Draw a diagram of the human heart and label its parts.

1. Why is there a difference in the rate of breathing between aquatic organisms and terrestrial organisms? Explain.
2. Draw a diagram of human respiratory system and label-pharynx, trachea, lungs, diaphragm and alveolar sac on it.

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

1. Draw a diagram of human alimentary canal and label on it: Oesophagus, Gallbladder, Liver and Pancreas.
2. Explain the statement, ‘Bile does not contain any enzyme but it is essential for digestion.’

When a person puts food in his mouth, then teeth cut it into small pieces, chew and grind it. The glands A in the mouth secrete a substance B which is mixed with the food by tongue. The substance B contains an enzyme C which starts the digestion of food in the mouth. The slightly digested food from the mouth goes down a tube D. The special type of movements E in the walls of tube D push the food into stomach for further digestion. The stomach wall secretes gastric juice containing three substance F, G and H. One of the functions of F is to kill bacteria which may enter the stomach with food. The substance G protects the inside layer of stomach from the damaging effect of substance F whereas substance H is and enzyme for digestion. The partially digested food then enters into small intestine for further digestion.

1. What is Gland A, Substance B and Enzyme C?
2. Name the tube D.
3. What is the movement E known as?
4. What are F, G and H?

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.

Each and every respiration organ is structurally specialised in its function. Justify with examples.

1. Draw a diagram of human alimentary canal and label - gall bladder, pancreas, liver and small intestine on it.
2. Give two reasons to explain why absorption of digested food occurs mainly in the small intestine.

What is lymphatic system? What are its functions?

Draw a labelled diagram of the human digestive system. With the help of this diagram, describe the process of digestion of food in man (humans).