12. Naučno-stručna konferencija Studenti u susret nauci – StES 2019 ZBORNIK RADOVA Prirodne nauke Istraživanja u prirodnim naukama 12 th scientifc conference Students encountering science – StES 2019 PROCEEDINGS Natural Sciences Research in Natural Sciences Banja Luka 2019. ISBN: 978-99976-49-00-3 ISSN 2637-1987 (Print) ISSN 2637-1928 (Online)