Class 8 Science Extra Questions Chapter 13 – Our Home: Earth, A Unique Life Sustaining Planet

Earth is our only home and the only known planet that supports life. It has air, water, land, and a suitable climate, making it a unique life-sustaining planet.

In Class 8 Science Chapter 13 – Our Home: Earth, students learn about the special features of Earth that make life possible.

To help in better revision and exam preparation, a2zly.com provides important extra questions with answers based on NCERT and NEP 2025 guidelines.

Let’s begin the chapter-wise extra question practice!

✅ True or False (10 Questions)

1. Earth is the only known planet where life exists because it has suitable conditions like air, water, and moderate temperature.
   True
2. The Earth’s crust, where all living organisms exist, is very thick compared to the size of the Earth.
   False
   (It is very thin like the skin of an apple.)
3. Venus is the hottest planet mainly because its thick atmosphere traps heat due to the greenhouse effect.
   True
4. The habitable zone is the region around the Sun where water can remain in liquid form.
   True
5. If Earth were much smaller, its gravity would not be able to hold the atmosphere properly.
   True
6. Mercury has a thick atmosphere that helps it trap heat like Venus.
   False
   (Mercury has almost no atmosphere.)
7. The ozone layer protects life on Earth by blocking harmful ultraviolet (UV) rays from the Sun.
   True
8. Earth’s magnetic field increases the temperature of the planet by trapping sunlight.
   False
   (It protects Earth from harmful cosmic rays and solar wind.)
9. Hydrosphere includes all forms of water present on Earth such as oceans, rivers, lakes, and groundwater.
   True
10. Climate change, biodiversity loss, and pollution together are known as the triple planetary crisis threatening life on Earth.
    True

✅ Fill in the Blanks (10 Questions)

1. Earth is called a unique planet because it is the only known planet that can sustain __________.
   Answer: life
2. The Earth’s crust is compared to the thin skin of an __________ because it is very delicate.
   Answer: apple
3. Venus is the hottest planet because its atmosphere traps heat due to the __________ effect.
   Answer: greenhouse
4. The region around the Sun where water can remain in liquid form is called the __________ zone.
   Answer: habitable
5. Earth appears blue from space because most of its surface is covered with __________.
   Answer: water
6. The layer of gases surrounding the Earth is known as the __________.
   Answer: atmosphere
7. The __________ layer acts as a shield against harmful ultraviolet rays from the Sun.
   Answer: ozone
8. The solid part of Earth made up of rocks, soil, and minerals is called the __________.
   Answer: geosphere
9. Reproductive cells that carry only half the genetic material are called __________.
   Answer: gametes
10. Climate change, biodiversity loss, and pollution together form the __________ planetary crisis.
    Answer: triple

✅ Multiple Choice Questions (15 MCQs)

1. Earth is considered a unique planet because:

A. It is the largest planet in the solar system
B. It has rings like Saturn
C. It supports life due to suitable conditions
D. It is closest to the Sun
✅ Answer: C

2. The layer of Earth where all life exists is mainly the:

A. Inner core
B. Mantle
C. Crust
D. Outer core
✅ Answer: C

3. The Earth’s crust is compared to the skin of an apple because it is:

A. Very thick
B. Very thin
C. Very hot
D. Made of gas
✅ Answer: B

4. Venus is hotter than Mercury because:

A. Venus is closer to the Sun
B. Venus has no atmosphere
C. Venus has a thick CO₂ atmosphere that traps heat
D. Venus receives less sunlight
✅ Answer: C

5. The greenhouse effect occurs because:

A. Oxygen cools the planet
B. Carbon dioxide traps heat in the atmosphere
C. Water freezes quickly
D. Winds blow strongly
✅ Answer: B

6. Earth lies at the right distance from the Sun, allowing water to exist in:

A. Solid form only
B. Liquid form
C. Gas form only
D. Ice form always
✅ Answer: B

7. The region around the Sun where conditions are suitable for liquid water is called:

A. Ozone zone
B. Magnetic zone
C. Habitable (Goldilocks) zone
D. Core zone
✅ Answer: C

8. Mars cannot support life like Earth mainly because:

A. It has too many forests
B. It has a very thick atmosphere
C. It lacks thick atmosphere and liquid water
D. It has too much oxygen
✅ Answer: C

