Biology
Chapter 14
Board Weightage: 12 Marks in Class 9 Exams
The Respiratory System
Prescribed Textbook: Selina Concise Biology (Class 9) - Chapter 14
Canonical Link:
https://icse.smartindia.pro/class9_biology_the_respiratory_system.html
Prerendered HTML Page: class9_biology_the_respiratory_system.html
📖 Syllabus Scope & Overview
Human respiratory organs (nasal cavity, pharynx, larynx, trachea with C-shaped rings, bronchi, lungs, alveoli), mechanism of breathing (inhalation vs exhalation, diaphragm, intercostal muscles), lung capacities (tidal volume, vital capacity), and gas exchange.
🔑 Mandatory ICSE Examiner Technical Keywords with Detailed Description
Official CISCE Evaluation Benchmark
According to CISCE board marking schemes, evaluators allocate marks based on the explicit presence of mandatory technical keywords. General or colloquial explanations fail to secure full marks. The table below details every required technical term, its scientific/academic description, the evaluator directive, and its exact model answer usage.
Mandatory Keyword #1
Core Definition
Chapter Concept: Mechanism of Breathing
1 Mark (Structural Location / Physiological Function)
"Diaphragm contracts and flattens"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Biology (The Respiratory System), "Diaphragm contracts and flattens" is an indispensable physiological term, anatomical structure, or biological process defined in the prescribed ICSE syllabus.
CISCE biology evaluators deduct marks for incorrect phonetic spelling or vague layperson descriptions. Candidates must use exact biological terminology: "Diaphragm contracts and flattens".
📝 Model Answer Application (Exact Phrasing for Board Exam):
"The physiological role of Mechanism of Breathing is characterized by "Diaphragm contracts and flattens", ensuring proper structural and functional regulation."
Mandatory Keyword #2
Core Definition
Chapter Concept: Mechanism of Breathing
1 Mark (Structural Location / Physiological Function)
"Ribs move upwards and outwards"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Biology (The Respiratory System), "Ribs move upwards and outwards" is an indispensable physiological term, anatomical structure, or biological process defined in the prescribed ICSE syllabus.
CISCE biology evaluators deduct marks for incorrect phonetic spelling or vague layperson descriptions. Candidates must use exact biological terminology: "Ribs move upwards and outwards".
📝 Model Answer Application (Exact Phrasing for Board Exam):
"The physiological role of Mechanism of Breathing is characterized by "Ribs move upwards and outwards", ensuring proper structural and functional regulation."
Mandatory Keyword #3
Core Definition
Chapter Concept: Mechanism of Breathing
1 Mark (Structural Location / Physiological Function)
"Thoracic volume increases"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Biology (The Respiratory System), "Thoracic volume increases" is an indispensable physiological term, anatomical structure, or biological process defined in the prescribed ICSE syllabus.
CISCE biology evaluators deduct marks for incorrect phonetic spelling or vague layperson descriptions. Candidates must use exact biological terminology: "Thoracic volume increases".
📝 Model Answer Application (Exact Phrasing for Board Exam):
"The physiological role of Mechanism of Breathing is characterized by "Thoracic volume increases", ensuring proper structural and functional regulation."
Mandatory Keyword #4
Core Definition
Chapter Concept: Mechanism of Breathing
1 Mark (Structural Location / Physiological Function)
"Alveoli large surface area for diffusion"
📘 Technical Definition & Detailed Description:
In ICSE Class 9 Biology (The Respiratory System), "Alveoli large surface area for diffusion" is an indispensable physiological term, anatomical structure, or biological process defined in the prescribed ICSE syllabus.
CISCE biology evaluators deduct marks for incorrect phonetic spelling or vague layperson descriptions. Candidates must use exact biological terminology: "Alveoli large surface area for diffusion".
📝 Model Answer Application (Exact Phrasing for Board Exam):
"The physiological role of Mechanism of Breathing is characterized by "Alveoli large surface area for diffusion", ensuring proper structural and functional regulation."
Complete step-by-step evaluator solutions for textbook problems and 5 generated practice sets adhering to CISCE marking schemes.
📘 Textbook Problem: Textbook Exercise 14 - Review Questions Q.5
Selina Concise Biology (Class 9) - Chapter 14 - End-of-Chapter Review
3 Marks Total
With reference to The Respiratory System: (i) Define the biological process of Mechanism of Breathing. (ii) State its exact location and physiological significance in the living organism.
Step-by-Step Marking Breakdown
Step 1: Scientific Definition with Technical Keywords: Define Mechanism of Breathing incorporating mandatory ICSE terminology: Diaphragm contracts and flattens, Ribs move upwards and outwards, Thoracic volume increases.
1 Mark
Step 2: Anatomical / Cellular Location: State the precise anatomical site or organelle where this biological process occurs.
1 Mark
Step 3: Biological Significance / Function: Explain the physiological necessity of this process for organismal survival, homeostasis, or reproduction.
1 Mark
Final Answer: Precise scientific definition, exact organ/organelle location, and physiological function
(Units: Biological Nomenclature)
💡 Examiner Tip: Underline key technical terms in biological definitions. CISCE examiners specifically look for mandatory keywords.
🎯 Generated Set: Generated Practice Set 1 - Core Concept (2 Marks)
ICSE Class 9 Exam Blueprint - Chapter 14
2 Marks Total
Define "Mechanism of Breathing" in the context of ICSE Class 9 Biology. State its primary characteristic or SI unit/standard symbol.
