Answer:
Bacteria
Explanation:
Bacteria have no true nucleus because it's a prokaryote. It couldn't have been a virus because all naturally occurring viruses are pathogenic unless treated by radiation.
We have two types of bacteria,
- Pathogenic
- Commensals
Pathogenic bacteria will definitely cause disease. Commensals, however, have don't harm us and have the ability to help us.
Eg: Flora (bacteria) in our intestines produce vitamin K and most of the vitamin B complex. They also compete with the pathogenic bacteria that you might've ingested and don't allow them to increase to the number that can cause disease.
