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12th Biology MCQ PDF - All Chapters
NCERT Based MCQ with Explanation:
1. What is the primary function of the respiratory system?
(a) Digestion of food
(b) Transport of nutrients
(c) Exchange of oxygen and carbon dioxide
(d) Regulation of body temperature
(Explanation: The respiratory system facilitates the uptake of oxygen and removal of carbon dioxide through breathing.
2. Which process allows the exchange of gases in organisms like sponges and flatworms?
(a) Cutaneous respiration
(b) Branchial respiration
(c) Simple diffusion
(d) Pulmonary respiration
(Explanation: Lower invertebrates exchange gases directly across their body surfaces via diffusion.
3. What is the role of alveoli in the respiratory system?
(a) Transport of blood
(b) Production of sound
(c) Gas exchange
(d) Filtration of air
(Explanation: Alveoli are thin-walled structures in the lungs where oxygen and carbon dioxide are exchanged with blood.
4. What structure prevents food from entering the larynx during swallowing?
(a) Epiglottis
(b) Diaphragm
(c) Trachea
(d) Bronchi
(Explanation: The epiglottis is a cartilaginous flap that covers the glottis during swallowing, directing food to the esophagus.
5. How many lungs do humans have?
(a) One
(b) Two
(c) Three
(d) Four
(Explanation: Humans have two lungs, each consisting of multiple lobes, enabling effective gas exchange.
6. Which structure is referred to as the “sound box” in the respiratory system?
(a) Pharynx
(b) Larynx
(c) Trachea
(d) Bronchi
(Explanation: The larynx contains vocal cords and is responsible for sound production.
7. What type of respiration involves the use of vascularized bags called lungs?
(a) Branchial respiration
(b) Pulmonary respiration
(c) Cutaneous respiration
(d) Tracheal respiration
(Explanation: Lungs are used by terrestrial animals for gas exchange, known as pulmonary respiration.
8. What is the function of pleural fluid in the lungs?
(a) Conducting air to alveoli
(b) Reducing friction during breathing
(c) Producing sound
(d) Filtering oxygen
(Explanation: Pleural fluid, located between pleural membranes, reduces friction as lungs expand and contract.
9. Which part of the respiratory system is responsible for humidifying inhaled air?
(a) Alveoli
(b) Nasal passage
(c) Bronchioles
(d) Diaphragm
(Explanation: The nasal passage warms, humidifies, and filters inhaled air before it enters the lungs.
10. What occurs during inspiration?
(a) Diaphragm relaxes
(b) Thoracic cavity volume decreases
(c) Intra-pulmonary pressure becomes negative
(d) Air is expelled from the lungs
(Explanation: During inspiration, the diaphragm contracts, increasing thoracic cavity volume and reducing intra-pulmonary pressure below atmospheric pressure.
Science MCQ, Class 10th, Chapter-13/15, Our Environment11. What is the average number of breaths per minute for a healthy human?
(a) 10-12
(b) 12-16
(c) 16-20
(d) 20-24
(Explanation: The normal respiratory rate for a healthy adult is approximately 12-16 breaths per minute.
12. Which structure divides into the primary bronchi?
(a) Larynx
(b) Pharynx
(c) Trachea
(d) Alveoli
(Explanation: The trachea bifurcates into the right and left primary bronchi, directing air to each lung.
13. What is tidal volume?
(a) The amount of air inspired or expired during normal breathing
(b) Maximum air inspired after a forced expiration
(c) Air remaining in lungs after forced expiration
(d) Additional air inspired during deep breathing
(Explanation: Tidal volume refers to the volume of air exchanged in a single normal breath, approximately 500 mL.
14. What instrument is used to measure lung volumes?
(a) Thermometer
(b) Spirometer
(c) Sphygmomanometer
(d) Stethoscope
(Explanation: A spirometer is a clinical tool used to measure lung volumes and capacities.
15. Which component of blood transports most oxygen?
(a) Plasma
(b) Platelets
(c) White blood cells
(d) Red blood cells
(Explanation: Hemoglobin in red blood cells binds oxygen and facilitates its transport throughout the body.
16. What is the average residual volume in the human lungs?
(a) 500-600 mL
(b) 800-900 mL
(c) 1100-1200 mL
(d) 1500-1600 mL
(Explanation: Residual volume refers to the air remaining in the lungs after a forceful expiration, typically 1100-1200 mL in adults.
17. Which muscles are involved in the process of expiration during forced breathing?
(a) Diaphragm only
(b) Internal intercostal muscles
(c) External intercostal muscles
(d) Both internal and external intercostal muscles
(Explanation: During forced expiration, internal intercostal muscles contract to reduce thoracic cavity volume and expel air.
18. The respiratory surface in insects is made of:
(a) Gills
(b) Alveoli
(c) Tracheal tubes
(d) Moist skin
(Explanation: Insects utilize a network of tracheal tubes for direct gas exchange with the atmosphere.
19. What type of respiration do frogs use apart from lungs?
(a) Branchial respiration
(b) Tracheal respiration
(c) Cutaneous respiration
(d) Pulmonary respiration
(Explanation: Frogs can exchange gases through their moist skin, a process called cutaneous respiration.
20. What is the partial pressure of oxygen in alveolar air?
(a) 40 mmHg
(b) 70 mmHg
(c) 104 mmHg
(d) 159 mmHg
(Explanation: In alveolar air, the partial pressure of oxygen (pO₂) is approximately 104 mmHg.
21. Which factor primarily drives the diffusion of oxygen into the blood from alveoli?
(a) Carbon dioxide solubility
(b) Partial pressure gradient of oxygen
(c) Alveolar membrane thickness
(d) Respiratory muscle contraction
22. What happens to carbon dioxide at the alveolar site?
(a) It combines with hemoglobin
(b) It is released into the alveoli
(c) It is converted into bicarbonates
(d) It combines with oxygen
23. What is the main carrier of oxygen in the blood?
(a) Hemoglobin
(b) Plasma
(c) White blood cells
(d) Platelets
24. Which gas is more soluble in blood?
(a) Oxygen
(b) Carbon dioxide
(c) Nitrogen
(d) Helium
25. What does the sigmoid shape of the oxygen dissociation curve indicate?
(a) Constant oxygen binding to hemoglobin
(b) Cooperative binding of oxygen to hemoglobin
(c) Decreased oxygen affinity
(d) Linear relationship of oxygen and hemoglobin
26. How much carbon dioxide is transported as bicarbonate in the blood?
(a) 10-15%
(b) 20-25%
(c) 50%
(d) 70%
27. What triggers the respiratory rhythm center in the medulla oblongata?
(a) Decreased oxygen levels
(b) Increased carbon dioxide and hydrogen ion levels
(c) Increased oxygen levels
(d) Decreased nitrogen levels
28. Which condition is caused by damage to alveolar walls?
(a) Asthma
(b) Bronchitis
(c) Emphysema
(d) Tuberculosis
29. What prevents the collapse of alveoli?
(a) Diaphragm contraction
(b) Surfactant
(c) Pleural fluid
(d) Epiglottis
30. Which muscle is the primary driver of inspiration?
(a) Diaphragm
(b) Internal intercostals
(c) Abdominal muscles
(d) Scalene muscles