Additional Questions - Chapter 6 Respiration 11th Biology Zoology Guide Samacheer Kalvi Solutions - SaraNextGen [2024-2025]

Updated By SaraNextGen

On April 24, 2024, 11:35 AM

Additional Questions & Answers
I. Multiple Choice Questions
Choose the correct answer
Question 1.
Insects respire through
(a) body surface
(b) trachea
(c) gills
(d) book lungs
Answer:
(b) trachea

Question 2.
Which of the following does not belong to the conducting zone of the respiratory system?
(a) trachea
(b) bronchioles
(c) larynx
(d) alveoli
Answer:
(d) alveoli
Question 3.
The trachea is supported by the
(a) long structure
(b) cartilage
(c) multiple cartilaginous rings
(d) ligaments
Answer:
(c) multiple cartilaginous rings
Question 4.
Which of the following is right regarding the bronchioles?
(a) trachea divides into bronchioles
(b) bronchioles have cartilaginous rings
(c) bronchioles collapse when the air pressure is more
(d) bronchioles are without cartilaginous rings
Answer:
(d) bronchioles are without cartilaginous rings
Question 5.
The lungs are protected ventrally by
(a) vertebral column
(b) sternum
(c) ribs
(d) diaphragm
Answer:
(b) sternum

Question 6.
The function of pleural fluid is to
(a) keep the lungs intact
(b) protect the lungs from getting firm
(c) maintain the texture of the lungs
(d) reduces friction when lungs expand and contract
Answer:
(d) reduce friction when lungs expand and contract
Question 7.
Which of the following happens during inspiration?
(a) Diaphragm becomes dome shaped
(b) internal intercostal muscles contract
(c) volume of the thoracic chamber increases
(d) ribs are pulled downward
Answer:
(c) volume of the thoracic chamber increases
Question 8.
The amount of air inspired or expired with each normal breath is called the
(a) residual volume
(b) inspiratory reserve volume
(c) dead space
(d) tidal volume
Answer:
(d) tidal volume
Question 9.
The normal value of IRV is
(a) $500 \mathrm{~mL}$
(b) $2500-3000 \mathrm{~mL}$
(c) $1100-1200 \mathrm{~mL}$
(d) $150 \mathrm{~mL}$
Answer:
(b) $2500-3000 \mathrm{~mL}$

Question 10.
$\mathrm{UV}+\mathrm{RV}=$
(a) EC
(b) TLC
(c) IC
(d) VC
Answer:
(b) TLC
Question 11.
Which of the following is not involved in gaseous exchange?
(a) expiratory reserve volume
(b) inspiratory reserve volume
(c) residual volume
(d) dead space
Answer:
(d) dead space
Question 12.
Each haemoglobin can combine with molecules of oxygen.
(a) one
(b) four
(c) three
(d) two
Answer:
(b) four
Question 13.
The ferric state of haemoglobin
(a) binds with oxygen
(b) binds with carbon dioxide
(c) does not bind with oxygen
(d) does not bind with carbon dioxide
Answer:
(c) does not bind with oxygen

Question 14.
Which of the following is incorrect with regard to the formation of oxyhaemoglobin in the alveoli?
(a) high $\mathrm{pCO}_2$
(b) less $\mathrm{H}+$ concentration
(c) low $\mathrm{pCO}_2$
(d) low temperature
Answer:
(a) high $\mathrm{pCO}_2$
Question 15.
Carbon dioxide is carried in the RBCs as
(a) bicarbonate ions
(b) carbon dioxide
(c) carbonic acid
(d) carbaminohaemoglobin
Answer:
(d) carbaminohaemoglobin
Question 16.
The formation of is catalysed by the enzyme carbonic anhydrase in RBCs
(a) carbonates
(b) carbaminohaemoglobin
(c) carbonic acid
(d) bicarbonates
Answer:
(c) carbonic acid
Question 17.
The chemosensitive area found close to the rhythm center is highly sensitive to
(a) $\mathrm{CO}_2$ alone
(b) $\mathrm{H}^{+}$alone
(c) $\mathrm{O}_2$
(d) $\mathrm{CO}_2$ and $\mathrm{H}^{+}$

