Science

Of course, a science student can pursue BCA. The general eligibility criteria for getting admission into BCA is 45% in +2, and you should have mathematics in high school so that it will be easier for you to study programming, if you don't have mathematics then it will be a little difficult for you. If you want to learn programming languages which you will be studying in your BCA course then you can check out this app which is specially designed and developed for BCA students. It has programs and assignments of languages like C, C+ and Java with their outputs. You'll be studying these languages in your 3 years of BCA.
https://play.google.com/store/apps/details?id=technark.bca_courprogramming

Yes you are eligible to appear for M.Sc. In botany. Eligibility criteria for M.Sc Botany is as follows. Recognized undergraduate degree in B.Sc. Or equivalent
A recommended minimum score at the level of graduation which can vary from college to college
For admission to M.Sc. Botany course, all universities follow their own admission norms. For instance, University of Delhi prepares a merit list on the basis of which University Colleges take admissions. Most of the institutions have direct entry as admission mode. However, there are some universities which prefer to conduct entrance tests for admissions. Hence, the students who have appeared in final year examination of under-graduation and await the result are allowed to apply for the course by such institutions.