In class 11th in India, you learn about differentiation. And 12 has Integration definite and indefinite both.
But since we're preparing for JEE Advanced (That's a tough paper here), we learn integration in class 11th so that we could work up to fine tune our skills in 12th grade. Because many formula derivations in physics of grade 11 like gravitation, Rotational motion, moment of inertia, e.t.c require the knowledge of Integration