Question

Which animal possesses the most primitive nervous system?

• A. Earthworm
• B. Hydra
• C. Frog
• D. Human

Hint:

The simplest nervous system in animals is the nerve net, found in Cnidarians such as Hydra and jellyfish. It lacks a central brain and allows impulses to move in different directions.

Answer 1

The Correct Option is B

Concept: The nervous system is responsible for coordination and response to stimuli. In the animal kingdom, the complexity of the nervous system increases progressively during evolution. The simplest type of nervous system is a nerve net, where nerve cells are loosely connected without forming a centralized brain or spinal cord. Primitive multicellular organisms show this basic organization. As animals evolved, the nervous system became more complex, forming ganglia and eventually a well-developed brain and spinal cord in higher animals.

Step 1: Understanding the nervous system of Hydra. Hydra, a member of the phylum Cnidaria, possesses the most primitive type of nervous system known as a nerve net. In this system:
• Nerve cells are distributed throughout the body.
• There is no central brain.
• Impulses can travel in multiple directions across the body.

Step 2: Comparison with other animals.
• Earthworm – possesses a well-developed nervous system with a nerve cord and ganglia.
• Frog – has a centralized nervous system with brain and spinal cord.
• Human – has a highly developed nervous system. Thus, among the given options, the organism with the most primitive nervous system is Hydra.