CBSE Class 9 Answered

Alimentary canal is also called digestive tract. It is the passage through which food passes, starting at the mouth and ending at the anus. It includes the mouth, pharynx, oesophagus, stomach, small intestine and large intestine. Alimentary canal is involved in consuming food, digesting it, and expels the waste products.

When the body can be divided into 2 symmetrical halves by only one longitudinal plane passing through the axis, the symmetry is called bilateral symmetry. In other words,  it is the symmetrical arrangement, as of an organism or a body part, along a central axis, so that the body is divided into equivalent right and left halves by only one plane.

Triploblastic refers to a complex level of tissue organization, consisting of three embryological layers i.e. ectoderm, endoderm and mesoderm.

Dorsal nerve cord is a hollow cord dorsal to the notochord, made up of a bundle of nerve fibers. It runs down the back and connects the brain with the lateral muscles and other organs. It is is one of the embryonic features unique to chordates. It is formed from a part of the ectoderm. It is later modified into the brain and spinal cord.