What type of microorganism is $Nostoc$?

The content of mucopeptide (peptidoglycan) in the cell wall is higher in which of the following?

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 introduced in eubacteria.

The main difference between Gram-positive $(+ve)$ and Gram-negative $(-ve)$ bacteria lies in their $........$.

Select the correct statements from the given statements $(1-4)$ regarding the characteristics of some organisms.
$(1)$ Methanogens are Archaebacteria that produce methane in marshy areas.
$(2)$ $Nostoc$ is a flagellated blue-green alga that fixes atmospheric nitrogen.
$(3)$ Chemosynthetic autotrophic bacteria synthesize cellulose from glucose.
$(4)$ Mycoplasma lacks a cell wall and can survive without oxygen.

Which type of organism are $PPLO$?