Science

M.tech from IIT off course.

For college selection, you need to give entrance competition examinations held by different colleges and universities.
Therefore, give entrance examination first.
Biotechnology is offered by IITs, NITs and other government colleges.
You can visit https://engineering.shiksha.com to explore colleges for biotechnology in different locations of India.
All the best.!!!

It is tough to say what you should do. Because your interest is in Biology and you want to go in Merchant Navy. It is same as if your interest is in Cricket and you want to be Tennis player. Both your interest and your want to be career are in two different domains.
Therefore, first decide where you want to go.
But whatever you do, make it your interest first then career.
All the best.!!!

when you completed B.Sc in IT then you can give the C- DAC exam and you can build career with various software

if you are interested in chemistry you will take petroleum engineering because in petroleum engineering chemistry is very important if you are good in chemistry you will do it it is best for your knowledge

You may pursue Ph.d if you want to go in research. UPSC exams are the way to enter govt sector. NET will lead to assistant professorship or JRF if cleared. If you plan to go into corporate sector, apply for PGDM/MBA. There are diploma programmes also available.

For good universities, master's requires 80% or more. You either need to have 4 years Bachelor's or be in first years of master's to apply abroad. GRE + TOEFL/IELTS are also required for international applicants.

this depends on you.
that what do you like more.
if you have interest in research then you should go with B SC
and if you have interest in a good job then you should go with B tech.

IMT Ghaziabad does not accept MAT scores. You can try applying with your CAT/XAT or GMAT score. Marketing or management for that matter is common sense. That is why any graduate can pursue marketing as a specialization.