Question

Which kingdom lacks a well-defined nucleus and membrane-bound cell organelles?

Answer 1

Hint: The five-kingdom classification was proposed by R.H. Whittaker (\[1969\]). The kingdoms classified by him were named Monera, Protista, Fungi, Plantae and Animalia. The criteria used by him for classification include cell structure, thallus organization, mode of nutrition, reproduction and phylogenetic relationships. Cell structure includes cell type (eukaryotic or prokaryotic), presence or absence of cell wall, presence or absence of nuclear membrane. Eukaryotic cells have a well-defined nucleus and membrane bound cell organelles while prokaryotic cells lack all these features.

Complete explanation:
Of the organisms belonging to the five kingdoms, kingdom Monera are the only prokaryotes (‘pro’ means old and ‘karyon’ means nucleus). Prokaryotes lack the membrane bound cell organelles and a well-defined nucleus. Monerans are unicellular prokaryotes and they contain most of the primitive living forms. Bacteria are the sole members of this kingdom. They are varied in nutrition. Their nutrition type includes saprobic, parasitic, chemoautotrophic, photoautotrophic and symbiotic. They include both aerobes and anaerobes. They are microscopic. Cell walls are generally present which help them to survive in extreme climatic conditions and in habitats like hot springs, deserts, snow and deep oceans where very few life forms can survive. Their cell wall contains peptidoglycan and polysaccharides other than cellulose. Cells have one envelope type of organization, i.e., the whole of the protoplast is covered by a plasma membrane but internal compartmentalization is absent. All membrane bound cell organelles, e.g., lysosomes, mitochondria, spherosomes, golgi bodies, plastids, etc. are absent.

Note:
Other characteristics of monerans are: Mitotic spindle is absent. Gametes are absent. They have the ability to convert dinitrogen into ammonia. Reproduction is by asexual methods. Genetic material is not organized into a nucleus, DNA is naked, i.e., not associated with histone proteins and it lies coiled inside the cytoplasm. Their flagella are single stranded, if present. These are the most abundant microorganisms that occur almost everywhere. Many of them live in or on other organisms as parasites.