NCERT Solutions Curiosity Chapter 13 Science • Society • Interdisciplinary Projects — Discover, design, and debate

Book page 227 Updated on2026-09-05

Q1.

Design an ‘Earth Survival Kit’. Imagine you’re building a tiny model of Earth for another planet. What must it have to support life, and why?

Answer

How to approach it. Do not start by listing objects. Start with the four Earth systems in Section 13.4 — atmosphere, hydrosphere, geosphere, biosphere — and ask what the kit must supply in place of each. Then add the two protections Earth gives for free: warmth and shielding. A good kit also explains how each item is replenished, because a supply that runs out is not survival.

Sample answer — the Earth Survival Kit:

Item in the kit	Which Earth system it replaces	Why it is needed
A sealed, pressurised dome filled with a breathable gas mixture	Atmosphere	Oxygen for respiration, carbon dioxide for photosynthesis, and pressure so that water can stay liquid
A water tank with a recycling and purification unit	Hydrosphere	Drinking, growing food, transporting nutrients; every drop must be used again
Soil, or a nutrient bed with nitrogen and potassium	Geosphere	Plants need nutrients and an anchorage for roots
Seeds and plants, plus decomposing microbes	Biosphere	Plants make food and release oxygen; decomposers return nutrients to the soil so the loop closes
A light and heat source (solar panels, a heater)	The Sun plus the greenhouse effect	Photosynthesis needs light; without warmth the water freezes
Thick shielding — metres of soil or rock over the dome	Ozone layer and magnetic field	To block ultraviolet rays and high-energy particles

Why it happens: The hardest part of the design is not any single item but making the loops close. On Earth nothing is consumed for good — oxygen, water and nutrients all cycle. A kit that only carries supplies has a fixed lifetime; a kit in which plants, animals and microbes feed one another can keep going. That is why the chapter insists that life is sustained by connections, not by resources alone.

Q2.

India is planning for a challenging lunar mission, Chandrayaan-4, which will bring back samples of soil from the Moon. If the Moon had water, could plants grow in that soil? Think of some experiment that could help you explore whether plant growth is possible on the Moon.

Answer

Water alone would not be enough — but lunar soil plus water plus Earth-like air, warmth and light might well work, and that is exactly what an experiment should test.

What lunar soil has and lacks. It is crushed rock and dust, so it contains minerals. What it does not have is the part of Earth's soil that comes from life — the nitrogen and other nutrients released by the breakdown of plant and animal remains. It also has no decomposers, and it has been exposed to raw solar particles for billions of years.

A fair experiment you could design (using a small quantity of returned sample, or a simulated lunar soil made from crushed volcanic rock):

Question: Can seeds germinate and grow in lunar soil given water, air and light?
Set-up: Four identical sealed transparent containers, each with the same mass of soil, the same number of seeds of a fast-growing plant such as moong or mustard, and the same water, temperature and light.
- A — lunar (or simulated lunar) soil
- B — ordinary garden soil, the control
- C — lunar soil with a little compost added
- D — lunar soil with no water added, to confirm water is the limiting factor
Keep everything else the same — only the soil differs. Change one thing at a time.
Measure: how many seeds germinate, on which day, the height after two weeks, the number of leaves, and the colour of the leaves.
Repeat each container at least three times, because a single pot can fail for reasons that have nothing to do with the soil.

Why it happens: A seed germinates on its own stored food, so it may well sprout in almost any damp medium — including lunar dust. The real test comes after that, when the seedling must draw nutrients from the soil. Comparing A with C tells you whether the missing ingredient is nutrients; comparing A with B tells you how far behind Earth soil it is; D confirms that you have not simply been watching the seeds' own food store.

Tip: Whatever the result, the experiment says nothing about growing plants on the Moon in the open. There is no atmosphere there, so this test is really about a sealed lunar greenhouse.

Q3.

Flowers are often brightly coloured and have a pleasant smell. How do you think these features help the plant reproduce?

Answer

They are advertisements — aimed at insects, birds and other animals that will carry pollen from one flower to another.

