Question Bank — Our Home: Earth, a Unique Life Sustaining Planet

QUESTION BANK

Class VIII – Science

Chapter 13: Our Home: Earth, a Unique Life Sustaining Planet

Section A — MCQs (10 questions, 1 mark each)

1. Which of the following best explains why Venus is hotter than Mercury despite being farther from the Sun?
   (a) Venus has a thicker layer of ozone
   (b) Venus has a thick atmosphere rich in carbon dioxide that traps heat
   (c) Venus rotates very slowly on its axis
   (d) Venus is closer to the habitable zone

2. The thin layer on Earth’s surface where all life exists is comparable to:
   (a) the core of an apple
   (b) the skin of an apple
   (c) the seeds inside an apple
   (d) the stem of an apple

3. Assertion (A): Earth’s nearly circular orbit around the Sun helps maintain moderate temperatures throughout the year.
   Reason (R): A circular orbit ensures that the distance from the Sun remains almost constant, preventing extreme seasonal variations.
   (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.

4. The ozone layer protects life on Earth by:
   (a) trapping infrared radiation from the Sun
   (b) blocking harmful ultraviolet rays
   (c) reflecting cosmic rays back into space
   (d) maintaining the greenhouse effect

5. Assertion (A): If Earth were much smaller but of the same density, it would not be able to sustain life as we know it.
   Reason (R): A smaller Earth would have weaker gravity, causing its atmosphere to escape into space.
   (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.

6. Which region around the Sun is known as the habitable or Goldilocks zone?
   (a) The area where water exists only as ice
   (b) The range of distances where water can remain in liquid form
   (c) The region where only rocky planets are found
   (d) The area beyond Neptune

7. The Earth’s magnetic field protects life mainly by:
   (a) generating heat in the core
   (b) deflecting harmful high-energy particles from the Sun and space
   (c) producing oxygen in the atmosphere
   (d) causing the formation of clouds

8. In sexual reproduction, gametes are special because they:
   (a) contain the full set of genetic material from one parent
   (b) carry only half the genetic material of the parent
   (c) are produced only by animals
   (d) develop directly into an embryo without fertilisation

9. Which of the following is an example of geodiversity?
   (a) Different species of birds in a forest
   (b) Variety of landforms such as mountains, valleys and deserts
   (c) Migration of whales across oceans
   (d) Photosynthesis carried out by plants

10. The triple planetary crisis refers to:
    (a) lack of water, soil and air on Earth
    (b) climate change, biodiversity loss and pollution
    (c) overpopulation, deforestation and mining
    (d) volcanic eruptions, earthquakes and tsunamis

Section B — Very Short Answer (6 questions, 2 marks each)

11. State two reasons why the presence of liquid water on Earth is considered essential for life.
12. What is the difference between the greenhouse effect on Venus and the greenhouse effect that occurs on Earth?
13. Why is the Earth often called the “Blue Planet”?
14. List two ways in which the Earth’s magnetic field helps sustain life.
15. Differentiate between asexual and sexual reproduction with one example of each from the chapter.
16. What is vegetative propagation? Give one example mentioned in the text.

Section C — Short Answer (5 questions, 3 marks each)

17. Explain, with the help of an example from the chapter, how the right size of Earth enables it to hold an atmosphere suitable for life.
18. Describe the role of the ozone layer and why its depletion would be harmful to living organisms.
19. How do the atmosphere, hydrosphere and geosphere interact to support life on Earth? Give one example of their interdependence.
20. What is pollination? Briefly describe how it leads to the formation of seeds and fruits in flowering plants.
21. Why is reproduction necessary for the continuity of life? How does it also allow variations to appear in successive generations?

Section D — Long Answer (3 questions, 5 marks each)

22. Draw a neat labelled diagram of a typical flower showing the male and female reproductive parts. Describe the process of pollination and fertilisation as explained in the chapter. (Diagram-based)
23. “Earth’s distance from the Sun, its size, atmosphere and magnetic field together make it a unique life-sustaining planet.” Justify the statement with suitable points from the chapter.
24. Explain the causes and consequences of the triple planetary crisis. Suggest any two measures that can help reduce its impact on life on Earth.

Section E — Case/Source-Based (2 questions, 4 marks each)

25. Read the passage and answer the questions that follow:
“Earth lies in a special region around the Sun where water can exist in liquid form. This region is called the habitable zone. Mars lies at the edge of this zone. Although spacecrafts have explored its surface, no proof of life has been found yet. Scientists believe that in the past Mars may have had liquid water and conditions that could have supported simple life forms.”

(a) What is the habitable zone? (1)
(b) Why is Mars considered to lie at the edge of the habitable zone? (1)
(c) State one reason why scientists continue to study Mars despite not finding life yet. (1)
(d) If a spaceship carried only soil and water to Mars, would plants be able to grow there? Give one reason based on the chapter. (1)

26. Read the passage and answer the questions that follow:
“Burning of fossil fuels releases extra carbon dioxide into the atmosphere. This enhances the greenhouse effect and leads to a steady rise in Earth’s temperature. Even a small increase can melt ice caps, raise sea levels and cause extreme weather. At the same time, cutting down forests reduces the number of trees that absorb carbon dioxide, disturbing the natural balance.”

(a) What is the enhanced greenhouse effect caused by human activities called? (1)
(b) Mention two visible consequences of rising global temperature mentioned in the passage. (1)
(c) How does cutting down forests worsen the problem? (1)
(d) Name one international agreement mentioned in the chapter that aims to reduce greenhouse gas emissions. (1)

Section F — HOTS and Application (4 questions, 3 marks each)

27. Predict-and-justify: What would happen to life on Earth if the planet’s magnetic field suddenly disappeared? Justify your answer.
28. Analyse an unexpected observation: In an experiment, two identical potted plants are kept — one in a closed glass jar and the other in an open jar — under the same sunlight. After a few days the plant in the closed jar wilts while the one in the open jar remains healthy. Analyse the possible reason using concepts from the chapter.
29. Apply to an unfamiliar real-life situation: A village near the coast experiences frequent flooding and loss of fertile soil after every monsoon. Using your understanding of the chapter, suggest how destruction of nearby forests could be contributing to this problem.
30. Compare two situations: Compare the development of the zygote in birds and in most mammals. Justify why the method used by mammals gives the embryo a different kind of advantage.