Makarand admissions to IISER 2018 will be through three channels:

• Kishore Vaigyanik Protsahan Yojana (KVPY) – Candidates will be offered admission on the basis of valid KVPY fellowship
• State and Central Boards Channel (SCB) channel – Candidates opting for this channel will have to appear in an aptitude test, the details of which are given below
• Joint Entrance Examination of Indian Institutes of Technology (JEE) channel – Candidates with valid JEE Advanced 2018 scores are eligible for direct admission

Among these 3 channels, only the students going through the SCB channel have to appear in IISER Aptitude Test 2018. This test comprises of four subjects of equal weightage: Physics, Chemistry, Mathematics, and Biology. 15 questions in each subject and gets you +3 marks for each correct question and -1 for incorrect answers.

Even when you don't have biology subject you don't have any other option and needs to give this test. Although questions in Biology will not be so difficult still I can imagine your problem, you can go through the syllabus and look out for some of the topics otherwise the only option you have to score more in the other 3 subjects.

Feel free to ask if you have any more queries. All the best!!