An Overview of Ncert Books Class 11 Biology Chapter 17 Free Download
FAQs on Ncert Books Class 11 Biology Chapter 17 Free Download
1. What is the mark-wise weightage for Chapter 17, Breathing and Exchange of Gases, in the Class 11 Biology exam for 2025-26?
As per the CBSE syllabus for 2025-26, Chapter 17 is part of Unit V, Human Physiology. This entire unit carries a significant weightage of approximately 18 marks in the final examination. Students can expect a mix of questions, including MCQs, 2-mark, 3-mark, and potentially a 5-mark question, covering various concepts from this chapter.
2. What are the most important topics to cover in this chapter for the final exams?
To secure high marks, students should focus on the following high-yield topics from Breathing and Exchange of Gases:
- Mechanism of Breathing: The roles of the diaphragm and intercostal muscles during inspiration and expiration.
- Exchange and Transport of Gases: The concept of partial pressure gradients, transport of O₂ as oxyhaemoglobin, and transport of CO₂ as bicarbonate.
- Respiratory Volumes and Capacities: Definitions and standard values for TV, IRV, ERV, and Vital Capacity.
- Regulation of Respiration: The function of the respiratory rhythm centre in the medulla.
- Disorders: Causes and effects of Asthma, Emphysema, and Occupational Respiratory Disorders.
3. What are some expected 5-mark important questions from Breathing and Exchange of Gases?
For the 5-mark section, you can expect questions that require detailed, comprehensive answers. Important questions include:
- Explain the mechanism of inspiration and expiration in humans with the help of a well-labelled diagram showing the action of the diaphragm and rib cage.
- Describe the transport of carbon dioxide in the blood. Explain why the majority is transported as bicarbonate ions.
- Draw a labelled diagram of the human respiratory system and explain the function of each part from the nostrils to the alveoli.
4. What type of 3-mark questions are frequently asked from this chapter?
Frequently asked 3-mark questions often test specific conceptual knowledge. Key examples include:
- Define and differentiate between Vital Capacity (VC) and Total Lung Capacity (TLC).
- Explain the process of gaseous exchange at the alveolar surface with reference to the partial pressures of O₂ and CO₂.
- Explain the role of the Oxygen-Haemoglobin Dissociation Curve in the transport and release of oxygen.
5. Why is the concept of partial pressure so critical for understanding the exchange of gases?
The concept of partial pressure is fundamentally important because it dictates the direction of gas flow. Gases always diffuse down a pressure gradient, from an area of higher partial pressure to an area of lower partial pressure. This principle single-handedly explains why oxygen moves from the alveoli into the blood and then from the blood into the tissues, while carbon dioxide moves in the opposite direction, ensuring efficient gas exchange for respiration.
6. How does the body regulate breathing, and why is this an important exam topic?
The regulation of breathing is a crucial topic as it involves the nervous system. The primary control lies with the respiratory rhythm centre in the medulla, which sets the basic breathing pace. A nearby chemosensitive area is highly sensitive to changes in blood CO₂ and H⁺ levels. An increase in these substances triggers the centre to increase the breathing rate to expel excess CO₂. This feedback loop is a common subject for application-based questions in exams.
7. From an exam perspective, what is the significance of the Bohr effect?
The Bohr effect is a highly important concept for exams. It describes the shift in the oxygen-haemoglobin dissociation curve to the right in response to an increase in carbon dioxide concentration or a decrease in pH. This shift decreases haemoglobin's affinity for oxygen, causing it to release oxygen more readily. This is physiologically significant in metabolically active tissues, like exercising muscles, which have high CO₂ levels and need more oxygen.
8. Why is carbon dioxide mainly transported as bicarbonate ions and not simply dissolved in blood plasma?
This is a key conceptual question. Carbon dioxide has low solubility in blood plasma. Transporting it as dissolved gas would be highly inefficient and would drastically lower the blood's pH, making it dangerously acidic. By converting CO₂ into bicarbonate ions (HCO₃⁻) within red blood cells, the body can:
- Transport large quantities of CO₂ efficiently from tissues to the lungs.
- Act as a crucial part of the blood buffering system, helping to maintain a stable blood pH.
