hello aspirant,

yes definitely a biology student can write the NEST exam.

These are the following eligibility criterion details:

1) candidates who are passing in 2019 or in 2017/2018 with a 60 percent of aggregate marks in class 12th. 

2) biology, physics, maths, chemistry related questions are asked in exam. 

so, definitely you are eligible for NEST. 

THANK YOU