NCERT Solutions for Class 11 Biology Chapter 17 Breathing and Exchange of Gases
These Solutions are part of NCERT Solutions for Class 11 Biology. Here we have given NCERT Solutions for Class 11 Biology Chapter 17 Breathing and Exchange of Gases.
Define vital capacity. What is its significance ?
The maximum volume of air a person can breathe in after a forced expiration. This includes ERV, TV and IRV or the maximum volume of air a person can breathe out after a forced inspiration.
It represent the maximum amount of air one can renew in the respiratory system in a single respiration. Thus, greater the vital capacity more is the energy available to the body for doing strenous work. Vital capacity is higher in athletes and mountain dwellers. Young persons would possess more vital capacity as compared to children or older persons.
State the volume of air remaining in the lungs after a normal breathing.
Volume of air remaining in lungs after a normal respiration is called functional residual capacity. It includes ERV + RV = Expiratory reserve volume + residual volume
volume Diffusion of gases occurs in the alveolar region only and not in the other parts of respiratory system. Why ?
Alveoli are the primary sites of exchange of gases. Alveolar region is having enough pressure gradient to facilitate diffusion of gases. Other regions of the respiratory sytsem don’t have the required pressure gradient. Additionally the membrane of alveoli is thin enough to facilitate exchange of gases in a convenient manner.
What are the major transport mechanisms for C02 ? Explain.
Transport of carbon dioxide : About 4 ml of carbon dioxide is transported by every 100 ml of blood.
C02 is transported in three forms in the blood.
(i) In the dissolved form in plasma about 7% of C02 dissolves in plasma of blood, just as it gets dissolved in water.
(ii) As bicarbonates
• Erythrocytes have a high concentration of the enzyme, carbonic anhydrase which catalyses the following reactions;
About 70% of C02 is transported as bicarbonates.
(iii) As carbaminohaemoglobin
• C02 combines with of the globin part of haemoglobin and forms carbamino haemoglobin. About 23% of C02 transported in this manner.
What will be the p02 and pC02 in the atmospheric air compared to those in the alveolar air ?
(i) p02 lesser, pC02higher
(ii) p02 higher, pC02lesser
(iii) p02 higher, pC02 higher
(iv) p02 lesser, pC02lesser
(ii) p02 higher, pC02 lesser
p02 higher will create the pressure gradient to facilitate the movement of 02 from atmosphere to alveoli and pC02 lesser will create the movement of C02 from alveoli to atmosphere.
Explain the process of inspiration under normal conditions.
- Inspiration occurs when pressure within lungs is less than the atmospheric pressure, i.e., there is a negative pressure in the lungs with respect to atmospheric pressure.
- Inspiration is initiated by the contraction of diaphram which increases the volume of thoracic chamber in the antero-posterior axis.
- The contraction of external inter-costal muscles lifts up the ribs and the sternum causing an increase in the volume of a thoracic chamber in the dorso- ventral axis.
- The overall increase in thoracic volume causes a similar increase in pulmonary volume.
- An increase in pulmonary volume decreases the intra pulmonary pressure, to less than atmospheric pressure which forces the air from outside to move into the lungs i.e., inspiration.
How is respiration regulated ?
- Respiratory rhythm centre, present in medulla region of brain is responsible for respiration regulation.
- Its function can be moderate by pneumotaxic centre, present in pons region of brain.
- A chemosensitive area present adjacent to rhythm centre, is highly sensitive to C02 and H+.
- Chemosenstive centre due to increase in C02 and H+ can signal the rhythm centre to make adjustment to eliminate these substances.
- Receptors associated with aortic arch and carotid artery also can recognise changes in C02 and H+ concentration and send necessary signals to rhythm centre for remedial actions.
What is the effect of pC02 on oxygen transport?
At low pC02,blood can carry the maximum amount of oxygen as oxyhaemoglobin. At high pC02, the affinity for oxygen decreases and oxyhaemoglobin dissociates to free oxygen.
So at high pC02, oxygen transport is inhibited.
What happens to the respiratory process in a man going up a hill ?
When a man is going uphill or doing some strenuous exercise then there is more consumption of oxygen. This decreases the partial pressure of oxygen in haemoglobin resulting in more demand of haemoglobin. As a result there is an increased breathing rate to fill the gap.
What is the site of gaseous exchange in an insect ?
Insect have a complex system of intercommunicating air tubes called tracheae to enable them to exchange gases between the environment and the body cells (tracheal respiration).
Define oxygen dissociation curve. Can you suggest any reason for its sigmoidal pattern?
- Oxygen dissociation curve: It is graphic respresentation of relationship between partial pressure of oxygen or p02 and percentage saturation of haemoglobin with oxygen.
- The graph is sigmoid as at low p02, there is reduced synthesis of oxyhaemoglobin. Percentage of oxyhaemoglobin rises with higher p02 till at about p02 is 100mm Hg, the haemoglobin becomes fully saturated with 02.
- Further rise in p02 cannot increase the value of oxyhaem-oglobin as the blood is already saturated with it.
Have you heard about hypoxia ? Try to gather information about it, and discuss with your friends.
