Question

Which among the following organisms belong to the kingdom Monera?
A. Blue-green algae
B. Anabaena
C. Bacteria
D. All of the above

Answer 1

Hint: The Kingdom: Monera consists of the prokaryotic organism, unicellular microscopic. Absence of true nucleus and cell organelles along with the presence of $70S$ ribosome, naked circular single-stranded DNA acting as the chromosome. They are associated with either autotrophic or heterotrophic mode of nutrition.

Complete answer:
Blue-green algae also known as Cyanobacteria are unicellular, prokaryotic organisms, autotrophic and are kept under the kingdom: Monera. Anabaena is also a type of cyanobacteria so it also comes under the kingdom: Monera. Bacteria are also prokaryotes having $70S$ ribosomes, do not contain membrane-bound cell organelles, can be autotrophic or heterotrophic, and bears a single circular chromosome so they are also members of the kingdom: Monera.
Hence the option D is correct.

Additional Information:
Though Blue-green algae belong to the kingdom: Monera due to their characteristic feature in structure and food habitat but the rest two organism in the options bears the same characteristic feature
hence only option A is incorrect.

Anabaena is a form of cyanobacteria and is also in the Kingdom: Monera but only Anabaena is not a member, the other two options are also under the same kingdom,
hence only option B is incorrect.

Bacteria is the most known organism of the kingdom: Monera but the other two organisms are also the same kingdoms.
Hence only option C is incorrect.

Note
The bacteria are of two types – a. Archaebacteria (most primitive and oldest anaerobic bacteria surviving under extreme environmental conditions) and b. Eubacteria (They are known as the true bacteria). The cyanobacteria Anabaena contains heterocysts (a specialized cell) which help them in nitrogen fixation. Spirulina is also a cyanobacterium that is used as a single-celled protein for cattle feeding.