Final answer:
To measure symmetry in organisms such as echinoderms, you would divide them into five equal parts. However, for bilateral symmetry like that of a human face, the division should be into two equal parts across the midsagittal plane.
Step-by-step explanation:
To measure symmetry in biology, specifically referring to the symmetry of organisms, you should ideally divide the organism based on the type of symmetry it displays. In the context of echinoderms, which exhibit radial symmetry, the organism could be divided into five equal parts as hinted by the illustration of the five-part radial symmetry of two echinoderms. However, when measuring the symmetry of a human face, which is typically an example of bilateral symmetry, the face should be divided into two equal parts. This split should be made across a unique plane, often referred to as the midsagittal plane. In the case of bilateral symmetry, an object can be divided into two symmetrical halves that are mirror images of each other.