Question

32.

Answer 1

Answer:

Part 1: Cephalization, an evolutionary trend in zoology, can be defined as the concentrating or development of the nervous tissue (nerve ganglia), sense organs and mouth towards the front end or head part of an animal.

Part 2: Cnidarians do not exhibit cephalization. They are radially symmetrical, meaning that similar parts of their body are arranged symmetrically in clusters around one central point or axis.

Yes and no. Cephalization would be both an advantage as well as a disadvantage to this organism.

Part 3: Two major disadvantages of cephalization are:

i) It is difficult for the animal to sense what is happening towards the posterior end of the body.

ii) Not all cephalized organisms can move their head 180 degrees, such as birds.

Explanation:

Part 1: In simple terms, animals that exhibit a defined anterior portion or head facing towards the front of their body are said to be fully cephalized.

Other characteristic features of cephalization in animals include bilateral symmetry, concentrated sense organs and a mouth towards the anterior (front) part of the body which results in forward movement.

Part 2: Cnidarians, the organisms belonging to the Phylum Cnidaria or Coelenterata, comprise of mostly primitive marine organisms such as corals, jellyfish and sea anemones. They do not have concentrated sensory organs or nerve ganglia in the anterior portion of their body, as in no head is distinctly present.

They have two layers of cells and tissues and lack distinctive organs. They are characterized by the presence of a sac-like coelenteron or body cavity with one opening which acts like a mouth for ingestion.

Cephalization would be an advantage to this organism because it would have led to the development of a brain, which would have made these primitive organisms more advanced in intelligence.

However, radially symmetrical and free-floating organisms like Cnidarians need to be able to find and ingest food, as well as detect danger from all directions, not only towards the front end of their body. Sense organs grouped towards the front end of the body would have been more of a disadvantage to them and made them prone to danger.

Part 3: Though acephalic organisms lack a brain and an advanced central nervous system, their bodies are well-adapted to their habitat. Nerve nets in their bodies have been developed in such a way that their neural tissue is able to generate rapid excitation in the muscles and exhibit adequate sensory processing.

These organisms, which can float or be tossed in any direction depending on the water currents, are better equipped to deal with danger by means of this nerve net as compared to cephalization.