Question

{"given":"We need to identify which animal has nerve cells but lacks organized nerves. The question asks about the presence of individual nerve cells versus organized nervous structures like nerve cords or central nervous systems.","key_observation":"Different animals have varying levels of nervous system organization. Cnidarians like Hydra have the most primitive nervous system consisting of scattered nerve cells forming a nerve net, but they lack organized nerves, nerve cords, or centralized nervous systems that are found in higher animals.","option_analysis":[{"label":"(A)","text":"Hydra","verdict":"correct","explanation":"Hydra is a cnidarian that possesses individual nerve cells arranged in a diffuse nerve net pattern throughout its body, but it completely lacks organized nerves, nerve cords, or any form of central nervous system. This represents the most primitive form of neural organization."},{"label":"(B)","text":"Tapeworm","verdict":"incorrect","explanation":"Tapeworms are flatworms (Platyhelminthes) that possess a simple but organized nervous system with nerve cords running along the body and a primitive brain-like structure called cerebral ganglia."},{"label":"(C)","text":"Earthworm","verdict":"incorrect","explanation":"Earthworms are annelids with a well-developed nervous system including a ventral nerve cord, segmental ganglia, and a brain-like cerebral ganglion, representing a much more advanced neural organization than just scattered nerve cells."},{"label":"(D)","text":"Frog's tadpole","verdict":"incorrect","explanation":"Frog tadpoles are vertebrates with a complete and complex nervous system including a well-developed brain, spinal cord, and peripheral nerves, representing the highest level of neural organization among the given options."}],"answer":"(A)","formula_steps":[]}