Answer:
(d) $\mathrm{CO}_2$ and $\mathrm{H}+$
Question 18.
Which is known as the respiratory rhythm centre?
(a) cerebellum
(b) pons varoli
(c) medulla oblongata
(d) infundibulium
Answer:
(c) medulla oblongata
Question 19.
When a person travels to higher elevations, he may develop the symptoms of acute mountain sickness. This is because of
(a) nitrogen narcosis
(b) high level of carbon dioxide in blood
(c) low immunity
(d) poor binding of $\mathrm{O}_2$ with haemoglobin
Answer:
(d) poor binding of $\mathrm{O}_2$ with haemoglobin
Question 20.
Erythropoietin hormone stimulates the bone marrow to produce more
(a) WBCs
(b) $\mathrm{RBCs}$
(c) Platelets
(d) Electrolytes
Answer:
(b) RBCs
Question 21.
When a person goes deep into the sea, he/she develops complications due to
(a) increased partial pressure of $\mathrm{O}_2$
(b) increase in blood nitrogen content

(c) increased partial pressure of $\mathrm{CO}_2$
(d) decrease in the pressure in the surrounding water
Answer:
(b) increase in blood nitrogen content
Question 22.
Scuba divers need to face the problem of
(a) nitrogen narcosis
(b) low oxygen content
(c) high carbon dioxide content
(d) lower pressure
Answer:
(a) nitrogen narcosis
Question 23.
Narrowing and inflammation of bronchi and bronchioles is called as
(a) emphysema
(b) bronchitis
(c) asthma
(d) pneumonia
Answer:
(c) asthma
Question 24.
Gradual break down of the thin walls of the alveoli decreasing the total surface area of the gaseous exchange is
(a) bronchitis
(b) emphysema
(c) asthma
(d) tuberculosis
Answer:
(b) emphysema
Question 25.
What causes bronchitis?
(a) Decrease in the surface area of alveoli

(b) inflammation of bronchi and bronchioles
(c) inflammation of bronchi
(d) collection of fluid in the bronchi
Answer:
(c) inflammation of bronchi
Question 26.
Which of the following is caused by bacteria?
(a) pneumonia
(b) emphysema
(c) silicosis
(d) tuberculosis
Answer:
(d) tuberculosis
Question 27.
Which of the following is the occupational respiratory disease?
(a) tuberculosis
(b) emphysema
(c) silicosis
(d) pneumonia
Answer:
(c) silicosis
Question 28.
Why does smoking affect oxygen supply to the body?
(a) haemoglobin fails to bind with $\mathrm{O}_2$
(b) haemoglobin binds with carbon monoxide
(c) Nicotine makes the heart heat faster
(d) Blood vessels are narrowed
Answer:
(b) haemoglobin binds with carbon monoxide
Question 29.
COPD is the
(a) emphysema and chronic bronchitis

(b) asthma and emphysema
(c) emphysema
(d) asthma, chronic bronchitis and emphysema
Answer:
(d) asthma, chronic bronchitis and emphysema
II. Fill in the Blanks
Question 1.
Oxygen is necessary for breakdown of .............................. to release energy.
Answer:
Glucose.
Question 2

........................ produce sound in human beings.
Answer:
Larynx/vocal cords.
Question 3.

........................ are the respiratory organs in most of the aquatic arthropods and molasses.
Answer:
Gills.
Question 4.
The ciliated epithelial cells lining the trachea, bronchi and bronchioles secrete ...................... 
Answer:
Mucus.
Question 5
........................ divides thoracic cavity and abdominal cavity.
Answer:
Diaphragm.
Question 6.
The movement of air between the atmosphere and the lungs is known as .....................

