Class 9 · ScienceNCERT 2026 Revised Syllabus
Chapter 13: Earth as a System: Energy, Matter, and Life (0906CH13)
Exploration · Biogeochemical cycles, greenhouse effect, climate change, ecosystems.
Chapter code: 0906ch13 · Book: Exploration · Class 9 Science
Find complete NCERT solutions for Class 9 Science, Exploration Chapter 13. Every question has a clear, step-by-step answer for chapter code 0906CH13.
Pause and Ponder(6 questions)
1
Visit the website https://phet.colorado.edu/en/simulations/greenhouse-effect and study the effect of the concentration of greenhouse gas on surface temperature.
School Level Solution
Ans.
In the simulation, increasing greenhouse-gas concentration increases the amount of outgoing infrared energy absorbed and re-emitted by the atmosphere, so the surface temperature rises. Record the values/observations from the simulation.
2
How does the cool mountain breeze benefit agriculture activity, particularly the crops and soil?
School Level Solution
Ans.
Cooler air over agricultural areas can moderate temperature, reduce heat stress on crops and can reduce excessive evaporation and moisture loss from soil. The exact effect depends on local terrain, humidity and timing.
3
What happens to the warm surface of water from the equator as it travels toward the poles? What impact does this movement have on the area?
School Level Solution
Ans.
Warm equatorial water is carried poleward by ocean currents. This transports heat energy from low to high latitudes, influencing coastal temperatures, weather and climate in the regions along the current.
4
The CO₂ dissolved in the ocean is disturbed when the global temperature increases. What will happen to marine life?
School Level Solution
Ans.
Global warming can reduce the ocean’s capacity to absorb CO₂, while increased dissolved CO₂ contributes to ocean acidification. Changes in acidity and temperature can stress plankton, corals and shell-forming organisms and disrupt food webs and marine ecosystems.
5
What would happen to plants and animals on Earth if the biogeochemical cycles were disrupted and stopped? Explain by giving a few examples.
School Level Solution
Ans.
Without the water, carbon, nitrogen and oxygen cycles, organisms would lose reliable supplies of essential matter. For example, disruption of the nitrogen cycle would reduce plant growth; disruption of the carbon/oxygen cycle would affect photosynthesis and respiration; a halted water cycle would disrupt freshwater availability and ecosystems.
6
Discuss how human activities increase the concentration of greenhouse gases in the atmosphere. What would you do as an individual to reduce the emission of greenhouse gas?
School Level Solution
Ans.
Major sources include burning fossil fuels, deforestation, industrial processes and agriculture. Individual actions include saving electricity, using efficient appliances, choosing walking/cycling/public transport where practical, reducing waste, reusing/recycling materials and supporting lower-carbon energy choices.
Activities — How to Do(1 questions)
1
Activity 13.2 (albedo table): complete Table 13.1 from authentic sources — Snow 0.80–0.90, Ice 0.50–0.70, Crushed rock 0.25–0.30 are given. What typical values go against Light coloured soil, Black soil and Ocean water, and what does albedo mean?
School Level Solution
Ans.
Albedo = reflected ÷ incoming solar radiation (0–1). Typical entries: Light coloured soil ≈ 0.30–0.40 (reflects well), Black soil ≈ 0.05–0.15 (absorbs most), Ocean water ≈ 0.06–0.10 (absorbs most, slight angle dependence). Confirm exact figures from IMD/NCERT sources and note why snow cools while oceans warm.