Nucleus
The major organelle of an amoeba is the nucleus. Its main function is to direct cellular activities—such as reproduction, feeding, and growth—by regulating the production of specific enzymes that drive the cell’s biochemical reactions. The nucleus contains the amoeba’s DNA, the “blueprint” for cellular function, which instructs the cell how to synthesize these enzymes.
Each amoeboid cell contains at least one nucleus, and larger cells are often multinucleate. The morphology, size, and number of nuclei can serve as useful differential characters. According to the classification of Raikov (1982), two principal types of nuclei occur in amoebae:
Vesicular nuclei, with one usually central nucleolus, sometimes accompanied by a few very small additional nucleoli.
Ovular nuclei, containing several to many small nucleoli (Fig. 1).
Fig. 1. Left: vesicular nuclei of Difflugia biconcava and Netzelia gramen. Right: ovular nuclei of Difflugia amphora and D. distenda.
Below: photomicrographs of some characteristic nuclei:
