Why is there more than one Torah Scroll kept in the Ark? Is the whole of the Torah written on a single scroll? Who decides which parts of the Torah are read in the synagogue service? Thank you?

In most synagogues there are several identical copies of the same ancient and eternal Torah scroll, which all include the entire Torah. Some synagogues read the weekly prophets portion, also from smaller parchment scrolls, but this in not obligatory. The Torah is internationally divided into 54 parts (parshas) which are read annually, with the goal of finishing the entire Torah every year, on the holiday of Simchat Torah.