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Chapter 14

The Respiratory System

Class 9 - Concise Biology Selina


Multiple Choice Type

Question 1

During inspiration, the diaphragm

  1. Relaxes
  2. Contracts ✓
  3. Expands
  4. Gets folded

Question 2

The ultimate end parts of the respiratory system in humans is known as

  1. Alveoli ✓
  2. Bronchioles
  3. Tracheoles
  4. Bronchi

Question 3

During respiration there is

  1. Gain in dry weight
  2. Loss in dry weight✓
  3. No change in dry weight
  4. Increase in the overall weight

Very Short Answer Type

Question 1

Choose the odd one out in each of the following groups of four items each:

(a) Trachea, Bronchus, Alveolus, Diaphragm

(b) Ethyl alcohol, Carbon dioxide, Starch, Oxygen absence

(c) Diffusion, Respiratory gases, Alveoli, Capillary network

(d) Trachea, ciliated epithelium, mucus, diffusion

(e) Oxyhaemoglobin, carbaminohaemoglobin, Hypoxia, Carboxyhaemoglobin

(f) Hairy, Moist, Nostril, Vocal cord

Answer

(a) Diaphragm is the odd one out in this group because Trachea, Bronchus and Alveolus are part of the respiratory tract whereas diaphragm is not a part of the respiratory tract. It helps in external exchange of gases.

(b) Starch is the odd one out in this group because the others in the group are related to anaerobic respiration. Anaerobic respiration occurs in Oxygen absence and the by-products are Carbon dioxide and Ethyl alcohol.

(c) Diffusion is the odd one out in this group because Diffusion is a process whereas Respiratory gases, Alveoli, Capillary network are physical entities which are part of the respiration process.

(d) Diffusion is the odd one out in this group because the inner lining of Trachea is formed of ciliated epithelium and mucus is secreted in Trachea for lubrication of the track whereas no exchange of gases via diffusion takes place in Trachea.

(e) Hypoxia is the odd one out in this group because Hypoxia is the deficiency of Oxygen reaching the tissues whereas Oxyhaemoglobin, Carbaminohaemoglobin and Carboxyhaemoglobin relate to how Oxygen, Carbon dioxide and Carbon monoxide are carried by the blood respectively when these gases come in contact with Haemoglobin.

(f) Vocal cord is the odd one out in this group because the lining of nostril is hairy and moist whereas Vocal cord produce sound when air is expelled forcibly through them.

Question 2

Name the body structure concerned with the given functional activity:

(a) Prevents food from entering the trachea during swallowing.

(b) Transports oxygen to the body cells.

(c) Helps to increase the volume of the chest activity lengthwise.

(d) Combines with the oxygen in the lungs.

(e) Protects the lungs from mechanical injuries.

(f) Provides actual diffusion of respiratory gases in lungs.

Answer

(a) Prevents food from entering the trachea during swallowing — Epiglottis

(b) Transports oxygen to the body cells — Capillaries

(c) Helps to increase the volume of the chest activity lengthwise — Diaphragm

(d) Combines with the oxygen in the lungs — Bronchioles

(e) Protects the lungs from mechanical injuries — Ribs

(f) Provides actual diffusion of respiratory gases in lungs — Air sacs/alveoli

Question 3

What is the normal percentage composition of gases in inspired air and expired air respectively?

Answer

The following table depicts the gas composition in percentage:

Name of the gasInspirationExpiration
Oxygen20.96%16.4%
Carbon dioxide0.04%4%
Nitrogen79.00%79.6%

Question 4

Which chemical compound inside a cell can be termed "Energy Currency".

Answer

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

Question 5

Match the items in Column I with the ones most appropriate in Column II. Rewrite the matching pairs:

Column IColumn II
(a) Alveoli(i) where aerobic respiration takes place
(b) Bronchioles(ii) lined with hair
(c) Nasal chamber(iii) diffusion of gases
(d) Bronchi(iv) small air tubes
 (v) An inverted Y-shaped tube
 (vi) A common passage for food and air

Answer

Column IColumn 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

Short Answer Type

Question 1

Given below is an example of a certain structure and its special functional activity:

"Kidney and excretion"

Fill in the blanks on a similar pattern.

(a) Alveoli and ........

(b) Mitochondria and ........

(c) Epiglottis and ........

(d) Pleura and ........

(e) Diaphragm and ........

(f) 'C' shaped cartilage rings and ........

Answer

(a) Alveoli and gaseous diffusion.

(b) Mitochondria and power house.

(c) Epiglottis and Trachea(guard of entrance).

(d) Pleura and Lung covering.

(e) Diaphragm and Distinguishes abdominal cavity and thoracic cavity.

(f) ‘C’ shaped cartilage rings and support.

