Question

Which of the following statements about the diversity of animal nervous systems is accurate?

a) animals that are not bilaterians do not have brains

b) all animals have nervous systems

c) all bilaterian animals have brains

d) chordates are the only animals with brains

Answer 1

The correct options are a and d

a. Basically, bilateral symmetry means the organism's body is divided into two halves-left and right mirror. Organisms with this bilateral symmetry have a proper well developed organized brain. In this symmetry, there is a tube that connects the cavity from mouth to anus* and a nerve cord with a large ganglion at the front which is the brain. As opposed to bilaterians, non-bilaterians do not have this organized proper structure called brain like the sponges.

b. Although most of the animals possess a nervous system, not all of them have this system. Sponges, placozoans, and mesozoans do not possess a nervous system. They have simple body plans. The proper organized nervous system can be seen in chordates, i.e in higher animals.

c. No, not all bilaterian animals have a brain. These include the sea cucumbers, brittle stars, sea stars that have other evolved feature i.e the nerve net. They don't have a properly organized central nervous system. This nerve net is spread somewhat more or less evenly across the body.

d. Yes, chordates are the only animals with brains. These include the vertebrates which are highly evolved animals. Basically, in these, the nerve cord develops into the brain and spinal cord and this comprise of the central nervous system. The brain is evolved in higher organisms to deal with various complex activities and accordingly co-ordinate them. They interact with special cells called neurons.