Hypoxia refers to shortage of oxygen supply to the body. It is of different types:
1. Anaemic hypoxia (deficiency of haemoglobin),
2. Cytotoxic hypoxia (impaired utilization as in cyanide poisoning)
3. Stagnant hypoxia. Due to heart failure or reduced pumping activity of heart.
4. Hypoxic hypoxia. Insufficient oxygen in air as at high altitude.
5. CO Poisoning. Carbon monoxide binds to haemoglobin irreversibly. Oxygen transport is correspondingly reduced.
(a) IRV and ERV
(b) Inspiratory capacity and Expiratory capacity.
(c) Vital capacity and Total lung capacity.
What is tidal volume ? Find out the tidal volume (approximate value) for a healthy human in an hour.
Volume of air inspired/breath during normal respiration. It is approximate 500mL.Number of breaths per minute 12 to 16.
Tidal volume per minute = 500 x 12 to 16 = 6000 – 8000 mL or 6 -8 litres Tidal volume per hour = 6 to 8 x 60 = 360 – 480 litres.
VERY SHORT ANSWER QUESTIONS
Name the enzyme which catalyses the bicarbonate formation in RBC’s.
Enzyme carbonic anhydrase.
What is carbamino haemoglobin ?
It is a complex formed by the combination of carbondioxide with the globin part of haemoglobin.
What is tidal volume?
The volume of air inspired or expired with every normal breath during effortless respiration is called tidal volume.
What term is used for the volume of air left in the lungs even after the most powerful expiration?
Name the respiratory organ of
(a) Butterfly and .
(b) Frog larva.
(i) Butterfly – trachea
(ii) Frog larva – gills.
What is the role of oxyhaemoglobin after releasing molecular oxygen in the tissue?
Oxyhaemoglobin after releasing oxygen collects carbon dioxide from the tissue and form carbaminohaemoglobin.
What are the two factors that contribute for the dissociation of oxyhaemoglobin in the atrial blood to release’ molecular oxygen in active tissue?
The two factors are :
Name the double-walled sac which covers the lungs in mammals.
What prevents the collapsing of our trachea during breathing ?
C-shaped cartilages at regular intervals.
Define inspiratory reserve volume.
The extra volume of air that can be inspired beyond the normal tidal volume, is called inspiratory reserve volume.
Which part(s) of the brain control(s) breathing movements?
Medulla and pons.
What is oxyhaemoglobin?
Oxyhaemoglobin is a complex formed when oxygen combies with the Fe2+ part of haemoglobin.
How much of oxygen is transported by 100 ml of blood under normal physiological conditions?
About 5 mL.
Write the chemical reaction catalysed by enzyme carbonic anhydrase.
Carbonic anhydrase catalyses the following reaction:
How does penumotaxic centre alter the respiratory rate?
Pneumotaxic centre can reduce the duration of inspiration and alter the respiratory rate.
What is the percentage of C02 transported as sodium bicarbonate?
70% of C02 is transported as sodium bicarbonate.
What will happen if the human blood becomes acidic?
Oxygen carrying capacity of haemoglobin will decrease.
SHORT ANSWER QUESTIONS
Write four conditions necessary to facilitates efficient gaseous exchange between human respiratory surface and environment.
Conditions for efficient gas exchange are as followings:
(a) The membrane should be thin.
(b) It should be highly vascularized.
(c) It should be highly permeable to gases.
(d) There should a partial pressure difference on both sides of lung.
Differentiate between pharynx and larynx.
The main differences between pharynx and larynx are as followings:
Why is haemoglobin called conjugated protein? What happen to the molecule at high and low partial pressure of oxygen?
Haemoglobin : It is called conjugated protein because it consists of a basic protein globin and a non-protein heme.
The haemoglobin when exposed to high partial pressure of oxygen combines with oxygen to form oxyhaemoglobin which carries 4 molecules of oxygen loosely bound to the four Fe2+ ions. When this oxyhaemoglobin reaches the tissues where there is low oxygen pressure oxyhaemoglobin dissociates into oxygen and deoxyhaemoglobin.
Differentiate between inspiratory capacity and expiratory capacity.
The differences between inspiratory and expiratory capacity are :
Diffusion of gases occurs in the alveolar region only and not in the other parts of the respiratory system. Why ?
The alveoli have very thin walls consisting of squamous epithelium. The alveolar wall is provided with as extensive network of blood capillaries; due to the intimate contact of the blood capillareis and alveolar wall, there is exchange of gases taking place easily. In the other part the membrane/wall is not so thin to allow for diffusion.
What percentage of oxygen is transported by erythrocytes in the blood? What happens to the remaining?
About 97% of the oxygen is transported by erthyrocytes. The remaining 3% is transported in dissolved form in the plasma.
What is asthma? Explain.
Asthma: It is the hypersensitivity of bronchioles to any foreign substance, characterised by the spasm of the smooth muscles of the walls of the bronchioles.
What is the emphysema? What is its major cause?
Emphysema: Emphysema is a chronic disorder is which alveolar walls are damaged and hence the surface area for exchange of. gases is reduced. It is caused mainly by cigarette smoking.
