The term "biological" itself refers to the study of living organisms. So, biology is the branch of science that is biological.

It's like asking "What branch of science is mathematical?" Mathematics is the branch of science that deals with numbers, quantities, and shapes.

Here are some of the sub-branches of biology:

* Zoology: The study of animals

* Botany: The study of plants

* Microbiology: The study of microorganisms

* Ecology: The study of how organisms interact with each other and their environment

* Genetics: The study of genes and heredity

* Physiology: The study of how organisms function

* Anatomy: The study of the structure of organisms

Let me know if you'd like to know more about any of these branches!