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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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