Answer: It is because it makes it more efficient to study organisms.
Explanation: Biologist classify organisms by considering similarities between them. The organisms which have closely related characteristics are placed in a separate domains by biologists. Domains are further divided into 6 Kingdoms. According to modern classification system, domain is largest unit of biological classification.
A) single loop Fish have a two-chambered heart in which a single-loop circulatory pattern takes blood from the heart to the gills and then to the body.