Keep the Curiosity Alive — Chapter Exercises — "Our Home: Earth, a Unique Life Sustaining Planet"

1. 11 mark

   What is one major reason Mars cannot currently support life like Earth? (i) It has too many volcanoes. (ii) It is too close to the Sun. (iii) It lacks a thick atmosphere and liquid water. (iv) Its magnetic field is too strong.

   Hint. The chapter states this directly using a comparison to Earth's own atmosphere thickness.

   ✦ (iii) It lacks a thick atmosphere and liquid water. The chapter states Mars's atmosphere is 100 times thinner than Earth's, and while Mars may have had liquid water in the past, no proof of present-day liquid water or life has been found — Mars is not too close to the Sun (option ii is false; it's farther than Earth), and the chapter never claims Mars has a magnetic field that is too strong (option iv).

2. 21 mark

   Which of these is an example of geodiversity? (i) Variety of bird chirping in a forest. (ii) Different landforms like mountains, valleys, and deserts. (iii) Changing weather during monsoons. (iv) Number of different types of fish in a pond.

   Hint. Geodiversity is specifically about the solid, non-living geosphere — landforms, rocks and soils, not living things or weather.

   ✦ (ii) Different landforms like mountains, valleys, and deserts. The chapter defines geodiversity as the variety of landforms, rocks and soils on Earth, along with the processes that shape and alter them — bird sounds (i) and fish variety (iv) are biodiversity, not geodiversity, and monsoon weather (iii) is an atmospheric phenomenon, not a geosphere one, since geodiversity is specifically about the solid, non-living Earth.

3. 31 mark

   If the Earth were smaller with the same density, what might happen to its atmosphere? (i) It would become thicker and hotter. (ii) It would escape into space due to weaker gravity. (iii) It would become frozen. (iv) It would cause stronger winds.

   Hint. The chapter states this directly, using Mars as a real example of exactly this scenario.

   ✦ (ii) It would escape into space due to weaker gravity. The chapter states: 'If Earth were much smaller (but with the same average density), its gravity would have been too weak to hold on to the gases in our atmosphere, and they would have escaped into space' — exactly why Mars, a smaller planet, has an atmosphere 100 times thinner than Earth's.

4. 41 mark

   In sexual reproduction, why are offspring different from their parents? (i) They grow in different climates. (ii) They eat different food. (iii) They acquire new instructions after birth. (iv) They get mixed instructions (genes) from both parents.

   Hint. The cause is set at the moment of fertilisation itself, not anything that happens afterwards during the offspring's life.

   ✦ (iv) They get mixed instructions (genes) from both parents. The chapter explains that each gamete carries a different set of instructions, and when they combine at fertilisation, the resulting mix is unique each time — this genetic mixing is why offspring differ from their parents and from each other, not environment (i, ii) or instructions acquired later in life (iii).

5. 53 marks

   You notice tiny green plants growing in cracks on your school wall after the monsoon. Where do you think the seeds came from? What conditions helped these plants grow there?

   Hint. The banyan-seed-in-a-wall-crack example earlier in the chapter describes almost exactly this scenario.

   ✦ The seeds most likely arrived via a bird or animal that ate fruit elsewhere and dropped or excreted the seed near the wall — exactly like the chapter's own banyan seed example, where a bird-dropped seed sprouted in a crack in a wall after the rains. The conditions that helped the seeds grow: monsoon rainfall provided the water needed for germination (since that water lets the seed use its stored nutrients to grow roots and shoots), and the crack itself likely trapped a small amount of soil, moisture and shelter, similar to the moist soil vegetative propagation needs in Activity 13.3.

6. 64 marks

   A city has recently cut down a large patch of forest to build new roads and buildings. Discuss the possible effects this could have on the local climate and biodiversity. How might this affect water availability or quality in the area?

   Hint. The chapter's own forest-cutting example in section 13.4.4 names several specific categories of effect to draw from.

   ✦ Following the chapter's own example of cutting down a forest, this could affect rainfall patterns (fewer trees means less water vapour released and less rain retained locally), soil quality (fewer roots to hold soil in place, increasing erosion), and air quality (fewer trees to absorb carbon dioxide and release oxygen), since all three depend directly on the trees being cut down. On biodiversity, animals and plants that depended on the forest habitat would lose their home, and — following the same reasoning as habitat loss in Chapter 12 — species further along the food chain could also be affected as their food sources disappear. On water, reduced rainfall retention and increased soil erosion could both reduce water availability and let more pollutants and sediment reach water sources, reducing water quality as well.

7. 74 marks

   A friend says, 'The Earth has always had climate changes in the past, so today's global warming is nothing new.' How would you respond using what you've learnt in this and other chapters of your science book?

