1. Which group of single-celled micro-organisms has many members found growing in extreme environments?

The answer is Archaea

Explanation:

Archaea are the single celled organisms similar to bacteria however they have different membranes.

They are known to be extremophilic since they can grow and survive in extreme condition. The environment extremity can be highly alkaline or acidic environment and hot springs etc. Also these can survive in high temperature and pressure conditions.