Our Home: Earth, a Unique Life Sustaining Planet — Hard

Q1. Consider the following statements about the greenhouse effect on Earth: I. Gases like CO₂ absorb radiation given off by the warmed Earth. II. It plays an important role in maintaining the right temperature on Earth. III. It works exactly like a plant greenhouse that traps warm air inside glass walls. Which are correct?

• A. I and II only
• B. II and III only
• C. I and III only
• D. All three

Q2. Assertion (A): If the Earth were much smaller but with the same average density, its atmosphere would have escaped into space. Reason (R): A smaller planet has weaker gravity, which cannot hold on to atmospheric gases. 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, R is false
• D. A is false, R is true

Q3. If the Earth were a much larger planet (with same average density), the chapter argues that gravity would become much stronger and

• A. It would perhaps pull us down with such a large force that our bones could get crushed
• B. Earth's atmosphere would escape into space
• C. Earth's distance from the Sun would change
• D. Earth's magnetic field would vanish

Q4. Consider these statements about Earth's magnetic field and high-energy particles from space: I. Particles from far across the universe are called cosmic rays. II. Earth's magnetic field pushes many of these particles away. III. Cosmic rays and solar wind can damage the atmosphere, reduce ozone and let in more UV. Which are correct?

• A. I and II only
• B. II and III only
• C. I and III only
• D. All three

Q5. All the Earth systems — the atmosphere, hydrosphere, biosphere and geosphere — are connected. This means that

• A. Only the hydrosphere supports life; the others have no role
• B. They never interact with each other
• C. Each sphere works fully independently of the others
• D. Damage to one sphere can affect the others, so all four must be protected together

Q6. Consider the following statements about sexual reproduction in Class 8 Curiosity: I. Two parents are involved, usually called male and female. II. Instructions from two parents combine to create offspring that are not exactly like either parent. III. Over many generations, small differences from this mixing can lead to big differences and even new life forms. Which of the above are correct?

• A. I and II only
• B. II and III only
• C. I and III only
• D. All three

Q7. Why is it that, even though both parents pass on their genetic material, the child does NOT end up with double the amount of instructions?

• A. Each parent makes specialised reproductive cells called gametes that carry only half of the parent's genetic material
• B. Half of the genes are destroyed during digestion
• C. Genetic material is reduced by half after the baby is born
• D. Only one parent ever passes on genetic material

Q8. Assertion (A): In birds, the female parent has to put into each egg enough 'food' to last for the developing embryo until it hatches. Reason (R): In birds, the fertilised egg (zygote) is laid by the female, and the development of the zygote into an embryo happens after the egg is laid, during the hatching process. Choose the correct option

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

Q9. From the table and discussion in the chapter, the planet with the highest average temperature in our solar system is Venus, even though it is the second planet from the Sun. The two factors that together produce this are

• A. Venus's small size and its absence of any atmosphere
• B. Venus's distance from the Sun and the lack of any greenhouse gases
• C. Venus's strong magnetic field and large icy oceans
• D. Venus's thick atmosphere and its almost entirely carbon dioxide composition, which trap heat through the greenhouse effect

Q10. Why does a cow give birth to a calf, never to a kitten? Consider these statements: I. Parents pass on instructions to their offspring about how to develop from a single cell. II. These instructions are called genetic material or genes. III. Genes act like a detailed instruction manual inside each cell, guiding it to make blood, bones, muscles, skin. Which are correct?

• A. I and II only
• B. II and III only
• C. I and III only
• D. All three

Q11. Burning fossil fuels like coal and oil releases greenhouse gases such as carbon dioxide and methane. According to the chapter, the most important consequence of releasing this 'extra' carbon dioxide is that

• A. The Earth cannot absorb the extra carbon fast enough, so heat builds up and causes long-term climate change
• B. The Earth's magnetic field disappears
• C. The Earth moves closer to the Sun
• D. The atmosphere is replaced entirely by ozone

Q12. The chapter argues that when natural habitats are destroyed, the loss of even a few species can weaken nature's ability to support life. Which sequence of consequences best illustrates this idea, drawing on Chapter 12?

• A. Tigers vanish → grasses vanish → deer multiply uncontrollably → soil becomes more fertile
• B. Grasses vanish → deer or grasshoppers struggle → predators like tigers or foxes lose their food
• C. Carbon dioxide increases → ozone layer thickens → UV rays reduce
• D. Soil pollution rises → ozone layer recovers → climate stabilises

Q13. Consider the following statements about global climate agreements as mentioned in the chapter: I. The Paris Agreement (2015) set a goal to limit global warming to below 1.5 °C. II. As of 2025, the world is not on track to meet that goal. III. The Earth Summit (1992) led to international efforts on climate change and biodiversity. Which of the above are correct?

• A. I and III only
• B. II and III only
• C. I and II only
• D. All three

Q14. Assertion (A): A little less ozone in the atmosphere of the Earth could endanger life on the planet. Reason (R): The ozone layer blocks harmful ultraviolet (UV) rays from the Sun that can damage living cells. Choose the correct option

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

Q15. If the Earth had no atmosphere at all, the most likely set of effects on life, temperature and water would be

• A. No breathable oxygen for respiration; no greenhouse effect, so heat would escape and Earth would become too cold; water cycle disrupted as water would not stay liquid
• B. More crops would grow because there would be no clouds
• C. Earth would behave like Venus and become much hotter than Mercury
• D. Earth's gravity would increase sharply and bones could be crushed