A plant cannot move, but its male gametes must reach another flower for fertilisation to happen. Pollen is carried by wind, insects or animals; this process is pollination. Bright colour and scent solve the plant's problem of attracting a carrier:

Colour is visible from a distance and tells an insect where to come. It works in daylight.
Scent works where colour cannot — at night, and among leaves. Flowers that open at night, like raat ki rani, are usually pale but strongly scented.
Nectar is the reward that makes the visit worthwhile, so the animal returns and visits other flowers of the same kind.

As the insect pushes in for nectar, pollen from the anther sticks to its body, and it rubs off on the next flower it enters. Male and female gametes then combine — that is fertilisation — forming a zygote that becomes the seed, while the fleshy part of the flower around the ovule develops into a fruit.

Why it happens: Colour and scent cost the plant energy to make, so they must be earning something. They are only found in plants pollinated by animals. Wind-pollinated plants — grasses, maize, many trees — have small, dull, scentless flowers, because there is no point advertising to the wind. That contrast is the strongest evidence that these features exist for pollination.

Check it yourself: Sit near a flowering plant for ten minutes and count the visitors. Then look closely at a grass flower or a maize tassel — no petals, no scent, but enormous quantities of light pollen. Two different solutions to the same problem.

Q4.

Why do animals like fish and frogs lay hundreds or even thousands of eggs at a time, while other animals lay only a few? What might be the advantages and disadvantages of laying so many eggs?

Answer

Because in fish and frogs almost nothing protects the eggs — so survival is a matter of numbers.

Recall how fertilisation works in these animals: male and female fish or frogs eject sperm and eggs into the water, where they combine to form the zygote, and the zygote develops into an embryo in the water. From that moment the eggs are on their own — floating in open water, uncared for, and eaten by other fish, insects and birds. Out of a thousand eggs, only a handful may reach adulthood. Laying a thousand is what makes that handful possible.

Advantages of laying very many eggs	Disadvantages
Even with heavy losses, some survive, so the species continues	Very little food can be put into each egg, so the young hatch small and helpless
Fertilisation in open water is uncertain; many eggs raise the chance that some are fertilised	No parental care is possible for so many, so most are lost to predators
Many eggs mean many different combinations of instructions, so more variation in the offspring	Producing thousands of eggs costs the female a great deal of energy each season
A population can recover quickly after a bad year	Numbers swing wildly with conditions rather than staying steady

Why other animals lay only a few. Birds lay a small number because each egg is loaded with enough food for the whole of development and is then guarded, warmed and defended. Investing heavily in a few and protecting them achieves the same end — some survive — by the opposite route.

Why it happens: A parent has a limited amount of energy for reproduction and can spend it in one of two ways: many cheap offspring with no protection, or few expensive offspring with a great deal of protection. Water makes the first strategy workable, because eggs do not dry out and gametes can meet by simply being released. On land the first strategy fails, so land animals almost always take the second.

Q5.

Birds like sparrows build nests and care for their eggs and chicks, while reptiles like snakes usually lay their eggs and leave them without protection. How might this difference in parental care affect the chances of survival for the young ones in each case?

Answer

Each individual sparrow chick has a far better chance of surviving than each individual snake hatchling — but the snake makes up for it with numbers.

	Sparrow — with parental care	Snake — without parental care
Number of eggs	Few	Usually many more
While the egg develops	The nest hides it, the parents warm it and drive off predators	Buried or hidden and then abandoned; many are eaten or destroyed
After hatching	Parents bring food and shelter until the chick can fly and feed itself	The hatchling must find its own food and escape predators from day one
Chance that any one young survives	High	Low
Cost to the parents	Very high — weeks of feeding and guarding	Low — the work ends when the eggs are laid

Why it happens: Both strategies survive the same test: enough young reach adulthood to keep the population going. The sparrow reaches that number by protecting a few very well; the snake reaches it by producing many and protecting none. Care is not simply 'better' — it is bought with the parents' own time and safety, and a parent busy guarding a nest is a parent that is not feeding or escaping. Which strategy wins depends on how dangerous the surroundings are and on how much a parent can afford to give.

Did you know? The same trade-off appeared in the previous question about fish and frogs, and again in the comparison between laying eggs and giving birth to young ones. It is one of the recurring patterns of biology — invest a little in many, or a lot in few.

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