Anabolic (building) reactions are typically

Answer: Endergonic, requiring energy input Building polymers from monomers requires energy input, often via ATP coupling.

Which process directly powers the conversion of ADP + Pi to ATP shown at the bottom?

Answer: Phosphorylation reactions in catabolism (e.g., glycolysis, oxidative phosphorylation) ADP is phosphorylated to ATP using energy from catabolic reactions (substrate-level and oxidative phosphorylation). ATP then hydrolyzes to do cellular work.

A reaction proceeds A → B → C with the energy diagram shown. Which step has the LARGEST positive ΔG?

Answer: A → B because ΔG is small or near zero (least exergonic) Each step has small or near-zero ΔG. A→B sees the smallest free-energy drop, so it's least favorable; the largest drop is between B and C, but the prompt asks for the LARGEST ΔG (most positive / least negative), so A→B fits.

AP Biology · Topic 3.4

Cellular Energy Practice

Part of Cellular Energetics.(ENE-1.O)

Practice questions

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Sample questions

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Sample 1difficulty 1/5
$Anabolic (building) reactions are typically$
- A
  $Endergonic, requiring energy input$
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- B
  $Exergonic, releasing free energy$
- C
  $Spontaneous, lowering system entropy$
- D
  $Coupled, releasing heat as a byproduct$
Why
$Building polymers from monomers requires energy input, often via ATP coupling.$
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Sample 2difficulty 1/5
$The diagram summarizes the cellular ATP/ADP cycle linking energy release to energy storage.$
$Which process directly powers the conversion of ADP + Pi to ATP shown at the bottom?$
- A
  $Spontaneous bond formation in solution$
- B
  $Phosphorylation reactions in catabolism (e.g., glycolysis, oxidative phosphorylation)$
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- C
  $Diffusion of water across membranes$
- D
  $Hydrolysis of glucose$
Why
$ADP is phosphorylated to ATP using energy from catabolic reactions (substrate-level and oxidative phosphorylation). ATP then hydrolyzes to do cellular work.$
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Sample 3difficulty 2/5
$A reaction proceeds A \to B \to C with the energy diagram shown. Which step has the LARGEST positive ΔG?$
- A
  $A \to C overall because reactions accumulate$
- B
  $B \to C because the products are higher in energy$
- C
  $All steps have equal ΔG$
- D
  $A \to B because ΔG is small or near zero (least exergonic)$
  check_circle
Why
$Each step has small or near-zero ΔG. A\toB sees the smallest free-energy drop, so it's least favorable; the largest drop is between B and C, but the prompt asks for the LARGEST ΔG (most positive / least negative), so A\toB fits.$
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Sample 4difficulty 2/5
$The diagram represents an endergonic reaction. How is such a reaction driven forward in cells?$
- A
  $Addition of an irreversible inhibitor$
- B
  $Spontaneous occurrence at standard temperature and pressure$
- C
  $Removal of all enzymes from the cytoplasm$
- D
  $Coupling with an exergonic reaction such as ATP hydrolysis$
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Why
$Endergonic reactions (ΔG > 0) are nonspontaneous. Cells couple them to exergonic reactions, most commonly ATP hydrolysis, to make the overall ΔG negative.$
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Sample 5difficulty 2/5
$Cells use ATP to drive endergonic reactions by$
- A
  $Lowering the activation energy without any free energy input$
- B
  $Adding inorganic catalysts that shift the chemical equilibrium$
- C
  $Coupling them with the highly exergonic hydrolysis of ATP$
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- D
  $Heating the cell to raise the kinetic energy of reactants$
Why
$Sum of two reactions: if combined ΔG is negative, the coupled reaction proceeds.$
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