Chapter-13 Earth — Online MCQ Test
SCIENCE (CURIOSITY) · CLASS 8th · Karnataka State Board
Practice Chapter-13 Earth with a free chapter-wise online MCQ test.
This chapter covers: a Unique Life Sustaining Planet.
AI-generated questions from basic to board-exam level, with instant results and explanations.
Chapter-13 Earth — Important Questions & Answers
Which of the following is the primary reason Earth is called a unique life-sustaining planet?
- A. It has the largest size among all planets
- B. It has liquid water, suitable temperature, and atmosphere
- C. It is closest to the Sun
- D. It has the most number of moons
Answer: B. It has liquid water, suitable temperature, and atmosphere
Earth sustains life due to the presence of liquid water, moderate temperatures within the biosphere, and a protective atmosphere containing oxygen and nitrogen.
Earth sustains life due to the presence of liquid water, moderate temperatures within the biosphere, and a protective atmosphere containing oxygen and nitrogen.
What percentage of Earth's surface is covered by water?
- A. About 50%
- B. About 71%
- C. About 85%
- D. About 95%
Answer: B. About 71%
Approximately 71% of Earth's surface is covered by water, making it the 'Blue Planet'. The remaining 29% consists of land.
Approximately 71% of Earth's surface is covered by water, making it the 'Blue Planet'. The remaining 29% consists of land.
Which layer of the atmosphere is closest to Earth's surface?
- A. Stratosphere
- B. Mesosphere
- C. Troposphere
- D. Thermosphere
Answer: C. Troposphere
The troposphere is the innermost layer of the atmosphere, closest to Earth's surface, where weather phenomena occur and most living organisms exist.
The troposphere is the innermost layer of the atmosphere, closest to Earth's surface, where weather phenomena occur and most living organisms exist.
What is the name of the hard outer layer of the Earth?
- A. Core
- B. Mantle
- C. Crust
- D. Lithosphere
Answer: C. Crust
The crust is the hard, thin outer layer of the Earth on which we live. It is divided into continental and oceanic crust.
The crust is the hard, thin outer layer of the Earth on which we live. It is divided into continental and oceanic crust.
Why is Earth's atmosphere important for sustaining life?
- A. It only provides oxygen for respiration
- B. It protects from harmful radiations, maintains temperature, and provides gases for respiration
- C. It only creates weather
- D. It only reflects sunlight
Answer: B. It protects from harmful radiations, maintains temperature, and provides gases for respiration
Earth's atmosphere serves multiple functions: it provides oxygen for respiration, protects from UV and cosmic radiation, maintains suitable temperature through greenhouse effect, and supports the water cycle.
Earth's atmosphere serves multiple functions: it provides oxygen for respiration, protects from UV and cosmic radiation, maintains suitable temperature through greenhouse effect, and supports the water cycle.
How does the presence of liquid water on Earth contribute to life?
- A. It only provides drinking water
- B. It dissolves nutrients, acts as a solvent for chemical reactions, regulates climate, and supports diverse ecosystems
- C. It only covers the surface
- D. It only creates currents
Answer: B. It dissolves nutrients, acts as a solvent for chemical reactions, regulates climate, and supports diverse ecosystems
Liquid water is essential for life as it dissolves essential nutrients, serves as a medium for biochemical reactions, regulates Earth's climate, and hosts diverse aquatic ecosystems.
Liquid water is essential for life as it dissolves essential nutrients, serves as a medium for biochemical reactions, regulates Earth's climate, and hosts diverse aquatic ecosystems.
Analyze: Why is biodiversity important for Earth's life-sustaining capacity?
- A. Biodiversity is only for aesthetic purposes
- B. Different species perform different ecological functions, maintain ecosystem balance, and ensure survival through genetic variation
- C. Biodiversity makes the planet heavier
- D. Biodiversity is harmful to life
Answer: B. Different species perform different ecological functions, maintain ecosystem balance, and ensure survival through genetic variation
Biodiversity ensures ecosystem stability by distributing ecological roles among species, providing resilience to environmental changes, and maintaining genetic resources for adaptation.
Biodiversity ensures ecosystem stability by distributing ecological roles among species, providing resilience to environmental changes, and maintaining genetic resources for adaptation.
How would a significant decrease in atmospheric oxygen affect Earth's ecosystems?
- A. It would have no effect on life
- B. Plants would thrive more
- C. Aerobic organisms would struggle; food chains would collapse; photosynthesis would decrease
- D. Anaerobic bacteria would increase and support all life
Answer: C. Aerobic organisms would struggle; food chains would collapse; photosynthesis would decrease
A decrease in atmospheric oxygen would cause aerobic organisms (including most animals) to suffer, disrupt food chains, and reduce plant photosynthetic rates, causing ecosystem collapse.
A decrease in atmospheric oxygen would cause aerobic organisms (including most animals) to suffer, disrupt food chains, and reduce plant photosynthetic rates, causing ecosystem collapse.
TRICKY: Which of these statements about Earth's uniqueness is MOST accurate?
- A. Earth is the only planet with an atmosphere
- B. Earth is the only planet with surface water due to its unique position, temperature, and atmospheric composition
- C. Earth is the hottest planet
- D. Earth has the thickest atmosphere
Answer: B. Earth is the only planet with surface water due to its unique position, temperature, and atmospheric composition
While other planets have thin atmospheres and some water (frozen or subsurface), Earth is uniquely positioned in the habitable zone with conditions allowing abundant liquid surface water.
While other planets have thin atmospheres and some water (frozen or subsurface), Earth is uniquely positioned in the habitable zone with conditions allowing abundant liquid surface water.
COMPETITIVE: A student argues that if we found a planet with 50% more oxygen, life would be 50% more abundant. What is the flaw in this reasoning?
- A. Oxygen is not important for life
- B. More oxygen doesn't automatically increase abundance; it could cause oxidative stress, fire hazards, and metabolic imbalances
- C. Extra oxygen would only affect plants
- D. This reasoning is completely correct
Answer: B. More oxygen doesn't automatically increase abundance; it could cause oxidative stress, fire hazards, and metabolic imbalances
Excess oxygen, while essential at moderate levels, can increase oxidative stress, spontaneous combustion risk, and cellular damage. Biological systems evolved for Earth's ~21% oxygen; excess would be detrimental.
Excess oxygen, while essential at moderate levels, can increase oxidative stress, spontaneous combustion risk, and cellular damage. Biological systems evolved for Earth's ~21% oxygen; excess would be detrimental.