Ascientist found two different sizes of a same protein obtained from plants and animals. this size difference in same type of protein doing identical function could be due to

Deletion and glycosylation.

Explanation:

Proteins is polymers of the alpha amino acids that are directly linked together through the peptide bond. Proteins plays an important role in the metabolic pathways as most enzymes are made of protein.

The same protein can exist in two different size. This might occur due to the deletion of the particular amino acids sequence in one organism and normal in other organisms. The glycosylation of the same protein at different position in the proteins may also leads to the difference in the protein size.

Thus, the correct answer is deletion and glycosylation.

so whats the answer