Both 11 and 12 syllabus have equal weigtage in the jipmer examination so you cant afford to miss nay one of them. 

Also practice and brush up your English and vocublary skills as they are important to determine your rank. 

No JIPMER entrance tests your class 11 and class 12 knowledge along with logical reasoning and english comprehension.

Best of luck. 

JIPMER MBBS 2018 syllabus will be based on the syllabus as prescribed for CBSE Class 11th and 12th standards. ..All the best