A student investigates two enzymes obtained from a mammal.
Enzyme X is collected from saliva. The student mixes a sample of saliva with a 1% starch solution and uses a colorimeter to measure the rate of disappearance of starch.
Enzyme Y is extracted from liver mitochondria. The student mixes the extract with hydrogen peroxide solution and measures the rate of oxygen production.
The student records the effect of pH on the activity of each enzyme. Their results are shown in the table.
| pH | Relative activity of Enzyme X (%) | Relative activity of Enzyme Y (%) |
|---|---|---|
| 4 | 10 | 0 |
| 5 | 30 | 5 |
| 6 | 80 | 20 |
| 7 | 100 | 50 |
| 8 | 70 | 80 |
| 9 | 30 | 100 |
| 10 | 5 | 60 |
The student concludes: 'Enzyme Y is an extracellular enzyme because it has an optimum pH of 9, which is higher than the neutral pH optimum of Enzyme X.'
Outline why the student's conclusion is incorrect, and explain how the properties and locations of these enzymes support your own classification of Enzyme X and Enzyme Y as either intracellular or extracellular.