If i want to take the KCET, do i have to do the bio part as well or can i just answer the PCM parts of the test?

No. Only PCM subjects would be considered if you are going to get admission in Engineering as there will be two papers which the candidates will have to answer in KCET 2018 on two different days. The first paper will comprise of questions from Physics and Chemistry. Paper 2 will be held on the next days and questions will be asked from Mathematics. Exam mode will be MCQs type, 1 mark will be given for right answer and there is no negative marking. Total number of marks would be 180 which means 60 each for PCM. Hope this helps!!!