Selina Concise Solutions for ICSE Class 9 Biology Chapter 14 The Respiratory System

Exercise 1

Question A.1:
Answer: 1. (b) contracts
2. (a) alveoli
3. (b) loss in dry weight
When we breathe in, the diaphragm contracts to create space for air. Cellular respiration in plants can lead to a slight weight loss as stored food is used for energy.
Teacher's Tip: Think of "C" for Contraction when "Creating" space for air.
Exam Tip: Always double-check if the question asks for "inhalation" or "exhalation" before choosing your answer.

Question B.1:
Answer: (a) Diaphragm (b) Ethyl alcohol (c) Diffusion (d) Diffusion (e) Hypoxia (j) Vocal cord
These terms represent the key physical structures and chemical outcomes of the respiratory process. For example, hypoxia occurs when the body or a region of it is deprived of adequate oxygen supply.
Teacher's Tip: Use "Vocal" to remember "Voice" - the vocal cords are what let you speak.
Exam Tip: Be sure to spell "Diaphragm" correctly as it has a silent 'g'.

Question B.2:
Answer: (a) Epiglottis (b) Capillaries (c) Diaphragm (d) Bronchioles (e) Ribs (f) Alveoli or air sacs
These are the various parts of the human respiratory tract that help filter, transport, and exchange gases. Alveoli are the final destination where oxygen actually enters the bloodstream.
Teacher's Tip: Alveoli sound like "Air-veoli" because they are tiny air sacs.
Exam Tip: If asked for the site of gas exchange, "alveoli" is the only correct scientific answer.

Question B.3:
Answer: COMPONENT - INSPIRED AIR - EXPIRED AIR
1. Oxygen - 20.96% - 16.40%
2. Carbon dioxide - 0.04% - 4.00%
3. Nitrogen - 79.00% - 79.60%
Notice how the amount of oxygen decreases while carbon dioxide increases significantly when we breathe out. Nitrogen stays almost the same because our bodies don't use it for respiration.
Teacher's Tip: Remember "Out with the Bad (CO₂), In with the Good (O₂)."
Exam Tip: Memorize the 0.04% and 4% values for carbon dioxide as they are frequently asked in exams.

Question B.4:
Answer: ATP or Adenosine Triphosphate is termed as “Currency of Energy” of the cell.
Every living cell needs energy to perform its daily tasks, and it gets this energy by "spending" ATP. It is the form of energy that our body can actually use for muscle movement and chemical reactions.
Teacher's Tip: Think of ATP like the "Cash" you need to buy "Actions" for your body.
Exam Tip: Always provide the full form "Adenosine Triphosphate" when writing about ATP.

Question B.5:
Answer: (a) Alveoli - (iii) diffusion of gases
(b) Bronchioles - (iv) small air tubes
(c) Nasal Chamber - (ii) lined with hair
(d) Bronchi - (v) an inverted Y shaped tube
This matching exercise connects respiratory structures with their physical descriptions or functions. The nasal chamber's hair acts as the first line of defense by filtering out large dust particles.
Teacher's Tip: An inverted Y looks exactly like the way the trachea splits into two bronchi.
Exam Tip: In matching questions, rewrite the correct pairs clearly side-by-side to avoid marking errors.

Question C.1:
Answer: (a) Alveoli and gaseous diffusion
(b) Mitochondria and power house (respiration)
(c) Epiglottis and guard of entrance to trachea
(d) Pleura and lung covering
(e) Diaphragm and differentiate thoracic cavity and abdominal cavity
(f) ‘C’ shaped cartilage rings and support
These functional pairs explain how each part contributes to the overall breathing and energy-making process. The 'C' shaped rings are crucial because they prevent the windpipe from collapsing.
Teacher's Tip: Think of Pleura as the "Plastic wrap" that protects the lungs.
Exam Tip: Use the term "thoracic cavity" when describing the chest area to sound more scientific.

Question C.2:
Answer: (a) Ciliated epithelium: It is the protective inner lining of the respiratory passage. It helps in motion, driving any fluid that is on them.
(b) Mitochondria: In mitochondria, pyruvic acid is further broken down step by step in a cyclic manner in the presence of oxygen.
(c) Diaphragm: Diaphragm contributes to the enlargement of the chest cavity lengthwise.
(d) Intercostal muscles: The muscles help the inward and outward movement of ribs enlarging the chest cavity all around.
(e) Pleural fluid: It provides lubrication for free movement of the expanding and contracting lungs.
Each tissue and muscle has a specific job in making sure air flows in and out smoothly. The pleural fluid is especially important because it prevents the lungs from rubbing against the chest wall.
Teacher's Tip: Cilia are like tiny "Brooms" that sweep dust out of your throat.
Exam Tip: For function-based questions, use action words like "lubrication," "protection," or "movement."

