there is any difference between ncert biology book 2019 and 2020 edition
There is no major difference in the Core Content and Theory of NCERT Biology 2019 and 2020 Editions, and you may definitely refer to former edition for educational purposes. A new NCERT edition has hardly few minor changes in exercises and revision of errors in them. According to a Circular by NCERT in April 2020, they had made 1334 changes in NCERT Books, at an average of 7 changes per book, which may be considered. You may take note of the changes later if required.