NCERT Class 11 Geography Fundamental of Physical Geography: Chapter 7 — Composition and Structure of Atmosphere
This chapter, "Composition and Structure of Atmosphere," from NCERT's Fundamental of Physical Geography for Class 11, emphasizes the critical role of the atmosphere for life on Earth. It details the atmosphere's composition, primarily gases like oxygen and carbon dioxide, and highlights the importance of carbon dioxide in the greenhouse effect and ozone in filtering UV radiation. The chapter also discusses water vapor as a variable gas, its role in regulating Earth's temperature, and its contribution to atmospheric stability. It explains that the proportion of gases changes with altitude, with oxygen becoming negligible at 120 km and carbon dioxide and water vapor diminishing significantly above 90 km. Understanding these components is crucial for comprehending weather, climate, and environmental changes, supporting CBSE learning objectives.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 11 |
| Subject | Geography |
| Book | Fundamental of Physical Geography |
| Chapter | Chapter 7 — Composition and Structure of Atmosphere |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 3 minutes |
| Word count | 591 |
Learning outcomes
- Identify the essential gases in the atmosphere and their functions.
- Explain the role of carbon dioxide and ozone in atmospheric processes.
- Understand the significance of water vapor as a variable atmospheric component.
- Describe how the composition of the atmosphere changes with altitude.
- Recognize the atmosphere's importance for life on Earth.
Vocabulary
| Word | Meaning |
|---|---|
| Atmosphere | A mixture of gases that surrounds the Earth. |
| Insolation | Incoming solar radiation. |
| Terrestrial Radiation | Radiation emitted by the Earth's surface. |
| Greenhouse Effect | The process by which atmospheric gases trap heat, warming the Earth. |
| Ozone | A gas that absorbs harmful ultraviolet (UV) radiation from the sun. |
| Water Vapour | Water in its gaseous state present in the atmosphere. |
| Altitude | The height of an object or point in relation to sea level or ground level. |
| Dust Particles | Tiny solid particles suspended in the atmosphere. |
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Practice questions
- Why is air essential for life on Earth? Answer: Air is essential because it contains life-giving gases like oxygen for animals and carbon dioxide for plants, and it is necessary for breathing.
- What is the significance of carbon dioxide in the atmosphere? Answer: Carbon dioxide is important because it absorbs terrestrial radiation, is largely responsible for the greenhouse effect, and its rising volume contributes to air temperature increase.
- How does ozone protect life on Earth? Answer: Ozone acts as a filter in the atmosphere, absorbing harmful ultraviolet (UV) rays from the sun and preventing them from reaching the Earth's surface.
- Describe the role of water vapour in regulating Earth's temperature. Answer: Water vapour absorbs insolation and preserves Earth's radiated heat, acting like a blanket to prevent extreme temperature fluctuations.
- How does the composition of the atmosphere change with altitude? Answer: The proportion of gases changes with altitude; oxygen becomes negligible at 120 km, and carbon dioxide and water vapour are found only up to 90 km from the Earth's surface.
Practice MCQs
Q1. What percentage of the atmosphere's mass is confined within 32 km from the Earth's surface?
Explanation: The text states that 99 per cent of the total mass of the atmosphere is confined to the height of 32 km from the Earth's surface.
Q2. Which gas is transparent to incoming solar radiation but opaque to outgoing terrestrial radiation?
Explanation: Carbon dioxide is described as meteorologically important because it is transparent to incoming solar radiation but opaque to outgoing terrestrial radiation.
Q3. Ozone is found in the atmosphere between which altitudes?
Explanation: The chapter mentions that ozone is an important component found between 10 and 50 km above the Earth's surface.
Q4. In warm and wet tropics, what percentage of air by volume can water vapour account for?
Explanation: The text states that in warm and wet tropics, water vapour may account for four per cent of the air by volume.
Q5. At what height above the Earth's surface does oxygen become almost negligible?
Explanation: The chapter notes that oxygen will be almost in negligible quantity at the height of 120 km from the surface of the Earth.
Frequently asked questions
What is the atmosphere?
The atmosphere is a mixture of different gases that envelops the Earth, containing essential elements for life.
Why is oxygen important in the atmosphere?
Oxygen is a life-giving gas essential for the survival of humans and animals.
What is the primary role of carbon dioxide in the atmosphere?
Carbon dioxide is crucial for the greenhouse effect, absorbing terrestrial radiation and helping to regulate Earth's temperature.
How does ozone benefit life on Earth?
Ozone acts as a protective layer by absorbing harmful ultraviolet (UV) rays from the sun, preventing them from reaching the Earth's surface.
Is the amount of water vapour constant in the atmosphere?
No, water vapour is a variable gas; its concentration decreases with altitude and varies between different climatic regions.
How does the atmosphere's composition change as you go higher?
As altitude increases, the concentration of certain gases changes significantly. Oxygen becomes negligible at about 120 km, and carbon dioxide and water vapour are found only up to about 90 km.
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NCERT Class 11 Geography — Fundamental of Physical Geography — Chapter 7 — Composition and Structure of Atmosphere. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.