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Biology for Advanced Level Secondary Schools
traditional kingdoms; Plantae and Animalia, photoautotrophic bacteria such as Purple
as it was still difficult to be seen, identified, sulphur bacteria, while the latter is called
and characterised. The discovery of the chemoautotrophic bacteria such as Iron
monerans therefore, came following the bacteria (Ferrobacillus). Some prokaryotes
discovery of the microscope, particularly such as Archaebacteria have interesting
the electron microscope and computer features such as the ability to survive in
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applications, which revealed the finer extremely harsh environments, including
details of the monerans. This simplified areas with low oxygen concentration
(anoxic condition), high alkaline or acidic
the understanding of differences across media, high salt concentration, and extreme
the members of this kingdom, leading to temperatures (in hot springs and volcanic
recognition of the three major divisions, domes), where other organism have
namely; division Archaea, Eubacteria, completely failed to inhabit. For example,
and Cyanobacteria. Earlier classification methanogens (Methanobrevibacter
system splited Monera into two groups, ruminantium), which produce methane gas
in this case, all Archaea bacteria were in anoxic conditions in ruminant’s digestive
grouped under kingdom Archaebacteria systems. These similar bacteria produce
while Cyanobacteria and Eubacteria were methane gas from cow dung that is used
classified under kingdom Eubacteria or as biogas, which is one of the renewable
Prokaryota. sources of energy.
The members of kingdom Monera 3.3.1 Characteristics of monerans
are cosmopolitan in distribution and (a) They are microscopic unicellular
predominant in all habitats, ranging from organisms, with an average diameter
aquatic; that is marine, brackish and fresh ranging from 0.1 mm to 10 mm.
waters to terrestrial environments; such (b) Their cells lack a well organised nucleus,
as in the air, dust, soils, on plants and since they have no nuclear membrane,
animals. They also range from parasitic,
free living to symbiotic. Some bacteria are and the nuclear materials are freely
saprophytes, especially decomposers, which suspended in the cytoplasm.
are very important in nutrient cycling. (c) They lack cytoskeletons and
Nitrogen fixing bacteria live in symbiotic membrane bound organelles, such as
association with leguminous plant roots mitochondria, plastids, and chloroplast.
while the cyanobacteria form symbiotic The photosynthetic moneras have
relationship with fungi to form lichens. photosynthetic lamella instead of
Parasitic prokaryotes including infectious chloroplasts.
bacteria, such as Salmonella typhi that
causes typhoid and Vibrio cholerae which (d) They have fewer and smaller ribosomes,
causes cholera, spend part or their entire specifically 70s ribosomes.
life in their hosts as facultative parasites (e) They have a smaller, circular DNA that
or obligate parasites, respectively. The free lacks the histone protein coat.
living bacteria are capable of synthesising (f) Most physiological processes, such as
their own food using energy obtained from respiration and food synthesis (for the
light or chemicals. The former is called autotrophs), occur in membrane systems.
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