USA Biology Olympiad (USABO) Practice Exam

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Prepare for the USA Biology Olympiad (USABO) Exam. Enhance your skills with engaging multiple-choice questions, detailed explanations, and essential biology concepts. Get exam-ready and boost your performance with expert tips and study resources!

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Which of the following is not a universal trait of all chordates?

Notochord
Dorsal nerve cord
Pharyngeal slits
Vertebrae

The correct answer is: Vertebrae

In the context of chordate anatomy, all members of the phylum share three key characteristics during some stage of their life cycle: a notochord, a dorsal nerve cord, and pharyngeal slits. The presence of a notochord provides structural support, the dorsal nerve cord is integral for the nervous system, and pharyngeal slits are involved in various functions including respiration and filter feeding. Vertebrae, on the other hand, are a characteristic feature of vertebrates, which represent a subphylum within chordates. While all vertebrates possess vertebrae, not all chordates do; for example, the subphylum Cephalochordata (lancelets) and Urochordata (tunicates) maintain only the basic chordate features mentioned earlier throughout their lives or in their larval stages. Therefore, vertebrae are not a universal characteristic of all chordates, distinguishing this trait from the others. This is why the answer indicating vertebrae is correct, as it does not apply to all members of the chordate lineage.