Question 2

State one function of each of the following:

(a) Ciliated epithelium lining the respiratory tract

(b) Mitochondria

(c) Diaphragm

(d) Intercostal muscles

(e) Pleural fluid

Answer

(a) Ciliated epithelium lining the respiratory tract — The entire lining of the larynx, trachea, bronchi and bronchioles is formed of 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 contracting and expanding lungs.

Question 3

Match the items in Column A with those in Column B.

Column AColumn B
CartilaginousEpiglottis
Large surface areaDiaphragm
Breathing movementsBronchi
VoiceAlveoli
Complemented airlarynx
SwallowingExtra inhalation

Answer

Column AColumn B
CartilaginousBronchi
Large surface areaAlveoli
Breathing movementsDiaphragm
VoiceLarynx
Complemented airExtra inhalation
SwallowingEpiglottis

Question 4

Under what conditions would the breathing rate increase?

Answer

Breathing rate can increase under the following circumstances:

  1. Accumulation of carbon dioxide in blood
  2. Vigorous physical exercise

Question 5

How would you prove that the air you breathe out is warmer?

Answer

During breathing, the air expelled out is always warmer or at the 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.

Question 6

How is the respiratory passage kept free of dust particles?

Answer

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 the trachea, larynx, bronchioles and bronchi. 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.

Question 7

What is wrong in the statement "We breathe in oxygen and breathe out carbon dioxide"?

Answer

We inhale air containing much oxygen and very little carbon dioxide and exhale air containing less of oxygen and more of carbon dioxide. Therefore, the statement “We breathe in oxygen and breathe out carbon dioxide” is wrong.

Long Answer Type

Question 1

Differentiate between the following pairs on the basis of the aspect given in the brackets.

(a) Aerobic and anaerobic respiration (end products of the process)

(b) Respiration and photosynthesis (gas released)

(c) Photosynthesis and respiration (reactants)

(d) Inspired air and alveolar air (carbon dioxide content)

(e) Respiration and breathing (organs involved)

(f) Tidal volume and residual volume (quantity of air)

Answer

(a) Aerobic and anaerobic respiration (end products of the process)

Aerobic respirationAnaerobic respiration
Carbon dioxide, water, ATP, Heat energyLactic acid, ATP, heat energy

(b) Respiration and photosynthesis (gas released)

RespirationPhotosynthesis
Carbon dioxideOxygen

(c) Photosynthesis and respiration (reactants)

PhotosynthesisRespiration
Water, carbon dioxide, sunlightGlucose (with/without oxygen)

(d) Inspired air and alveolar air (carbon dioxide content)

Inspired airAlveolar air
0.04%4%

(e) Respiration and breathing (organs involved)

RespirationBreathing
Lungs, bronchi, alveoliNasal cavity, trachea, diaphragm

(f) Tidal volume and residual volume (quantity of air)

Tidal volumeResidual volume
500mL1500mL

Question 2

Give suitable explanations for the following:

(a) Breathing through the nose is said to be healthier than through the mouth.

(b) Why does gaseous exchange continue in the lungs even during expiration?

(c) Why does a person feel breathlessness at higher altitudes?

(d) Why do you shiver and why do your teeth chatter when it is very cold in winter?

Answer

(a) Breathing through the nose is said to be healthier than through the mouth because the external part of the nose bears two nostrils separated by a cartilaginous septum. The hairs present in the nostrils prevent large particles from entering the respiratory system. So, always breathe through the nose and not through the mouth.

(b) Gaseous exchange continue in the lungs even during expiration because expiration is the result of reverse movements of the ribs and diaphragm. As a result 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) A person feel breathlessness at higher altitudes because as we go higher up, the air we breathe in decreases in pressure accompanied by a gradual decrease in oxygen content.

(d) We shiver and our teeth chatter when it is very cold in winter in order to increase the heat production in the body. To maintain the temperature of the body constant in extremely cold conditions, the production of heat is increased through heightened metabolic rate and greater muscular activity and shivering and teeth chattering involves a lot of muscular activity.

Question 3

With regard to the respiratory system and the process of respiration in man, answer the following questions:

(a) Name the two muscles that help in breathing.

(b) Briefly describe how the above mentioned muscles help in the inspiration of air.

(c) Give the overall chemical equation to represent the process of respiration in humans.

(d) What is meant by:

  1. Residual air
  2. Dead air space

Answer

(a) The two muscles that help in breathing are — intercostal muscles and abdominal muscles.

(b) When the intercostal muscles stretch between the ribs, they move outwards and inwards causing them to enlarge the chest cavity.

