CBSE Class 11 Biology Breathing and Exchange of Gases Assignments

Solve the MCQ questions below

Question. Assertion :- Primary bronchi branches to form secondary bronchi.
Reason :- Diameter of primary bronchi is greater than secondary bronchi.
(a) A
(b) B
(c) C
(d) D
Answer: B

Question. Assertion :- Tracheal cartilaginous rings are incomplete dorsally.
Reason :- Complete rings would obstruct oesophagus.
(a) A
(b) B
(c) C
(d) D
Answer: A

Question. Assertion :- Any change in volume of thoracic cavity reflects on pulmonary volume.
Reason :- Parietal pleura is closely connected to rib cage.
(a) A
(b) B
(c) C
(d) D
Answer: A

Question. Assertion :- Lungs expand due to filling up of air in them.
Reason :- Internal intercostal muscles help in this expansion.
(a) A
(b) B
(c) C
(d) D
Answer: D

Question. Assertion :- Residual volume is excluded in vital capacity.
Reason :- Residual volume can't be measured by spirometer.
(a) A
(b) B
(c) C
(d) D
Answer: B

Question. 6. Assertion :- Solubility of the gases can affect the rate of diffusion.
Reason :- Thickness of the membrane involved in diffusion can also affect the rate of diffusion.
(a) A
(b) B
(c) C
(d) D
Answer: B

Question. Assertion :- 3% of \( \text{O}_2 \) is transported in dissolved state.
Reason :- 97 percent of \( \text{O}_2 \) is transported via RBC's.
(a) A
(b) B
(c) C
(d) D
Answer: B

Question. Assertion :- Oxygen dissociation curve is sigmoidal in shape.
Reason :- Binding of \( \text{O}_2 \) with Hb increases Hb's affinity towards \( \text{O}_2 \).
(a) A
(b) B
(c) C
(d) D
Answer: A

Question. Assertion :- \( \text{HCO}_3^– \) diffuses into plasma and \( \text{Cl}^– \) diffuses into erythrocytes.
Reason :- This exchange balances charges on both sides.
(a) A
(b) B
(c) C
(d) D
Answer: A

Question. Assertion :- Pneumotaxic centre increases the duration of inspiration.
Reason :- It sends singnals to intercostal muscles.
(a) A
(b) B
(c) C
(d) D
Answer: D

Question. Assertion :- Diffusion membrane is made of three major layers.
Reason :- The layers are alveolar epithelium, Endothelium of blood capillary and basement membrane between them.
(a) A
(b) B
(c) C
(d) D
Answer: A

Question. Assertion :- \( \text{O}_3 \) reacts with Hb to form methemoglobin.
Reason :- \( \text{O}_3 \) gets oxidised in this process.
(a) A
(b) B
(c) C
(d) D
Answer: C

Question. Assertion :- Volume of air present in conducting zone is dead space volume.
Reason :- It averages around 150 ml in humans.
(a) A
(b) B
(c) C
(d) D
Answer: B

Question. Assertion :- Breathing stops during swallowing of food.
Reason :- Gullet is dorsal to Glottis.
(a) A
(b) B
(c) C
(d) D
Answer: B

Question. Assertion :- Expiration is not always a passive process.
Reason :- Internal intercostal muscles and abdominal muscles are involved in forceful expiration.
(a) A
(b) B
(c) C
(d) D
Answer: A

Question. Assertion :- Mechanism of breathing vary among different groups of animals.
Reason :- It vary mainly due to their habitats and level of organisation.
(a) A
(b) B
(c) C
(d) D
Answer: A

Question. Assertion :- Fishes use gills for respiration.
Reason :- Gills are special vascularised structures.
(a) A
(b) B
(c) C
(d) D
Answer: B

Question. Assertion :- Amphibians like frog can respire through their skin.
Reason :- Skin of frog moist, glandular and highly vascular.
(a) A
(b) B
(c) C
(d) D
Answer: A

Question. Assertion :- Larynx is called sound box.
Reason :- It is a cartilaginous box which help in sound production.
(a) A
(b) B
(c) C
(d) D
Answer: A

Question. Assertion :- The wall of trachea, primary secondary and tertiary bronchi and initial bronchioles is non-collapsible.
Reason :- Their wall is supported by incomplete cartilaginous rings.
(a) A
(b) B
(c) C
(d) D
Answer: A

Question. Assertion :- Lungs are covered by a double layered pleura.
Reason :- Lungs are located in thoracic cavity.
(a) A
(b) B
(c) C
(d) D
Answer: B

