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Comparative studies of natural groups of organisms
Chapter
Three

Comparative studies of natural groups of
organisms
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Introduction

In comparative studies of natural groups, organisms are classified on the basis of
their shared characteristics and common ancestry. The grouping is done in relation to
physiology, embryonic development, and phylogenetic relationship. In this chapter, you
will learn about viruses, and five kingdoms of organisms, namely, Monera, Protoctista,
Fungi, Plantae, and Animalia. The competence developed will enable you to appreciate
diversity of life, evolutionary processes, ecological roles, human health, biotechnology,
and conservation.

autotrophs) were conceived. This system was
Think adopted by many taxonomists and gained a
wider popularity over the artificial system
The world without knowledge on of classification.
classification.
In 1866, the third kingdom of unicellular
3.1 General overview of classification
The natural groups of organisms are the broad organisms, Protista was put forward by
categories of organisms formed by placing Ernst Haeckel after its long placement under
together organisms which are naturally kingdom Animalia since when it was first
or evolutionarily related for comparative discovered by Antonie van Leeuwenhoek
purposes. This enables taxonomists across in 1674. The discovery of the scanning
the world to compare for various reasons electron microscope facilitated microscopic
how individual groups of organisms are studies, and it made it possible to discern
related. The number of natural groups of eukaryotes (organisms with distinct nucleus)
organisms, for example at kingdom level from prokaryotes (organisms lacking a
has been steadily increasing since the 18 clearly defined nucleus but have their DNA
th
century, when Carolus Linnaeus introduced lying free in the cytoplasm). This led to
the natural classification system from the establishment of kingdom Monera, in
which kingdom Animalia (multicellular which all types of bacteria were placed.
heterotrophs) and Plantae (multicellular The placement of multicellular eukaryotic

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