Question C.3:
Answer: Cartilaginous - Bronchi
Large surface area - Alveoli
Breathing movements - Diaphragm
Voice - Larynx
Complemental air - Extra inhalation
Swallowing - Epiglottis
These associations help identify the physical characteristics and special capacities of the respiratory system. For instance, the larynx contains the vocal cords that vibrate to produce sound.
Teacher's Tip: The Larynx is your "Voice Box."
Exam Tip: Always associate "Large surface area" with "Alveoli" as it is their most important structural feature.

Question C.5:
Answer: During breathing, the air expelled out is always warmer or at body temperature. It can be felt by breathing out the air on our own hand. One can feel the warmth of the air expelled out during breathing.
Inside our bodies, chemical reactions generate heat, which is transferred to the air in our lungs. This is why exhaled air is moist and warm compared to the surrounding environment.
Teacher's Tip: Try breathing on a cold mirror; the fog you see is the warm moisture escaping.
Exam Tip: Mention "body temperature" to explain why exhaled air feels warm.

Question C.6:
Answer: The nasal cavity is lined by ciliated epithelium and mucous glands. The mucous glands secrete mucous. The ciliated epithelium is present on the entire lining of larynx, trachea, bronchi and bronchioles. The constant motion of cilia and mucous trap dust, micro-organisms, pollen and other minute particles present in the air. In this way, the respiratory passage is kept free of dust particles.
The combination of sticky mucus and moving cilia creates a natural air-cleaning system. This protects the delicate inner parts of our lungs from pollution and infection.
Teacher's Tip: Cilia and mucus work together like a "Sticky Belt" that carries dirt away.
Exam Tip: Explain how "trapping" and "moving" work together for a complete answer on respiratory defense.

Question C.7:
Answer: We inhale air which contains more of oxygen and less of carbon dioxide. We exhale air which contains more of carbon dioxide and less of oxygen. Therefore, the statement “We breathe in oxygen and breathe out carbon dioxide” is wrong.
We don't just breathe pure gases; we breathe a mixture of air that contains nitrogen, oxygen, and other gases. We only absorb a portion of the oxygen and release a portion of the carbon dioxide.
Teacher's Tip: We are "Air breathers," not "Oxygen breathers."
Exam Tip: Use the percentages from the component chart to prove why this statement is incorrect.

Question D.1:
Answer: (a) Aerobic respiration - CO₂, H₂O, ATP, Heat energy; Anaerobic respiration - Lactic acid, ATP, Heat energy
(b) Respiration - CO₂; Photosynthesis - O₂
(c) Photosynthesis - CO₂ + sunlight + H₂O; Respiration - Glucose (with or without oxygen)
(d) Inspired air - 0.04%; Alveolar air - 4.00%
(e) Respiration - lungs, bronchi, alveoli; Breathing - nasal cavity, trachea, diaphragm
(f) Tidal volume - 1500 ml; Residual volume - 500 ml
These comparisons show the chemical and physical differences between various life processes and lung capacities. For instance, breathing is just a physical act, while respiration is a chemical process happening in cells.
Teacher's Tip: Respiration happens in the "Kitchen" (cell), while breathing is the "Delivery" (lungs).
Exam Tip: Always list the "Byproducts" or "Chemical Equations" when asked to differentiate biological processes.

Question D.2:
Answer: (a) Breathing through the nose is said to be healthier than through the mouth because the hair present in the nostrils prevent large dust particles from entering inside the respiratory system.
(b) Gaseous exchange continues in the lungs even during expiration because expiration is the result of reverse movements of the ribs and diaphragm. As consequence of the movements of the ribs and the diaphragm, the thoracic cavity is diminished and the lungs are compressed, forcing the air out into the atmosphere.
(c) At higher altitudes, the oxygen content of the air is low. So, a person feels breathlessness at higher altitudes.
Breathing through the nose also warms and moistens the air, which is better for the lungs. The continuous exchange of gases ensures that the blood always has a supply of oxygen, even when we are blowing air out.
Teacher's Tip: Think of the nose as a "Filter, Heater, and Humidifier" for your lungs.
Exam Tip: Use the term "oxygen concentration" to explain altitude sickness.

Question D.3:
Answer: (a) (i) Abdominal muscles (ii) Intercostal muscles
(b) (i) The ribs are moved inwards and outwards by the intercostal muscles stretched between them and thereby, enlarges the chest cavity.
(ii) The diaphragm flattens and presses the organs inside the abdomen. When the abdominal muscles relax, the abdominal wall moves outwards.
(c) The overall chemical equation for the process of respiration in humans: C₆H₁₂O₆ + 6O₂ → {Enzymes} 6CO₂ + 6H₂O + 38ATP + 420{ kcal}
(d) 1. Residual air: Some air is always left in the lungs even after forcibly breathing out. This is the left over or residual air. This volume is 1500 mL.
2. Dead air space: Some tidal air is left in the respiratory passages such as trachea and bronchi, where no diffusion of gases can occur. This volume is called dead air space. It is 150 mL.
Muscles like the diaphragm and intercostals work like a pump to change the pressure inside our chest. This pressure change is what physically moves air in and out of the body.
Teacher's Tip: The diaphragm is the "Floor" of your chest that moves down to let air in.
Exam Tip: Memorize the chemical equation for respiration perfectly; it is a high-scoring question.

