Have you ever wondered why, when your child reaches adolescence, s/he argues with you more and questions your parenting? Why has my little darling become obnoxious? S/he wasn't like this when younger.
This is not unusual at this developmental stage. Peer relationships become important and very influential and, with increased contact with the families of their friends and acquaintances, adolescents see values and ways of doing things that are different to their own family. Some of these they like and this is when the questioning begins. This leads to a value system which they take into their own adulthood which is mainly based around their own family value system but incorporates others.
So try to show some understanding and acceptance during this developmental period. Some of your adolescent's behaviours might be occurring around the question of "Who am I?" Of course puberty and hormonal factors are occurring on top of this which can make it a vulnerable and crucial time for your teenager.