a)Protozoa are unicellular organisms that present some characteristics in common with animal cells.
In comparison to pluricellular organisms, protozoa are closer to the animal kingdom than to plants, as they are heterotrophs, they have a rudimentary locomotion system (amoeboid movements, cilia, flagella), they do not have cell wall, and some species present structures that resemble the structures of a primitive digestive system, with a cytostome (mouth) and cytopyge (anus) specialized in digestion and excretion.
There is strong support for the hypothesis that animal cells evolved from protozoa.
Protozoa are eukaryotic cells and, as a result, have organelles and structures common to this kind of cell: endoplasmic reticula, a Golgi apparatus, digestive vesicles, ribosomes, mitochondria, a nucleus with genetic material, karyotheca, etc. All these elements are found dispersed throughout the cytoplasm. Protozoa do not have cell walls.
Protozoa from the mastigophora group (such as trichomonas) have flagella and others from the ciliated group (like paramecium) have cilia.