Step-by-Step Marking Breakdown
Step 1: Precise Technical Definition: Inhalation: Diaphragm contracts and flattens, external intercostal muscles pull ribs upwards and outwards, thoracic volume increases, lung pressure decreases, air rushes in. Exhala...
1 Mark
Step 2: Mandatory Technical Criteria: Ensure the definition contains mandatory keywords: Diaphragm contracts and flattens, Ribs move upwards and outwards, Thoracic volume increases.
1 Mark
Final Answer: Accurate scientific/scholarly definition containing all mandatory ICSE evaluation keywords.
(Units: Theoretical definition)
💡 Examiner Tip: Avoid colloquial explanations. Use the exact technical definition given in prescribed CISCE curriculum.
🎯 Generated Set: Generated Practice Set 2 - Method & Application (3 Marks)
ICSE Question Bank & Specimen Framework - Biology
3 Marks Total
Explain the procedural method or practical demonstration used to verify "Mechanism of Breathing". State the working apparatus/setup and key precautions.
Step-by-Step Marking Breakdown
Step 1: State the Formula / Conceptual Principle: State the fundamental principle governing Mechanism of Breathing.
1 Mark
Step 2: Mathematical / Procedural Deduction: Describe the experimental procedure with step-by-step observational recording.
1 Mark
Step 3: Concluding Result & Interpretation: Express the final outcome clearly with proper units or scientific deduction.
1 Mark
Final Answer: Verified procedural conclusion for Mechanism of Breathing
(Units: Procedural steps)
💡 Examiner Tip: In derivation and numerical questions, every intermediate mathematical step carries fractional credit.
🎯 Generated Set: Generated Practice Set 3 - Comparative Analysis (3 Marks)
ICSE Exemplar Practice Paper - Biology
3 Marks Total
Differentiate between "Mechanism of Breathing" and "Mechanism of Breathing" on the basis of: (i) Fundamental definition/mechanism, (ii) Key working condition or formula, (iii) Real-world practical example or application.
Step-by-Step Marking Breakdown
Point 1: Conceptual Difference: Contrast the primary mechanisms: Mechanism of Breathing focuses on Diaphragm contracts and flattens, whereas Mechanism of Breathing emphasizes Diaphragm contracts and flattens.
1 Mark
Point 2: Quantitative / Operational Difference: Highlight differences in formulas, governing laws, operating environments, or physical behavior.
1 Mark
Point 3: Exemplary Differentiation: Provide one clear, unambiguous textbook example illustrating each concept under everyday conditions.
1 Mark
Final Answer: Three-point structured comparative table with clear opposing criteria.
(Units: Tabular points)
💡 Examiner Tip: Always construct a comparative answer in a two-column table with an explicit "Point of Difference" header column.
🎯 Generated Set: Generated Practice Set 4 - Board Standard Structured (4 Marks)
ICSE Board Marking Blueprint - Class 9
4 Marks Total
A comprehensive ICSE examination question based on "The Respiratory System":
(i) State the fundamental law or rule governing "Mechanism of Breathing". [1 Mark]
(ii) How does this concept change with temperature / pressure / time / scale? [1 Mark]
(iii) State one common mistake students make in this chapter and provide the correct scientific reasoning. [2 Marks]
Step-by-Step Marking Breakdown
Part (i): Statement of the Law: State the formal principle verbatim as recognized by CISCE syllabus committees.
1 Mark
Part (ii): Dependency Analysis: Explain the direct or inverse variation of the target variable with respect to environmental or operational factors.
1 Mark
Part (iii): Error Analysis & Correct Resolution: Identify the frequent pitfall: Students often confuse Diaphragm contracts and flattens with related quantities. The correct understanding requires strict application of Mechanism of Breathing.
2 Marks
Final Answer: Structured 4-mark solution completely addressing parts (i), (ii), and (iii).
(Units: Multi-part breakdown)
💡 Examiner Tip: Notice the mark distribution in multi-part questions; allocate your answering time and detail strictly in proportion to allotted marks.
🎯 Generated Set: Generated Practice Set 5 - Higher Order Thinking (HOTS) (4 Marks)
ICSE High-Achiever Challenge Series - Class 9
4 Marks Total
A critical scenario-based problem in "The Respiratory System": An experiment is performed under non-ideal conditions involving "Mechanism of Breathing" and "Mechanism of Breathing".
(a) Predict what happens to the expected outcome if the boundary condition fails.
(b) Give complete scientific justification.
(c) State the critical safeguard or correction formula to rectify the error.
Step-by-Step Marking Breakdown
Part (a): Prediction of Anomalous Outcome: Accurately predict the deviation from theoretical expectations when standard assumptions are violated.
1 Mark
Part (b): Scientific Justification: Provide a rigorous scientific explanation using first principles and mandatory keywords: Diaphragm contracts and flattens, Ribs move upwards and outwards, Thoracic volume increases, Alveoli large surface area for diffusion.
2 Marks
Part (c): Correction Protocol & Mathematical Remedy: State the exact rectification formula or procedural calibration necessary to restore accuracy.
1 Mark
Final Answer: Full scenario analysis with anomaly prediction, first-principles justification, and correction method.
(Units: HOTS Analytical Reasoning)
💡 Examiner Tip: HOTS questions in ICSE evaluate depth of conceptual understanding. Avoid superficial guessing; reason backward from core laws.