Final answer:
Anatomical structures are used in Dichotomous Keys due to their distinct and identifiable nature, which helps differentiate and correctly classify organisms based on evolutionary relationships discerned through homologous structures, compared to analogous structures that serve similar functions but do not imply close relatedness.
Step-by-step explanation:
Anatomical structures are often used when constructing a Dichotomous Key because they provide clear, visible, and distinct characteristics that can be used to differentiate and classify organisms. Anatomical features, especially those that are homologous, reflect an organism's evolutionary history and provide a reliable basis for categorization. Homologous structures, such as the bones in a whale's flipper and human arms, have a common embryonic origin, suggesting shared ancestry.
On the other hand, analogous structures perform similar functions but do not indicate close evolutionary relationships. For instance, the wings of a butterfly and a bird are analogous but not homologous. Utilizing anatomical characteristics helps ensure accurate identification and proper placement on the phylogenetic tree, avoiding confusion with analogous features.