GSEB Class 11 Biology Solutions Chapter 17 Breathing and Exchange of Gases

Question 1. Define vital capacity. What is its significance?
Answer: Vital capacity is the highest amount of air an individual can take in after a strong exhale. It represents the total of Inspiratory reserve volume (\( \text{IRV} \)), Expiratory reserve volume (\( \text{ERV} \)), and the Tidal volume (\( \text{TV} \)). This capacity varies among different people. It tends to be greater in sportsmen compared to non-athletes, in people living in mountains rather than on flatlands, and in younger individuals rather than older ones. Smoking cigarettes decreases this vital capacity.
In simple words: Vital capacity is the largest breath you can take after breathing all the way out. It is higher in fit, young people and those in mountains, but smoking makes it lower.

Exam Tip: Remember to include all three components (IRV, ERV, TV) when defining vital capacity, and mention its variability across individuals and factors affecting it.

Question 2. State the volume of air remaining in the lungs after a normal breathing.
Answer: The amount of air that stays in the lungs even after a strong breath out is typically around 1100 mL to 1200 mL.
In simple words: After you forcefully breathe out, some air, about 1100 to 1200 mL, still remains in your lungs.

Exam Tip: Clearly state the approximate volume and specify that it's after a *forcible* expiration, not just normal breathing out.

Question 3. Diffusion of gases occurs in the alveolar region only and not in the other parts of the respiratory system. Why?
Answer: Alveoli serve as the main places where gas exchange happens. Gas exchange also takes place between the blood and tissues. Oxygen (\( \text{O}_2 \)) and carbon dioxide (\( \text{CO}_2 \)) move at these locations through simple diffusion, primarily guided by the pressure or concentration difference. The solubility of the gases and the thickness of the membranes involved in this transfer are also key elements that can influence the speed of diffusion.

The pressure an individual gas contributes in a gas mixture is termed partial pressure, shown as \( \text{p}\text{O}_2 \) for oxygen and \( \text{p}\text{CO}_2 \) for carbon dioxide. The partial pressures of these two gases in the atmosphere and at the two diffusion points are presented in Table 17.1 and Figure 17.1. The information in the table clearly shows a concentration difference for oxygen from the alveoli to the blood, and from the blood to the tissues. Likewise, a difference exists for \( \text{CO}_2 \) in the reverse way, moving from the tissues to the blood and from the blood to the alveoli. Since \( \text{CO}_2 \)'s solubility is 20-25 times greater than that of \( \text{O}_2 \), the quantity of \( \text{CO}_2 \) that can move across the diffusion membrane is much higher compared to \( \text{O}_2 \).

The diffusion membrane consists of three main layers (Figure 17.2): the delicate squamous epithelium of the alveoli, the endothelium of alveolar capillaries, and the basement material found between them. However, its overall thickness is much less than a millimeter. Consequently, all conditions in our body support the movement of \( \text{O}_2 \) from the alveoli to the tissues and \( \text{CO}_2 \) from the tissues to the alveoli. Table 17.1 shows the partial pressures of oxygen and carbon dioxide in various parts involved in diffusion, compared to those in the atmosphere.
In simple words: Gas exchange only happens in alveoli because they have a thin membrane and a good pressure difference for oxygen and carbon dioxide to move easily.

Exam Tip: To explain why gas diffusion occurs only in the alveoli, focus on the presence of a steep partial pressure gradient, the thinness of the alveolar-capillary membrane, and the high solubility of gases, especially \( \text{CO}_2 \).

