NCERT Solutions for Class 9 Science Chapter 14 Natural Resources
NCERT Solutions for Class 9 Science Chapter 14, "Natural Resources," explains the role of the atmosphere, water, and soil in sustaining life on Earth. It also covers the major biogeochemical cycles and the impact of human activities on environmental pollution.
Overview of Topics & Subtopics (Click to Jump)
1. The Breath of Life: Air & Air Pollution
Short Note:
• Atmosphere: The blanket of air that covers the whole Earth. It acts as a bad conductor of heat, keeping the average temperature of the Earth fairly steady during the day and preventing sudden cooling at night.
• Winds and Rain: Winds are caused by the uneven heating of the atmosphere by the sun. Rain is formed when water bodies heat up, causing water to evaporate, rise, cool, and condense into water droplets.
• Air Pollution: An increase in the content of harmful substances (like unburnt carbon particles, oxides of nitrogen and sulfur) in the air. This leads to respiratory issues, smog during winters, and acid rain.
2. Water: A Wonder Liquid & Water Pollution
Short Note:
• Importance of Water: Covers about 75% of the Earth's surface. All cellular processes take place in a water medium. It dictates the availability of plants and animals in a specific region and regulates body temperature.
• Water Pollution: The addition of undesirable substances to water bodies (like fertilizers, pesticides, industrial effluents) or the removal of desirable substances (like dissolved oxygen). A sudden change in water temperature also constitutes thermal pollution, which is highly dangerous to aquatic life.
3. Mineral Riches in the Soil & Soil Erosion
Short Note:
• Soil Formation: Formed over millions of years by the breakdown of rocks at or near the surface of the Earth by various physical, chemical, and biological processes (sun, water, wind, and living organisms like lichens and mosses).
• Soil Composition: Contains rock particles, humus (decayed living organisms), and various microscopic life forms. Humus largely decides the soil structure as it makes it porous.
• Soil Erosion: The removal of the nutrient-rich topsoil by strong winds or flowing water. It is prevented by vegetative cover, afforestation, contour ploughing, and step farming.
4. Biogeochemical Cycles & The Ozone Layer
Short Note:
• Biogeochemical Cycles: The constant interaction between the biotic (living) and abiotic (non-living) components of the biosphere makes it a dynamic but stable system. Examples include:
- Water Cycle: Evaporation, transpiration, condensation, and precipitation.
- Nitrogen Cycle: Nitrogen fixation by bacteria (like Rhizobium), ammonification, nitrification, and denitrification.
- Carbon Cycle: Cycled through photosynthesis by plants and respiration by animals, as well as combustion of fossil fuels.
• Greenhouse Effect: Some gases (like CO₂) prevent the escape of heat from the Earth, increasing the global average temperature.
• Ozone Layer: A layer of O₃ molecules in the stratosphere that absorbs harmful ultraviolet (UV) radiation from the Sun. It is being depleted by man-made chemicals like CFCs (Chlorofluorocarbons).
Intext Questions & Textbook Exercise Answers
Earth's atmosphere contains a life-supporting mixture of gases, primarily nitrogen (78%) and oxygen (21%), along with a small fraction of carbon dioxide and water vapor.
In contrast, the atmospheres on Venus and Mars consist mostly of carbon dioxide (about 95% to 97%) and lack oxygen entirely, making it impossible to support the kind of life found on Earth.
1. Afforestation: Planting more trees and maintaining vegetative cover so roots bind the soil firmly.
2. Contour Ploughing: Ploughing along the contours of the land in hilly areas to prevent water from washing down the topsoil.
3. Terrace Farming: Creating step-like flat areas on slopes to slow down the flow of rainwater.
4. Preventing Overgrazing: Managing cattle grazing to ensure grass and small plants are not entirely uprooted, leaving the soil exposed.
• It acts as a protective blanket, maintaining the average temperature of Earth and preventing extreme temperature changes between day and night.
• It contains life-sustaining gases like Oxygen (for respiration) and Carbon Dioxide (for photosynthesis).
• The ozone layer within the atmosphere absorbs harmful ultraviolet (UV) rays from the sun, protecting living organisms from radiation damage.
Read More & Chapter Resources
These short notes are designed for quick revision. Read the main points once, then use the related material below to practise the same chapter. Revising a concept and checking it with questions can make your preparation more focused.