What does serology study in relation to viruses?

Serology focuses specifically on the study of antigen-antibody reactions, particularly in the context of immune responses to infections, including viral infections. In the case of viruses, serological techniques are often used to detect the presence of specific antibodies in the blood serum of an organism, which indicates whether that organism has been exposed to the virus. This form of analysis can help diagnose viral infections, assess immune status, and track the spread of viral diseases.

By detecting antibodies that respond to viral antigens, researchers and medical professionals can gather important information about an individual's past exposure to a virus or their current state of infection. This is particularly useful in epidemiological studies and for monitoring disease progression in populations.

The other choices do not pertain to serology; for instance, soil composition relates more to agronomy and plant health, the relationship between pests and plants pertains to entomology and pest management, and photosynthetic efficiency involves plant biology and physiology. Thus, the focus on antigen-antibody reactions is what clearly defines serology's relevance in the context of viruses.