who serves as head of their political party
Party leader In politics, a party leader is the most powerful official within a political party.[1] The leader speaks to their designated political party, while acting as the party representatives. The party leader is typically responsible for managing the party's relationship with the general public. As such, he or she will take a leading role in developing and communicating party policy, especially election platforms, to the electorate. He or she is also typically the public face of the party and the principal media contact.
Head of state In republics with a parliamentary system (such as India, Germany, Austria, Italy and Israel) the head of state is usually titled president and the principal functions of such presidents are mainly ceremonial and symbolic, as opposed to the presidents in a presidential or semi-presidential system.