BIOLOGY 2 Marks Questions

Cnidarians exhibit two basic body forms called polyp and medusa. The former is a sessile and cylindrical form like Hydra, Adamsia, etc. Whereas, the latter is umbrella-shaped and free-swimming like Aurelia or jelly fish.

The aquatic animals come under the class Amphibia. That is, members of this class live in both aquatic and terrestrial habitats, hence they are called amphibians.
The names of four amphibians are as follows:
1. Rana tigrina
2. Salamander
3. Ichthyophis
4. Hyla

Superclass Tetrapoda has been classified into four classes which are the following:
(1) Amphibia
(2) Reptilia
(3) Aves
(4) Mammals

Similarities in Hemichordata and Chordata:
1. Notochord is found in both.
2. Dorsal tubular nerve cord is found in both.
3. Gill holes are found in the pharynx in both, that is, the wall of the pharynx is perforated
4. The tendency of formation of mesoderm is similar.
5. Trisegmental body cavity is found in both.

Radial symmetry is found in phyla Cnidaria, Ctenophora and Echinodermata. Cnidaria and Ctenophora phyla have been placed in Radiata. Radial symmetry is found in Echinodermata but many of their properties are not found in Cnidaria and Ctenophora. Therefore, the radial symmetry found in Echinodermata has originated from bilateral symmetry. Hence it is called second symmetry.

Triploblastic : Those animals in which the developing embryo has a third germinal layer, mesoderm, in between the ectoderm and endoderm, are called triploblastic animals (platyhelminthes to chordates).
Diploblastic: Animals in which the cells are arranged in two embryonic layers, an external ectoderm and an internal endoderm, are called diploblastic animals, e.g.. coelenterates.

Segmentation: Dividing the body into parts is called segmentation. Segmentation is of two types:
(i) Superficial segmentation: In this type of segmentation the animal appears segmented only from outside, but is not divided from inside. This kind of segmentation is found in coelenterate and some other pseudocoelomate animals.
(ii) Metameric segmentation: In some animals, the body is externally and internally divided into segments with a serial repetition of at least some organs. For example, in earthworm, the body shows this pattern called metameric segmentation and the phenomenon is known as metamerism. This type of segmentation is found in Annelida, Arthropoda and vertebrates.