Question

Assertion: Locomotion in Hydra is carried out by two types of contractile cells.
Reason Muscle fibres are lacking in Hydra.
A) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
C) Assertion is correct but Reason is incorrect
D) Both Assertion and Reason are incorrect

Answer 1

Hydra belongs to phylum Cnidaria, class Hydrozoa of small freshwater species. They are native to temperate and tropical climates. Hydra fascinates biologists because of their capacity to regenerate – they do not appear to die of old age, or to age at all.

Complete answer:
Hydra is a species of sessile Coelenterate that lives in freshwater. It stays attached to those objects (substratum) in the water using its pedal disc. Hydra moves about in search of food or in response to light or chemical stimulus. Hydra is deficient in muscle cells.

As a result, the periodic expansion and contraction of two groups of contractile cells, epitheliomuscular cells and nutritive muscular cells, contribute significantly to Hydra locomotive movements. Hydra locomotion takes many forms, including floating, looping, and somersaulting, thanks to the aid of these cells.

Additional Information: The muscle fibres are the fibres that are present along the length of the muscles. In the case of humans, the muscle fibres comprise actin and myosin filaments. The contraction and expansion of the muscle fibres bring about movement. The contraction of the muscles is brought about by the calcium ion which is released in response to the nerve impulses.

So, the correct answer is 'Both Assertion and Reason are correct and Reason is the correct explanation for Assertion' option A.

Note: The phylum Cnidaria, which is distinguished by radially symmetrical bodies, the presence of stinging tentacles, and a simple gut with only one opening (gastrovascular cavity). The body is a hollow tube made up of two cell layers separated by an unstructured gelatinous layer (mesoglea).