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NCERT Solutions Curiosity Chapter 13 Chapter opener — Probe and ponder

Book page 210 Updated on2026-09-05

Q1.
What do you think Earth would look like if there were no life on it at all?
Answer

It would still be a blue planet, but a bare one — rock, sand and water, with no green anywhere.

The changes go far deeper than colour, because much of what we think of as 'the Earth' is actually the work of living things:

  • No green land. Forests, grasslands and crops are all life. The continents would look like the bare rock and dust of the Mars pictures in this chapter.
  • Almost no oxygen in the air. The oxygen we breathe is released by plants during photosynthesis. With no plants and no ocean plankton, the atmosphere would hold hardly any of it — and with little oxygen there would be no ozone layer, so ultraviolet rays would reach the surface unchecked.
  • No soil, only broken rock. Soil is rich in nitrogen and potassium because rock breaks down slowly and the remains of plants and animals are added to it. Without life it would be lifeless mineral dust.
  • Still oceans, still weather. Water would remain liquid, clouds would still form and rain would still fall, because that depends on Earth's distance from the Sun and its atmosphere, not on life.
Why it happens: Earth's conditions made life possible, but life then changed the Earth in return — the oxygen, the ozone shield and the soil are all products of living things. That two-way link is exactly what the chapter calls the balance between living and non-living parts of the planet.
Q2.
Life on Earth has survived for billions of years. What allows it to keep going despite major changes and disasters?
Answer

Two different kinds of reason work together — the planet keeps its conditions inside a narrow range, and life itself keeps changing enough to fit whatever range it finds.

1. The physical conditions stay steady.

  • Earth stays in the habitable zone, and its orbit is nearly circular, so sunlight and heat hardly vary through the year.
  • Its gravity holds the atmosphere, whose mild greenhouse effect keeps water liquid and whose ozone layer blocks ultraviolet rays.
  • Its magnetic field turns away cosmic rays and the solar wind.

2. Reproduction lets life adapt. Parents pass on instructions (genes), so each kind continues. But the instructions are not copied perfectly and, in sexual reproduction, instructions from two parents are mixed. So every generation contains individuals that are slightly different from one another. When the surroundings change, some of those individuals happen to cope better and it is their line that continues.

Did you know? The chapter's own examples are camels, which over time developed humps that store fat and let them survive in deserts, and bacteria that have become resistant to antibiotics. Same mechanism, very different timescales.
Why it happens: A disaster does not have to be survived by every individual — only by enough of them. Variation means a population is never a single design, so a change that kills most members can still leave a few that carry on.
Q3.
Why don’t dogs lay eggs? Or hens give birth to live chicks?
Answer

Because a dog and a hen use two different strategies for feeding the developing embryo, and each animal inherits only its own kind's set of instructions.

Hen (a bird)Dog (a mammal)
Where the zygote developsOutside the body, after the egg is laid, during hatchingInside the female's body, until birth
How the embryo is fedFrom the food the mother packs into the egg — it must last until hatchingThe mother's body supplies food and oxygen continuously
What the body must haveLarge yolk-filled eggs and a shell; the behaviour to sit on themAn internal space in which the embryo can grow, and a way to nourish it there

A hen's body is built to make big, food-filled, shelled eggs; a dog's body is not, and vice versa. Reproduction can only pass on the instructions the parents already carry — it cannot swap one whole body plan for another.

Why it happens: Both are answers to the same problem: how do you supply nutrition to a growing embryo? A bird solves it in advance, all at once, by loading the egg. A mammal solves it as it goes, through the mother's body. Neither is 'better' — they simply cost the parent in different ways.
Q4.
If a spaceship carried soil and water to Mars, could plants start growing there?
Answer

Not out in the open. Soil and water are necessary, but they are only two items on the list — and Mars fails most of the others.

A plant needsOn Mars today
Water in the liquid stateThe atmosphere is 100 times thinner than Earth's and the planet is far colder — poured water would mostly freeze or escape as vapour
Carbon dioxide and air pressureCarbon dioxide is there, but the air is far too thin
SunlightAvailable, though weaker than on Earth
A temperature that does not freeze the rootsWell below freezing on average
Protection from ultraviolet rays and high-energy particlesNo ozone layer and no protective global magnetic field like Earth's

Inside a sealed, heated and pressurised chamber, yes. If you also carry the air, the pressure, the warmth and a light source — that is, if you carry a small piece of Earth's atmosphere with you — plants can grow in Martian conditions.

Try this: That is exactly the design problem in the 'Earth Survival Kit' task at the end of this chapter. Make a list of everything the sealed chamber must supply, and you have written the answer to both questions.
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