Class 9 Science Exploration Chapter 13 MCQs – Earth as a System: Energy, Matter and Life – questions help you see how our planet works as one connected unit in Earth as a System. The chapter introduces the five spheres (geosphere, hydrosphere, cryosphere, atmosphere and biosphere) and explains how uneven heating by the Sun affects them. Key topics include the electromagnetic spectrum, insolation, the solar constant, albedo, layers of the atmosphere, local and planetary winds and ocean currents. It also covers the water, carbon, nitrogen and oxygen cycles and how human activity disturbs them.
Class 9 Science Exploration Chapter 13 MCQs with Answers
Class 9 Science Chapter 13 MCQs Set 1
Q1. Which of Earth’s spheres contains rocks, soil, landforms and the planet’s interior?
[A]. Biosphere
[B]. Geosphere
[C]. Atmosphere
[D]. Cryosphere
Q2. Which example belongs specifically to the cryosphere?
[A]. Living plankton
[B]. Liquid river water
[C]. A glacier
[D]. Air above a forest
Q3. Which example shows an interaction between Earth’s spheres?
[A]. A mountain exists without any surroundings
[B]. A rock has a fixed name
[C]. An organism has a scientific name
[D]. Less snowfall reduces summer water supply and plant growth
Q4. How does the Sun’s energy reach Earth through space?
[A]. By conduction through a continuous solid
[B]. Through electromagnetic radiation
[C]. Only through ocean currents
[D]. Only through sound waves
Q5. Which part of solar radiation mainly supplies energy for photosynthesis?
[A]. Visible light
[B]. X-rays
[C]. Radio waves
[D]. Gamma rays
Class 9 Science Chapter 13 MCQs Set 2
Q6. What does insolation mean?
[A]. Heat released only by Earth’s core
[B]. Solar radiation received at Earth’s surface
[C]. Only sunlight reflected by ice
[D]. Only heat emitted by animals
Q7. A surface of area 1 m² receives solar power at 1 kW/m² for one hour. How much energy does it receive? A
[A]. 3600 J
[B]. 1000 J
[C]. 3.6 × 10³ J
[D]. 3.6 × 10⁶ J
Q8. What is albedo?
[A]. The depth of groundwater
[B]. The mass of a surface
[C]. The fraction of incoming solar radiation reflected by a surface
[D]. The temperature of a surface
Q9. Which surface generally has a high albedo?
[A]. Dark asphalt
[B]. Black soil
[C]. Fresh snow
[D]. Dark ocean water
Q10. Why are equatorial regions generally warmer than polar regions?
[A]. Sunlight is more concentrated per unit area near the equator
[B]. The Sun produces heat only above the equator
[C]. Polar regions receive no sunlight at any time
[D]. The equator has no atmosphere
Class 9 Science Chapter 13 MCQs Set 3
Q11. What helps cause the urban heat island effect?
[A]. Cities contain no air
[B]. Cities have no gravity
[C]. Built surfaces absorb and retain heat, with less cooling vegetation
[D]. Concrete permanently destroys solar energy
Q12. In which atmospheric layer does most weather occur?
[A]. Exosphere
[B]. Thermosphere
[C]. Stratosphere
[D]. Troposphere
Q13. Why does temperature generally increase with height in the stratosphere?
[A]. Ozone absorbs ultraviolet radiation
[B]. All gases turn into ice
[C]. There is no radiation there
[D]. Ocean currents pass through it
Q14. What is the main protective role of the stratospheric ozone layer?
[A]. Blocking all visible sunlight
[B]. Preventing every cloud from forming
[C]. Producing all atmospheric nitrogen
[D]. Absorbing much of the Sun’s harmful ultraviolet radiation
Q15. How do greenhouse gases help warm Earth?
[A]. They eliminate the water cycle
[B]. They absorb some outgoing infrared radiation
[C]. They turn nitrogen into rocks
[D]. They stop all solar energy entering the atmosphere
Class 9 Science Chapter 13 MCQs Set 4
Q16. Because of a pressure difference, air tends to move in which direction?
[A]. Equal pressure to equal pressure only
[B]. Always from north to south
[C]. Low pressure to high pressure only
[D]. From higher pressure towards lower pressure
Q17. What is a daytime valley breeze?
[A]. Air moving from a valley up warmer mountain slopes
[B]. An ocean current flowing towards the equator
[C]. Air moving from the stratosphere to space
[D]. Cold air flowing downhill after sunset
Q18. What causes a mountain breeze at night?
[A]. Rapid heating of the mountain slopes
[B]. Cool, dense air flowing down slopes into the valley
[C]. Warm ocean water reaching the mountain
[D]. The disappearance of all air pressure
Q19. How does Earth’s rotation deflect large-scale winds in the Northern Hemisphere?
[A]. It never affects their paths
[B]. Towards the left of their motion
[C]. Towards the right of their motion
[D]. Only vertically upwards
Q20. How do ocean currents help regulate global climate?
[A]. They prevent all evaporation
[B]. They stop solar radiation at the ocean surface
[C]. They transport heat between regions
[D]. They eliminate the seasons
Class 9 Science Chapter 13 MCQs Set 5
Q21. At the same temperature, how does greater salinity generally affect seawater?
[A]. It always makes water less dense
[B]. It turns all water into vapour
[C]. It increases density and can favour sinking
[D]. It removes the effect of gravity
Q22. What is the main role of biogeochemical cycles?
