US Department of Agriculture
U.s Department of Agriculture: Plants Fight Off Foreign Invaders
Information as to how a plant protects itself from bugs and other harsh elements that seek to injure it. Also provides links for users to learn more about agricultural research for further study.
Khan Academy
Khan Academy: Pathogenesis
An explanation of how tuberculosis causes damage to lungs and other organs in the body. Latent and secondary tuberculosis is also examined. Of note is once infected with tuberculosis it's with you forever and may cause subsequent issues.