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Assertion Reason Questions for Biology Chapter 17 Breathing and Exchange of Gases

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Directions: In the following questions, a statement of assertion is followed by a statement of reason.
Mark the correct choice as:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

Q.1. Assertion : Most fish when out of water, die of suffocation.
Reason : Atmospheric air contains far less oxygen content than the dissolved oxygen in water.

Answer Answer: (c) Although atmospheric air contains far more oxygen content than the water (air contains 21% oxygen and water contains 0.5-0.9% oxygen by volume depending on the temperature), still most fish when out of water die of suffocation due to lack of oxygen. When fish is taken out of water the gills stick together thereby reducing the surface area. Reduced surface area lowers gas exchange and so death occurs.

Q.2. Assertion : Gill-lamellae in aquatic animals help in exchange of gases.
Reason : Each gill lamella carries many blood capillaries.

Answer Answer: (a) Gills are the main respiratory organs of aquatic animals. Each gill bears rows of comb-like, soft, thin gill-filament, each gill filament bears many flat, parallel membranelike gill-lamellae. Each gill lamella carries many blood capillaries. Water taken through the mouth, is made to flow from the pharynx in a single direction between the gill lamella. This greatly helps in the gaseous exchange across the lamellar membrane between the capillary blood and the flowing water.

Q.3. Assertion : In mammals, complex respiratory system has developed.
Reason : Mammalian skin is impermeable to gases.

Answer Answer: (b) Mammalian skin is impermeable so that water loss through it, is minimised. But mammals need far more oxygen to maintain their high metabolic rates than lower animals; so they need a more extensive respiratory surface. Thus a complex respiratory system has evolved in mammals to meet this need. The mammalian respiratory system consists of the nasal cavity, nasopharynx, larynx, trachea, bronchi, bronchiole and lungs

Q.4. Assertion : Insects develop a complex system of air tubes called trachea for respiratory purpose.
Reason : Exchange through body surface is not possible in insects.

Answer Answer: (a) As the integument of insect is thick and impermeable to minimise lose of body water, they can not carry out gas exchange through their body surface. To overcome this difficulty they have developed a complex system of air tubes called trachea to reach the air directly near the tissue cells. Each trachea communicates with the exterior through openings in the body wall.

Q.5. Assertion : Coughing and sneezing are necessary.
Reason : Coughing and sneezing are reflex actions

Answer Answer: (b)

Q.6. Assertion : Aerobic animals are not truely aerobic.
Reason : They produce lactic acid anaerobically.

Answer Answer: (a) In most animals, tissue oxidation are carried out by aerobic respiration. But sometimes in aerobically respiring animals, anaerobic metabolism take place in certain tissues like skeletal muscles which do not immediately get as much oxygen as in necessary for metabolize glucose during vigorous movements.

Q.7. Assertion : If there is no air in trachea, it will not collapse.
Reason : Trachea is having the cartilagenous ring.

Answer Answer: (a) There is no air in trachea, it does not collapse due to the presence of C-shaped narrow cartilagenous ring or discs.

Q.8. Assertion : Inspiration occurs due to muscular relaxation.
Reason : During inspiration, the diaphragm and external intercostal muscle contract simultaneously.

Answer Answer: (a) Inspiration is the result of muscular contraction. The diaphragm and external intercoastal muscle contracts simultaneously. The lateral thoracic wall moves outward and upward.

Q.9. Assertion : Aerobic respiration involves the exchange of respiratory gases twice.
Reason : Exchange occurs from lung to heart and then heart to lung.

Answer Answer: (c) Aerobic respiration involves the exchange of respiratory gases at two places in muticellular animals-one between the body surface and surrounding medium, the other between the individual cells and the extracellular fluid. Lungs are involved in the first step of exchange, but not the heart.

Q.10. Assertion: Alveoli are the primary sites for exchange of gases.
Reason: All factors in our body are favourable for diffusion of O2 from alveoli to tissues and that of CO2 from tissues to alveoli.

Answer Answer: (b)

Q.11. Assertion: Tracheae, primary, secondary and tertiary bronchi are supported by incomplete cartilaginous rings.
Reason: These rings of cartilage make the wall non-collapsible.

Answer Answer: (a) The cartilage rings are present in the trachea to prevent it from collapsing. This enables the lumen of trachea to stay open during breathing.

Q.12. Assertion: Respiratory rhythm centre is moderated by pneumotaxic centre, located in the medulla region of the brain.
Reason: Pneumotaxic centre controls the switch ‘ON’ point of inspiration.

Answer Answer: (d) Pneumotaxic centre in the pons region of the brain can moderate functions of the respiratory rhythm centre. Neural signals from this centre can reduce the duration of inspiration and thereby alter the respiratory rate. A chemosensitive area is situated adjacent to the rhythm centre to make necessary adjustments in the respiratory process. Receptors associated with aortic arch and carotid artery also can recognize changes in CO2 and H+ concentration and send necessary signals to the rhythm centre for remedial actions. The role of oxygen in the regulation of respiratory rhythm is quite insignificant.

Q.13. Assertion: Excessive inflation of the lungs is prevented by Hering-Breuer reflex.
Reason: On overstretching of the lungs, the stretch receptors send impulses along the vagus nerve to stimulate the expiratory centre.

Answer Answer: (c) In the walls of bronchi and bronchioles stretch receptors are located and are stimulated by overstretching of the lungs. Nerve impulses are sent along the vagus nerve to inhibit the inspiratory area. The result is that expiration begins. Therefore, it is mainly a protective mechanism for preventing excessive inflation of the lungs.

Q.14. Assertion: The lungs are situated in thoracic chamber which is anatomically an air-tight chamber.
Reason: Such an arrangement is essential to avoid any change in pulmonary volume.

Answer Answer: (c)

Q.15. Assertion: Vocal cords consist of three pairs of mucous membrane that extend into the lumen of the larynx.
Reason: Only two pairs of cords are responsible for production of sound.

Answer Answer: (d) Inside the larynx are present two pairs of vocal cords. One pair is of false vocal cords which has little to do with sound production and the second inner pair is true vocal cords. When air is forced through the larynx, it causes vibration of the true vocal cords and sound is produced. The pitch of sound is determined by the tension on the vocal cords-the greater the tension, the higher the pitch.

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