In the sentence "The scientist looked at the bacterial culture through her microscope", the word culture referes to the following definition from Cambridge Dictionary: Cells, tissues, organs, or organisms grown for scientific purposes, or the activity of breeding and keeping particular living things in order to get the substances they produce. The words that give us clues are scientist, bacterial and microscope. They refer to a specific field of work/study which is Biology or Science.
In the sentence, " My friends know I'm interested in culture, so they often ask me about music, plays, and books.", the word culture implies a completely different meaning. According to the dictionary, thr right definition would be: The arts of describing, showing, or performing that represent the traditions or the way of life of a particular people or group; literature, art, music, dance, theater, etc. The words that help us choose the correct definition are music, plays and books since they are examples of the means people choose to represent traditions and ideas.
The word culture in the last sentence, "My grandparents took me to Italy to learn about their native culture", has another meaning and it is the way of life, especially the general customs and beliefs, of a particular group of people at a particular time. In this last sentence, the words grandparents and native are the words that act as clues in order to select he right definition. They imply a particular group of people from a specific point in time, not necessarily present time.