Which data field is the vector crated from

In the chapter “Vector Databases”, it wasn’t very clear as to which specific data field was sent to the embedding model to create the vector. We have 3 fields - Category, Question, and Answer. Is the vector generated from Question or Category or Answer field of the data?
One of the headings in the notebook says " Let’s Extract the vector that represents each question!" which means the vector was based on the Question field, but where was this defined in the code? How would weaviate know which field to create the vector from?