A lab observation notes that a zoologist identifies a digestive tract, excretory organs, and reproductive organs working together in one animal. The observation points to:

Correct Answer: D

organ-system level of organization

Organ-system level organization occurs when organs are arranged into coordinated systems. It is found in more complex animals such as annelids, molluscs, arthropods, and echinoderms. This MCQ belongs to the Animal organization topic in Animal Diversity-I and is written to test concept understanding rather than memorized wording.