Draw a labelled diagram of a section of an alveolus with a pulmonary capillary.
What will happen if the patient has been inhaling polluted air containing high content of CO?
Haemoglobin has much more affinity about 250 times for CO than oxygen. It readily combines with CO to form most stable compound called carboxyhaemoglobin. It may be fatal for the patient.
What is pneumonia? What are its causes?
Pneumonia is a respiratory disease in which oxygen has difficulty in diffusing through the in flammed alveoli and the blood 02 may be drastically reduced and blood PC02 remains normal. It is caused by streptococcus penumoniae. Its symptoms are trembling, pain in chest, fever, cough, etc. It is mostly observed in children and old age.
Long ANSWER QUESTIONS
What do you mean by occupational lung disease? Enumerate the prevention measure that should be adopted by a person likely to be exposed to substances that cause occupational diseases ?
Occupational lung disease as the name suggests it is the disease of lung due to the occupation of the human.
Cause : These are caused by the harmful substances, such as gas fumes or dusts, present in the environment where a person works. Silicosis and asbestoses are common examples, which occur due to chronic exposure of silica and asbestos dust in the mining industry.
Symptoms: It is characterised by proliferation of fibrous connective tissue (fibrosis) of upper part of lung, causing inflammation.
Prevention : The occupational disease expresses symptoms after chronic exposure (i.e., 10-15 years or even more). Most of occupational diseases including silicosis and asbestosis is are incurable. Therefore, the person which is exposed to such irritants should adopt preventive measures. These protective measures are as follows:
(i) Minimize the exposure of harmful dust at the workplace.
(ii) Workers should be informed about the harm of the exposure to such dusts.
(iii) Workers must have the protective gears and clothing at the work place.
(iv) health of the workers should be regularly checked up.
Explain the regulation of respiration by nervous system.
Regulation of respiratory rhythm
• The ability to maintain and moderate the respiratory rhythm according to the demand of the body tissues is due to the neural control.
• Respiratory rhythm centre located in the medulla of the brain, is primarily responsible for this regulation, f Pneumotaxic centre present in the brainfunctions as the ‘switch off point for regulation; by altering the duration of inspiration, it can alter the respiratory rate.
• A chemosensitive area is situated adjacent to the rhythm centre; it is highly sensitive to carbon dioxide and hydrogen ions.
• An increase in the concentration of these substances activates this centre which in turn sends signals to rhythm centre to make necessary adjustments in the ’respiratory process.
• Receptors associated with aortic arch and carotid artery also are sensitive to carbon di oxi de and H+ ions; they too send signals to the respiratory rhythm centre.
• Oxygen plays only an insignificant role in the regulation of respiratory rhythm.
How does exchange of respiratory gases take place in the alveoli or lungs ?
Gaseous exchange in alveoli:
• The alveolar wall is very thin and contains a rich network of inter connected capillaries.
• Due to this the alveolar wall seems to be sheet of flowing blood, and is called the respiratory membrane.
• It consists mainly of alveolar epithelium, epithelial basement membrane, a thin interstitial space, capillary basement membrane and capillary endothermal membrane. All these layer cumulatively form a membrane of 0.2 mm thickness.
• The respiratory membrane has a limit of gases exchange between alveoli and pulmonary blood. It is called diffusing capacity. It is dependent on the solubility of respiratory gases.
• The partial pressure of oxygen (p02) in the alveoli is higher (104 mm Hg) than that in the deoxygenated blood in the capillaries of the pulmonary arteries (40 mm Hg). As the gases diffuse from higher to a lower concentration, the movement of oxygen is from the alveoli to the blood. The reverse is the case in relation to carbon dioxide.
• The partial pressure of carbon dioxide (pC02) is higher in deoxygenated blood (45 mm Hg), than in alveoli (40 mm Hg), therefore, C02 passes from blood to alveoli.
How are inspiration and expiration take place in human ?
The inflow (inspiration) and outflow (expiration) of air occurs between atmosphere and lungs by the expansion and contraction of lungs.
Inspiration : It is the process by which fresh air enters the lungs.
• The external intercostal muscles present between the ribs contract and pull this ribs and sternum upward and outward increasing the volume to thoracic cavity.
• Diaphragm becomes flats and gets lowered by the contraction of its muscles thereby increasing the volume of thoracic cavity.
• The abdominal muscles relax and allow on the compression of abdominal organ by diaphragm.
• As the volume of the thoracic cavity increases and as a result there is a decrease of air pressure in the lungs. The greater pressure outside the body causes air to flow rapidly into nostrils through the respiratory track to the lungs.
Expiration : It is a process by which the foul air (C02) is expelled out from the lungs.
• Internal intercostal muscles contract so that they pull in ribs downward and inward decreasing the size of thoracic cavity.
• The muscle fibres of diaphragm relax making it convex, decreasing the volume of the thoracic cavity.
• Contraction of abdominal muscles compresses this abdomen and pushes its towards the diaphragm.
The overall volume of the thoracic cavity decrease and foul air goes outside from the cavities of alveoli through the respiratory tract.
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