Rinderpest disease is caused by a virus that affects hoofed animals, including cattle and wildebeest. In the 1950s, a cattle vaccination program was implemented to eradicate the disease in the Serengeti, and this led to dramatic changes in the populations of wildebeest and other species. The figure shows the number of wildebeest in the Serengeti ecosystem (shaded circles, left y-axis) and the prevalence (i.e., percentage) of individuals infected by rinderpest disease (unshaded squares and triangles, right y-axis) from 1958 to 2003.
Hans Krebs as the scientist who was pivotal in making some type of discovery that led to our understanding of the basic nature of cells.
Hans Krebs (25 August 1900 – 22 November 1981) was a British physician and biochemist born in Germany. He discovered that nutrients are broken down in our cells to release energy for the construction of cells
The pathogen that cause is infection in bacteria
I believe the answer you're looking for is photosynthesis, where plants release oxygen and humans use this to release carbon dioxide to the plants.