Question

In which of the following the nuclear dimorphism is seen?
A. Entamoeba
B. Leishmania
C. Trypanosoma
D. Paramoecium

Answer 1

Hint: Nuclear dimorphism can be defined as the presence of two different types of nuclei i.e., macronucleus (somatic type) and micronucleus (generative type), within the single cell. It is the characteristic feature of certain ciliate protozoa.

Complete answer:
Option (A) is incorrect. Entamoeba exists in two forms: trophozoite and cystic forms. The trophozoite is a mature or active form of Entamoeba and it resembles completely to amoeba in its structure possessing a single nucleus, pseudopodia for movement, and the cytoplasm is differentiated into outer ectoplasm and inner endoplasm. The cystic form is the inactive form of Entamoeba and resembles the trophozoite except that it is smaller than trophozoite having no pseudopodium. Hence, Entamoeba does not show nuclear dimorphism because of the presence of only a single nucleus in the cell.
Option (B) is incorrect. Leishmania, a flagellated protozoan, does not show nuclear dimorphism because of the presence of only one well-defined nucleus within the cell.
Option (C) is incorrect. Trypanosoma is a flagellated protozoan that does not show nuclear dimorphism. It has an elongated body having a streamlined shape that is tapering at its ends. The cell contains a single nucleus along with other cell organelles and also an unusual organelle called kinetoplast (functions as a single large mitochondria).
Option (D) is correct. Paramoecium is a ciliated protozoan that is known to show the nuclear dimorphism due to the presence of two different types of nuclei within the cell. These nuclei are micro and macronuclei which are known to perform the function of reproduction and controlling metabolism, respectively.

Structure of Paramoecium.

Hence, the correct option is (D).

Note: The term dimorphism means the existence of two forms or shapes, especially within the species that differ in one or more characteristics such as size, shape, function, etc. Paramoecium is a slipper-shaped unicellular ciliate protozoan that possesses numerous cilia on its body wall. It possesses two nuclei of different nature within the cell. The micronucleus is known to perform reproductive functions and is known to generate the macronucleus which has its role in regulating and controlling the metabolism.