Hey aspirant

As you are pcm student first study and revise physics, maths, chemistry thoroughly because scoring well in 3subjects are enough to get a seat in IISER. So by daily mock test, revision and systemic preparations you could score good marks. If you have enough time after this you can look important chapters in biology. Sone of the must chapters are

Genetics and evaluation

Reproduction

Biotechnology and application

Cell structure and function

Biology and human welfare

Ecology and Environment.