Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst.

Scientists investigated the action of the enzyme ATP synthase. They made reaction mixtures each containing:

• ATP synthase • buffer (to control pH) • substrates.

One of the substrates required in these reaction mixtures is inorganic phosphate (Pi).

Tick (✓) one box to show which other substrate the scientists must add to the reaction mixtures to produce ATP.

☐ Adenine

☐ Adenosine diphosphate

☐ Glucose

☐ Ribose

The scientists investigated the effect of concentration of inorganic phosphate (Pi) on ATP synthase activity.

After 2 minutes, they stopped each reaction and then measured the concentration of ATP.

Figure 1 shows the scientists' results.

Suggest and explain a procedure the scientists could have used to stop each reaction.

Explain the change in ATP concentration with increasing inorganic phosphate concentration.