The Protozoa in Broad Perspective

Abstract

Knowledge of the diversity of life, within a context of unifying biological concepts, is a valuable source of insight in advancing biological theory. A thorough understanding of biological diversity including variations in form, function, ecological roles, modes of reproduction, and genetic control of life processes is a rich source of information whereby creative and often practical insights are generated into the nature of life. Hence, a complete understanding of the broad range of living things (particularly some of the smallest and also most intricately organized forms of life) is an asset in advancing biological theory and devising innovative approaches to modern biological research. The diversity of protozoa provides a unique opportunity to explore some of these major biological themes in a comparative format. Protozoa span a spectrum of sizes from microscopic forms, barely larger than many bacteria, to those clearly visible with the unaided eye, and comparable in size to some of the smallest metazoa. The protozoa comprise a vast ensemble of organisms with wide diversity in morphology and environmental adaptations. One of the major unifying principles, however, amidst this diversity is the central defining idea of a protozoan; ie, a one-celled or colonial (polycellular) organism possessing all of the elegantly coordinated processes of life, usually (though not exclusively) animallike, within the boundaries of a single cell. Even the colonial forms, designated here as polycellular, may be considered fundamentally a loosely coupled set of single cells with most functions of the colony duplicated within each of the member unit cells.