Answer:
Ventilation/breathing.
Question 7

....................  is the movement of atmospheric air into the lungs.
Answer:
Inspiration.
Question 8.

...................... In a relaxed stage, the diaphragm is shaped.
Answer:
Dome.
Question 9.
The expulsion of air from the lungs to the atmosphere is known as ...............
Answer:
Expiration.
Question 10
........................... in an instmment used to measure the volume of air involved in breathing movements.
Answer:
Spirometer.
Question 11.
The volume of air remaining in the lungs after a forceful expiration is............................
Answer:
Residual volume. .
Question 12.
The maximum volume of air that can be moved out during a single breath following a maximal inspiration is ......................
Answer:
Vital capacity.

Question 13.
The total volume of air a person can inhale after normal inspiration is ..................
Answer:
Inspiratory capacity.
Question 14.
The total volume of air a person can exhale after normal inspiration is .....................
Answer:
Expiratory capacity.
Question 15.
......................... is the total volume of air which the lungs can accommodate after forced inspiration.
Answer:
Total lung capacity.
Question 16.
The amount of air that moves into the respiratory passage per minute is called ....................
Answer:
Minute respiratory volume.
Question 17
....................... is the air that is not involved in gaseous exchange.
Answer:
Dead space.
Question 18

......................... is the pressure contributed by an individual gas in a mixture of gases.
Answer:
Partial pressure.
Question 19.
Haemoglobin belongs to the class of ..................

Answer:
Conjugated protein.
Question 20.
Haemoglobin is made up of the iron and the rest colourless protein
Answer:
Haem, globin.
Question 21.
The ferric state of haemoglobin is called
Answer:
Methemoglobin.
Question 22
......................... is the respiratory pigment present in the blood.
Answer:
Haemoglobin.
Question 23.
The blood of human being is red due to the presence of .....................
Answer:
Haemoglobin.
Question 24.
Every $100 \mathrm{~mL}$ of oxygenated blood can deliver about ....................... $\mathrm{mL}$ of $\mathrm{O}$, to the tissues.
Answer:
5.
Question 25.
About $70 \%$ of $\mathrm{CO}_2$ transport occurs as ................... ions.
Answer:
Bicarbonate.
Question 26.
The reversible reaction of formation of carbonic acid from carbon dioxide and water is catalyzed by the enzyme called ....................

Answer:
Carbonic anhydrase.
Question 27
....................... center present in pons Varoli region of the brain moderates the function of respiratory rhythm center.
Answer:
Pneumotaxic.
Question 28
........................ is the hormone secreted by kidneys to stimulate bone marrow to produce more $\mathrm{RBCs}$.
Answer:
Erythropoietin.
Question 29.
The increase in the nitrogen content in blood heads to a condition called...................... 
Answer:
Nitrogen narcosis.
Question 30.
The skin turns bluish black during ......................... poisoning.
Answer:
Carbon dioxide.
Question 31.
Dust, drugs, pollen grains, fish, prawns are common for ............................. asthma.
Answer:
Allergens.
Question 32.
Cigarette smoking reduces the respiratory surface of the alveolar walls and it is known as ......................
Answer:
Emphysema.

Question 33.
Cough, shortness of breath and sputum in the lungs are the symptoms of ........................
Answer:
Bronchitis.
Question 34.
Tuberculosis is caused by ..............
Answer:
Mycobacterium tuberculae
Question 35.
Collection of fluid between the lungs and the chest wall is the complication of the disease ..........................
Answer:
Tuberculosis.
Question 36.
Long exposure to dust gives rise to inflammation leading to ......................
Answer:
Fibrosis.
Question 37
........................ and asbestosis are occupational respiratory diseases resulting from inhalation of particles of silica from sand grinding and asbestos into the respiratory tract.
Answer:
Silicosis.
Question 38
......................... causes narrowing of blood vessels resulting in increase in blood pressure and coronary heart disease.
Answer:
Nicotine.
Question 39.
........................ Smoking lowers count in men.