Question 4. What are the major transport mechanisms for CO2? Explain
Answer: Almost 70% of \( \text{CO}_2 \) moves in the body in the form of bicarbonates.
(1) \( \text{CO}_2 \) made by the tissues moves easily into the bloodstream and enters the red blood cells (\( \text{RBCs} \)). Inside, \( \text{CO}_2 \) combines with water to create carbonic acid. This chemical process completes in less than one second.
\( \text{CO}_2 + \text{H}_2\text{O} \)
\( \implies \) Carbonic anhydrase (Erythrocytes)
\( \implies \)\( \text{H}_2\text{CO}_3 \)
(2) After this, it quickly breaks down into hydrogen and bicarbonate ions.
\( \text{H}_2\text{CO}_3 \)
\( \implies \)\( \text{H}^+ + \text{HCO}_3^- \)
(3) The oxyhemoglobin from red blood cells is acidic and stays connected with potassium (\( \text{K}^+ \)) ions as \( \text{KHbO}_2 \). The hydrogen (\( \text{H}^+ \)) ion that comes from \( \text{HCO}_2 \) then joins with hemoglobin after it separates from the \( \text{K}^+ \) ion.
\( \text{KHbO}_2 \)
\( \implies \)\( \text{KHb} + \text{O}_2 \)
Most bicarbonate (\( \text{HCO}_3^- \)) ions move into the plasma following a concentration gradient.
(4) The bicarbonate ion also connects with hemoglobin to make Haemoglobin acid (\( \text{H-Hb} \)).
\( \text{H}^+\text{HCO}_3 + \text{KHb} \)
\( \implies \)\( \text{H.Hb} + \text{KHCO}_3 \)
(5) Because of this, chloride (\( \text{Cl}^- \)) ions travel from the plasma into the red blood cells to keep the electrical balance. This event is known as the chloride shift.
In simple words: Carbon dioxide is mostly carried as bicarbonate in the blood. It reacts with water in red blood cells to form carbonic acid, which then splits into hydrogen and bicarbonate ions. These ions move around, helping to keep the blood's balance.

Exam Tip: When explaining CO2 transport, remember to detail the roles of bicarbonate formation, carbaminohemoglobin, and the chloride shift, along with the relevant enzymes and ions involved.

Question 5. What will be the pO2 and pCO2 in the atmospheric air compared to those in the alveolar air?
(1) pO2 lesser, pCO2 higher
(2) pO2 higher, pCO2 lesser
(3) pO2 higher, pCO2 higher
(4) pO2 lesser, pCO2 lesser
Answer: (2) pO2 higher, pCO2 lesser
In simple words: Atmospheric air has more oxygen pressure and less carbon dioxide pressure than the air inside your alveoli.

Exam Tip: Remember that atmospheric air has higher oxygen partial pressure and lower carbon dioxide partial pressure than alveolar air, which drives the movement of gases into and out of the lungs.

Question 6. Explain the process of inspiration under normal conditions.
Answer: Breathing in happens when the pressure inside your lungs (called intrapulmonary pressure) becomes lower than the air pressure outside (atmospheric pressure). This means there's a lower pressure in the lungs compared to the outside air. Inhaling starts when the diaphragm muscle tightens, which makes the chest cavity bigger from front to back.

When the external intercostal muscles contract, they raise the ribs and the sternum, making the chest cavity's volume larger from back to front. This total rise in chest volume causes a similar rise in lung volume. A bigger lung volume then lowers the pressure inside the lungs to below atmospheric pressure, which pulls outside air into the lungs; this is known as inspiration (Figure 17.3a).

We can make our breaths stronger by using extra muscles in the abdomen. Generally, a healthy person breathes 12-16 times each minute. The amount of air moved during breathing can be measured with a spirometer, a tool used for checking lung health in medical settings.
In simple words: Breathing in happens when lung pressure drops below outside air pressure. This pressure change is caused by the diaphragm and rib muscles contracting, which expands your chest and pulls air in. We can also make breaths stronger using stomach muscles.

Exam Tip: For a complete explanation, describe the roles of the diaphragm and intercostal muscles, the resulting change in thoracic and pulmonary volume, and how this pressure gradient draws air into the lungs.

Question 7. How is respiration regulated?
Answer: Humans possess a notable capability to manage and adjust their breathing rhythm to meet the needs of their body tissues. This process is managed by the nervous system. A specific area in the brain's medulla, known as the respiratory rhythm center, is mainly in charge of this control. Another area in the pons of the brain, called the pneumotaxic center, can modify how the respiratory rhythm center works. Signals from this center can shorten how long inspiration lasts, and thus change the breathing rate. A chemosensitive zone is located next to the rhythm center, which is sensitive to hydrogen ions.

