Which of the following cannot be digested by the enzymes in an animals digestive tract?

Cellulose

Enzymes and substrates are  often specific for one another. They have shapes that can be modified to fit into each other which allows them to bind together (induced fit).Together, Enzymes and substrates undergo some transformations  as they interact. They interact by forming hydrogen bonds, covalent bonds  and what is also called hydrophobic interactions.

The enzyme returns to its original shape and state after the reaction but the substrate is often modified or changed completely into a new, different product.

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.