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PCAT Biological Processes – Bacterial Species

Two bacterial species independently evolved mechanisms for deactivating penicillin and thus being able to grow on media containing penicillin. Species A developed an enzyme pathway involving three reactions, with the end result of turning penicillin into products X and Y. Species B developed a much more efficient pathway only requiring a single step to turn penicillin into the same products. If EBis the energy change associated with the overall reaction carried out by Species B and EA is the energy change for the overall process carried out by Species A, then which of the following is true?

A) EA = 3 x EB
B) EA = EB
C) EA = 1/3 x EB
D) The relationship between EA and EB cannot be determined

Click for Explanation

Remember that the overall change in energy is a state function only depending on the initial and final state of a system. Because both bacteria start with the same reactant (penicillin) and end with the same product (X and Y) they will have the same overall change in energy. Therefore, (B) is the answer.

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