Answer:
Sperm.
Question 40

........................  is the chemical present in the cigarette smoke that causes addiction.
Answer:
Nicotine.
Question 41.
Chronic obstructive pulmonary disease is due to ......................
Answer:
Smoking.
Question 42.
A non-smoker who inhales cigarette smoke involves in smoking.
Answer:
Passive.
Question 43.
Emphysema, chronic bronchitis and asthma, COPD, cancer may be caused due to .................
Answer:
Smoking.
Question 44.
Cigarette smoke contains thousands of chemicals and even small quantities of ..................

Answer:
Arsenic.
Question 45.
The present in the cigarette smoke damages the gaseous exchange.
Answer:
Tar.
III. Answer the following Questions

Question 1.
What is excretion?
Answer:
The exchange of oxygen and carbon dioxide between environment and cells of our body, where organic nutrients are broken down oxygenatically to release energy.
Question 2.
What are the functions of the respiratory system?
Answer:
The five primary functions of the respiratory system are -
- To exchange $\mathrm{O}_2$ and $\mathrm{CO}_2$ between the atmosphere and the blood.
- To maintain homeostatic regulation of body $\mathrm{pH}$.
- To protect us from inhaled pathogens and pollutants.
- To maintain the vocal cords for normal communication (vocalization).
- To remove the heat produced during cellular respiration through breathing.
Question 3.
The rate of breathing in aquatic animals is faster than the terrestrial animals.
Give reason.
Answer:
The amount of dissolved oxygen is very low in water compared to the amount of oxygen in the air. Hence the rate of breathing in aquatic animals is faster than the terrestrial animals.
Question 4.
What is the function of hairs and mucus in the nasal cavity?
Answer:
The hairs and mucus filter the dust particles present in the air passing through the nostrils.
Question 5.
What is the function of epiglottis?
Answer:

Epiglottis is a thin elastic flap at the junction of nasopharynx and larynx. It prevents the food from entering into the larynx and avoids choking on food.
Question 6.
What are the layers of the diffusion membrane of the alveolus?
Answer:
The diffusion membrane of the alveolus is made up of three layers. They are:
- The thin squamous epithelial cells of the alveoli.
- The endothelium of the alveolar capillaries and
- The basement substance found in between them.
Question 7.
What are the cells of the squamous epithelial cells of the alveoli?
Answer:
The thin squamous epithelial cells of the alveoli are composed of Type I and Type II cells. Type I cells are very thin so that gases can diffuse rigidly through them. Type Il cells are thicker. They synthesize and secrete a substance called surfactant. It lowers the surface tension in the alveoli and prevents pulmonary edema.
Question 8.
How are lungs protected?
Answer:
The lungs are light spongy tissues enclosed in the thoracic cavity surrounded by an air tight space. It is bound dorsally by the vertebral column and ventrally by the sternum, laterally by the ribs and on the lower side by the dome shaped diaphragm.
Question 9.
What is pleura? What is its function?
Answer:
The lungs are covered by double layered pleural membrane containing several layers of elastic connective tissues and capillaries. It encloses the pleural fluid which reduces friction when the lungs expand and contract.

Question 10.
What are the characteristic features of respiratory surface?
Answer:
The surface area of respiratory surface is large and richly supplied with blood vessels.
- It is extremely thin and kept moist.
- It is in direct contact with the environment.
- It is permeable to respiratory gases.
Question 11.
Explain the human respiratory system.
Answer:
The human respiratory system constitutes the conducting zone and the respiratory zone. The conducting zone includes the external nostril, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles and the lungs which contain alveoli.
The parts from the external nostrils up to the bronchioles conduct the air and hence they are called the conducting zone. This zone humidifies and warms the incoming air. The nasal cavity has fine hairs and mucus which filter dust particles in the incoming air.

