Enzyme Catalysis Explains P's Breakdown

Steps:

• Mixing P and Q results in P's concentration decreasing over 24 hours while Q remains unchanged, indicating a reaction where Q facilitates P's decomposition without being consumed.
• Conclusion 1 is supported because the decrease in P shows it breaks down over time in the presence of Q.
• Conclusion 2 is supported as Q's unchanged concentration suggests it acts as a biological catalyst, like an enzyme, that speeds up reactions without depletion.
• Conclusion 3 is supported because P's role as the reacting species identifies it as the substrate for Q's catalytic action.

Why A is correct:

• In enzyme kinetics, biological catalysts (enzymes) remain constant while substrate concentration decreases, matching the observed changes in P and Q.

Why the others are wrong:

• B omits 3, but P's decrease directly supports it being the substrate.
• C ignores 2 and 3, as Q's stability implies catalysis and P's role as substrate.
• D excludes 1, but P's concentration drop confirms its breakdown.

Final answer: A