This is the 10194th most frequent Russian word.
биологические
"Biological."
Here, 'биологические' is used as an adjective describing 'исследования', indicating their subject matter refers to biology.
Биологические исследования позволяют лучше понять природу.
Biological studies allow us to better understand nature.
In this sentence, 'биологические' describes 'процессы', showing that they pertain to natural or biologically intrinsic operations.
Биологические процессы происходят в организме ежедневно.
Biological processes occur in the body daily.
Here, 'биологические' modifies 'структуры', specifying their characteristics as related to biology.