Which one is the smallest organism capable of autonomous growth and reproduction?

Which of the following cyanobacteria can fix atmospheric nitrogen?
$I.$ Anabaena
$II.$ Oscillatoria
$III.$ Nostoc
Choose the correct option.

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

Consider the following four statements $(A-D)$ and select the option which includes all the correct ones only.
$(A)$ Archaebacteria differ from other bacteria in having a different cell wall structure.
$(B)$ Bacteria as a group show the most extensive metabolic diversity.
$(C)$ All Eubacteria have chlorophyll ' $a$' pigment similar to green plants.
$(D)$ Mycoplasma can survive without oxygen.

Which of the following is characterized by having a cell wall made of peptidoglycan?

Refer to the given figures of a bacterial cell and Nostoc and choose the option which shows the correct labels for the structures marked as $A$,$B$,$C$,$D$,and $E$.