In a teamwork is it important to have a leader among the team member?

Yes the team leader is very important part of the team work.
This is mainly requires to resolve the conflict. 

Yes it is important to have a team leader because The team leader has the stake holder's mandate He directs the team members and guides them to the team goals The leader communicates at all levels and takes important decisions In case of any conflict or dispute he would intervene and resolve the issue amicably He is responsible for all project deliverables and project close out