CBSE Class 8 Science Chapter 13 Our Home Earth, A Unique Life Sustaining Planet MCQs Set 01

Science Objective Questions and Answers: Chapter 13 Our Home Earth, A Unique Life Sustaining Planet

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Download Chapter 13 Our Home Earth, A Unique Life Sustaining Planet MCQs with Answers

Access the complete set of multiple-choice questions for Chapter 13 Our Home Earth, A Unique Life Sustaining Planet below. This focused format allows students to isolate specific topics for thorough review and uninterrupted practice alongside official CBSE textbooks.

Question: Which layer of Earth is described as being as thin as an apple's skin when Earth is compared to the size of an apple?
A. The upper mantle
B. The outer core
C. The crust
D. The inner core
Show Answer & Explanation

Answer: (C) The crust

Explanation:
The chapter explicitly states that if Earth were the size of an apple, the crust—where all life exists—would be as thin as the apple's skin, making it a delicate and life-supporting layer.

Question: Why is Venus hotter than Mercury, despite Mercury being closer to the Sun?
A. Mercury has no magnetic field to trap heat
B. Venus has a thick atmosphere that traps heat through the greenhouse effect
C. Venus rotates faster than Mercury
D. Mercury is too small to retain heat
Show Answer & Explanation

Answer: (B) Venus has a thick atmosphere that traps heat through the greenhouse effect

Explanation:
Venus's thick atmosphere, composed almost entirely of carbon dioxide, traps heat through the greenhouse effect, making it hotter than Mercury even though Mercury is closer to the Sun.

Question: What is the term used to describe the range of distances from the Sun where liquid water can exist on a planet?
A. The thermal zone
B. The habitable zone
C. The atmospheric zone
D. The radiation zone
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Answer: (B) The habitable zone

Explanation:
The chapter introduces this concept as the 'habitable zone' or 'Goldilocks zone'—the range of distances where conditions allow water to remain in liquid form, essential for life.

Question: If Earth were much smaller but maintained the same average density, which consequence would most likely occur?
A. The atmosphere would become denser and trap more heat
B. Gravity would weaken, allowing atmospheric gases to escape into space
C. The planet would move closer to the Sun
D. Rainfall would increase significantly
Show Answer & Explanation

Answer: (B) Gravity would weaken, allowing atmospheric gases to escape into space

Explanation:
• Smaller Earth = weaker gravity
• Weaker gravity cannot hold atmospheric gases
• Gases would escape into space
• Mars demonstrates this: its atmosphere is 100 times thinner than Earth's due to its smaller size and weaker gravity.

Question: What role does the ozone layer play in protecting life on Earth?
A. It prevents water evaporation from the oceans
B. It blocks harmful ultraviolet rays from the Sun
C. It regulates atmospheric pressure
D. It produces oxygen for respiration
Show Answer & Explanation

Answer: (B) It blocks harmful ultraviolet rays from the Sun

Explanation:
Ozone, formed from oxygen in the atmosphere, acts as a shield blocking harmful UV rays that can damage living cells.

Question: In the context of reproduction, what is the key difference between asexual and sexual reproduction?
A. Asexual reproduction is faster; sexual reproduction is slower
B. Asexual reproduction produces identical offspring; sexual reproduction produces offspring with variation
C. Asexual reproduction requires two parents; sexual reproduction requires one
D. Asexual reproduction occurs only in plants; sexual reproduction occurs only in animals
Show Answer & Explanation

Answer: (B) Asexual reproduction produces identical offspring; sexual reproduction produces offspring with variation

Explanation:
Asexual reproduction yields exact copies of the parent, while sexual reproduction combines genetic material from two parents, creating offspring that share traits from both but are not identical to either.

Question: Why do gametes carry only half the genetic material of the parent rather than the full set?
A. To conserve energy during reproduction
B. To prevent offspring from having twice the genetic instructions
C. To ensure diversity in offspring
D. To speed up the reproduction process
Show Answer & Explanation

Answer: (B) To prevent offspring from having twice the genetic instructions

Explanation:
Each parent contributes half their genetic material through gametes so that when male and female gametes join, the offspring receives a complete set of instructions—half from each parent—rather than doubling the genetic material every generation.

Question: What do scientists believe may have existed on Mars in the past that could have supported simple life forms?
A. A thick atmosphere similar to Venus
B. Liquid water and habitable conditions
C. Strong magnetic fields
D. Dense forests and vegetation
Show Answer & Explanation

Answer: (B) Liquid water and habitable conditions

Explanation:
The chapter mentions that Mars lies at the edge of the Sun's habitable zone and scientists think it may have had liquid water and possibly lakes, along with conditions that could support simple life forms.

