focuses on physical and genetic traits rather than ecological roles. Similarly, 'According to their ability to interbreed and produce fertile offspring' applies to species, not phylum. Lastly, 'By similarities in their DNA sequences only' is too narrow for phylum classification, which includes structural features.
4. Focus on the correct classification criteria: Organisms within a phylum are grouped based on shared fundamental body plans and major structural features, such as symmetry, presence of a backbone, or segmentation.
5. Conclude the reasoning: The correct answer is 'Based on shared fundamental body plans and major structural features,' as this aligns with the principles of taxonomy at the phylum level.