Question

Hydra recognizes its prey by

• A. Special organs
• B. Chemical stimulus of prey
• C. Nematocyst
• D. Mechanical stimulus of prey

Answer 1

The correct option is D Mechanical stimulus of prey

• Hydra recognizes its prey by mechanical stimulus. Despite, their simple construction, the tentacles of Hydra are extraordinarily extensible and can be four to five times the length of the body.
• Once fully extended, the tentacles are slowly maneuvered around waiting for contact with a suitable prey animal. Upon contact, nematocysts on the tentacle fire into the prey, and the tentacle itself coils around the prey. Within 30 seconds, most of the remaining tentacles will have already joined in the attack to subdue the struggling prey.
• Within two minutes, the tentacles will have surrounded the prey and moved it into the opened mouth aperture. Within ten minutes, the prey will have been enclosed within the body cavity, and digestion will have started.
• Hydra is able to stretch its body wall considerably in order to digest prey more than twice its size. After two or three days, the indigestible remains of the prey will be discharged by contractions through the mouth aperture.