If these substances increase, they can turn on this center, which then tells the rhythm center to alter the breathing process to get rid of them. Receptors linked to the aortic arch and carotid artery can also detect shifts in \( \text{CO}_2 \) and \( \text{H}^+ \) levels and send signals to the rhythm center for corrective steps. Oxygen's influence on controlling breathing rhythm is quite small.
In simple words: Breathing is controlled by special centers in your brain's medulla and pons, which adjust your breath rate to match your body's needs. These centers react to changes in carbon dioxide and hydrogen ion levels. Oxygen plays a very minor role in regulating breathing.

Exam Tip: Focus on the roles of the respiratory rhythm center (medulla) and pneumotaxic center (pons), and the primary stimuli for regulation being \( \text{CO}_2 \) and \( \text{H}^+ \) concentration, not primarily \( \text{O}_2 \).

Question 8. What is the effect of pCO2 on oxygen transport?
Answer: The partial pressure of \( \text{CO}_2 \), along with hydrogen ion levels and temperature, are elements that manage how \( \text{O}_2 \) links with hemoglobin to create oxyhemoglobin. In the alveoli, where oxygen pressure is high, carbon dioxide pressure is low, hydrogen ion concentration is less, and the temperature is lower, these conditions promote the creation of oxyhemoglobin. Conversely, in the body's tissues, where oxygen pressure is low, carbon dioxide pressure is high, hydrogen ion concentration is also high, and the temperature is higher, these factors encourage oxygen to separate from oxyhemoglobin.
In simple words: High carbon dioxide pressure in tissues makes oxygen leave hemoglobin to go to cells, while low carbon dioxide pressure in the lungs helps oxygen bind to hemoglobin.

Exam Tip: Explain the Bohr effect: high \( \text{p}\text{CO}_2 \) (and resultant \( \text{H}^+ \) and lower pH) reduces hemoglobin's affinity for oxygen, leading to its dissociation in tissues, and vice-versa in the lungs.

Question 9. What happens to the respiratory process in a man going up a hill?
Answer: When climbing a hill or at high altitude, the air pressure drops, meaning a person cannot get enough oxygen into their lungs for proper diffusion into the blood. Because of this lack of sufficient \( \text{O}_2 \), the person experiences breathing difficulties at higher elevations. They may feel symptoms like shortness of breath, head pain, lightheadedness, irritation, feeling sick, throwing up, tiredness, and a blue tinge on their skin, nails, and lips.
In simple words: At high altitudes, air pressure is lower, so less oxygen gets into the lungs. This causes difficulty breathing and symptoms like breathlessness, headache, and a blue appearance on skin.

Exam Tip: Describe the primary effect (reduced atmospheric pressure leading to reduced partial pressure of oxygen) and the physiological consequences on the body and respiratory process.

Question 10. What is the site of gaseous exchange in an insect?
Answer: Insects possess a system of tubes, called tracheal tubes, that carry air throughout their bodies. Air enters through small openings called spiracles during inhalation and travels to tiny tubes called tracheoles, which hold tissue fluids. The oxygen in this air then dissolves into these fluids and reaches the body's cells.
In simple words: In insects, gas exchange happens in tiny tubes called tracheoles, where oxygen dissolves into tissue fluids and reaches the cells.

Exam Tip: Identify the tracheoles as the direct site of gaseous exchange, emphasizing the role of the spiracles and tracheal system for air transport.

Question 11. Define oxygen dissociation curve. Can you suggest any reason for its sigmoidal pattern?
Answer: A sigmoid curve appears when the percentage of hemoglobin saturated with \( \text{O}_2 \) is charted against the partial pressure of \( \text{O}_2 \) (\( \text{p}\text{O}_2 \)). This graph is known as the oxygen dissociation curve and is very helpful for examining how factors such as \( \text{p}\text{CO}_2 \) and hydrogen ion (\( \text{H}^+ \)) concentration impact oxygen binding to hemoglobin.

Each hemoglobin molecule can transport up to four \( \text{O}_2 \) molecules when oxygen binds to it. This process is mainly linked to the partial pressure of \( \text{O}_2 \). Other elements like the partial pressure of \( \text{CO}_2 \), hydrogen ion concentration, and temperature can also affect this binding.
In simple words: The oxygen dissociation curve, which looks like an 'S' shape, shows how much oxygen binds to hemoglobin at different oxygen pressures. It's curved because hemoglobin's ability to bind oxygen changes as more oxygen attaches.

