Page 120 - Biology_F5

Comparative studies of natural groups of organisms

Exercise 3.2 were placed under kingdom Monera, while
all single-celled eukaryotes constituted
1. Briefly explain why the Carolus kingdom Protoctista.
Linnaeus classification system
was silent about kingdom Monera. Recent phylogenetic studies have shown

2. Citing the significance of each, that even Protoctista is no longer a group
FOR ONLINE READING ONLY
explain two ways by which of naturally related organisms. This makes
bacteria can reproduce. it difficult to clearly define the kingdom
Protoctista. For example, protoctists such
3. Give any four reasons to justify as algae have chloroplasts; hence, they are
the placement of cyanobacteria photoautotrophs. Amoeba is a heterotroph,
under division Eubacteria.
while slime molds and water molds
4. Explain why some taxonomists are saprophytes, sharing many features
separate Cyanophytes from in common with fungi than with other
division Eubacteria and place protoctists. It is for this reason, kingdom
them in division Cyanobacteria. Protoctista is deemed controversial by

5. Using relevant examples, explain contemporary taxonomists. This is why the
the ways in which bacteria are classification system has advanced from
ecologically and economically five to eight kingdoms. Members under
important. kingdom Protoctista have been separated
6. With examples, explain why into two kingdoms, namely Protozoa and
bacteria are said to be the Chromista. More recently, they have been
successful colonisers. separated into three kingdoms: Protozoa,
Chromista, and Archezoa. However, this
3.4 Kingdom Protoctista text will focus on Protoctista as a kingdom
for convenience.
Task 3.4
Use internet sources and the library to Protoctists can be defined as unicellular
search for information on the kingdom eukaryotic organisms other than fungi,
Protoctista. plants, and animals. Evolutionarily,

In the early classification of living organisms members in high kingdoms such as Fungi,
into four kingdoms, all organisms which Plantae and Animalia, have their ancestors
could not fit into kingdoms Fungi, Plantae in the Protoctista kingdom. This is based
and Animalia were placed under kingdom on the studies of the base sequence of
Protista. This made the kingdom Protista mitochondrial and chloroplast DNA.
very diverse, as it accommodated both Therefore, protoctists are eukaryotes,
unicellular prokaryotes and eukaryotes. consisting of unicellular and multicellular
Later, with the use of molecular taxonomy, members. The multicellular protoctists
prokaryotes were separated from Protista consist of an assembly of similar cells such
to form a group of unicellular organisms as Spirogyra. The major difference between
lacking a well organised nucleus. These protists and protoctists is that the former

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