Chapter: 05. Human Respiratory System
A. Multiple Choice Questions
(d) Both diaphragm and rib muscles contract Exhaled air contains more The breathing rate in humans under normal conditions is The process of gaseous exchange in lungs between air and blood is called B. Assertion-Reason Type Questions
Assertion [A]: Respiration involves exchange of oxygen and carbon dioxide.
Reason [R]: Plants and animals utilise oxygen for respiration and produce carbon dioxide. (a) Both Assertion [A] and Reason [R] are true. Assertion [A]: During inspiration, volume of lungs increases to provide more space for the incoming air.
Reason [R]: The volume of thoracic cavity decreases due to the flattening of diaphragm and raising of rib cage. © Assertion [A] is true but Reason [R] is false. C. Fill in the blanks with suitable words.
Cellular respiration occurs inside cells. During inhalation, ribs move upwards and outwards. End products of respiration are carbon dioxide, water and energy. Breathing involves two steps inhalation and exhalation. Opening of larynx in the pharynx is protected by epiglottis. D. State whether these statements are true or false. If false, rewrite the correct form of statements.
1. The air we breathe out is rich in oxygen and moisture.
* False. The air we breathe out is rich in carbon dioxide and moisture.
2. During last running or heavy exercise, we breathe last and irregularly
* False. During fast running or heavy exercise, we breathe fast and deeply.
3. Trachea has a large surface area for gaseous exchange.
* False. Alveoli have a large surface area for gaseous exchange.
E. Give one word for the following.
1. Air sacs inside the lungs
* Alveoli
2. The muscular partition that separates thoracic cavity and abdominal cavity
* Diaphragm
3. The gas which turns limewater milky
* Carbon dioxide
4. The temporary compound formed by haemoglobin with oxygen
* Oxyhaemoglobin
5. The structures that help in breathing
* Ribs and Diaphragm
6. Substance broken down during respiration to release energy
* Glucose
F. Mention the role of the following.
Nasal passages filter, warm, and moisten the air before it enters the lungs, trapping dust, smoke particles, pollen, and microbes. Alveoli provide a large surface area for the efficient exchange of gases (oxygen from air into blood, and carbon dioxide from blood into air). Ribs, along with rib muscles, move upwards and outwards during inhalation to increase thoracic volume, and downwards and inwards during exhalation to decrease it, facilitating air movement. Haemoglobin is a respiratory pigment in red blood cells that temporarily combines with oxygen to form oxyhaemoglobin, transporting oxygen from the lungs to body cells. Epiglottis is a muscular flap that guards the glottis (opening of the trachea), closing it during swallowing to prevent food from entering the windpipe. G. Give reasons for the following.
1. We need to breathe.
* We need to breathe to continuously supply oxygen to our body cells for the oxidation of food, which releases the energy required to carry out all life processes, and to remove carbon dioxide, a waste product of respiration.
2. Breathing rate increases during fast physical activities.
* Breathing rate increases during fast physical activities because the body’s demand for energy significantly rises. This requires more oxygen for the increased rate of cellular respiration and leads to a higher production of carbon dioxide, necessitating faster removal.
3. We sneeze.
* We sneeze when unwanted particles, such as dust, smoke, or pollen, are not adequately trapped by the nasal hairs and irritate the sensitive lining of the nasal passages, triggering a forceful expulsion to clear them out.
H. Differentiate between the following.
Breathing and respiration Breathing is a mechanical process involving the physical pumping of air into and out of the lungs to provide oxygen for respiration. It occurs in the lungs, outside the cells. Respiration is a biochemical process that involves both the exchange of gases (between blood and air in lungs, and between blood and cells) and the oxidation of food inside cells to release energy for life activities. It occurs both in the lungs and within the cells. External and internal respiration External respiration is the exchange of gases that occurs in the lungs between the air in the alveoli and the blood. Oxygen moves from the alveoli into the blood, and carbon dioxide moves from the blood into the alveoli. Internal respiration is the exchange of gases that occurs between the blood and the body cells. Oxygen moves from the blood into the cells, and carbon dioxide moves from the cells into the blood. Exhalation and inhalation Inhalation is the process of taking in fresh, oxygen-rich air. During inhalation, the ribs move upwards and outwards, and the diaphragm contracts and moves downwards, increasing the volume of the thoracic cavity and lungs, which causes air to rush in due to lower internal pressure. Exhalation is the process of giving out used, carbon dioxide-rich air. During exhalation, the ribs move downwards and inwards, and the diaphragm relaxes and moves upwards, decreasing the volume of the thoracic cavity and lungs, which forces air out due to higher internal pressure. I. Match the columns.
