Respiration in Terrestrial Animals: Terrestrial organisms use atmospheric oxygen for respiration, which is absorbed by different organs in different animals.

All these organs have a structure that increase the surface area and is in contact with the oxygen rich atmosphere.

Since, the exchange of oxygen and carbon dioxide has to take place across this surface, it is very fine and delicate. To protect this surface it is usually placed within the body wall – protected so there are numerous passages that will take air to numerous passages that will take air to this area.

The Human Respiratory System consists of a pair of lungs and a series of air passages leading to the lungs.

The entire respiratory tract (passages) consists of the nose, pharynx, larynx, trachea, bronchi and bronchioles. Air enters the nose through the nostrils.

When air passes through the nose, it is warmed, moistened and filtered. The hairs present in the nose filter out particles in the incoming air. The air is moistened by the mucus present in the nose, and it is warmed by the blood flowing through the capillaries in the nose.

The respiratory tract from the nose to the bronchioles is lined by mucus membranes and cilia. The mucus and cilia act as additional filters.

Behind the nose lies the ‘pharynx (throat)’. There are two passages here – one for food and the other for air. The air passes from the pharynx to the larynx, or the voice box. The opening leading to the larynx is called ‘glottis’. It is protected by a lid called ‘epiglottis’, which prevents food from entering the passage to the lungs.

From the larynx the air goes to the trachea, or the windpipe. The trachea is about 11cm long. It is guarded by 16 – 20 C shaped cartilage rings, which prevent the trachea from collapsing. The trachea divides into two tubes called ‘bronchi.’ Each ‘bronchus’ divides and branches out in the form of thinner tubes called ‘bronchioles’.

Each bronchioles enter the lungs and divide further into finer branches called alveolar ducts. These open into extremely thin – walled, grape shaped air sacs called ‘alveoli’. Each alveolus is covered by a web of blood capillaries.

The lungs are a pair of spongy organ lying in the chest cavity formed by ribs. The actual exchange of gases between the air and the body takes place in the capillary covered alveoli inside the lungs. Here, oxygen from the air in the alveoli goes into the blood, and the carbon dioxide in the blood goes out.

The oxygen binds to the haemoglobin molecules present in the red blood corpuscles and is taken to different parts of the body.

The total surface area through which the exchange of gases can take place increases because of the millions of alveoli in the lungs. Their total surface area can be about a hundred times that of the body.

The large surface area allows sufficient oxygen intake needed for releasing the large amount of energy required by us.

Sample Questions

(More Questions for each concept available in Login)

Question : 1

Which of the following are correct ? (a) Terrestrial organisms use atmospheric oxygen for respiration, which is absorbed by different organs in different animals. (b) There are two passages one for food and the other for air. The air passes from the pharynx to the larynx, or the voice box. The opening leading to the larynx is called ‘glottis’. (c) The large surface area allows sufficient oxygen intake needed for releasing the large amount of energy required by us.
A. Only (a) and (b) is correct .	B. Only (b) and (c) is correct .	C. Only (a) and (c) is correct .	D. All of these .
Right Option : D
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Question : 2

To prevent the entry of food into the trachea, the opening is guarded by
A. epiglottis
B. glottis
C. hard palate
D. soft palate
Right Option : A
View Explanation

Question : 3

Bronchi divide into
A. bronchus
B. bronchioles
C. alveoli
D. air sacs
Right Option : B
View Explanation

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Respiration in Human Beings

Respiration in Human Beings