(c) The overall chemical equation for the process of respiration in humans is as given below:

C6H12O6+6O2enzymes6CO2+6H2O+38ATPchemical energy+420kcalheat energyC_6H_{12}O_6 + 6O_2 \overset{\text{enzymes}}{\longrightarrow} 6CO_2 + 6H_2O + \underset{\text{chemical energy}}{38 ATP} + \underset{\text{heat energy}}{420 kcal}

(d) The meanings of Residual air and Dead air space are as follows:

  1. Residual Air — Even after forcibly breathing out, some air always remains in the lungs. This air is referred to as residual air. The volume of this air is 1500mL.
  2. Dead air space — Some tidal air is remaining in the respiratory passages such as bronchi and trachea. Here no gas diffusion takes place. This volume is referred to as dead air space and its volume is 150mL.

Question 4

Starting from the nostrils, trace the path in sequence which the transpired air takes until it reaches the air sacs.

Answer

The path taken by the transpired air through the nostrils until it reaches the air sacs is as follows:

Nose → Pharynx → Larynx → Trachea → Bronchi

Question 5

What are the functions of the following in breathing?

(a) Ribs

(b) Diaphragm

(c) Abdominal muscles

Answer

(a) Ribs — The ribs move upwards and outwards due to the contraction of the external intercostal muscles stretched between them thus enlarging the chest cavity all around. (The internal intercostal muscles are relaxed).

(b) Diaphragm — The diaphragm contracts and 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 — It helps to increase the size of the thoracic cavity through the motion of the diaphragm which assists in inspiration.

Structured / Application / Skill Type

Question 1

Given alongside is a diagrammatic sketch of a part in human lungs

Given alongside is a diagrammatic sketch of a part in human lungs. Name the parts numbered 1-4. What do the arrows 5 and 6 indicate? Respiratory System, Concise Biology Selina Solutions ICSE Class 9.

(i) Name the parts numbered 1-4

(ii) What do the arrows 5 and 6 indicate?

Answer

(i) The parts numbered 1-4 are:

  • 1 → Thin walls of capillary
  • 2 → Red blood corpuscles
  • 3 → Plasma
  • 4 → Thin wall of alveoli

(ii) Arrows at 5 & 6 indicate diffusion of carbon dioxide outside and diffusion of oxygen inside respectively.

Question 2

Given below is an overall chemical reaction of a certain process:

C6H12O6 → lactic acid + 2ATP + heat energy

(a) Name the process.

(b) Is this reaction applicable to animals or to plants or to both animals and plants?

(c) Name one tissue in which this reaction may occur.

Answer

(a) The process is anaerobic respiration.

(b) The reaction is applicable to animals only.

(c) The reaction may occur in skeletal muscular tissues.

Question 3

Given below are chemical reactions (1 to 5) involving glucose and five other chemical products (A-E).

Given below are chemical reactions (1 to 5) involving glucose and five other chemical products (A-E). Respiratory System, Concise Biology Selina Solutions ICSE Class 9.

(a) Write the reaction number of the following:

(i) Anaerobic respiration in plants ........

(ii) End-products in aerobic respiration ........

(iii) Reaction occurring in liver ........

(iv) Anaerobic respiration in animals ........

(v) Storage in the liver ........

(b) Which reactions (1-5) in the above correspond to the following (write the corresponding number of reaction next to them).

(i) Aerobic respiration

(ii) Change taking place in the liver

(iii) Anaerobic respiration in yeast

(iv) Change taking place in a plant storage organ – e.g. potato.

(v) Anaerobic respiration in animals

Answer

(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

(b) The corresponding reaction number is as follows:

(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

Question 4

The volume of air in the lungs and the rate at which it is exchanged during inspiration and expiration was measured.

The following diagram shows a group of the lung volumes and capacities:

The volume of air in the lungs and the rate at which it is exchanged during inspiration and expiration was measured. The diagram shows a group of the lung volumes and capacities. Respiratory System, Concise Biology Selina Solutions ICSE Class 9.

Study the diagram carefully and explain briefly the following:

  1. Tidal volume
  2. Inspiratory reserve volume
  3. Expiratory reserve volume
  4. Vital capacity
  5. Residual volume

Answer

  1. Tidal volume — It is the air breathed in and out in a normal quiet breathing. The tidal volume(TV) is 500mL.
  2. Inspiratory reserve volume — Air that can be drawn in forcibly over and above the tidal air is known as inspiratory reserve volume. It is referred to as IRV or complemental air and is 3000mL.
  3. Expiratory reserve volume — It is the air that can be expelled out forcibly after a normal expiration. It is referred to as ERV or supplemental air and is 1000mL.
  4. Vital capacity (VC) — It is the volume of air that can be inhaled and exhaled by maximum inspiration and expiration respectively and is about 4500mL.
  5. Residual volume (RV) — Even after forcible expiration, there is some air left in the lungs and is referred to as residual volume. It is about 1500mL.
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