Question

Sugars are used by many chemoheterotrophs as an important source of carbon and energy. Indeed, complete oxidation of glucose using oxygen as a terminal electron acceptor has a free energy change of -2,883.0 kJ/mol. What strategy do cells use to minimize the amount of that energy that is lost as heat during the catabolism of sugars? Choose one: A Energy is harvested using a series of smaller oxidations B. Oxidations of sugars directly power membrane-bound ATP synthases. C. The cells employ high-capacity energy carriers (e.g. A Gºof hydrolysis - -1000 kJ/mol). O D. Oxidation is directly coupled to biomass synthesis E. The oxidation reaction occurs within insulated organelles.

Answer 1

It's correct answer is option A.

Cells harvest the energy stored in the bonds of sugars by using a series of smaller oxidations rather than harvesting it in a large reaction. It confers an advantage to the cell as during each oxidation reaction, the product( electron acceptor) has the lower energy than the donor molecule that preceded it in the pathway and at that time the electron acceptor molecule captures some of the energy released by the sugar breakdown during successive oxidation reactions and store it for the later use as ATP or NADH.

On the other hand if this reaction has to take place in one go, it would require a high activation energy and although the same total energy will be released at the end as in stepwise small oxidations, but this could not be captured as ATP and most of the energy will be lost in the form of heat.

This all will get more clear with following diagram :

Large Mexose activation Hexose 1 Small activation energies energy FREE ENERGY ACTIVATION/ CONVERSION

Hope it helps you. Good luck :)