At some point in their lives, all chordates have a flexible supporting rod in their backs called a
A. notochord****
B. gill.
C. nerve cord.
D. backbone.
correct
Gill
The correct answer is A. notochord.
To answer this question, we need to understand what a chordate is and what distinguishes them from other organisms. Chordates are a group of animals that belong to the phylum Chordata. They are characterized by certain key anatomical features. One of these features is a flexible supporting rod in their backs called a notochord.
To find the correct answer, we can rule out the options that are not applicable.
Option B - Gill: While many chordates do possess gills, this is not the defining characteristic of a chordate.
Option C - Nerve cord: Chordates do have nerve cords, but again, this is not the specific anatomical feature that distinguishes them from other organisms.
Option D - Backbone: Chordates do have backbones, but not all chordates have developed a true backbone.
Therefore, the correct answer is A - Notochord. The notochord is a characteristic feature of all chordates at some point in their lives. It serves as a flexible support structure and plays a key role in their development.