Objectives: by the end of this unit, students will...Describe what it means for an animal to be ‘healthy’.Determine the difference between an infectious and a noninfectious disease.Determine the difference between a contagious and a non-contagious disease.Define: disease, pathogen, host, vector, virulence, environment.Summarize how a host’s defense mechanisms prevent a disease from  occurring and why these mechanisms sometimes break down.Identify and explain the parts of a disease triangle and how they affect disease transmission.Summarize the difference between resistance and immunity.Summarize the difference between active and passive immunity as well as natural and artificial active immunity.Explain how antigens and antibodies interact in order to create immunity in an organism.Summarize how herd immunity works and how it affects the health of a  group of organisms.Define and explain the differences between  each of the following:a. Pandemic   b. Endemic   c. Epidemic   d. Zoonotic