J. Encircle the odd one out. Give reasons for your choice. Thoracic cavity, abdominal cavity, diaphragm, ribcage Odd one out: Abdominal cavity Reason: The thoracic cavity, diaphragm, and ribcage are all direct components involved in forming the chest cavity and the mechanics of human breathing. The abdominal cavity is separate and not directly part of the respiratory mechanism. Alveoli, lungs, skin, bronchi, bronchioles Reason: Alveoli, lungs, bronchi, and bronchioles are all integral parts or structures of the human respiratory system. Skin is not a respiratory organ in humans. Ammonia, glucose, CO2, lungs Reason: Glucose is the fuel for respiration, CO2 is a product of respiration, and lungs are the primary organs for gas exchange in respiration. Ammonia is a nitrogenous waste product from protein metabolism, not directly involved in the process of respiration as defined in this chapter. K. Answer these questions.
Explain the mechanism of breathing in human beings. The mechanism of breathing in human beings involves two alternating processes: inhalation and exhalation, which are coordinated by the rib muscles and the diaphragm. Inhalation: During inhalation, the rib muscles contract, causing the ribs to move upwards and outwards. Simultaneously, the diaphragm contracts and flattens, pulling downwards. These actions increase the volume of the thoracic cavity and, consequently, the lungs. This increase in volume leads to a decrease in air pressure inside the lungs compared to the outside atmosphere, causing fresh air to rush in through the nasal passages and air tubes to fill the lungs. Exhalation: During exhalation, the rib muscles relax, allowing the ribs to move downwards and inwards. The diaphragm also relaxes and moves upwards, returning to its dome shape. These movements decrease the volume of the thoracic cavity and lungs. This reduction in volume increases the air pressure inside the lungs, which then pushes the air, now rich in carbon dioxide, out of the lungs through the air passages and nostrils. How does exchange of gases take place in human body? The exchange of gases in the human body occurs in two main stages: External Respiration (in the Lungs): This occurs in the tiny air sacs called alveoli within the lungs. When we inhale, the alveoli are filled with fresh, oxygen-rich air. The thin walls of the alveoli are surrounded by a dense network of blood capillaries. Oxygen from the air in the alveoli diffuses across the thin alveolar and capillary walls into the blood. At the same time, carbon dioxide, a waste product carried by the blood from body cells, diffuses from the blood into the alveoli to be exhaled. Oxygen then binds with haemoglobin in red blood cells to form oxyhaemoglobin. Internal Respiration (in the Body Cells): The oxygenated blood (containing oxyhaemoglobin) is transported by the circulatory system to all body cells. Upon reaching the cells, oxyhaemoglobin breaks down, releasing oxygen. This oxygen then diffuses from the blood into the cells, where it is used for cellular respiration (the breakdown of glucose to produce energy). Concurrently, carbon dioxide, produced as a waste product by the cells, diffuses from the cells into the blood to be carried back to the lungs for exhalation. With the help of an experiment, prove that the exhaled air contains carbon dioxide. Aim: To show that exhaled air contains CO2 produced during respiration. Materials required: Two glasses, a marker, freshly prepared limewater, two cardboard covers, cellotape, and two straws. Take two clean glasses and label them A and B. Pour an equal amount of freshly prepared limewater into each glass. Cover each glass tightly with a cardboard cover and seal the edges with cellotape to make them airtight. Make two small holes in each cardboard cover. Insert one straw into each hole. Ensure that one straw in each glass dips into the limewater, while the other straw remains above the limewater. In glass A, gently suck air out through the straw that dips in limewater. As you suck, atmospheric air will bubble through the limewater via the other straw. Repeat 2-3 times. In glass B, gently blow your exhaled air into the limewater through the straw that dips into it. Repeat 2-3 times. Observe the appearance of the limewater in both glasses. Observation: The limewater in glass B (where exhaled air was blown in) turns milky, while the limewater in glass A (where atmospheric air was sucked in) remains clear. Conclusion: Limewater turns milky in the presence of carbon dioxide. Since only the limewater in glass B turned milky, it proves that the exhaled air contains a significantly higher concentration of carbon dioxide compared to the atmospheric air. L. Diagram-based Questions
