B.Sc

Are you talking about B.Arch examination or IIT?
Your board percentage is low as JEE has the policy of 75%.

Hello,
You have to apply online for admission and then only you will be eligible.
Follow this link for more information:
http://www.srmuniv.ac.in/content/department-physical-education-0

B.Sc graduates have a wide variety of options available in terms of topics, subjects and field. They have an option to pursue a post-graduation degree in their respective field. Students can also join non-science Master's degree courses such as animation, management, journalism, computer technology, etc. after the completion of B.Sc degree.

Yes, you can apply for SI police after graduating because for SI police only graduation is required.

Kindly visit this link:
https://www.shiksha.com/aviation/colleges/colleges-india-8

As you are looking for the B.Sc Life Science. Basically, you need to score 60% minimum for almost each and every college wherever you go for admission. With this percentage, you are eligible to get admission in any college except some top colleges. Thanks.

You have both the options which are really good. You can opt as per your interest where you want to look yourself in future. It totally depends on what you want to do. But, it is good option to do B.Sc. And then M.Sc which is a better option than other. Thanks.