3-year course. Most widely accepted and preferred undergraduate degree for someone doing basic sciences. B.Sc Hons. courses give the student the opportunity to specialize in their chosen subject. For example, a B.Sc Hons. in Zoology will give you exposure to the details of animal sciences, and all other branches of biology that are relevant to it. It also gives the choice to pick elective courses from other subjects. This is the most suitable degree for pursuing higher studies in India/ abroad, and also for job applications. The majority of government colleges have this course only.
BSc general ( referred to as pass course)
It is a 3 years course. In most colleges, it is less intensive than the corresponding honors degree, and therefore easier to get selected (lower cutoffs). But for higher studies/ job applications this may not be preferable (as compared to an honors degree), since candidates do not get such deeper exposure to any particular subject. These courses do not allow specialization in any particular subject, rather, they have a combination of topics from different related subjects. For example, a B.Sc. course in Biological Sciences may have a combination of topics from Zoology, Botany, and Chemistry. However, this interdisciplinary approach may be advantageous in some cases.
5 years course. It is equivalent to doing a B.Sc followed by an M.Sc. Usually, the students have to study all subjects of basic sciences ( physics chemistry maths biology computers) for their first 3/4 semesters. Then they have the freedom to choose their major and minor subjects. This course is usually taught in IISERs, IISC, and NISER. This course provides a solid foundation in Natural Sciences before taking up a specialization and gives students the time to figure out their preferred field of studies. This interdisciplinary approach is very good for research and academia.
This system is prevalent in private universities. It is similar to the education system followed in the USA or Europe. Each student has the option of selecting specific courses from different subjects. In order to have biology as a major, they will have to study a certain number of courses in Biology, along with other courses from subjects of their choice. This gives them the freedom to explore their academic interests and also gives wider exposure to concepts of Physics, Chemistry, or Maths. Some universities may also allow one to pick courses from humanities, which can be a very appealing opportunity for those students who have an interest in those subjects.