Question

Assertion: The Ambulacral system plays a major role in locomotion of echinoderms.
Reason: Hydraulic pressure of fluid and contraction of muscle of tube feet make possible movement of echinoderm.
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

Hint: The Echinoderms are able to move due to the hydraulically governed system in their body which also governs the vital functions of the body such as respiration and excretion.

Complete answer
Echinoderms are inhabitants of deep marine water. They are invertebrates with spiny skin that helps them to protect themselves from predators. The ambulacral system involves typical grooves that extend from the mouth to the respective terminal body part of the organism. The ambulacral system is a hydraulic system which consists of circular rings around the oesophagus and has radial canals which lead to the ambulacrum. Each of these radial canals in the crinoids run along each arm into an ambulacral groove and the tube feet. It is due to this that the locomotion of the echinoderms is possible.
This water vascular system is also a very unique type of system in the body which helps in vital functions of the body such as respiration, excretion, locomotion and even feeding. The principle of hydraulics governs this system and the echinoderms are able to locomote from one place to another.
Therefore, we can say that both the assertion as well as the reason are correct statements and the reason mentioned above is the correct explanation for the assertion.

Hence, option A is the correct answer.

Note:
Besides locomotion this system helps in respiration, muscle contraction, etc. echinoderms have poor respiratory systems. Thus, they use their ambulacral tubes to respire along with typical gills. These ambulacral tubes help them to take in oxygen and give out carbon dioxide throughout the body. This system is commonly observed in star-fish.