At the junction of the pharynx and larynx there is a flap called epiglottis. This closes the respiratory tract while swallowing thus preventing the entry of food particles into the trachea and choking. The ciliated epithelial cells of trachea, bronchi and bronchioles secrete mucus rich in glycoprotein.

Microorganism and dust particles attach in the mucus films and are carried upwards to pass down the gullet during normal swallowing. The trachea is a semi-flexible tube supported by multiple cartilaginous rings which expands upto the mid thoracic cavity.
And the level of the 5th theoretic vertebra, it divides into right and left bronchi which divide into secondary and tertiary bronchi and further divide into terminal bronchioles and respiratory bronchioles. Bronchi have ' $c$ ' shaped curved Cartilage plates to ensure that the air passage does not collapse as air pressure changes during breathing. The bronchioles do not have cartilaginous rings but they have rigidity to prevent them from collapsing but are surrounded by smooth muscle which contracts or relaxes to adjust the diameter of these airways.

The fine respiratory bronchioles terminate into highly vascularised thin-walledpouch like air sacs called alveoli. It is made up of thin squamous epithelial
cells, the endothelium of the alveolar capillaries and the basement substance are found in between them.
The thin squamous epithelial cells of the alveoli, the endothelium of the alveolar capillaries and the basement substance found in between them. The thin squamous epithelial cells of the alveoli are composed of Type I and Type Il cells.

Type I cells are very thin so that gases can diffuse rapidly through them. Type Il cells are thicker, synthesize and secrete a substance called Surfactant. The lungs are light spongy tissues endorsed in the thoracic cavity bound dorsally by the vertebral column and ventrally by the sternum, laterally by the ribs and on the lower side by the dome shaped diaphragm. The lungs are covered by double walled pleural membrane containing several layers of elastic connective tissues and capillaries. It encloses the pleural fluid. It reduces friction when the lungs expand and contract.
Question 12.
Explain the mechanism of breathing.
Answer:
The movement of air between the atmosphere and the lungs is known as ventilation or breathing. Inspiration and expiration are the two phases of breathing. Inspiration is the movement of atmospheric air into the lungs and expiration is the movement of alveolar air that diffuse out of the lungs.

Lungs do not contain muscle fibres but expands and contracts by the movement of the ribs and diaphragm. The diaphragm is a sheet of tissue which separates the thorax from the abdomen. In a relaxed state, the diaphragm is dome shaped.
Ribs are moved by the intercostal muscles. External and internal intercostal muscles found between the ribs and the diaphragm helps in creating pressure gradients. Inspiration occurs if the pressure inside the lungs (intrapulmonary pressure) is less than the atmospheric pressure; likewise expiration takes place when the pressure within the lungs is higher than the atmospheric pressure.
Inspiration is initiated by the contraction of the diaphragm muscles and external intercostal muscles, which pulls the ribs and sternum upwards and outwards and increases the volume of the thoracic chamber in the dorsoventral axis, forcing the lungs to expand the pulmonary volume. The increase in pulmonary volume and decrease in the intrapulmonary' pressure forces the fresh air from outside to enter the air passages into the lungs to equalize the pressure.
This process is called inspiration. Relaxation of the diaphragm allows the diaphragm and sternum to return to its dome shape and the internal intercostal muscles contract, pulling the ribs downward reducing the thoracic volume and pulmonary volume. This results in an increase in the intrapulmonary pressure slightly above the atmospheric pressure causing the expulsion of air from the lungs. This process is called expiration.
Question 13.