Question: How does cutting down a large forest affect local water systems and climate?
A. Trees have no impact on water or climate patterns
B. Fewer trees mean less evaporation, leading to reduced rainfall and drier conditions
C. Deforestation always increases rainfall in surrounding areas
D. Forest removal causes underground water to rise
Show Answer & Explanation

Answer: (B) Fewer trees mean less evaporation, leading to reduced rainfall and drier conditions

Explanation:
Forests release water through transpiration and influence rainfall patterns; removing large forest patches reduces water vapour in the air, leading to less rainfall and changes in local climate conditions.

Question: Which of the following is NOT mentioned as part of the 'triple planetary crisis' facing Earth today?
A. Climate change
B. Biodiversity loss
C. Pollution
D. Depletion of mineral resources
Show Answer & Explanation

Answer: (D) Depletion of mineral resources

Explanation:
The chapter explicitly identifies the triple planetary crisis as climate change, biodiversity loss, and pollution. Mineral resource depletion is not mentioned as part of this specific trio of challenges.

Question: What is geodiversity, and why is it important for life on Earth?
A. It is the variety of weather patterns that sustain ecosystems
B. It is the diversity of rock types in the Earth's core
C. It is the variety of landforms, rocks, and soils that creates unique habitats for different life forms
D. It is the process by which minerals are extracted from the Earth
Show Answer & Explanation

Answer: (C) It is the variety of landforms, rocks, and soils that creates unique habitats for different life forms

Explanation:
Geodiversity refers to the variety of landforms, rocks, soils, and related processes that help create unique habitats where different types of life can thrive, making it crucial for supporting diverse ecosystems.

Question: According to the chapter, how does the Earth's magnetic field protect life on the planet?
A. It reflects sunlight and keeps the planet cool
B. It pushes harmful high-energy particles away, protecting the atmosphere and life
C. It controls weather patterns and prevents storms
D. It regulates ocean currents and water temperature
Show Answer & Explanation

Answer: (B) It pushes harmful high-energy particles away, protecting the atmosphere and life

Explanation:
Earth's magnetic field acts like a protective shield, pushing away high-energy particles from space and the solar wind that could otherwise damage the atmosphere, ozone layer, and allow harmful UV rays to reach life on Earth.

Question: What happens during pollination in flowering plants?
A. Male and female gametes combine inside the ovule
B. Pollen grains are transferred from the anther to another flower by wind, insects, or animals
C. Seeds are dispersed by birds eating the fruit
D. The ovule develops into a root system
Show Answer & Explanation

Answer: (B) Pollen grains are transferred from the anther to another flower by wind, insects, or animals

Explanation:
Pollination is the process by which pollen (containing male gametes) is carried from the anther of one flower to another flower, typically by wind, insects, or animals, allowing fertilisation to occur.

Question: Why is liquid water essential for life to evolve on a planet?
A. Water is the only substance that can dissolve oxygen
B. Liquid water provides the medium where chemical reactions necessary for life can occur
C. Water is the source of all atmospheric oxygen
D. Liquid water prevents planets from rotating
Show Answer & Explanation

Answer: (B) Liquid water provides the medium where chemical reactions necessary for life can occur

Explanation:
From what scientists know so far, liquid water is essential because it serves as a medium for the complex chemical reactions and biological processes required for life to develop and thrive.

Question: Which global agreement specifically helped reduce harmful chemicals like CFCs that were damaging the ozone layer?
A. The Kyoto Protocol
B. The Paris Agreement
C. The Montreal Protocol
D. The Earth Summit
Show Answer & Explanation

Answer: (C) The Montreal Protocol

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

Question: If a scientist were studying why Earth appears blue when viewed from space, which feature would be the primary reason for this observation?
A. The reflection of the sky in the atmosphere
B. The vast coverage of water on Earth's surface
C. The presence of the magnetic field surrounding the planet
D. The colour of minerals in the Earth's crust
Show Answer & Explanation

Answer: (B) The vast coverage of water on Earth's surface

Explanation:
The chapter explicitly states that Earth is called the Blue Planet because most of its surface is covered with water, and when seen from space, this vast amount of water makes Earth appear blue.

Question: In the context of the solar system, how does Earth's nearly circular orbit contribute to its habitability?
A. It allows the planet to receive equal sunlight year-round
B. It keeps the amount of sunlight and heat nearly steady throughout the year, preventing extreme seasons
C. It prevents the planet from rotating
D. It increases the strength of the gravitational pull from the Sun
Show Answer & Explanation

Answer: (B) It keeps the amount of sunlight and heat nearly steady throughout the year, preventing extreme seasons

Explanation:
Nearly circular orbits maintain consistent distance from the Sun, ensuring moderate and relatively stable temperatures. This prevents extreme seasonal variations that would make conditions harsh for most life forms.