Question D.4:
Answer: Path taken by the inspired air: Nose -> Pharynx -> Larynx -> Trachea -> Bronchi
This is the specific sequence air follows as it travels from the outside world into our lungs. Each structure along the way helps prepare the air for the delicate alveoli.
Teacher's Tip: Remember the order: N-P-L-T-B (Nose, Pharynx, Larynx, Trachea, Bronchi).
Exam Tip: Use arrows to show the direction of airflow when writing this sequence in an exam.

Question D.5:
Answer: (a) Ribs: The ribs move inwards and outwards by the muscles stretched between them, thus enlarging the chest cavity all around.
(b) Diaphragm: On contraction, the diaphragm falls or flattens from the dome-shaped outline to an almost horizontal plane and thus, contributes to the enlargement of the chest cavity lengthwise.
(c) Abdominal muscles: Abdominal muscles help to increase the size of the thoracic cavity by the movement of diaphragm and therefore, aids in inspiration.
These three parts work in coordination to change the volume of the chest cavity. When the volume increases, air is sucked in because the pressure inside the lungs becomes lower than the outside air.
Teacher's Tip: Think of the chest like a "Bellows" used to blow air into a fire.
Exam Tip: Mention "pressure difference" to explain why air moves during inspiration.

Question E.1:
Answer: (i) 1: Thin walls of capillary; 2: RBCs (Red blood corpuscles); 3: Plasma; 4: Thin wall of the alveolus
(ii) 5: CO₂ diffuses out; 6: O₂ diffuses in
This diagram illustrates the interface between our blood and the air we breathe. Gases only have to pass through two very thin cell layers to get where they need to go.
Teacher's Tip: The alveolus wall is so thin that gases just "Float" right through it.
Exam Tip: Labeling diagrams precisely is key; distinguish clearly between the alveolar wall and the capillary wall.

Question E.2:
Answer: (a) Anaerobic respiration
(b) This reaction is applicable to animals only.
(c) This reaction may occur in muscular tissues (skeletal muscles).
This type of respiration happens when we exercise very hard and our muscles can't get oxygen fast enough. It results in the buildup of lactic acid, which can make muscles feel sore.
Teacher's Tip: Lactic acid is the "Muscle Burn" you feel when sprinting.
Exam Tip: State clearly that anaerobic respiration in animals produces "Lactic acid," not alcohol.

Question E.3:
Answer: (a) (i) Anaerobic respiration in plants: 5 (ii) End products in aerobic respiration: 4 (iii) Reaction occurring in liver: 2 (iv) Anaerobic respiration in animals: 1 (v) Storage in the liver: 3
(b) (i) Aerobic respiration: 4 (ii) Change taking place in the liver: 3 (iii) Anaerobic respiration in yeast: 5 (iv) Change taking place in a plant storage organ, e.g., potato: 2 (v) Anaerobic respiration in animals: 1
These numerical associations link biological locations with specific chemical reactions. For instance, anaerobic respiration in yeast is what creates the alcohol used in various industries.
Teacher's Tip: Liver is like the "Warehouse" and "Processing Plant" for the body's chemicals.
Exam Tip: Matching numbers to processes requires careful reading; double-check each pairing before finalizing.

Question E.4:
Answer: (a) Tidal volume (TV): Air breathed in and out, in a normal quiet breathing is called tidal volume. It is 500 mL.
(b) Inspiratory reserve volume (IRV): Air that can be drawn in forcibly over and above the tidal air is called inspiratory reserve volume. It is also known as complemental air. It is 3000 mL.
(c) Expiratory reserve volume (ERV): Air that can be forcibly expelled out after a normal expiration is called expiratory reserve volume. It is also called supplemental air. It is 1000 mL.
(d) Vital capacity (VC): Volume of air that can be taken in and expelled out by maximum inspiration and expiration is called vital capacity. It is 4500 mL.
(e) Residual volume (RV): Air left in the lungs, even after forcible expiration is called residual volume. It is 1500 mL.
These measurements help doctors understand how well our lungs are functioning. Even when we try to empty our lungs completely, the residual volume stays behind to keep the air sacs from collapsing.
Teacher's Tip: Imagine the "Tidal" volume is like the regular "Tide" of the ocean coming in and out.
Exam Tip: Vital Capacity is the sum of TV + IRV + ERV; knowing this formula helps you remember the definition.