The students who have enrolled for Bachelor of Medicine/ Bachelor of Surgery (MBBS) are eligible for this course but need special permission from AAMC Authorities. Also, Students who holds MBBS degree are also eligible to write MCAT exam without taking any special permission. No, diploma in Biology students are not eligible for this exam.
Full form of MCAT is Medical College Admission Test. It is conducted for prospective Medical students in Canada, United States, Carribean Islands and Australia.
For more details about MCAT exam go through below link.
Hope this information helped you.