Question

Assertion: Nerve cells in coelenterate have complete coordination in their body
Reason: True nerve cell occur for the first time in coelenterate
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

Coelenterate possesses a very primitive type of nerve system. There is a constant need to maintain coordination between these systems. Nerve in hydra is the beginning in the evolution of the nervous system.

Complete answer:
Coelenterates have the separate mechanism for digestion, respiration and excretion etc evolved for the first time. Thus, there is a constant need to maintain a coordination between these systems. Nerve cells are developed for this purpose for the first time in the coelenterate. True nerve cell or ganglion cell occur for the first time in coelenterata. A polar neuron is found in coelenterata. Nervous System well developed and concentrated. It consists of three parts: central nervous system and rectal nervous system and peripheral nervous system.
The nervous system of prawn or arthropods is of the annelidan type however it is somewhat larger and has more fusion of ganglia. Nervous System well developed and formed by ectoderm. It is formed by the central nervous system, peripheral nervous system and autonomic nervous system. At certain places the nervous tissue is concentrated to form distinct nerve cords. A nerve net consists of interconnected neurons lacking a brain or any form of cephalization. A nerve net is a simplest form of a nervous system found in multicellular organisms. This nervous system allows cnidarians to respond to physical contact.
Therefore, the correct answer is A i.e. Both assertion and reason are correct and reasons is the correct explanation for assertion.

Note: The anatomy and positioning of nerve nets can vary from organism to organism. This is better suited to controlling more complex movements than a diffuse nerve net. It can detect food and other chemicals in a rudimentary way.