Answer: The correct answer for the blank is-
Morphology.
Step-by-step explanation:
Morphology can be described as a branch of biology, which deals with the study of structure and forms (morphological/ physical traits such as height and color of individual, eye color, hair color and shape etc) of organisms without considering their function/roles.
Sometimes appearance of an organism is a key to determine a taxon.
Therefore, in this aspect, scientists use morphology that corresponds to appearance of organisms.