Write short note on respiratory volumes.
Answer:
Tidal Volume (TV) Tidal volume is the amount of air inspired or expired with each normal breath. It is approximately $500 \mathrm{~mL}$., i.e. a normal human adult can inspire or expire approximately 6000 to $8000 \mathrm{~mL}$ of air per minute. During vigorous exercise, the tidal volume is about 4-10 times higher.
Inspiratory Reserve volume (IRV) Additional volume of air a person can inspire by forceful inspiration is called Inspiratory Reserve Volume. The normal value is $2500-3000 \mathrm{~mL}$.
Expiratory Reserve volume (ERV) Additional volume of air a person can forcefully exhale by forceful expiration is called Expiratory Reserve Volume. The normal value is $1000-1100 \mathrm{~mL}$. Residual Volume (RV) The volume of air remaining in the lungs after a forceful expiration. It is approximately $1100-$ $1200 \mathrm{~mL}$.
Question 14.
Write a short note on respiratory capacities.
Answer:
Vital capacity (VC) the maximum volume of air that can be moved out during a
single breath following a maximal inspiration. A person first inspires maximally then expires maximally. VC = ERV + TV + IRV
1. Inspiratory capacity (IC) The total volume of air a person can inhale after normal expiration. It includes tidal volume and inspiratory reserve volume. IC $=T V+I R V$

2. Expiratory capacity (EC) The total volume of air a person can exhale after normal inspiration. It includes tidal volume and expiratory reserve volume. EC $=\mathrm{TV}+\mathrm{ERV}$
3. Total Lung Capacity (TLC) The total volume of air which the lungs can accommodate after forced inspiration is called Total Lung Capacity. This includes the vital capacity and the residual volume. It is approximately 6000 $\mathrm{mL} . \mathrm{TLC}=\mathrm{VC}+\mathrm{RV}$
4. Minute Respiratory Volume The amount of air that moves into the respiratory passage per minute is called minute respiratory volume.
Question 15.
What is dead space?
Answer:
Some of the inspired air never reaches the gas exchange areas but fills the respiratory passages where exchange of gases does not occur. This air is called dead space. Dead space is not involved in gaseous exchange. It amounts to approximately $150 \mathrm{~mL}$.
Question 16.
How does gaseous exchange take place in the alveoli?
Answer:
The primary site for the exchange of gases is the alveoli. The uptake of 02 and the release of $\mathrm{CO}_2$ occur between the blood and tissues by simple diffusion driven by partial pressure gradient of $\mathrm{O}_2$ and $\mathrm{CO}_2$. Partial pressure is the pressure contributed by an individual gas in a mixture of gases.

It is represented as $\mathrm{pO}_2$ for oxygen and $\mathrm{pCO}_2$ for carbon- dioxide. Due to pressure gradients, $\mathrm{O}_2$ from the alveoli enters into the blood and reaches the 

tissues. $\mathrm{CO}_2$ enters into the blood from the tissues and reaches alveoli for elimination. As the solubility of $\mathrm{CO}_2$ is $20-25$ times higher than that of $\mathrm{O}_2$, the partial pressure of $\mathrm{CO}_2$ is much higher than that of $\mathrm{O}_2$.
Question 17.
Write the note on respiratory pigments.
Answer:
Haemoglobin Haemoglobin belongs to the class of conjugated protein. The iron containing pigment portion haem constitutes only $4 \%$ and the rest colourless protein of the histone class globin. Haemoglobin has a molecular weight of 68,000 and contains four atoms of iron, each of which can combine with a molecule of oxygen.

Methaemoglobin If the iron component of the haem moieties is in the ferric state, than the normal ferrous state, it is called methaemoglobin.
Methaemoglobin does not bind $\mathrm{O}_2$. Normally RBC contains less than $1 \%$ methaemoglobin.
Question 18.
Explain the transport of oxygen In blood.
Answer:
Molecular oxygen is carried in blood in two ways: bound to haemoglobin within the red blood cells and dissolved in plasma. Oxygen is poorly soluble in water, so only $3 \%$ of the oxygen is transported in the dissolved form. $97 \%$ of oxygen binds with haemoglobin in a reversible manner to form oxyhaemoglobin $\left(\mathrm{HbO}_2\right)$. The rate at which haemoglobin binds with $\mathrm{O}_2$ is regulated by the partial pressure of $\mathrm{O}_2$.

