The free-living,aerobic,and saprotrophic $N_2$-fixing microbe is

An episome in bacteria is

Purple sulphur bacteria are

Archaebacteria differ from other bacteria in having a ..........

The current classification of organisms is into three domains of life ($Bacteria$,$Archaea$,and $Eukarya$). Which of the following statements is true for $Archaea$?

Gram-negative bacteria detect and respond to chemicals in their surroundings by: