after reading ncert thoroughly we can surely secure 300+ in biology. Analysing last few years question paper,i found out that every year questions are coming from outside of the ncert book. The number vary from 3 to 7 question,being on safer side make it 10,that is 40 marks.
But just stick to ncert first…do PhD. on ncert coz every line of ncert contains lot of concepts…when you feel that u mastered ncert then search for other contents.but till then just read ncert…… it is pretty sufficient to score 330 marks if u r lucky enough …. i guess.
hope this will help.