Question. Assertion :- Alveoli and their ducts form the respiratory or exchange part of the respiratory system.
Reason :- These are the site of actual diffusion of \( \text{O}_2 \) and \( \text{CO}_2 \) between blood and atmospheric air.
(a) A
(b) B
(c) C
(d) D
Answer: A

Question. Assertion :- Diaphragm and external intercostal muscles are inspiratory muscles.
Reason :- Whenever these muscles relaxed result into expiration.
(a) A
(b) B
(c) C
(d) D
Answer: B

Question. Assertion :- Volume of air inspired or expired during a normal respiration is called tidal volume.
Reason :- Additional volume of air, a person can inspire by a normal inspiration is called as IRV (Inspiratory reserve volume).
(a) A
(b) B
(c) C
(d) D
Answer: C

Question. Assertion :- Alveoli are the primary site of exchange of gases.
Reason :- Exchange of gases also occur between blood and tissue.
(a) A
(b) B
(c) C
(d) D
Answer: B

Question. Assertion :- Pressure contributed by an individual gas in a mixture of gases is called partial presure.
Reason :- Partial pressure of \( \text{O}_2 \) in alveoli is 104 mmHg.
(a) A
(b) B
(c) C
(d) D
Answer: B

Question. Assertion :- The amount of \( \text{CO}_2 \) that can diffuse through diffusion membrane per unit difference in partial pressure is much higher compared to that of \( \text{O}_2 \).
Reason :- Solubility of \( \text{CO}_2 \) is 20-25 times higher than that of \( \text{O}_2 \).
(a) A
(b) B
(c) C
(d) D
Answer: A

Question. Assertion :- Blood is the medium of transport for \( \text{O}_2 \) and \( \text{CO}_2 \) in human.
Reason :- 100% \( \text{O}_2 \) and 100% \( \text{CO}_2 \) is transported by blood in human.
(a) A
(b) B
(c) C
(d) D
Answer: A

Question. Assertion :- Each haemoglobin molecule can carry a maximum of four molecules of \( \text{O}_2 \).
Reason :- Each haemoglobin molecule has 4 globin chains 4 heme part and 4 iron atom.
(a) A
(b) B
(c) C
(d) D
Answer: A

Question. Assertion :- At the tissue site partial pressure of \( \text{CO}_2 \) is high.
Reason :- It is due to catabolism.
(a) A
(b) B
(c) C
(d) D
Answer: A

Question. Assertion :- Every 1000 ml of deoxygenated blood delivers approximately 40 ml of \( \text{CO}_2 \) to the alveoli.
Reason :- Every 1000 ml of oxygenated blood can deliver around 50 ml of \( \text{O}_2 \) to the tissue under normal physiological conditions.
(a) A
(b) B
(c) C
(d) D
Answer: B

Question. Assertion :- Emphysema is a chronic disorder in which alveolar wall are damaged.
Reason :- It is due to hypoactivity of elastase enzyme.
(a) A
(b) B
(c) C
(d) D
Answer: C

Question. Assertion :- Central chemoreceptors are highly sensitive to \( \text{CO}_2 \) and \( \text{H}^+ \) ions.
Reason :- Central chemoreceptors is situated adjacent to the rhythm centre.
(a) A
(b) B
(c) C
(d) D
Answer: B

Question. Assertion :- The role of oxygen in the regulation of respiraotry rhythm is quite insignificant.
Reason :- Central and peripheral chemoreceptor highly sensitive to changes in \( \text{CO}_2 \) and \( \text{H}^+ \) ions not \( \text{O}_2 \).
(a) A
(b) B
(c) C
(d) D
Answer: A

Question. Assertion :- A pneumotaxic centre in the pons region of the brain can alter respiratory mechanism.
Reason :- Apnestic centre present in pons.
(a) A
(b) B
(c) C
(d) D
Answer: B

Chapter-17

BREATHING AND EXCHANGE OF GASES

POINTS TO REMEMBER

Breathing: (External respiration) The process of exchange of \(\text{O}_2\) from the atmosphere with \(\text{CO}_2\) produced by the cells.

Inspiration: Oxygen from fresh air taken by lungs and diffuses into the blood.

Expiration: \(\text{CO}_2\) given up by venous blood in the lungs is sent out to exterior.

Respiration: The sum total of physical and chemical processes by which oxygen and carbohydrates (main food nutrient) etc. are assimilated into the system and the oxidation products like carbon dioxide and water are given off.

