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.
What is W known as?
What is (i) X, and (ii) Y?
What are organisms Z?
State one way of removing layer W from the teeth.
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W is the dental plaque.
X refers to the saliva.
Y refers to the salivary glands.
Organisms Z are bacteria.
Layer of W, i.e. dental plaque, can be removed by regular brushing of teeth.
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A liquid X of colour Y circulates in the human body only in one direction: from body tissues to the heart. Among other things, liquid X contains germs from cells and dead cells. The liquid X is cleaned of germs and dead cells by a special type of white blood cells called Z. This cleaned liquid is then put into blood circulatory system in subclavian veins.
What is (i) liquid X and (ii) colour Y?
What are Z.
The liquid X is somewhat similar to a component of blood. Name this component.
If a person holds his breath after expiration for about 25sec, would there be occurrence of any exchange of respiratory gases in the lungs during this period? Explain.