Page 2 - 11-Bio-7 The Kingdom protista

7. The Kingdom Protista (or protoctista) eLearn.Punjab

The Kingdom Protista consists of a vast assortment of primarily aquatic eukaryotic organisms whose
diverse body forms, types of reproduction, modes of nutrition and lifestyles make them difficult to
characterize. Basically, this kingdom is defined by exclusion i.e., all members have characteristics
that exclude them from the other four kingdoms.

All protists are eukaryotic and have evolved from prokaryotes. Another reason for creating a
separate kingdom arises from the difficulty in placing certain eukaryotic organisms in the appropriate
kingdom. This difficulty is a consequence of the fact that the other eukaryotic kingdoms have their
evolutionary origin in kingdom Protista. The other eukaryotic kingdoms Plantae, Fungi, and Animalia
arose from protists in various ways.

The protists are unicellular, colonial or simple multi cellular organisms that possess a eukaryotic
cell organization. Eukaryotic cells, the unifying feature of protists, are common to complex multi-
cellular organisms belonging to the three eukaryotic kingdoms (Fungi, Plantae and Animalia) but
clearly differentiate protists from members of the prokaryotic kingdom (Monera). Unlike plants
and animals, however, protists do not develop from a blastula or an embryo.

The kingdom protista contains four major groups of eukaryotic organisms which are : single celled
protozoans, unicellular algae, multicellular algae, slime molds and oomycotes.

HISTORICAL PERSPECTIVE

In 1861, John Hogg proposed the kingdom Protoctista for microscopic organisms. In 1866, Ernst
Haeckel suggested creating the Kingdom Protista to include bacteria and other microorganisms
(such as Euglena) that kingdom. He, however, separated blue green algae and bacteria (prokaryotes)
from nucleated protists and placed them in a separate group he called Monera, within the kingdom
Protista.

In 1938, Herbert Copeland elevated the prokaryotes to kingdom status, thus separating them from

Protista. In five kingdom system of Robert Whittaker (1969) only unicellular eukarayotes were

placed in kingdom Protista. Currently this kingdom also includes colonial and simple multicellular

eukaryotes as well. Margulis and Schwartz (1988) modified the five kingdom system. Protista or

Protoctista is one of the five kingdoms.

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