Using the chapter's own apple analogy, explain how thin Earth's crust really is compared to the whole planet.
Hint. The chapter compares the crust to a very specific, everyday part of a familiar fruit.
✦ 'If Earth were the size of an apple, the crust would be as thin as the apple's skin.' All of life — mountains, rivers, forests, animals and people — exists on this single, extremely thin outer layer, since it is tiny compared to the size of the whole Earth.
Why does the chapter call this thin crust 'delicate,' and what does that word suggest about protecting it?
Hint. Consider what 'delicate' implies about how easily something can be disturbed or damaged.
✦ The chapter calls the crust 'this delicate, life supporting layer,' since it is both extremely thin relative to the whole planet and the ONLY place where life exists at all — meaning there is no backup layer or safety margin if this thin zone is damaged. Calling it delicate suggests that even relatively small disturbances to this layer (as later sections on pollution and habitat loss describe) could have outsized effects on the life it supports.
Explain, using what you learnt in Chapter 7, why the air we breathe doesn't simply drift off into space.
Hint. Activity 13.1's own first example points you back to an earlier chapter's fact about how gas particles behave.
✦ Activity 13.1 states: 'The air we breathe doesn't fly off and disappear into space' — this is because, as learnt in Chapter 7, particles of a gas move freely and gases do not have a fixed volume, which might suggest they could simply escape upward. Instead, Earth's gravity holds the atmosphere's gas particles close enough to the planet that they stay bound to it rather than drifting away, exactly the same gravitational effect that keeps you standing on the ground.
Activity 13.1 also notes: 'we can stand on the ground held by gravity, but our heart can pump blood up to our head.' Why is this listed as an interesting feature rather than a contradiction?
Hint. Two different forces are at work here, at two very different scales — one holding you down, one working inside you.
✦ It isn't a contradiction because two separate things are happening at once: Earth's overall gravity pulls your whole body toward the ground, keeping you standing on the surface, while your heart is a much smaller, localised pump strong enough to push blood against that same gravity over the short distance up to your head. The example is 'interesting' because it shows the same force (gravity) constraining you at a large scale while still being easily overcome by a small, specialised biological mechanism at a small scale.
List, in your own words, three things Earth provides that the chapter names directly, and classify each as biotic or abiotic in origin.
Hint. The chapter names air, water, soil, and materials for building — think about whether each comes from a living or non-living source.
✦ The chapter states Earth 'provides us with the air that we breathe, the water that we drink, and the soil that helps in growing crops,' plus 'materials like rock and timber with which we build our homes.' Air and water are abiotic (non-living) resources; soil is a mix, since it forms partly from decomposed living matter; and building materials split by type — rock is abiotic, while timber comes from trees, a biotic source.
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.
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