Can a bio student do Diploma in plastic engineering? What is its scope in India?

Yes, Diploma students get admission on the basis of 10th and also 12th, if you want to pursue with 12th then lateral entry means direct admission in second year. You will not get a good package. You will get around 1.44 LPA but after an experience of above 3 years your earnings will jump to 4 LPA.

Yes, a bio student can get admission for Diploma in Plastic through regular entry. But it does not have much scope in India or anywhere else. The best job you will get is of Injection Moulding Operator.