Probe and Ponder — The Opening Questions — "Our Home: Earth, a Unique Life Sustaining Planet"

1. 12 marks

   What do you think Earth would look like if there were no life on it at all?

   Hint. Think about which features of Earth this whole chapter attributes directly to living things, versus which are purely physical/geological.

   ✦ Without life, Earth would likely still have its oceans, atmosphere, mountains and weather, since these are shaped by physical processes. But it would look very different in other ways — no forests or grasslands to cover the land, no soil built up from decomposed organic matter (since the chapter states nutrients in soil come partly 'from the slow breakdown of rocks and the remains of plants and animals'), and possibly a different atmosphere altogether, since photosynthesis by plants is what continually releases oxygen into the air.

2. 23 marks

   Life on Earth has survived for billions of years. What allows it to keep going despite major changes and disasters?

   Hint. The chapter's own answer to this appears much later, in section 13.5 — a single biological process that ensures continuity.

   ✦ Reproduction is what allows life to keep going, because 'if plants and animals didn't reproduce, life would eventually disappear from Earth.' Beyond simply continuing, reproduction also allows small changes to pass down between generations — such as camels developing humps to survive in deserts, or bacteria evolving antibiotic resistance — which is exactly what lets life adapt to major changes over time rather than simply being wiped out by them.

3. 32 marks

   Why don't dogs lay eggs? Or hens give birth to live chicks?

   Hint. Section 13.5.2 splits sexual reproduction in animals into two different strategies for nourishing the developing embryo.

   ✦ Dogs are mammals, and in most mammals, the development of the zygote into an embryo takes place inside the body of the female, who provides food and oxygen directly until birth — so dogs give birth to live puppies rather than laying eggs. Hens are birds, and in birds, the fertilised egg (zygote) is laid by the female, with the embryo developing afterwards during hatching, nourished by food packed into the egg itself — so hens lay eggs rather than giving birth to live young. Each animal group follows its own reproductive strategy, and does not switch to the other's.

4. 43 marks

   If a spaceship carried soil and water to Mars, could plants start growing there?

   Hint. The chapter lists several factors beyond just soil and water that make Earth suitable for life — check which of those Mars is missing.

   ✦ Probably not successfully, because soil and water alone aren't enough — plants also need the right temperature, a suitable atmosphere (with carbon dioxide for photosynthesis and protection from harmful radiation), and enough gravity to hold that atmosphere in place. Mars's atmosphere is 100 times thinner than Earth's, and Mars sits at the very edge of the Sun's habitable zone, so even with imported soil and water, a plant would likely struggle without also recreating Earth's atmosphere, temperature range, and radiation shielding.

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.