Question

If the teeth are not cleaned regularly, they become covered with a sticky yellowish layer W of food particles and bacteria. Since layer W covers the teeth, the alkaline liquid X secreted by glands Y inside the mouth cannot reach the teeth surface to neutralise the acid formed by the action of organisms Z on sugary food, and hence tooth decay sets in.

1. What is W known as?
2. What are (i) X and (ii) Y?
3. What are organisms Z?
4. State one way of removing layer W from the teeth.

Answer 1

(a) Layer W is known as Dental Plaque. It is a sticky, yellowish film that constantly forms on the teeth when food particles and bacteria are not cleaned away.

(b)

1. Liquid X: Saliva (which is slightly alkaline and helps neutralize acids in the mouth). 
2. Glands Y: Salivary glands (the glands inside the mouth that secrete saliva).

(c) Organisms Z are Bacteria (such as Streptococcus mutans). They ferment the sugars left over from food residues to produce harmful acids.

(d) The most effective way to remove dental plaque (layer W) is regular and thorough brushing of teeth (especially after meals or at least twice a day) using a toothbrush and toothpaste. Flossing regularly also helps remove plaque from between the teeth where toothbrush bristles cannot reach.