Ph.D

Definitely not, they can offer consultancy and entrepreneurial services as well as apply for suitable positions in public and private sector companies.

Yes, you can pursue integrated PhD in biological sciences after completing BDS. Kindly refer to the link below:
http://www.winentrance.com/admission_notification/tata-institute-fundamental-research-admission.html

You have to qualify the entrance exam of the university for pursuing Ph.D.

Hello Prerna,
International Centre for Stem Cells, Cancer and Biotechnology (ICSCCB) offers 1-year Post-Graduate Programme in Stem Cell Biology & Molecular Medicine (PGP-SCBMM).
NCCS also offers opportunities in carrying out research in all areas of modern biology leading to Ph.D degree. Students are admitted in these programmes as per the requirement and against advertisement only. The advertisements are published as per the need/schedule. The required qualification is a Master's degree in any branch of science and a fellowship of CSIR, UGC, DBT_INSPIRE, etc.

Hi Priyanka,
Please check these, they are the world's best for biotechnology and overall biological sciences.
Harvard
Stanford
University of Pennsylvania
University of California- Berkeley
MIT
John Hopkins
University of California-San Francisco
Heidelberg University
University of Munich
University of Queensland Australia
and University of Melbourne
Please visit the university websites for integrated Ph.D options and other criteria.

Hi Onkar,
If you are planning to study abroad you must know your interests and career plans. Think about which field you want to research in and select your area. Firstly, you have to know what you want and then you must look for the country. Go abroad only if you have good plans rather than going for the sake of it.