Question

Biologists are not sure about how many prokaryotic species on earth might be present. The problem is that

• A. Microbes are too small so not easily visible under
  the microscopes
  
• B. Many prokaryotic species are simply not culturable
  under laboratory conditions
  
• C. Conventional taxonomic methods are not suitable
  for identifying microbial species
  
• D. Both A and B

Answer 1

The correct option is D Both A and B

Global species diversity

According to the IUCN (2004) the total number of described species on earth is more than 1.5 million and a scientifically sound estimate given by Robert May states that the total number of species (plants and animals) in the world is around 7 million.

Prokaryotes

But these numbers do not include the number of species belonging to Kingdom Monera (prokaryotes). The reason being -

1. The conventional taxonomic methods are unable to identify and classify prokaryotic species.
2. Many prokaryotic organisms are impossible to culture in vitro and hence cannot be studied properly.

Thus biologists are not very certain about the number of existing prokaryotic species.

Even if we consider biochemical or molecular characteristics as criteria for distinguishing and identifying the prokaryotic species, the chances are that the numbers might cross millions.

Final answer

(d) Both A and B