Question: Planaria and hydra are mentioned in the chapter as examples of organisms that reproduce asexually. What makes their reproductive strategy notable?
A. They produce seeds like flowering plants do
B. They can regrow into complete new individuals from body fragments or buds
C. They require two parents to create offspring
D. They lay eggs that must be fertilised in water
Show Answer & Explanation

Answer: (B) They can regrow into complete new individuals from body fragments or buds

Explanation:
• Hydra grows tiny buds that break off and become new individuals
• Planaria can regrow from just a small piece of its body
• Both demonstrate remarkable regeneration ability in asexual reproduction.

Question: When pollen from one flower is carried by wind to another flower, which term describes this process?
A. Fertilisation
B. Pollination
C. Germination
D. Vegetative propagation
Show Answer & Explanation

Answer: (B) Pollination

Explanation:
The chapter defines pollination as the process where pollen is carried to another flower by wind, insects, or animals. Fertilisation occurs later when male and female gametes combine.

Question: How does the presence of oxygen in Earth's atmosphere serve life in two distinct ways according to the chapter?
A. It allows photosynthesis and prevents global warming
B. It enables respiration and forms the protective ozone layer when converted
C. It dissolves in water and regulates temperature
D. It creates clouds and brings rainfall
Show Answer & Explanation

Answer: (B) It enables respiration and forms the protective ozone layer when converted

Explanation:
Oxygen is directly needed for respiration by most organisms. Additionally, some atmospheric oxygen converts to ozone, which forms a protective shield blocking harmful ultraviolet rays from the Sun.

Question: The chapter describes how species like camels and certain bacteria have changed over time. Which reproductive process makes such adaptations to new environments possible?
A. Asexual reproduction through vegetative propagation
B. Sexual reproduction, which introduces genetic variation through mixed instructions from two parents
C. Fragmentation, where organisms split into equal pieces
D. Pollination by insects and wind
Show Answer & Explanation

Answer: (B) Sexual reproduction, which introduces genetic variation through mixed instructions from two parents

Explanation:
Sexual reproduction combines instructions from two parents, creating variation. Over many generations, small differences accumulate, allowing beneficial traits—like camels developing humps—to become established as organisms adapt to their surroundings.

Question: According to the chapter, what structural feature of flowers enables the production of male gametes?
A. The ovule deep inside the flower
B. The anther, which contains pollen grains
C. The fruit tissue surrounding the seed
D. The stem that supports the petals
Show Answer & Explanation

Answer: (B) The anther, which contains pollen grains

Explanation:
Pollen grains found inside the anther of a flower are identified in the chapter as the male gametes in sexual reproduction of plants.

Question: Why might birds like sparrows have better survival rates for their young compared to reptiles like snakes, based on parental behaviour discussed in the chapter?
A. Birds lay fewer eggs, so they can care for each one more carefully
B. Snakes are not able to lay eggs at all
C. Birds build nests and care for their eggs and chicks, while snakes lay eggs and leave them unprotected
D. Reptile eggs are less likely to hatch than bird eggs
Show Answer & Explanation

Answer: (C) Birds build nests and care for their eggs and chicks, while snakes lay eggs and leave them unprotected

Explanation:
The chapter contrasts these two strategies: sparrows invest time and energy building nests and protecting their young, whereas snakes lay many eggs and provide no parental care. This difference directly affects survival chances for the offspring.

Question: In the development of mammals like humans and cows, where does the embryo receive food and oxygen while developing?
A. From nutrients stored in an egg laid by the mother
B. From the mother's body through direct physical connection until birth
C. From water and soil where the embryo grows
D. From the father's contribution during fertilisation
Show Answer & Explanation

Answer: (B) From the mother's body through direct physical connection until birth

Explanation:
The chapter explains that in most mammals, the zygote develops into an embryo inside the female's body, where the mother's body provides all necessary food and oxygen until the baby is born—a different strategy from birds that lay eggs.

Question: What does the chapter suggest would be a consequence if both parents passed on their complete genetic material to offspring without modification?
A. Offspring would be stronger and more adapted
B. The amount of genetic instructions would double every generation, creating an unsustainable situation
C. Sexual reproduction would be impossible
D. All individuals would be identical to their parents
Show Answer & Explanation

Answer: (B) The amount of genetic instructions would double every generation, creating an unsustainable situation

Explanation:
The chapter poses this question to explain why gametes carry only half the parent's genetic material—if both parents contributed their full set, the genetic instructions would accumulate and keep doubling each generation, which does not happen in nature.

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Chapter 13 Our Home Earth, A Unique Life Sustaining Planet Objective Questions & Solutions for Class 8 Science

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