Human Respiratory System MCQs— Class 6 Science

Human Respiratory System | NCERT CBSE Curriculum

Practice 100+ MCQs on Human Respiratory System for Class 6 Science. Covers breathing, lungs, alveoli, gas exchange, and respiration - with instant answers and performance report.

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Quick Revision: Human Respiratory System

  • Respiration: The process of taking in oxygen and giving out carbon dioxide. Essential for releasing energy from food.
  • Breathing: The mechanical process of inhaling (taking air in) and exhaling (pushing air out). Also called external respiration.
  • Respiratory System Pathway: Nostrils → Nasal Cavity → Pharynx → Larynx (voice box) → Trachea (windpipe) → Bronchi → Bronchioles → Alveoli → Lungs.
  • Nostrils & Nasal Cavity: Air enters through nostrils. Nasal cavity warms, moistens, and filters air with hair and mucus.
  • Pharynx: Common passage for food and air. Contains tonsils that trap germs.
  • Larynx (Voice Box): Contains vocal cords that vibrate to produce sound. Air passes from pharynx to larynx.
  • Trachea (Windpipe): A tube supported by C-shaped cartilage rings that keep it open. Lined with mucus and cilia to trap and push out dust.
  • Bronchi & Bronchioles: Trachea divides into two bronchi (one per lung). Bronchi branch into finer tubes called bronchioles.
  • Alveoli: Tiny air sacs at the end of bronchioles. Surrounded by capillaries. This is the actual site of gas exchange (O₂ enters blood, CO₂ leaves blood).
  • Lungs: Paired, spongy, elastic organs in the chest cavity. The right lung has three lobes, the left has two (to accommodate the heart).
  • Diaphragm: A dome-shaped muscular sheet below the lungs. Inhalation — diaphragm contracts and flattens, chest cavity expands, air rushes in. Exhalation — diaphragm relaxes and moves up, chest cavity contracts, air is pushed out.
  • Rib Cage & Intercostal Muscles: The rib cage protects the lungs. Intercostal muscles between ribs help in breathing movements.
  • Cellular Respiration: Inside body cells, glucose combines with oxygen to release energy, carbon dioxide, and water. Glucose + O₂ → Energy + CO₂ + H₂O.
  • Breathing Rate: Number of breaths per minute. Normal adult: 15–18 breaths/min. Increases during exercise, fever, or excitement.
  • Inhaled vs Exhaled Air: Inhaled air — 21% O₂, 0.04% CO₂. Exhaled air — 16% O₂, 4.4% CO₂. Exhaled air has more CO₂, is warmer, and contains water vapour.
  • Smoking and Respiratory Health: Smoking damages the cilia in the trachea, destroys alveoli (emphysema), and increases risk of lung cancer and bronchitis.
  • Common Respiratory Diseases: Asthma (narrowing of airways), Bronchitis (inflammation of bronchi), Pneumonia (infection of alveoli), Tuberculosis (bacterial lung infection).
  • Yoga & Breathing: Pranayama (yogic breathing exercises) improves lung capacity, oxygen uptake, and overall respiratory health.

Chapter Summary: Human Respiratory System

The human respiratory system enables the body to take in oxygen and expel carbon dioxide. Air enters through the nostrils, passes through the nasal cavity (warmed, moistened, filtered), pharynx, larynx (voice box), and trachea (windpipe supported by cartilage rings). The trachea divides into two bronchi (one per lung), which further branch into bronchioles ending in tiny air sacs called alveoli. Alveoli are surrounded by capillaries and are the actual site of gas exchange — oxygen diffuses into the blood while carbon dioxide diffuses out.

Breathing is driven by the diaphragm and intercostal muscles. During inhalation, the diaphragm contracts and flattens, expanding the chest cavity and drawing air in. During exhalation, the diaphragm relaxes and moves upward, pushing air out. Cellular respiration inside cells uses oxygen to break down glucose and release energy. Inhaled air contains 21% oxygen and 0.04% carbon dioxide, while exhaled air contains 16% oxygen and 4.4% carbon dioxide. The normal breathing rate is 15–18 breaths per minute. Smoking damages respiratory tissues and increases the risk of lung diseases. Pranayama and regular exercise improve lung capacity and overall respiratory efficiency.

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