Diaphragm: A muscular, membranous partition separating the thoracic cavity from the abdominal cavity.

Partial Pressure: The pressure contributed by an individual gas in a mixture of gases. It is represented as \(\text{pO}_2\) for oxygen and \(\text{pCO}_2\) for carbondioxide.

Pharynx: The tube or cavity which connects the mouth and nasal passages with oesophagus. It has three parts (i) Nasopharynx (anterior part) (ii) Oropharynx (middle part) and (iii) Laryngopharynx (posterior part which continues to larynx).

Adam's Apple: The projection formed by the thyroid cartilage and surrounds the larynx at the front of the neck.

Tidal volume (TV): Volume of air during normal respiration (500 mL.)

Inspiratory Reserve Volume (IRV): Additional volume of air inspired by a forcible inspiration. 2500 mL to 3000 mL.

Expiratory Reserve Volume (ERV): Additional volume of air, a person can expire by a forcible volume (RV) volume of air remaining in the lungs even after a forcible expiration (1100 mL to 1200 mL)

PULMONARY CAPACITIES: Use in clinical diagnosis.

Inspiratory capacity \((\text{IC}) = (\text{TV} + \text{IRV})\)

Expiratory Capacity \((\text{EC}) = (\text{TV} + \text{ERV})\)

Functional Residual Capacity \((\text{FRC}) = (\text{ERV} + \text{RV})\)

Vital Capacity \((\text{VC}) = (\text{ERV} + \text{TV} + \text{IRV})\) or the maximum volume of air a person can breathe out after a forced inspiration.

Total Lung Capacity: It includes RV, ERV, TV and IRV or vital capacity + residual volume.

Pulmonary - Anything associated with the lungs is given the prefix 'pulmonary'

Steps involved in respiration -

(i) Breathing or pulmonary ventilation (intake of atmospheric air and releasing out \(\text{CO}_2\) rich alveolar air)

(ii) Diffusion of gases (\(\text{O}_2\) and \(\text{CO}_2\)) across alveolar membrane.

(iii) Transport of gases by the blood

(iv) Diffusion of \(\text{O}_2\) and \(\text{CO}_2\) between blood and tissues.

(v) Utilisation of \(\text{O}_2\) by the cells for catabolic reactions and resultant release of \(\text{CO}_2\).

MECHANISM OF BREATHING

Inspiration:

If the pressure within the lungs (intrapulmonary pressure) is less than the atmospheric pressure, i.e., there is negative pressure in the lungs with respect to the atmospheric pressure.

- The contraction of diaphragm increases the volume of thoracic chamber in the antero-posterior axis.

- The contraction of external intercostal muscles lifts up the ribs and the sternum causing an increase in the volume of thoracic chamber in the dorso ventral axis.

- It causes an increase in pulmonary volume decrease the intra-pulmonary pressure to less than the atmospheric pressure.

- It forces the air outside to move in to the lungs, i.e., inspiration.

Expiration:

Relaxation of diaphragm and sternum to their normal positions and reduce the thoracic and pulmonary volume.

- It increases in intrapulmonary pressure slightly above the atmospheric pressure.

- It causes the expulsion of air from the lungs, i.e., expiration.

Respiratory Tract:

A pair of external nostrils \(\rightarrow\) nasal chamber through nasal passage \(\rightarrow\) nasopharynx \(\rightarrow\) glottis \(\rightarrow\) larynx \(\rightarrow\) trachea \(\rightarrow\) Left and right primary bronchi \(\rightarrow\) secondary and tertiary bronchi \(\rightarrow\) bronchioles \(\rightarrow\) vascularised bag like structures (alveoli) or air-sacs. Each lung is covered with double layered membrane known as pleura with pleural fluid between them.

Respiratory organs in animals:

(i) General body surface - Protozoans, annelids

(ii) Gills - Fishes, tadpole stage of frog and many other aquatic animals.

(iii) Air bladder - Bony fishes (Lung fishes)

(iv) Tracheae or Tracheal Tube - Insects and a few other arthropods.

(v) Lungs - All land vertebrates (amphibians, reptiles, aves and mammal)

Intercostal muscles: The muscles present between the ribs.

Physiology of Respiration:

(a) Exchange of gases - Diffusion of gases takes place from the region of higher partial pressure to lower (lesser) partial pressure

(i) \(\text{pO}_2\) in alveolar air = 104 mm Hg.

\(\text{pO}_2\) in venous blood = 40 mm Hg.

\(\text{O}_2\) diffuses from alveoli to venous blood.

