Final answer:
Infectious diseases are caused by bacteria, viruses, fungi, and parasites, with a reservoir being the source from which these pathogens can spread. The mode of transmission is the manner in which an infection is spread from one individual to another.
Step-by-step explanation:
Bacteria, viruses, fungi, and parasites are microorganisms and organisms that can cause infectious diseases. The source location from which agents can spread to cause disease is called a reservoir. The way an infection is spread from one person to another is known as the mode of transmission.
Infectious diseases can be spread through direct contact, through the air, by ingesting contaminated food or water, or by vectors such as insects. A vector is an organism that carries pathogens from one host to another, facilitating the spread of the disease. It's important to understand that not all microorganisms are harmful; many are essential to human health and the environment.