9. Earth’s atmosphere is held by:

A. Solar wind
B. Earth’s gravity
C. Volcanoes
D. Moonlight
✅ Answer: B

10. The ozone layer is important because it:

A. Produces carbon dioxide
B. Blocks harmful ultraviolet rays
C. Causes rainfall
D. Makes soil fertile
✅ Answer: B

11. Earth’s magnetic field helps life by:

A. Increasing the planet’s size
B. Protecting Earth from cosmic rays and solar wind
C. Producing clouds
D. Creating minerals
✅ Answer: B

12. All water bodies such as rivers, oceans, lakes, and groundwater form the:

A. Biosphere
B. Hydrosphere
C. Geosphere
D. Lithosphere
✅ Answer: B

13. The solid part of Earth made up of rocks, soil, and minerals is called:

A. Atmosphere
B. Biosphere
C. Geosphere
D. Hydrosphere
✅ Answer: C

14. In asexual reproduction, offspring are:

A. Completely different from parent
B. Exact copies of the parent
C. Produced only by animals
D. Produced by two parents
✅ Answer: B

15. Climate change, biodiversity loss, and pollution together are known as:

A. Natural cycle
B. Triple planetary crisis
C. Water cycle
D. Seasonal change
✅ Answer: B

✅ Assertion–Reason Questions (10)

Directions:

For each question, choose the correct option:

A. Both A and R are true and R is the correct explanation of A
B. Both A and R are true but R is not the correct explanation of A
C. A is true but R is false
D. A is false but R is true

1.

Assertion (A): Earth is a unique planet in our solar system.
Reason (R): Earth has the right conditions such as liquid water, atmosphere, and suitable temperature for life.
✅ Answer: A

2.

Assertion (A): Venus is hotter than Mercury even though Mercury is closer to the Sun.
Reason (R): Venus has a thick atmosphere rich in carbon dioxide that traps heat.
✅ Answer: A

3.

Assertion (A): Earth lies in the habitable zone of the Sun.
Reason (R): In this zone, water can remain in liquid form, which is essential for life.
✅ Answer: A

4.

Assertion (A): Earth’s gravity helps sustain life on the planet.
Reason (R): Gravity holds the atmosphere around Earth and prevents gases from escaping into space.
✅ Answer: A

5.

Assertion (A): Mercury does not have a significant atmosphere.
Reason (R): Mercury’s gravity is too weak to hold gases around it.
✅ Answer: A

6.

Assertion (A): The ozone layer is important for the survival of living organisms.
Reason (R): The ozone layer blocks harmful ultraviolet rays from reaching Earth’s surface.
✅ Answer: A

7.

Assertion (A): Earth’s magnetic field protects life on Earth.
Reason (R): It deflects harmful solar wind and cosmic rays away from the planet.
✅ Answer: A

8.

Assertion (A): Hydrosphere plays an important role in sustaining life.
Reason (R): Water is essential for plant growth, animal survival, and regulation of body temperature.
✅ Answer: A

9.

Assertion (A): Asexual reproduction produces offspring with many variations.
Reason (R): In asexual reproduction, offspring are exact copies of the parent.
✅ Answer: D

10.

Assertion (A): Climate change is a major threat to life on Earth.
Reason (R): Rising temperatures can melt ice caps, raise sea levels, and disturb ecosystems.
✅ Answer: A

✅ Very Short Answer Questions (10 Questions)

1. Why is Earth called a unique life-sustaining planet?

Answer:
Earth is called a unique life-sustaining planet because it has air, water, suitable temperature, and an atmosphere that supports the existence of living organisms.

2. What is meant by the habitable zone or Goldilocks zone?

Answer:
The habitable zone is the region around the Sun where the temperature is just right for water to exist in liquid form, making it suitable for life.

3. Why is Venus the hottest planet in the solar system?

Answer:
Venus is the hottest planet because its thick carbon dioxide atmosphere traps heat due to the greenhouse effect.

4. What role does Earth’s atmosphere play in sustaining life?

Answer:
Earth’s atmosphere provides oxygen for breathing, protects from harmful radiation, and helps maintain a suitable temperature for life.

5. What is the importance of the ozone layer?

Answer:
The ozone layer acts as a protective shield by blocking harmful ultraviolet (UV) rays from the Sun, which can damage living cells.

6. How does Earth’s magnetic field protect life?

Answer:
Earth’s magnetic field deflects harmful cosmic rays and solar wind particles, protecting the atmosphere and living organisms.

7. What is the hydrosphere?

Answer:
The hydrosphere includes all forms of water on Earth such as oceans, rivers, lakes, groundwater, and water vapour in the atmosphere.

8. Define geosphere.

Answer:
The geosphere is the solid part of Earth consisting of rocks, soil, minerals, and landforms that support life indirectly.

