What are pathogens?

Pathogens are defined as organisms that cause diseases in their hosts. These can include bacteria, viruses, fungi, protozoa, and even some parasites. Pathogens invade an organism, disrupt normal biological functions, and can lead to illness or disease. Their ability to cause harm is a key aspect of their definition, distinguishing them from other organisms that may coexist with or benefit their hosts.

The first option refers to beneficial organisms that aid in plant growth, which is unrelated to the concept of pathogens. The second option discusses chemicals used in agriculture, such as pesticides or fertilizers, which may not be living entities nor inherently related to disease. The last option focuses on insects that feed on crops, which may be pests but are not classified as pathogens unless they transmit disease-causing agents. Thus, understanding that pathogens are directly associated with causing disease clarifies why the third option is the correct definition.