The definitions of fastidious and conceited are provided based on contextual clues in the sentences.
Fastidious means excessively particular, critical, or demanding, especially when it comes to details. The clue in the sentence that leads to this definition is John's mother's disappointment over his A- grade in Biology, indicating that she is highly selective and exacting when it comes to academic performance.
Conceited refers to having an excessively favorable opinion of one's abilities, appearance, or accomplishments. In the sentence provided, Jana's concern about her daughter's behavior points towards the definition of conceited, as she worries that Kylie is becoming overly self-centered and vain.