CBSE Class 8 Science Chapter 13 Our Home Earth, A Unique Life Sustaining Planet MCQs Set 02

Practice MCQs for Class 8 Science Chapter 13 Our Home Earth, A Unique Life Sustaining Planet

Explore reliable objective questions for Chapter 13 Our Home Earth, A Unique Life Sustaining Planet tailored for Class 8 learners. Utilizing these Science multiple-choice formats ensures thorough preparation and strengthens problem-solving speed for upcoming school assessments.

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Question: When scientists refer to Earth as the 'Blue Planet,' which feature of the planet is primarily responsible for this appearance when viewed from space?
A. The thick layer of ice covering most landmasses
B. The vast amount of water covering Earth's surface
C. The dense atmosphere reflecting blue light
D. The blue minerals found in Earth's crust
Show Answer & Explanation

Answer: (B) The vast amount of water covering Earth's surface

Explanation:
The chapter explicitly states that most of Earth's surface is covered with water, and when seen from space, the Earth looks blue because of this vast amount of water.

Question: Which of the following best explains why Venus, despite being the second planet from the Sun, has a higher average temperature than Mercury, which is closer to the Sun?
A. Venus is larger and retains heat better
B. Venus has a thick atmosphere made mainly of carbon dioxide that traps heat
C. Mercury's orbit is closer to the asteroid belt
D. Venus rotates faster, generating internal heat
Show Answer & Explanation

Answer: (B) Venus has a thick atmosphere made mainly of carbon dioxide that traps heat

Explanation:
The chapter explains that Venus is hottest because its thick atmosphere, almost entirely made of carbon dioxide, traps heat through the greenhouse effect—not because of its distance from the Sun.

Question: If a planet orbits within the habitable zone of its star, what does this zone represent in terms of conditions for life?
A. The region where the planet's gravity is strongest
B. The distance range where water can exist in liquid form
C. The area protected by the planet's magnetic field
D. The zone where stellar radiation is most intense
Show Answer & Explanation

Answer: (B) The distance range where water can exist in liquid form

Explanation:
The habitable zone, also called the Goldilocks zone, is the range of distances from the Sun where temperature conditions allow water to remain in liquid form—essential for life as we know it.

Question: The chapter mentions that bacteria and certain microbes have evolved resistance to antibiotics over time. Which type of reproductive process makes such evolutionary changes and adaptations possible?
A. Asexual reproduction through cell division
B. Sexual reproduction combining genetic material from two parents
C. Vegetative propagation of plant tissues
D. Budding and fragmentation alone
Show Answer & Explanation

Answer: (B) Sexual reproduction combining genetic material from two parents

Explanation:
• Sexual reproduction allows mixing of genetic instructions from two parents
• This creates variation in offspring that can include beneficial traits
• Over generations, useful traits like antibiotic resistance can become more common
• Asexual reproduction produces exact copies, limiting adaptation potential

Question: When a male and female gamete join together during fertilisation to form a zygote, why does the offspring not end up with double the genetic instructions of a single parent?
A. Gametes contain complete genetic material, and extras are discarded after birth
B. Each parent's gamete carries only half the parent's genetic material
C. The developing embryo destroys half of the inherited instructions
D. Environmental factors eliminate excess genetic information
Show Answer & Explanation

Answer: (B) Each parent's gamete carries only half the parent's genetic material

Explanation:
The chapter explains that each parent makes specialised reproductive cells called gametes, which carry only half of the parent's genetic material. When male and female gametes join, they create a complete set with half from each parent.

Question: In flowering plants, which structure inside the flower produces the male gametes that will eventually be carried to another flower?
A. The ovule
B. The anther
C. The stem
D. The sepal
Show Answer & Explanation

Answer: (B) The anther

Explanation:
Pollen grains, which are the male gametes, are found inside the anther of a flower. These pollen grains are then carried to another flower by wind, insects, or animals during pollination.

