Which of the following organisms derives energy for $N_2$ fixation through photosynthesis?

Cyanobacteria do not possess

Statement $S$: Methanogens are responsible for the production of methane. Statement $R$: They can survive even in acidic and high-temperature conditions.

Cyanobacteria and heterotrophic bacteria have been clubbed together in eubacteria of kingdom-Monera as per the "five kingdom classification", even though the two are vastly different from each other. Is this grouping of the two types of taxa in the same kingdom justified? If so, why? Discuss the cellular composition of cyanobacteria and heterotrophic bacteria that make them classified as eubacteria.

Which of the following prokaryotes are most abundant in nature and are helpful in making curd from milk and in the production of antibiotics?

Match the following columns:

Column-$I$ (Habitat)	Column-$II$ (Archaebacteria)
$P$. Salty areas	$I$. Thermoacidophiles
$Q$. Marshy areas	$II$. Methanogens
$R$. Hot springs	$III$. Halophiles