Levels of organisation

Abstract

Those animals and plants which are described as acellular, or non-cellular, that is, whose body plan is not organised on a multicellular basis, form the least conspicuous organisms in the biosphere. Their share of the total planetary biomass, however, is considerable and they play a vital role in the biotic economy, both as primary producers and as scavengers. They include the Protophyta, diatoms, bacteria, the simpler algae, the Protozoa and the simpler fungi. Many groups have parasitic forms which are frequently pathogenic in higher plants and animals.