State two economically important uses of:
$(a)$ Heterotrophic bacteria
$(b)$ Archaebacteria

(N/A) Heterotrophic bacteria:
$(1)$ They act as decomposers and help in the formation of humus.
$(2)$ They help in the production of curd from milk.
$(3)$ Many antibiotics are obtained from some species of bacteria.
$(4)$ Many soil bacteria help in the fixation of atmospheric nitrogen.
$(b)$ Archaebacteria:
$(1)$ Methane gas is produced from the dung of ruminants by methanogens.
$(2)$ Methanogens are also involved in the formation of biogas and sewage treatment.