Hello revathi

You should do nothing about that. Physics, chemistry and biology comes as separate subject only once you reached in class 8th. Till then it's all come under subject science.

So your school will be prescribing you certain book for your subject science,so read that book only and in upcoming higher class you will get to learn about these subjects separately. So learn the science book which is provided by your school to have basic knowledge of physics chemistry and biology.

Hope this helps you

Good luck