How is it possible that over 20 million living organisms on the planet are made up of only 5 types of nucleotide bases arranged in long chains

Answer

It is because of different arrangements of nucleotide bases.

Explanation

There are only five types of nucleotide basis are present in the genetic material which makes up the all the genetic information of the individuals. These nucleotides are named as Adenine, Thymine, Guanine, Cytosine and Uracil. In all the living beings on the earth, these only five nucleotides are present which decides their behaviour and functions on the earth. These five bases have features to get any arrangements according to the situation. Their different arrangement at the heredity material makes the difference in all living beings regarding their behaviour.