Question: Which of the following correctly describes what geodiversity refers to in the context of this chapter?
A. The variety of different animal species living in an ecosystem
B. The range of different landforms, rocks, soils, and the processes that shape them
C. The diversity of weather patterns across different seasons
D. The variety of plants found in different geographical regions
Show Answer & Explanation

Answer: (B) The range of different landforms, rocks, soils, and the processes that shape them

Explanation:
Geodiversity is the variety of landforms, rocks, soils, and related processes. The chapter notes this variety helps create unique habitats where different types of life can thrive.

Question: According to the chapter, Earth's magnetic field is generated by movement of which material in the planet's interior?
A. Solid iron in the inner core
B. Molten iron in Earth's core
C. Silicate rocks in the mantle
D. Frozen water at the poles
Show Answer & Explanation

Answer: (B) Molten iron in Earth's core

Explanation:
The chapter states it is believed that the movement of molten iron in Earth's core may be the origin for Earth's magnetic field.

Question: What is the primary mechanism by which Earth's magnetic field protects life on the planet?
A. It reflects harmful ultraviolet rays back to space
B. It pushes many harmful particles from space away from Earth
C. It creates an insulating layer that traps heat
D. It neutralises chemical pollutants in the atmosphere
Show Answer & Explanation

Answer: (B) It pushes many harmful particles from space away from Earth

Explanation:
The chapter explains that Earth's magnetic field acts like a protective shield, pushing many harmful high-energy particles (from cosmic rays and solar wind) away from Earth, keeping the atmosphere and life safe.

Question: In birds, how does the development of a fertilised egg differ from the development in most mammals like humans and cows?
A. Birds develop the embryo before laying the egg, mammals develop it after
B. In birds, the embryo develops outside the body after the egg is laid; in mammals, it develops inside the mother's body
C. Birds do not produce fertilised eggs, only mammals do
D. Mammals lay eggs that hatch immediately, birds keep them inside
Show Answer & Explanation

Answer: (B) In birds, the embryo develops outside the body after the egg is laid; in mammals, it develops inside the mother's body

Explanation:
The chapter describes that in birds, the fertilised egg is laid by the female and the embryo develops after the egg is laid. In contrast, in most mammals, the embryo develops inside the mother's body, which provides food and oxygen until birth.

Question: Why can organisms like planaria flatworms regenerate from just a small fragment of their body, and what does this demonstrate about their reproduction?
A. They have superior healing abilities compared to other animals
B. They reproduce asexually and can produce new individuals from body fragments
C. They have evolved from organisms that required minimal genetic material
D. Their blood cells contain complete copies of all genetic information
Show Answer & Explanation

Answer: (B) They reproduce asexually and can produce new individuals from body fragments

Explanation:
Planaria can regrow from a fragment of its body, which is an example of asexual reproduction. This demonstrates that certain organisms can produce complete new individuals without requiring genetic material from a second parent.

Question: If soil nutrients like nitrogen and potassium are depleted from an area, according to the chapter, how would this most directly affect the ecosystem?
A. Animals would migrate to find better hunting grounds
B. Plant growth would be severely limited, affecting herbivores and their predators
C. The atmosphere would become thinner
D. Water sources would become contaminated
Show Answer & Explanation

Answer: (B) Plant growth would be severely limited, affecting herbivores and their predators

Explanation:
The chapter explains that soil is rich in nutrients like nitrogen and potassium that plants need to grow. If these nutrients are depleted, plant growth would be affected, which would then impact herbivores that feed on plants and the predators that feed on herbivores.

Question: The Montreal Protocol and the Paris Agreement are mentioned as examples of international efforts. What environmental problem does the Montreal Protocol specifically address?
A. Global warming and greenhouse gas emissions
B. Reduction of harmful chemicals like CFCs that damage the ozone layer
C. Deforestation and habitat loss
D. Ocean acidification and marine pollution
Show Answer & Explanation

Answer: (B) Reduction of harmful chemicals like CFCs that damage the ozone layer

Explanation:
The chapter states that the Montreal Protocol (1987) helped reduce harmful chemicals like Chlorofluorocarbons (CFCs), allowing the ozone layer to slowly recover.