Exam Tip: Define the curve correctly as a plot of % saturation vs. \( \text{p}\text{O}_2 \). For its sigmoidal shape, mention cooperative binding: oxygen binding to one heme group increases hemoglobin's affinity for subsequent oxygen molecules.

Question 12. Have you heard about hypoxia? Try to gather information about it, and discuss it with your friends.
Answer: Hypoxia refers to a state where there is not enough oxygen available at the tissue level in the body.

• Arterial hypoxia: This happens due to insufficient oxygen in the blood. It occurs when the air lacks enough oxygen or when there's a blockage in the breathing passages.
• Anaemic hypoxia: This results from a very low amount of hemoglobin in the blood.
• Stagnant hypoxia: This is caused by insufficient blood circulation to supply oxygen to the tissues.
• Histotoxic hypoxia: This is because of harmful chemicals in the oxygen breathed in, for example, cyanide poisoning.

Exam Tip: Clearly define hypoxia as oxygen deficiency at the tissue level and list the different types, providing a brief cause for each to demonstrate comprehensive understanding.

Question 13. Distinguish between
(1) IRV and ERV
(2) Inspiratory capacity and Expiratory capacity
(3) Vital capacity and Total lung capacity
Answer:
(1) IRV and ERV
Inspiratory Reserve Volume (\( \text{IRV} \)): This is the extra amount of air a person can breathe in with a strong inhale. It typically ranges from 2500 mL to 3000 mL.
Expiratory Reserve Volume (\( \text{ERV} \)): This refers to the extra amount of air a person can breathe out with a forceful exhale. It typically ranges from 1000 mL to 1100 mL.

(2) Inspiratory Capacity and Expiratory Capacity
Inspiratory Capacity: This is the total amount of air an individual can breathe in after a regular exhale. It includes both the tidal volume and the inspiratory reserve volume \( (\text{TV} + \text{IRV}) \).
Expiratory Capacity: This is the total amount of air an individual can breathe out after a regular inhale. It includes both the tidal volume and the expiratory reserve volume \( (\text{TV} + \text{ERV}) \).

(3) Vital Capacity and Total Lung Capacity
Vital Capacity: This represents the highest amount of air a person can breathe in following a forceful exhale. It comprises the Expiratory Reserve Volume (\( \text{ERV} \)), Tidal Volume (\( \text{TV} \)), and Inspiratory Reserve Volume (\( \text{IRV} \)), or it is the greatest amount of air a person can breathe out after a strong inhale.
Total Lung Capacity: This is the complete amount of air that the lungs can hold after a maximum inhale. It comprises the Residual Volume (\( \text{RV} \)), Expiratory Reserve Volume (\( \text{ERV} \)), Tidal Volume (\( \text{TV} \)), and Inspiratory Reserve Volume (\( \text{IRV} \)), or vital capacity plus residual volume.
In simple words: These terms describe different amounts of air your lungs can move. IRV is extra air you can inhale, ERV is extra air you can exhale. Inspiratory capacity is normal plus extra inhale; Expiratory capacity is normal plus extra exhale. Vital capacity is the maximum air you can move in and out, while total lung capacity is all the air your lungs can hold.

Exam Tip: For distinction questions, always define both terms clearly and concisely, including typical volumes or constituent parts where applicable to highlight their differences.

Question 14. What is Tidal volume? Find out the Tidal volume (approximate value) for a healthy human in an hour.
Answer: Tidal volume is the amount of air inhaled or exhaled during a regular breath. It is roughly 500 mL. A healthy person can breathe in or out about 360 L to 480 L of air each hour.
In simple words: Tidal volume is the amount of air you breathe in or out with each normal breath, about 500 mL. Over an hour, a healthy person breathes 360 to 480 liters of air.

Exam Tip: Define tidal volume precisely and remember the typical volume per breath, then use an average breathing rate (e.g., 12-16 breaths/min) to calculate the hourly volume for a healthy human.