Answer the following : Sometimes the pH of our mouth gets lower than 5·5. Why ?
Generated by claude-sonnet-4-6 · 2026-06-15 06:45 · grounding rag
Model Answer
When we eat sugary or starchy food, bacteria present in the mouth break down (degrade) the sugar and food particles remaining in the mouth. This process produces acids, which lower the pH of the mouth below 5.5.
At this low pH, the tooth enamel (made of calcium hydroxyapatite) gets corroded, leading to tooth decay.
Source: Chapter 2, Section 2.3.1 — pH change as the cause of tooth decay
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Explanation
- The key cause is bacterial degradation of sugar → acid production.
- Mention that pH drops below 5.5 (the threshold given in the textbook).
- Examiners expect: (1) bacteria in mouth, (2) degradation of sugar/food particles, (3) acid produced → pH falls below 5.5. All three points together make a complete answer for 2 marks.
- Do not confuse this with stomach acidity — this question is specifically about the mouth.