[A]. To move nutrients only into space
[B]. To recycle matter between living and non-living components
[C]. To stop interactions between Earth’s spheres
[D]. To create new chemical elements continually
Q23. Which process allows surface water to enter soil and help recharge groundwater?
[A]. Photosynthesis
[B]. Denitrification
[C]. Combustion
[D]. Infiltration
Q24. Which process removes carbon dioxide from the atmosphere and incorporates its carbon into plant food?
[A]. Animal respiration
[B]. Photosynthesis
[C]. Decomposition
[D]. Combustion
Q25. Why does burning fossil fuels increase atmospheric carbon dioxide?
[A]. It stops every process of decomposition
[B]. It rapidly releases carbon stored over long periods
[C]. It permanently removes carbon from Earth
[D]. It converts all oxygen into nitrogen
Class 9 Science Chapter 13 MCQs Set 6
Q26. What is the role of Rhizobium in legume root nodules?
[A]. Fixing atmospheric nitrogen into usable nitrogen compounds
[B]. Producing sunlight
[C]. Removing every nutrient from soil
[D]. Converting all nitrate into oxygen
Q27. Which sequence represents nitrification?
[A]. Nitrate → nitrogen gas only
[B]. Carbon dioxide → glucose
[C]. Water → vapour → rain
[D]. Ammonia → nitrite → nitrate
Q28. Which process returns nitrogen gas to the atmosphere from nitrates?
[A]. Denitrification
[B]. Condensation
[C]. Photosynthesis
[D]. Assimilation
Q29. Which pair correctly identifies an atmospheric oxygen source and an oxygen-consuming process, respectively?
[A]. Photosynthesis and respiration
[B]. Combustion and photosynthesis
[C]. Respiration and photosynthesis
[D]. Denitrification and condensation
Q30. How can excessive fertiliser runoff harm fish in a lake?
[A]. By causing algal blooms followed by oxygen depletion
[B]. By preventing every algal cell from growing
[C]. By removing all nitrogen instantly
[D]. By increasing the lake’s albedo alone
Top 10 Concepts from Chapter 13 Earth as a System
- The Earth has five interacting spheres: geosphere (rocks and soil), hydrosphere (liquid water), cryosphere (ice and snow), atmosphere (air) and biosphere (living things). A change in one sphere affects the others.
- About 99% of the Sun’s energy reaching Earth arrives as UV, visible and infrared radiation. The ozone layer absorbs most UV, visible light powers photosynthesis and infrared warms the surface.
- Insolation is the solar radiation that reaches the Earth’s surface. The solar constant at the top of the atmosphere is about 1.4 kW m⁻², while clear-sky insolation at the surface is about 1 kW m⁻².
- Albedo is the fraction of sunlight a surface reflects. Snow (0.80–0.90) and ice have high albedo, while black soil and ocean water absorb more and stay warmer.
- Because the Earth is a sphere with a tilted axis, the equator receives concentrated sunlight and the poles receive spread-out sunlight. This uneven heating drives winds and ocean currents.
- Almost all weather happens in the troposphere (0–12 km), where temperature falls by about 6.5 °C per km. In the stratosphere (12–50 km), the ozone layer absorbs UV, so temperature rises with height.
- Valley breezes blow up the slopes during the day and mountain breezes blow down at night. Planetary winds move between pressure belts at the equator, 30°, 60° and the poles and the Earth’s rotation bends them.
- Ocean currents are driven by winds, differences in temperature and salinity, and the Earth’s rotation. They form gyres that turn clockwise in the Northern Hemisphere and the warm North Atlantic Drift keeps European ports ice-free in winter.
- Biogeochemical cycles recycle water, carbon, nitrogen and oxygen between living and non-living parts of the Earth. In the nitrogen cycle, Rhizobium fixes nitrogen, Nitrosomonas and Nitrobacter carry out nitrification and Pseudomonas carries out denitrification.
- Since 1960, atmospheric CO₂ has risen about 35%, from 315 ppm to 420 ppm, as shown by the Keeling curve. Excess fertiliser causes eutrophication and deforestation reduces rainfall and increases soil erosion.
Exam Hacks for Earth System and Biogeochemical Cycle MCQs
- Ozone in the stratosphere protects life, while ozone at ground level is a harmful pollutant.
- Greenhouse gases trap outgoing infrared heat. They do not absorb incoming sunlight directly.
- For energy numericals, use E = intensity × area × time, and convert hours to seconds.
- Learn the nitrogen cycle steps in order: fixation → nitrification → assimilation → ammonification → denitrification.
- Remember the direction of deflection: winds bend to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
As the final chapter of the Exploration textbook, Class 9 Science Exploration Chapter 13 brings together ideas from physics, chemistry, biology and geography. Practising these MCQs helps you connect familiar examples, such as the southwest monsoon, Himalayan mountain breezes, the urban heat island effect, Anna Mani’s solar radiation atlas and the Montreal Protocol, with the science behind them. Spend extra time on diagrams of the atmosphere’s layers, pressure belts and the carbon and nitrogen cycles, because many objective questions are based on them.
Get Step-by-Step Chapter 13 NCERT Solutions
To finish your preparation, read our NCERT Solutions for Class 9 Science Exploration Chapter 13. They answer every exercise question clearly, including how climate change affects the water cycle, how albedo controls surface temperature, how mountain and valley breezes form, how carbon returns to the air, and what would happen if the Earth were flat. Using the solutions with this quiz will build a strong understanding of “Earth as a System: Energy, Matter, and Life”.
