CBSE 12th

Yes, it is necessary to have knowledge of grad level mathematics if you're going to pursue a degree in biotech. If you're in 12th standard and if it's possible that you can still add a subject in your current curriculum then go for it.
Mathematics is compulsory for admission in government colleges, only private colleges don't have maths as a compulsory. Since you'll be opting for a biotech course (most probably a B.Tech in biotech) then you will require the knowledge of mathematics (grad level).
If you want to improve your maths grade/score then try consulting Math Online Tutor at: https://tutstu.com/tutors/Math/sub/18/COLLEGE
This way you'll be able to prepare for admission exams at your pace and at your own timings.

For banking exams you should do graduation after finishing 12th standard. Graduation is the minimum requirement for the banking exams especially by the Institute of Banking Personnel Services.
IBPS conducts the banking exams for 20 Public Sector Banks. But to appear for the exams like IBPS Clerical and IBPS Bank PO, you should have graduation degree. Therefore I will recommend you to pursue graduation.
Course could be any of your choice. Once you have finished graduation, you can apply for the Clerical or Bank PO job depending on the marks obtained in graduation. In case you are eligible for both the exams, I will recommend to go with Bank PO.
IBPS Clerical/Bank PO Eligibility
1. Required qualification is graduation degree.
2. With 60 percent marks for Bank PO.
3. The requirement is 55 percent for SC/ST.
4. No relaxation for OBC.
5. Diploma/degree in Computers is required.
6. Or you can have Computer Science/IT subject in high school or college.
7. A certificate in Computer operations is also accepted.
8. Age limit is same for both exams - 20 to 28 years.
9. Relaxation is 3 years for OBC.
10. 5 years for SC/ST and 10 years for PWD.
If you want better jobs in banking sector, especially private sector then after completing graduation you should go for Master of Business Administration. You will have to complete MBA is either Banking or Finance.
There are several entrance exams for MBA but most popular is the Common Admission Test. You can appear for it if completed graduation with 50 percent marks. SC/ST can appear if scored 45 percent marks in graduation.
Please remember that Indian Institutes of Management offer admission for the MBA courses through Common Admission Test.
If could not score sufficient marks to appear for CAT, then consider Management Aptitude Test.