Biological agents are living organisms or their products that can cause harm to humans, animals, or plants. These agents include bacteria, viruses, fungi, and toxins. For example, the bacteria that cause diseases like tuberculosis or the viruses responsible for the flu are considered biological agents. They can spread through various means, such as air, water, or direct contact. In addition to causing illness, biological agents can also be used in research and medicine. For instance, some bacteria are used in vaccines to help the body build immunity. Understanding these agents is crucial for public health and safety, as well as for developing effective treatments.