Draw and label a diagram of the structure of lungs. (Referring to Fig. 5.1 Human lungs for labels of the respiratory system structure.) Labels for a human respiratory system diagram: With the help of a diagram show the respiratory process in humans. (Referring to Fig. 5.5 Summary of respiratory process in humans.) Labels for the summary of respiratory process in humans: Oxygen (entering lungs from environment) Transport of Oxygen (via blood) Transport of Carbon dioxide (via blood) Carbon dioxide (leaving lungs to environment) Given below is the picture of internal structure of lungs. (Referring to Fig. 5.14) 2: Pulmonary Artery (or Blood Vessel) 3: Alveolar sac (or Alveoli cluster) 4: Alveolus (or individual Alveoli) (b) What prevents trachea and bronchi from collapsing when air is pushed out during expiration? The C-shaped rings of cartilage that support their walls prevent the trachea and bronchi from collapsing. © What is the exhaled air rich in? The exhaled air is rich in carbon dioxide. The figure shows the process of inhalation (Referring to Fig. 5.15) 4: Thoracic Cavity (indicating increased volume) 5: Lungs (indicating expansion) 6: Diaphragm (indicating contraction and downward movement) (b) Write the changes that occur in these parts during exhalation Airway (1): Air moves out of the airway. Thoracic Wall (2): Moves inwards. Ribs (3): Move downwards and inwards, returning to their original position. Thoracic Cavity (4): Volume decreases. Lungs (5): Contract and decrease in size. Diaphragm (6): Relaxes and moves upwards, returning to its dome shape. M. Case-based Questions
Why is jogging or exercise essential to keep body healthy? Jogging or exercise is essential to keep the body healthy because it strengthens the respiratory system by increasing breathing rate and efficiency. This allows the lungs to inhale and exhale more air, ensuring a more effective exchange of gases. Consequently, more oxygen is supplied to body cells for energy production, and waste carbon dioxide is removed more efficiently, contributing to overall physical fitness and well-being. Name the gases which are exchanged during respiration. The gases exchanged during respiration are Oxygen and Carbon dioxide. What is the role of lungs or respiratory system in our body? The primary role of the lungs and the entire respiratory system in our body is to facilitate gas exchange. This involves taking in oxygen from the atmosphere (which is crucial for the oxidation of food and subsequent energy release for all life processes) and expelling carbon dioxide, a waste product generated during cellular respiration, from the body. ThinkZone
We should breathe through our nose only and not through mouth. Why? We should breathe through our nose only because the nasal passages are specifically designed to prepare the air before it enters the lungs. The hair in the nasal passages filters out dust, smoke, pollen, and microbes, while the nasal lining warms the air to body temperature and moistens it. Breathing through the mouth bypasses these protective mechanisms, allowing unfiltered, colder, and drier air to enter the delicate respiratory system, which can cause irritation or lead to infections. An athlete breathes faster and deeper. Why? An athlete breathes faster and deeper because their body’s energy demands increase significantly during physical activity. To meet this higher energy requirement, more oxygen is needed to break down glucose in the cells, and consequently, more carbon dioxide is produced as a waste product. Breathing faster and deeper ensures a greater intake of oxygen and a more efficient expulsion of carbon dioxide, optimizing the supply of energy to their muscles and removing metabolic wastes. 
Answers to textbook exercises
J. Encircle the odd one out. Give reasons for your choice.