Each haemoglobin carries maximum of four molecules of oxygen. In the alveoli high $\mathrm{pO}_2$, low $\mathrm{pCO}_2$, low temperature and less $\mathrm{H}+$ concentration, favours the formation of oxyhaemoglobin, whereas in the tissues low p02, high $\mathrm{pCO}_2$, high $\mathrm{H}+$ and high temperature favours the dissociation of oxygen from oxyhaemoglobin.
A sigmoid curve (S-shaped) is obtained when percentage saturation of haemoglobin with oxygen is plotted against $\mathrm{pO}_2$. This curve is called oxygen haemoglobin dissociation curve. This S-shaped curve has a steep slope for $\mathrm{pO}_2$ values between 10 and $50 \mathrm{~mm} \mathrm{Hg}$ and then flattens between 70 and 100 $\mathrm{mm} \mathrm{Hg}$. Under normal physiological conditions, every $100 \mathrm{~mL}$ of oxygenated blood can deliver about $5 \mathrm{~mL}$ of $\mathrm{O}_2$ to the tissues.
Question 19.
Explain the transport of carbon dioxide.
Answer:
Blood transports $\mathrm{CO}_2$ from the tissue cells to the lungs in three ways:
1. Dissolved in plasma :
About $7-10 \%$ of $\mathrm{CO}_2$ is transported in a dissolved form in the plasma.
2. Bound to haemoglobin :
About $20-25 \%$ of dissolved $\mathrm{CO}_2$ is bound and carried in the RBCs as carbaminohaemoglobin $\left(\mathrm{Hb} \mathrm{CO}_2\right)$
$
\mathrm{CO}_2+\mathrm{Hb} \rightarrow \mathrm{Hb} \mathrm{CO}
$
3. As bicarbonate ions in plasma about $70 \%$ of $\mathrm{CO}_2$ is transported as bicarbonate ions. This is influenced by $\mathrm{pCO}_2$ and the degree of haemoglobin oxygenation. RBCs contain a high concentration of the enzyme, carbonic anhydrase, whereas small amounts of carbonic anhydrase is present in the plasma.
$\rightarrow$ At the tissues the $\mathrm{pCO}_2$ is high due to catabolism and diffuses into the blood to form $\mathrm{HCO}_2$ and $\mathrm{H}^{+}$ions. When $\mathrm{CO}_2$ diffuses into the $\mathrm{RBCs}$, it combines with water forming carbonic acid $\left(\mathrm{H}_2 \mathrm{CO}_2\right)$ catalyzed by carbonic anhydrase. Carbonic acid is unstable and dissociates into hydrogen and bicarbonate ions.
Carbonic anhydrase facilitates the reaction in both directions.

The $\mathrm{HCO}_3-$ moves quickly from the RBCs into the plasma, where it is carried to the lungs. At the alveolar site where $\mathrm{pCO}_2$ is low, the reaction is reversed leading to the formation of $\mathrm{CO}_2$ and water. Thus $\mathrm{CO}_2$ trapped as $\mathrm{HCO}_3{ }^{-}$at the tissue level is transported to the alveoli and released out as $\mathrm{CO}_2$. Every $100 \mathrm{~mL}$ of deoxygenated blood delivers $4 \mathrm{~mL}$ of $\mathrm{CO}_2$ to the alveoli for elimination.
Question 20.
How is respiration regulated?
Answer:
A specialised respiratory center present in the medulla oblongata of the hind brain called respiratory rhythm center is responsible for this regulation.
Pneumotaxic centre present in ponsvaroli region of the brain moderates the function of the respiratory rhythm centre to ensure normal breathing.