(ii) \(\text{pCO}_2\) in venous blood = 45 mm Hg.

\(\text{pCO}_2\) in alveolar air = 40 mm Hg

\(\text{CO}_2\) diffuses from venous blood to alveoli

(b) Transport of \(\text{O}_2\) by the blood - about 10% of \(\text{CO}_2\) forms carbonic acid with water of plasma.

\(\text{Hb}_4 + 4\text{O}_2 \underset{\text{Tissue Cells}}{\overset{\text{Lungs}}{\rightleftharpoons}} \text{Hb}_4\text{O}_8\) (Oxyhaemoglobin)

(c) Transport of \(\text{CO}_2\) in the blood:-

\(\text{CO}_2 + \text{H}_2\text{O} \xrightarrow{\text{Carbonic anhydrase}} \text{H}_2\text{CO}_3\) (Carbonic acid) \(\xrightarrow{\text{Carbonic anhydrase}} \text{HCO}_3^- + \text{H}^+\)

about 20% of \(\text{CO}_2\) is transported by combining with free amino group of Haemoglobin, in RBC.

70% of \(\text{CO}_2\) is transported as bicarbonates of sodium (\(\text{NaHCO}_3\)) and potassium (\text{KHCO}_3\))

QUESTIONS

Very Short Answer Questions (1 mark each)

Question 1. Name the organ in human respiratory system which produces sound.
Answer: Larynx (Sound box)
In simple words: The larynx is responsible for producing sound and is commonly known as the voice box.

Exam Tip: Remember both terms: larynx and voice box.

Question 2. How many oxygen molecules can be carried out by one haemoglobin molecule.
Answer: Four molecules
In simple words: Each haemoglobin molecule has four iron-containing heme groups, allowing it to bind up to four oxygen molecules.

Exam Tip: Note that one haemoglobin molecule carries four \(\text{O}_2\) molecules (or eight oxygen atoms).

Question 3. Give the name and function of a fluid filled double membranous layer which surrounds the lungs.
Answer: Pleuron (Pleura). It reduces friction and keeps the two pleura together and the lungs inflated.
In simple words: The pleural membrane surrounds the lungs and contains lubricating fluid to prevent friction during breathing movements.

Exam Tip: Mention both the reduction of friction and the maintenance of intrapleural pressure.

Question 4. Which organ of our respiratory system acts as primary site of exchange of gases?
Answer: Alveoli of lungs
In simple words: Alveoli are tiny air sacs where oxygen enters the blood and carbon dioxide leaves it.

Exam Tip: Always specify alveoli, not just lungs broadly.

Question 5. Cigarette smoking causes emphysema. give reason.
Answer: Cigarette smoking damages alveolar walls due to alveolar sacs remaining filled with air leading to decreased respiratory surface for exchange of gases.
In simple words: Smoking destroys the delicate walls of the alveoli, reducing the surface area available for breathing.

Exam Tip: Key terms to include: destruction of alveolar walls and decreased surface area.

Question 6. Name the principle of exchange of gases.
Answer: Diffusion.
In simple words: Gases move passively from a region of higher partial pressure to a region of lower partial pressure.

Exam Tip: State simple diffusion driven by partial pressure gradients.

Question 7. What is the role of oxyhaemoglobin after releasing molecular oxygen in the tissues?
Answer: Amino group of reduced haemoglobin combines with \(\text{CO}_2\) forming carbaminohaemoglobin to transport \(\text{CO}_2\).
In simple words: After delivering oxygen, the remaining haemoglobin helps pick up and transport carbon dioxide back to the lungs.

Exam Tip: Mention the formation of carbaminohaemoglobin.

Question 8. Name the muscles which fascilitate breathing.
Answer: External and internal intercostal muscles, situated between ribs, along with the diaphragm.
In simple words: Breathing is driven by the diaphragm and the intercostal muscles between the ribs.

Exam Tip: Include both diaphragm and intercostal muscles for complete credit.

Question 9. How is the entry of food prevented in the respiratory tract?
Answer: During swallowing a cartilaginous flap like structure called epiglottis covers the glottis and prevents the entry of food into respiratory tract.
In simple words: The epiglottis acts as a lid over the windpipe when we swallow food.

Exam Tip: Keywords: epiglottis and glottis.

Question 10. About 97% of \(\text{O}_2\) is transported by RBCs in the blood. How does the remaining 3% of \(\text{O}_2\) transported?
Answer: In simple solution form through plasma.
In simple words: A tiny fraction of oxygen dissolves directly into the liquid plasma of the blood.

