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Class 9 SELINA Solutions Biology Chapter 14 - The Respiratory System

The Respiratory System Exercise Ex. 1

Solution A

1. (b) contracts

2. (a) alveoli

3. (b) loss in dry weight

Solution B.1

(a) Diaphragm

(b) Ethyl alcohol

(c) Diffusion

(d) Diffusion

(e) Hypoxia

(j) Vocal cord

Solution B.2

(a) Epiglottis

(b) Capillaries

(c) Diaphragm

(d) Bronchioles

(e) Ribs

(f) Alveoli or air sacs

Solution B.3




1. Oxygen



2. Carbon dioxide



3. Nitrogen




Solution B.4

ATP or Adenosine Triphosphate is termed as "Currency of Energy" of the cell.

Solution B.5

Column I

Column II

(a) Alveoli

(iii) diffusion of gases

(b) Bronchioles

(iv) small air tubes

(c) Nasal Chamber

(ii) lined with hair

(d) Bronchi

(v) an inverted Y shaped tube


Solution C.1

(a) Alveoli and gaseous diffusion

(b) Mitochondria and power house (respiration)

(c) Epiglottis and guard of entrance to trachea

(d) Pleura and lung covering

(e) Diaphragm and differentiate thoracic cavity and abdominal cavity

(f) 'C' shaped cartilage rings and support

Solution C.2

(a) Ciliated epithelium: It is the protective inner lining of the respiratory passage. It helps in motion, driving any fluid that is on them.

(b) Mitochondria: In mitochondria, pyruvic acid is further broken down step by step in a cyclic manner in the presence of oxygen.

(c) Diaphragm: Diaphragm contributes to the enlargement of the chest cavity lengthwise.

(d) Intercostal muscles: The muscles help the inward and outward movement of ribs enlarging the chest cavity all around.

(e) Pleural fluid: It provides lubrication for free movement of the expanding and contracting lungs.

Solution C.3

Column A

Column B



Large surface area


Breathing movements




Complemental air

Extra inhalation




Solution C.4

The breathing rate increases after a vigorous physical exercise. Also, accumulation of CO2 in the blood increases the rate of breathing.

Solution C.5

During breathing, the air expelled out is always warmer or at body temperature. It can be felt by breathing out the air on our own hand. One can feel the warmth of the air expelled out during breathing.

Solution C.6

The nasal cavity is lined by ciliated epithelium and mucous glands. The mucous glands secrete mucous. The ciliated epithelium is present on the entire lining of larynx, trachea, bronchi and bronchioles. The constant motion of cilia and mucous trap dust, micro-organisms, pollen and other minute particles present in the air. In this way, the respiratory passage is kept free of dust particles.

Solution C.7

We inhale air which contains more of oxygen and less of carbon dioxide. We exhale air which contains more of carbon dioxide and less of oxygen. Therefore, the statement "We breathe in oxygen and breathe out carbon dioxide" is wrong.

Solution D.1

(a) Aerobic respiration :- CO2, H2O, ATP, Heat energy

Anaerobic respiration :- Lactic acid, ATP, Heat energy

(b) Respiration :- CO2

Photosynthesis :- O2

(c) Photosynthesis :- CO2 + sunlight + H2O

Respiration :- Glucose (with or without oxygen)

(d) Inspired air :- 004%

Alveolar air :- 4.00%

(e) Respiration :- lungs, bronchi, alveoli

Breathing :- nasal cavity, trachea, diaphragm

(f) Tidal volume :- 1500 ml

Residual volume :- 500 ml

Solution D.2

(a) Breathing through the nose is said to be healthier than through the mouth because the hair present in the nostrils prevent large dust particles from entering inside the respiratory system.


(b) Gaseous exchange continues in the lungs even during expiration because expiration is the result of reverse movements of the ribs and diaphragm. As a consequence of the movements of the ribs and the diaphragm, the thoracic cavity is diminished and the lungs are compressed, forcing the air out into the atmosphere.


(c) At higher altitudes, the oxygen content of the air is low. So, a person feels breathlessness at higher altitudes. 

(d) In order to maintain the body temperature constant in very cold conditions in winter, heat production is increased by enhanced metabolic rate and increased muscular activity. Shivering and chattering of teeth involves a lot of muscular activity. That is why we shiver and our teeth chatter in winter in order to increase heat production in the body.

Solution D.3

(a) (i) Abdominal muscles (ii) Intercostal muscles

(b) (i) The ribs are moved inwards and outwards by the intercostal muscles stretched between them and thereby, enlarges the chest cavity.

(ii) The diaphragm flattens and presses the organs inside the abdomen. When the abdominal muscles relax, the abdominal wall moves outwards.

(c) The overall chemical equation for the process of respiration in humans:

C6H12O6 + 6O2    6CO2 + 6H2O + 38ATP + 420 kcal

(d) 1. Residual air: Some air is a1ways left in the lungs even after forcibly breathing out. This is the left over or residual air. This volume is 1500 mL.

2. Dead air space: Some tidal air is left in the respiratory passages such as trachea and bronchi, where no diffusion of gases can occur. This volume is called dead air space. It is 150 mL.

Solution D.4

Path taken by the inspired air:

Nose Pharynx Larynx Trachea Bronchi

Solution D.5

(a) Ribs: The ribs move inwards and outwards by the muscles stretched between them, thus enlarging the chest cavity all around.

(b) Diaphragm: On contraction, the diaphragm falls or flattens from the dome-shaped outline to an almost horizontal plane and thus, contributes to the enlargement of the chest cavity lengthwise.

(c) Abdominal muscles: Abdominal muscles help to increase the size of the thoracic cavity by the movement of diaphragm and therefore, aids in inspiration.

Solution E.1

(i) 1: Thin walls of capillary; 2: RBCs (Red blood corpuscles);

3: Plasma; 4: Thin wall of the alveolus

(ii) 5: CO2 diffuses out; 6: O2 diffuses in

Solution E.2

(a) Anaerobic respiration

(b) This reaction is applicable to animals only.

(c) This reaction may occur in muscular tissues (skeletal muscles).

Solution E.3


(i) Anaerobic respiration in plants: 5

(ii) End products in aerobic respiration: 4

(iii) Reaction occurring in liver: 2

(iv) Anaerobic respiration in animals: 1

(v) Storage in the liver: 3


(i) Aerobic respiration: 4

(ii) Change taking place in the liver: 3

(iii) Anaerobic respiration in yeast: 5

(iv) Change taking place in a plant storage organ, e.g., potato: 2

(v) Anaerobic respiration in animals: 1

Solution E.4

(a) Tidal volume (TV): Air breathed in and out, in a normal quiet breathing is called tidal volume. It is 500 mL.

(b) Inspiratory reserve volume (IRV): Air that can be drawn in forcibly over and above the tidal air is called inspiratory reserve volume. It is also known as complemental air. It is 3000 mL.

(c) Expiratory reserve volume (ERV): Air that can be forcibly expelled out after a normal expiration is called expiratory reserve volume. It is also called supplemental air. It is 1000 mL.

(d) Vital capacity (VC): Volume of air that can be taken in and expelled out by maximum inspiration and expiration is called vital capacity. It is 4500 mL.

(e) Residual volume (RV): Air left in the lungs, even after forcible expiration is called residual volume. It is 1500 mL. 

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