Example 1
In A→B→C, the B−to−C enzyme is blocked while A−to−B continues. Predict changes.
B tends to accumulate and C production decreases. The actual amounts depend on alternative pathways and feedback.
Year 12 · SACE Stage 2
Respiration, ATP and metabolism
Practise energy transfers, pathway sequences and inhibitor consequences.
Loading saved practice…
Method and worked examples
Aerobic respiration transfers chemical energy from organic molecules to ATP and heat. The simplified equation is glucose + oxygen → carbon dioxide + water. Glycolysis occurs in the cytosol; mitochondria support later aerobic stages. Folded inner membranes increase area for electron transport and ATP production. ATP formation from ADP and phosphate requires energy; ATP hydrolysis can be coupled to energy-requiring cellular processes.
Fermentation allows glycolysis to continue without oxygen by regenerating NAD+. Yeast commonly produces ethanol and carbon dioxide; animal cells can form lactate. ATP yield per glucose is lower than with aerobic respiration. Metabolic pathways have enzyme-controlled steps and intermediates. Blocking one enzyme can reduce downstream products and cause upstream accumulation. Inhibitor effects depend on the targeted pathway and cell type, rather than every chemical affecting all cells identically.
Example 1
Example 2
Two cultures use equal glucose. One respires aerobically and one ferments. Which has higher ATP yield per glucose?
The aerobic culture normally has the larger ATP yield because more energy is captured through the aerobic pathway.
Watch out: Bond breaking requires energy; overall energy change depends on both breaking and forming bonds in a reaction.