Dear aspirant

I appreciate your interest to want to work for the environment. IISERs can provide you excellent environment if you would like to work for the environment. There is BS MS in Earth and environmental sciences course that you can do. IISERs offer a great environment to give you a strong foundation to pursue a research career. The course structure, exposure you get here is unparalleled. You will also have an option to explore other fields if you join IISER which you won't usually get in other colleges. You will learn all the subjects in the first two year and then course will get more focused on your area of interest as you progress through years. If you are interested in biotechnology you can join engineering colleges to pursue a btech in biotechnology. As for competitive exam preparation, you are on the right path, in my opinion. You can join IISERs through KVPY/IISER SCB/ JEE Advanced. The preparation for JEE will help you prepare for other competitive exams as well.  Make sure you go through biology class 11 and class 12 NCERT thoroughly before attempting SCB exam. IISER SCB exam is the most straightforward way to get into IISER, so make sure you focus on doing well in boards as well because you have to get a  minimum cut off in board exam to be eligible to write the SCB exam. If you get into top 1 percent of your board, you will also be eligible for INSPIRE scholarship (only of you are doing a science degree) which amounts to about 1lakh per year.

I hope this helps

All the very best for your future