What does microbiology primarily focus on studying?

Microbiology primarily focuses on studying microorganisms, which include bacteria, viruses, fungi, and parasites, and their interactions with living organisms and the environment. This discipline delves into the roles these microorganisms play in various aspects of health, including their beneficial uses in medicine and agriculture, as well as their potential to cause disease. Understanding these impacts is crucial for developing vaccines, antibiotics, and other medical treatments, and it also helps in managing diseases in both humans and animals.

The other options encompass broader biological fields; for instance, studying large mammals involves ecology and zoology, while exploring environmental ecosystems focuses on interactions within larger biological systems. Additionally, examining plant growth and development falls under botany rather than microbiology. Thus, the emphasis on microorganisms and their specific effects on health is what distinctly defines microbiology.