Final answer:
A used needle is a biohazard because it could harbor blood contaminated with a disease-causing organism. Bacteria grown in a laboratory are also biohazards if they could potentially cause disease.
Step-by-step explanation:
A biohazard is any biological material that could make someone sick, including disease-causing organisms. Therefore, a used needle is a biohazard because it could harbor blood contaminated with a disease-causing organism. Bacteria grown in a laboratory are also biohazards if they could potentially cause disease.