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.
The outer layer of the skin covering the exterior body surface<span> of vertebrates ... the primary tissue of higher plants composed of </span>thin<span>-walled </span>cells<span> that remain capable of ... a swelling on a plant stem consisting of overlapping immature </span>leaves<span> or petals ... Older xylem </span>near<span> the center of a woody stem that no longer conducts water.</span>