Final answer:
For biological monitoring of the LTGP sterilizer, Geobacillus stearothermophilus is used because of its endospore-forming ability, which challenges the sterilization process.
Step-by-step explanation:
The microorganism used to biologically monitor the Low Temperature Gas Plasma (LTGP) sterilizer is Geobacillus stearothermophilus. This microorganism is known to form endospores, which are highly resistant to various sterilization processes. In the context of LTGP sterilization, biological indicators containing endospores of Geobacillus stearothermophilus are employed due to their ability to withstand the sterilization process conditions and thus, serve as a challenge to the effectiveness of the sterilization.