9. What are genes?

Answer:
Genes are units of genetic material present in cells that carry instructions from parents to offspring and control the development of organisms.

10. Name any two major threats to life on Earth today.

Answer:
Two major threats to life on Earth are climate change and pollution. Biodiversity loss is also a serious threat.

✅ Short Answer Questions (10 Questions)

1. Explain why Earth’s distance from the Sun is important for life.

Answer:
Earth is located at the right distance from the Sun, where the temperature is neither too hot nor too cold. This allows water to exist in liquid form, which is essential for life processes. If Earth were closer, water would evaporate; if farther, it would freeze.

2. What is the greenhouse effect? Why is it important for Earth?

Answer:
The greenhouse effect is the trapping of heat by gases like carbon dioxide in the atmosphere. It helps maintain Earth’s temperature at a level suitable for living organisms. Without it, Earth would become too cold to support life.

3. How does Earth’s size help it to sustain life?

Answer:
Earth is the right size to have enough gravity to hold its atmosphere. If Earth were smaller, gases would escape into space. If it were much larger, gravity would become too strong and could harm living beings.

4. Describe the role of the ozone layer in protecting life.

Answer:
The ozone layer is formed from oxygen in the atmosphere. It acts as a shield by absorbing harmful ultraviolet (UV) rays from the Sun. This protects living cells from damage and helps life survive on Earth.

5. How does Earth’s magnetic field help sustain life?

Answer:
Earth’s magnetic field acts as a protective barrier. It deflects harmful cosmic rays and solar wind particles coming from space. This prevents damage to the atmosphere and reduces the entry of harmful radiation.

6. What is meant by hydrosphere? State its importance.

Answer:
The hydrosphere includes all water bodies on Earth such as oceans, rivers, lakes, groundwater, and water vapour. Water is essential for all living organisms, supports aquatic life, and helps regulate climate and body functions.

7. What is geodiversity? How does it support life?

Answer:
Geodiversity refers to the variety of landforms, rocks, soils, and minerals on Earth. It creates different habitats for organisms and provides soil nutrients and minerals needed for plant growth and human use.

8. Differentiate between sexual and asexual reproduction.

Answer:
In asexual reproduction, a single parent produces offspring that are exact copies. In sexual reproduction, two parents contribute genetic material, producing offspring with variations. Sexual reproduction helps in evolution and adaptation.

9. Why is reproduction necessary for the continuity of life?

Answer:
Reproduction ensures that living organisms produce offspring of their own kind. Without reproduction, species would gradually disappear from Earth. It also allows variations, helping organisms adapt to changing environments.

10. What is the triple planetary crisis? Explain briefly.

Answer:
The triple planetary crisis refers to three major threats to Earth: climate change, biodiversity loss, and pollution. These disturb the balance of ecosystems and endanger life by affecting air, water, soil, and living organisms.

✅ Case-Based Questions (4 Cases)

(4 Marks Each | Sub-questions: 1 + 1 + 2 Marks)

Case 1: Earth in the Habitable Zone

Earth is located at the right distance from the Sun. This distance allows the planet to have a moderate temperature where water can remain in liquid form. Liquid water is essential for life to evolve and survive. This region is called the habitable zone or Goldilocks zone.

Questions:

Q1. (1 Mark) What is the habitable zone also called?
Answer: The habitable zone is also called the Goldilocks zone.

Q2. (1 Mark) Why is liquid water necessary for life?
Answer: Liquid water is necessary because it supports life processes and helps organisms survive.

Q3. (2 Marks) What would happen if Earth were much closer to the Sun?
Answer: If Earth were closer to the Sun, the temperature would become too high and water would evaporate, making life impossible.

Case 2: Earth’s Atmosphere and Protection

Earth has an atmosphere rich in oxygen, which supports respiration. The atmosphere also contains ozone, which forms the ozone layer. This layer acts like a shield and protects Earth from harmful ultraviolet rays.

Questions:

Q1. (1 Mark) Which gas in the atmosphere is essential for breathing?
Answer: Oxygen is essential for breathing.

Q2. (1 Mark) What is the function of the ozone layer?
Answer: It blocks harmful ultraviolet (UV) rays.

Q3. (2 Marks) How does the atmosphere help in maintaining Earth’s temperature?
Answer: The atmosphere traps some heat due to the greenhouse effect, keeping Earth warm enough for water to remain liquid.

Case 3: Earth’s Magnetic Field

Earth behaves like a giant magnet and has a magnetic field. High-energy particles such as cosmic rays and solar wind constantly hit Earth. The magnetic field deflects many of these harmful particles and protects life.

