Answer:
Number of bacteria required 
Explanation:
Given -
Size of each bacterium
micrometers long
These bacteria are arranged end to end.
The size of chain to be formed is equal to
centimetres
Let us say that in forming a chain of
centimetres nearly X number of individual bacterium are required.
hence, number of bacterium required to form
centimetres chain can be represented as

Number of bacteria required 
Methanogens can be found in B.human intestines
Roots of plants and synthetic fertilizers can contain oxygen or come into contact with oxygen.
Conjugation. I hope this helps!
The units of genetic distance derived from bacterial conjugation studies are called minutes. Bacterial conjugation is the process by which a bacterium transfers genetic materials to another through direct contact. One bacterium serves as a donor of the genetic material and the other serves as the recipient.