Exam Tip: Specify physical solution dissolved in plasma.

Short Answer Questions-II (2 marks each)

Question 11. Draw a labelled diagram of a section of an alveolus with a pulmonary capillary.
Answer: Refer to NCERT Textbook Class XI Biology, Figure 17.4, Page 273.
In simple words: The diagram shows the thin alveolar membrane closely apposed to capillary endothelial walls for efficient gas diffusion.

Exam Tip: Practice drawing the basement membrane, squamous epithelium of alveolus, and endothelium of capillary.

Question 12. Following is the table showing partial pressure (in mm Hg) of oxygen and carbondioxide at different parts involved in diffusion in comparision to those in atmosphere. Fill in the blanks - a, b, c and d.

Answer:
\(a = 95\) mm Hg
\(b = 45\) mm Hg
\(c = 40\) mm Hg
\(d = 45\) mm Hg
In simple words: These values represent the partial pressure gradients that drive oxygen into tissues and carbon dioxide into lungs.

Exam Tip: Memorize standard partial pressure values for \(\text{O}_2\) and \(\text{CO}_2\) in atmospheric air, alveoli, deoxygenated blood, oxygenated blood, and tissues.

Question 13. Name the organs of respiration in the following organisms.
a) Flatworms
b) Birds
c) Frog
d) Cockroach
Answer:
a) Body surface
b) Lungs
c) Skin and lungs
d) Network of trachea (Tracheal tubes)
In simple words: Different animal groups have evolved specialized respiratory structures suited to their habitat and body size.

Exam Tip: Amphibians like frogs can respire cutaneously (skin) as well as pulmonary (lungs).

Question 14. What are occupational respiratory disorders? What are their harmful effects? What precautions should a person take to prevent such disorders?
Answer: Refer to NCERT Textbook Class XI Biology, Page 276.
In simple words: These are chronic lung diseases caused by prolonged exposure to dust or chemicals in workplaces like mining, leading to fibrosis.

Exam Tip: Mention pneumoconiosis, fibrosis, and preventive measures like wearing protective masks.

Short Answers Questions-I (3 marks each)

Question 15. Explain the role of neural system in regulation of respiration is human.
Answer: Refer to NCERT Textbook Class XI Biology, Page 275 (Section 17.5).
In simple words: The respiratory rhythm center in the medulla oblongata regulates the basic rate of breathing, modulated by the pneumotaxic center in the pons.

Exam Tip: Clearly distinguish between the medullary respiratory center and the pneumotaxic center.

Question 16. Explain the neural control of respiration in human.
Answer: Refer to content 17.5 regulation of respiration on page no. 275 (NCERT Text Book XI-Biology).
In simple words: Neural signals from the brainstem control the rate and depth of inspiration and expiration based on chemical feedback from blood \(\text{CO}_2\) and \(\text{H}^+\) levels.

Exam Tip: Emphasize the role of chemoreceptors sensitive to \(\text{CO}_2\) and hydrogen ions.

Long Answer Questions (5 marks each)

Question 17. With the help of labelled diagram explain the structure of human respiratory system.
Answer: Refer to NCERT Textbook Class XI Biology, Content 17.1.1, Page 29, Diagrams 17.1.
In simple words: The human respiratory system consists of conducting passages (nostrils to bronchioles) and respiratory exchange sites (alveoli enclosed in lungs).

Exam Tip: Draw a neat, fully labeled diagram showing larynx, trachea, bronchi, lungs, and diaphragm.

Question 18. Explain the mechanism of breathing with the help of labelled diagram involving both stages - inspiration and expiration.
Answer: Refer to NCERT Textbook Class XI Biology, Content 17.2 and Figure 17.2, Pages 270-271.
In simple words: Inspiration creates negative pressure by expanding the thoracic cavity, while expiration relaxes muscles to expel air.

Exam Tip: Explain pressure gradient changes alongside rib and diaphragm movements.

Question 19. Explain the process of exchange of gases with the help of a diagrammatic representation in human respiratory system.
Answer: Refer to NCERT Textbook Class XI Biology, Content 17.3 and Figure 17.3, Pages 272-273.
In simple words: Gases diffuse across the alveolar-capillary membrane due to differences in partial pressures between alveolar air, blood, and body tissues.

Exam Tip: Include partial pressure values for \(\text{O}_2\) and \(\text{CO}_2\) at respiratory surfaces and tissues in your explanation.