Questions:

Q1. (1 Mark) What are the harmful particles coming from the Sun called?
Answer: They are called solar wind particles.

Q2. (1 Mark) What does Earth’s magnetic field act as?
Answer: It acts as a protective shield.

Q3. (2 Marks) How does the magnetic field help sustain life on Earth?
Answer: It prevents harmful particles from damaging the atmosphere and ozone layer, protecting living organisms from radiation.

Case 4: Threats to Life on Earth

Human activities such as burning fossil fuels increase greenhouse gases in the atmosphere. This causes global warming and climate change. Pollution and biodiversity loss also disturb Earth’s balance. Together, these are called the triple planetary crisis.

Questions:

Q1. (1 Mark) Name one greenhouse gas released by burning fossil fuels.
Answer: Carbon dioxide.

Q2. (1 Mark) What is the triple planetary crisis?
Answer: Climate change, biodiversity loss, and pollution.

Q3. (2 Marks) Mention two harmful effects of climate change on Earth.
Answer: Climate change can melt ice caps, raise sea levels, cause extreme weather, and threaten ecosystems.

✅ Long Answer Questions (5 Questions)

(5 Marks Each – CBSE Class 8 Standard, High-Quality Answers)

1. Explain the factors that make Earth a unique life-sustaining planet.

Answer:
Earth is a unique planet because it provides the perfect conditions needed to support life. The main factors are:

• Right distance from the Sun: Earth lies in the habitable zone, where temperature allows water to exist in liquid form.
• Presence of atmosphere: The atmosphere provides oxygen for respiration and carbon dioxide for photosynthesis.
• Suitable size and gravity: Earth’s gravity is strong enough to hold the atmosphere but not so strong as to crush living beings.
• Ozone layer protection: The ozone layer blocks harmful ultraviolet rays from the Sun.
• Magnetic field: Earth’s magnetic field protects the planet from harmful solar wind and cosmic rays.

Thus, all these features together make Earth the only known planet where life can thrive.

2. Describe the role of atmosphere, greenhouse effect, and ozone layer in sustaining life on Earth.

Answer:
The atmosphere plays an important role in sustaining life on Earth:

• It contains oxygen, which is needed for respiration by humans and animals.
• It provides carbon dioxide used by plants during photosynthesis.
• The atmosphere helps maintain Earth’s temperature through the greenhouse effect. Gases like carbon dioxide trap heat and prevent Earth from becoming too cold.
• Some oxygen forms ozone, creating the ozone layer. This layer acts as a shield by blocking harmful ultraviolet rays.

Therefore, the atmosphere supports life by providing gases, regulating temperature, and offering protection.

3. Explain how Earth’s spheres interact to sustain life.

Answer:
Earth supports life through the interaction of four major spheres:

• Atmosphere: Provides air for breathing and regulates climate.
• Hydrosphere: Includes all water bodies, essential for life processes and habitats of aquatic organisms.
• Geosphere: Consists of rocks, soil, and minerals that provide nutrients and land for plants and animals.
• Biosphere: Includes all living organisms that depend on air, water, and soil.

These spheres work together in balance. For example, plants use water and carbon dioxide to make food, animals depend on plants, and decomposers return nutrients to soil. This interaction sustains life on Earth.

4. Compare sexual and asexual reproduction with examples.

Answer:

Reproduction is essential for the continuity of life. There are two main types:

Asexual Reproduction

• Involves only one parent.
• Offspring are exact copies of the parent.
• Example: Vegetative propagation in money plant, potato, ginger.

Sexual Reproduction

• Involves two parents (male and female).
• Offspring show variation because genes from both parents combine.
• Example: Humans, birds, flowering plants.

Sexual reproduction helps organisms adapt and evolve, while asexual reproduction is faster and simpler.

5. What are the major threats to life on Earth? Suggest measures to protect our planet.

Answer:
Life on Earth is threatened by human activities that disturb natural balance. Major threats include:

• Climate change: Caused by greenhouse gases from burning fossil fuels, leading to global warming, melting ice caps, and extreme weather.
• Pollution: Air, water, and soil pollution harm living organisms and ecosystems.
• Biodiversity loss: Destruction of habitats leads to extinction of plants and animals.

Measures to protect Earth:

• Use renewable energy like solar and wind.
• Reduce pollution through recycling and proper waste management.
• Plant more trees and protect forests.
• Conserve water and natural resources.

Protecting Earth is essential for sustaining life for future generations.

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