First impressions matter but don’t think all is lost if you had a bad start. There’s always a chance to bring an interview round.
Any preparation you do should not just be cosmetic ‘grooming’ for the ‘interview’ but for the whole process of application.
Knowledge in isolation is not as useful as context. Think about your answer and how it has relevance to circumstances.
Your performance at interview is only one of a number of factors that recruiters and admissions tutors will take into account.
Where is your subject featuring in the news of the moment? If you can make connections, then this will often help in the interview.
What motivates you? Common job interview question, designed to determine what environment you’d work best in.
Put yourself in the interviewers’ shoes. What’s going to ensure they enjoy meeting you? Enthusiasm and potential to succeed are key.