Question

Which one of the following is diploblastic?
(a)Pennatula
(b)Paramoecium
(c)Polystomella
(d)Entamoeba

Answer 1

Hint: Among the group of organisms given, the genus that shows diploblastic organisation belongs to marine, colonial cnidarians. These organisms exhibit the property of bioluminescence. A typical example is sea pens.

Complete answer:
Pennatula has a diploblastic organisation. Let's begin the explanation by learning about the diploblastic organisation. As diplo means double and blastic means cell layer, animals in which the cells are arranged in two embryonic layers, an external ectoderm and an internal endoderm, are said to be ‘diploblastic.’ When a mesodermal layer is present between ectoderm and endoderm, the organism is said to be ‘triploblastic.’

Additional Information: There are certain characters that help in the classification of an organism. These are:
Level of body organisation: It means the organism is made of only cells, or cell combines to form tissues, have organ or organ system organization.
Body Symmetry: It is the distribution of body parts in an organism in reference to the body axis. If the organism does not divide into two equal halves, it is known as ‘asymmetrical’ like sponges. The other two are radial and bilateral. ‘Radial symmetry’ is in which the organism can be divided into two halves through any plane while when an organism can be divided into identical right and left halves only in one plane, it is said to be ‘bilateral.’
Germ layers: It is defined as layers that are responsible for the formation of tissues and organs. Based on this, organisms are of two types. The ones who have two layers are ‘diploblastic’ while higher organisms have three layers known as ‘triploblastic.’ All animal phyla except sponges and coelenterates are triploblastic
Body Cavity: Scientists also keep the presence of the body cavity in consideration while classifying organisms. This body cavity is known as coelom and is lined by the mesoderm layer. Annelids, molluscs, arthropods, echinoderms, hemichordates and chordates are coelomates. In some organisms like in aschelminthes, there exist pouches in between ectoderm and endoderm. Such organisms are called ‘pseudocoelomates.’
So, the correct answer is, ‘Pennatula.’

Note: -Paramoecium is one of the simplest and most abundant life forms of the group Protozoa. Specialized tissues are absent in paramoecium. Instead, it is a mass of protoplasm, perhaps representing a single cell.
-Polystomella is also a unicellular, dimorphic protozoan. It is about 1 mm in diameter.
-Along with the above organisms, entamoeba is also included in the Protozoa. It lives as internal parasites or commensals of animals.