Question: Why does the chapter describe Earth's atmosphere as 'essential for life' rather than merely 'helpful'?
A. It is the only source of carbon dioxide for plants
B. It provides oxygen for respiration, contains the ozone layer for UV protection, and traps heat through the greenhouse effect
C. It prevents animals from flying too high into space
D. It is the only place where water can be found
Show Answer & Explanation

Answer: (B) It provides oxygen for respiration, contains the ozone layer for UV protection, and traps heat through the greenhouse effect

Explanation:
• Atmosphere provides oxygen needed for respiration by most life forms
• Ozone layer blocks harmful UV rays that damage living cells
• Greenhouse effect keeps Earth warm enough for water to remain liquid
• All three functions are essential, not optional, for life to thrive

Question: When the chapter describes how small changes in global temperature, oxygen levels, or the ozone layer 'can put life at risk,' which concept does this illustrate?
A. Life on Earth depends on complete isolation from environmental changes
B. Life on Earth requires a delicate balance of interconnected natural systems
C. Only extreme temperature changes affect life on Earth
D. Animals can easily adapt to any environmental change
Show Answer & Explanation

Answer: (B) Life on Earth requires a delicate balance of interconnected natural systems

Explanation:
The chapter emphasises that life on Earth depends on a delicate balance of living and non-living things working together. Small changes to any critical component—temperature, oxygen, or the ozone layer—can disrupt this balance and threaten life, showing how interconnected these systems are.

Question: Why is Earth's position in the solar system considered the most crucial factor for supporting life?
A. It receives more sunlight than any other planet in the system
B. It orbits at a distance where temperature permits water to remain liquid
C. It has the strongest magnetic field among all planets
D. It is the largest planet capable of holding an atmosphere
Show Answer & Explanation

Answer: (B) It orbits at a distance where temperature permits water to remain liquid

Explanation:
The chapter explicitly states that Earth's distance from the Sun is the most important reason it can support life, as this positioning allows water to exist in liquid form—essential for life to evolve and persist.

Question: How does the greenhouse effect on Earth differ fundamentally from how a plant greenhouse traps heat?
A. Plant greenhouses use carbon dioxide while Earth's atmosphere uses nitrogen
B. Atmospheric greenhouse gases absorb radiation, whereas plant greenhouses trap warm air in an enclosed space
C. Earth's greenhouse effect makes the planet colder than plant greenhouses
D. They operate identically through the same physical principle
Show Answer & Explanation

Answer: (B) Atmospheric greenhouse gases absorb radiation, whereas plant greenhouses trap warm air in an enclosed space

Explanation:
• Gases like carbon dioxide in Earth's atmosphere absorb radiation given off after the planet warms
• Plant greenhouses simply trap warmed air because they are enclosed spaces with glass walls
• Both keep things warm but use different mechanisms

Question: If Earth's gravity were significantly weaker due to a smaller planet size, what would most likely escape into space?
A. All the water in the oceans would evaporate
B. The gases comprising the atmosphere would dissipate
C. The planet's magnetic field would reverse direction
D. All rocks and soil would float upward into space
Show Answer & Explanation

Answer: (B) The gases comprising the atmosphere would dissipate

Explanation:
With weaker gravity, the planet would be unable to hold onto atmospheric gases, and they would escape. The chapter notes that Mars has an atmosphere 100 times thinner than Earth's, and Mercury has no atmosphere at all, illustrating how insufficient gravity causes gas loss.

Question: What distinguishes sexual reproduction from asexual reproduction in terms of genetic variation?
A. Sexual reproduction produces offspring that are identical copies while asexual introduces variation
B. Asexual reproduction combines instructions from two parents
C. Sexual reproduction mixes genetic material from both parents, creating uniqueness while asexual produces exact copies
D. Neither type produces any genetic variation in offspring
Show Answer & Explanation

Answer: (C) Sexual reproduction mixes genetic material from both parents, creating uniqueness while asexual produces exact copies

Explanation:
In sexual reproduction, gametes from both parents contribute different genetic instructions, creating offspring that are unique blends. Asexual reproduction, by contrast, yields individuals that are exact genetic copies of the single parent.