The chemosensitive area found close to the rhythm centre is highly sensitive to $\mathrm{CO}_2$ and $\mathrm{H}^{+}$. And $\mathrm{H}^{+}$are eliminated out by respiratory process. Receptors associated with the aortic arch and carotid artery send necessary signals to the rhythm center for remedial action. The role of $\mathrm{O}_2$ is insignificant in the regulation of respiratory rhythm.
Question 21.
Write the flow chart of the events during inspiration and expiration.
Answer:

Events in inspiration and expiration 

Question 22.
What is nitrogen narcosis? What is its effect?
Answer:
When a person descends deep into the sea, the pressure in the surrounding water increases which causes the lungs to decrease in volume. This decrease in volume increases the partial pressure of the gases within the lungs. This effect can be beneficial, because it tends to drive additional oxygen into the circulation, but this benefit also has a risk, the increased pressure can also
drive nitrogen gas into the circulation. This increase in blood nitrogen content can lead to a condition called nitrogen narcosis.

When the diver ascends to the surface too quickly a condition called 'bends' or decompression sickness occurs and nitrogen comes out of solution while still in the blood forming bubbles. Small bubbles in the blood are not harmful, but large bubbles can lodge in small capillaries, blocking blood flow or can press on nerve endings. Decompression sickness is associated with pain in joints and muscles and neurological problems including stroke.

The risk of nitrogen narcosis and bends is common in scuba divers. During carbon-dioxide poisoning, the demand for oxygen increases. As the $\mathrm{O}_2$ level in the blood decreases it leads to suffocation and the skin turns bluish black.
Question 23.
Explain the disorders of the respiratory system.
Answer:
Asthma - It is characterized by narrowing and inflammation of bronchi and bronchioles and difficulty in breathing. Common allergens for asthma are dust, drugs, pollen grains, certain food items like fish, prawn and certain fruits etc. Emphysema - Emphysema is chronic breathlessness caused by gradual breakdown of the thin walls of the alveoli decreasing the total surface area of a gaseous exchange, i.e., widening of the alveoli is called emphysema. The major cause for this disease is cigarette smoking, which reduces the respiratory surface of the alveolar walls.
Bronchitis- The bronchi when it gets inflated due to pollution smoke and cigarette smoking, causes bronchitis. The symptoms are cough, shortness of breath and sputum in the lungs. Pneumonia- Inflammation of the lungs due to infection caused by bacteria or virus is called pneumonia. The common symptoms are sputum production, nasal congestion, shortness of breath, sore throat, etc.
Tuberculosis- Tuberculosis is caused by Mycobacterium tuberculae. This infection mainly occurs in the lungs and bones. Collection of fluid between the lungs and the chest wall is the main complication of this disease. Occupational respiratory disorders- The disorders due to one's occupation of working in
industries like grinding or stone breaking, construction sites, cotton industries, etc.
Dust produced affects the respiratory tracts. Long exposure can give rise to inflammation leading to fibrosis. Silicosis and asbestosis are occupational respiratory diseases resulting from inhalation of particle of silica from sand grinding and asbestos into the respiratory tract. Workers, working in such industries must wear protective masks.

Question 24.
What are the effects of smoking?
Answer:
Smoking is inhaling the smoke from burning tobacco. There are thousands of known chemicals which includes nicotine, tar, carbon monoxide, ammonia, sulphur- dioxide and even small quantities of arsenic. Carbon monoxide and nicotine damage the cardiovascular system and tar damages the gaseous exchange system.
Nicotine is the chemical that causes addiction and is a stimulant which makes the heart beat faster and the narrowing of blood vessels results in raised blood pressure and coronary heart diseases. Presence of carbon monoxide reduces oxygen supply. Lung cancer, cancer of the mouth and larynx is more common in smokers than non-smokers.

Smoking also causes cancer of the stomach, pancreas and bladder and lowers sperm count in men. Smoking can cause lung diseases by damaging the airways and alveoli and results in emphysema and chronic bronchitis. These two diseases along with asthma are often referred as Chronic Obstructive Pulmonary Disease (COPD). When a person smokes, nearly $85 \%$ of the smoke released is inhaled by the smoker himself and others in the vicinity, called passive smokers, are also affected. Guidance or counselling should be done in such users to withdraw this habit.