   Hint. Distinguish between the FACT that climate has changed before and the specific claim that today's warming isn't different or concerning.

   ✦ It's true that Earth's climate has changed before, but this chapter explains that today's climate change is different because it is being driven primarily by human activity — specifically, burning fossil fuels releases carbon that had been locked underground for millions of years, faster than trees, plants and ocean plankton can absorb it, so the Earth cannot keep its natural balance. This is unlike past natural climate changes because it is happening on a much faster timescale, driven by a clearly identifiable human cause rather than only natural cycles, and the chapter states this human-driven change is already causing melting ice caps, rising sea levels, extreme weather, and species loss — real, measurable consequences that justify treating it as a serious current crisis rather than dismissing it as 'nothing new.'

8. 84 marks

   Imagine Earth's magnetic field suddenly disappeared. What kinds of problems could arise for life on Earth? Explain.

   Hint. Trace what the magnetic field currently blocks, and follow through to what would then reach the atmosphere and surface unchecked.

   ✦ Without Earth's magnetic field acting as a protective shield, cosmic rays and the solar wind would no longer be pushed away from Earth, and these high-energy particles could then damage the atmosphere directly and reduce the ozone layer. A thinner ozone layer would let in more harmful UV rays, which can damage living cells — so the combined effect could be a weakened atmosphere and increased UV exposure reaching the surface, both of which the chapter identifies as serious threats to life.

9. 94 marks

   You are tasked with designing a new settlement for humans on Mars. Name three things you would need to recreate from Earth to support human life there. Which of these do you think is the hardest to replicate, and why?

   Hint. Draw from everything this chapter says Earth provides that Mars currently lacks — atmosphere, temperature, water, gravity, magnetic shielding.

   ✦ Three things to recreate: a breathable atmosphere with enough pressure and oxygen (since Mars's atmosphere is 100 times thinner than Earth's and unsuitable for breathing), a stable, warm-enough temperature to keep water liquid (since Mars sits at the edge of the habitable zone), and protection from cosmic rays and solar wind (since Mars, unlike Earth, does not have Earth's protective magnetic field). Of these, recreating a planet-scale magnetic field is arguably the hardest to replicate, since Earth's field arises from the movement of molten iron deep in an entire planet's core — something that cannot realistically be engineered artificially, unlike atmosphere or temperature, which could at least in principle be managed within an enclosed settlement.

10. 103 marks

    In a village, the temperature has been increasing and rainfall has become unpredictable over the past few years. What could be causing this change? Suggest two ways the village could adapt to these new conditions.

    Hint. Link the observed local symptoms back to the chapter's own global-scale explanation, then suggest practical local responses.

    ✦ Rising temperature and unpredictable rainfall are consistent with the chapter's description of climate change — long-term changes in temperature, rainfall, and weather patterns caused by greenhouse gases trapping extra heat in the atmosphere. Two ways the village could adapt: adopting water conservation and storage practices (like the sustainable farming and natural resource use the chapter recommends) to cope with unpredictable rainfall, and shifting to crop varieties or farming schedules better suited to warmer, less predictable conditions, since that reduces dependence on a single rainfall pattern that may no longer be reliable.

11. 114 marks

    If there were no atmosphere on the Earth, would it affect life, temperature, and water on the planet? Explain.

    Hint. Trace three separate consequences — one for breathing, one for heat, one for water's physical state.

    ✦ Yes, the effects would be severe on all three counts. Life would be affected because there would be no oxygen for respiration and no protective ozone layer, exposing living things directly to harmful UV rays. Temperature would be affected because, without the atmosphere's greenhouse effect trapping some of the Sun's heat, Earth would lose heat to space and become far too cold. Water would be affected because, without the right temperature range that the greenhouse effect helps maintain, water could no longer remain reliably in its liquid form — undermining the exact habitable-zone condition the chapter identifies as the single most important reason Earth supports life.

12. 124 marks

    Discuss five examples of vegetative propagation.

    Hint. The chapter itself names three examples directly and hints at two more through a posed question.

    ✦ Five examples: (1) a stem cutting of a money plant grown in soil or water; (2) the 'eyes' of a sprouted potato planted in soil; (3) a piece of ginger planted in moist soil; (4) bamboo, which the chapter notes grows into new plants without students ever seeing its seeds; and (5) sugarcane, named alongside bamboo for the same reason — since all five involve growing a new plant from a part of an existing plant (leaf, stem, or root) rather than from a seed produced through sexual reproduction.

Solutions written by the tuition.in editorial team and checked against NCERT Curiosity — Textbook of Science for Grade 8, Chapter 13 (hecu113.pdf), Reprint 2026-27, pages 210-228. Questions are referenced from the NCERT textbook for identification.