Question

Which one of the following animals possesses nerve cells but no nerves?

• A. Hydra
• B. tapeworm
• C. earthworm
• D. frog's tadpole.

Answer 1

The Correct Option is A

The question asks which animal possesses nerve cells but does not have an organized set of nerves. Let's analyze each option to identify the correct answer.

1. Hydra: Hydra, belonging to the phylum Cnidaria, is a simple organism with a nerve net. Although it has nerve cells (neurons), these are not organized into distinct nerve strands. Instead, they form a decentralized network throughout the body, which allows it to respond to stimuli. This setup means that while hydras have nerve cells, they do not have centralized nerves like more complex organisms.
2. Tapeworm: Tapeworms are parasitic flatworms which have a simple nervous system consisting of a pair of nerve cords and transverse nerves that connect them. This constitutes a more organized nerve structure compared to a simple nerve net.
3. Earthworm: Earthworms possess a more advanced nervous system with a central nerve cord and ganglia. These components form a distinct nerve structure, which assists in coordinated movement and responses.
4. Frog's Tadpole: Tadpoles, the larval stage of frogs, have a well-developed nervous system with a spinal cord and nerves, as they are vertebrates. This means they possess organized nerves.

Therefore, the correct answer is that a Hydra possesses nerve cells but no centralized nerves.

The other options have more complex and organized nervous systems, making Hydra unique among the given choices.