Yes, you can definitely prepare for the GATE exam in Civil Engineering even though you are a Biotechnology graduate. There are no restrictions on educational background for appearing in the GATE exam, you can choose any stream you're interested in. However, it will be a challenging path  because the GATE Civil Engineering syllabus covers subjects very different from Biotechnology.

The GATE Civil Engineering syllabus includes subjects like Engineering Mechanics, Strength of Materials, Structural Analysis, Geotechnical Engineering , which you likely haven't studied in detail during your Biotechnology degree.

You need to dedicate significant time and effort to grasp these new concepts and practice solving related problems.

Utilize resources like standard Civil Engineering textbooks, online courses, or coaching institutes to build a strong foundation in these core subjects. Practice solving problems from previous years' GATE Civil Engineering exams to get familiar with the question format and difficulty level.

Create a study schedule that allocates sufficient time for understanding new concepts, practicing problems, and revising.

https://engineering.careers360.com/exams/gate

I hope it helps!