Question: Why do some plants reproduce through vegetative propagation when seeds and flowers also exist?
A. Vegetative propagation is faster and produces genetically identical plants suited to their environment
B. Seeds are too expensive to produce for most plants
C. Vegetative propagation requires more energy than seed production
D. Only tropical plants can reproduce through vegetative propagation
Show Answer & Explanation

Answer: (A) Vegetative propagation is faster and produces genetically identical plants suited to their environment

Explanation:
Vegetative propagation—growing new plants from stems, leaves, or roots—is an efficient asexual method that quickly produces clones of the parent plant, each adapted to the same local conditions, without needing pollination or seed germination.

Question: According to the chapter, which environmental problem has been specifically addressed by the Montreal Protocol?
A. Greenhouse gas emissions causing global warming
B. Reduction of harmful chemicals damaging the ozone layer
C. Pollution in rivers and groundwater systems
D. Loss of biodiversity in tropical rainforests
Show Answer & Explanation

Answer: (B) Reduction of harmful chemicals damaging the ozone layer

Explanation:
The Montreal Protocol (1987) helped reduce CFCs and other harmful chemicals, allowing the ozone layer to slowly recover. This was one of the first major global agreements to address a specific environmental threat.

Question: How do fish and frog reproduction strategies in water differ from the strategies used by birds and mammals?
A. Fish and frogs lay eggs on land while birds and mammals use water for reproduction
B. Fish and frogs undergo fertilisation in water where eggs and sperm combine, with embryo development also in water; birds and mammals have internal fertilisation with different developmental pathways
C. All four groups use identical reproductive processes regardless of environment
D. Fish and frogs develop embryos internally like mammals while birds lay eggs externally
Show Answer & Explanation

Answer: (B) Fish and frogs undergo fertilisation in water where eggs and sperm combine, with embryo development also in water; birds and mammals have internal fertilisation with different developmental pathways

Explanation:
Fish and frogs eject gametes into water where fertilisation occurs and the embryo develops in an aquatic environment. Birds lay fertilised eggs where embryos develop after laying. Mammals undergo internal fertilisation and development inside the female's body before birth.

Question: What does the chapter suggest is the primary cause of today's rapid climate change compared to natural climate variations of the past?
A. Changes in Earth's distance from the Sun
B. Human burning of fossil fuels releasing extra carbon locked underground for millions of years
C. Increased volcanic activity on the planet
D. Natural variations in solar radiation
Show Answer & Explanation

Answer: (B) Human burning of fossil fuels releasing extra carbon locked underground for millions of years

Explanation:
The chapter explains that burning fossil fuels releases carbon dioxide and methane trapped for millions of years, adding greenhouse gases faster than Earth can absorb them, causing heat to accumulate—a distinct change driven by human activity rather than natural processes alone.

Question: Why are gametes—not complete cells with full genetic material—produced during sexual reproduction?
A. Because full cells would be too large to combine
B. Because gametes carry only half the genetic material, so when they join, the offspring receives a complete set from both parents without doubling
C. Because it takes less energy to produce gametes than complete cells
D. Because organisms with full genetic material cannot survive in nature
Show Answer & Explanation

Answer: (B) Because gametes carry only half the genetic material, so when they join, the offspring receives a complete set from both parents without doubling

Explanation:
Each parent makes specialised gametes carrying half their genetic instructions. When male and female gametes join, they form a new cell with a complete set—half from each parent—preventing endless doubling of genetic material across generations.

Question: Which factor most directly explains why the biosphere (all living things) depends on the geosphere (rocks, soil, minerals)?
A. Living organisms do not actually depend on non-living rocks and minerals
B. Soil provides essential nutrients like nitrogen and potassium from rock breakdown and decomposed organisms
C. Rocks generate heat that keeps organisms warm
D. The geosphere produces oxygen for respiration
Show Answer & Explanation

Answer: (B) Soil provides essential nutrients like nitrogen and potassium from rock breakdown and decomposed organisms

Explanation:
Soil nutrients arise from slow weathering of rocks and decomposition of dead matter. Plants require these nutrients to grow, and animals depend on plants, making the cycle of rock breakdown and nutrient cycling foundational to all life.

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Multiple Choice Questions (MCQs) for Class 8 Science Chapter 13 Our Home Earth, A Unique Life Sustaining Planet

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