Apentix/AP Biology/Unit 3: Cellular Energetics/Question
AP Biologyhardmcq1 pt

Early glycolysis consumes two ATP per glucose before any ATP is harvested. What does this upfront investment actually buy the cell?

A.It phosphorylates the sugar early, trapping glucose inside the cell and priming it for cleavage into two three-carbon sugars
B.It breaks glucose directly into pyruvate while storing the released energy as heat
C.It converts NAD+ into NADH so the payoff phase starts with electrons already banked
D.It strips phosphate groups off so the sugar can diffuse out of the cell for storage

Explanation

Core Concept

Hexokinase and phosphofructokinase attach phosphate groups to glucose and fructose 6 phosphate during the investment phase. A charged phosphate cannot cross the plasma membrane, so the sugar stays locked in the cytosol where the pathway operates. Adding phosphates also raises the energy of the six-carbon sugar, making its later split into glyceraldehyde 3 phosphate and dihydroxyacetone phosphate feasible. The four ATP earned in the payoff phase repay the loan and leave a net gain of two.

Correct Answer

AIt phosphorylates the sugar early, trapping glucose inside the cell and priming it for cleavage into two three-carbon sugars

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