Which of the following is responsible for the production of methane?

Which of the following statements are incorrect for $Nostoc$ and $Anabaena$?
$(a)$. Possess tissue level organization
$(b)$. Have heterocysts
$(c)$. Can fix atmospheric hydrogen
$(d)$. They are eubacteria

Bacteria are considered primitive organisms because they

In the vast marine ecosystem, certain seas develop red colouration. This red colour is due to the presence of a large population of which one of the following organisms?

Provide the full forms of the following abbreviations:
$(i)$ $PPLO$
$(ii)$ $RNA$

One of the following is not a characteristic feature of cyanobacteria: