Class 7 Science Chapter 1 – The Ever-Evolving World of Science | Solutions
Curiosity • Textbook of Science • Grade 7
Chapter 1 — The Ever-Evolving World of Science
Complete solutions of every question given in the chapter, explained step by step with diagrams.
In-Text Questions — Activity 1.1: Question the Answer
What the activity asks: Normally you are given a question and asked to find the answer.
Here the answer is already given and you must invent the question. There are no wrong
questions — only more interesting or less interesting ones. Below, each answer is solved with a
best question plus several alternative questions, so you can see how the same answer can fit
many different situations.
Fig. 1 — Science is a way of thinking, not just a set of facts.
Q1
Question: ____________________________________? Answer: Just add some milk.
SOLUTION
Best question
“My tea has become too strong and bitter — what should I do to make it lighter?”
How to think about it (step by step)
Step 1 – Read the answer carefully. “Just add some milk” is an
instruction. So the question must be a problem for which adding milk is the cure.
Step 2 – Ask where milk is useful. Milk makes things lighter in colour,
less bitter, less spicy, thinner, creamier, and it makes dry things wet.
Step 3 – Build situations around each use. Each use gives a completely
different — but perfectly correct — question.
Other creative questions that fit
Everyday: “How do I make my coffee less bitter?” • “The curry has become too spicy — how do I cool it down?” •
“How can I finish this dry cornflakes when there is nothing to pour on it?” Science-flavoured: “How can I make a transparent glass of water look cloudy (translucent), so that a laser beam becomes visible in it?” •
“What can I add to water to turn it into a colloid?” • “The batter for the dosa is too thick — how do I make it flow easily?” Funny: “What is the only way to make my cat come running?” • “How do I turn plain tea into ‘doodh-patti’?”
Key idea: One answer can be the ending of many different stories. A good
question is the one that makes the answer surprising and interesting, not obvious.
Q2
Question: ____________________________________? Answer: Because the cat’s teeth were crooked.
SOLUTION
Best question
“Why did the mouse manage to escape from the cat even after being caught?”
How to think about it (step by step)
Step 1 – Spot the word “Because”. The answer begins with “because”, so the
question must begin with “Why …?” — it is asking for a reason or a cause.
Step 2 – Find what crooked teeth can cause. Crooked teeth mean the cat
cannot bite properly, cannot hold prey, chews slowly, its smile looks odd, it may need a vet.
Step 3 – Turn each effect into a “Why …?” question.
Other creative questions that fit
Story type: “Why did the cat visit the dentist?” • “Why could the cat not hold the fish in its mouth?” •
“Why did the cat give up hunting and start drinking only milk?” Observation type: “Why did the bite marks on the biscuit look zig-zag instead of straight?” •
“Why did the scientist say that this tooth fossil belonged to that cat and not to any other animal?” Funny: “Why did the cat lose the ‘best smile’ competition?”
Key idea: A cause-and-effect answer (“because …”) always pairs with a
Why question. Scientists ask exactly this kind of question: why do events happen the way
they do?
Q3
Question: ____________________________________? Answer: Don’t panic, I have my towel.
SOLUTION
Best question
“The water bottle has spilled all over my books — what do we do now?”
How to think about it (step by step)
Step 1 – Notice two parts in the answer. “Don’t panic” → somebody is
worried about a small emergency. “I have my towel” → the towel is the solution.
Step 2 – List what a towel can do. It absorbs water, wipes a spill, dries hair,
holds a hot vessel, covers you, can be waved as a signal, can be a picnic mat.
Step 3 – Make a small emergency for each use.
Other creative questions that fit
Everyday: “It has started raining and we are still on the ground — how will we dry ourselves?” •
“The beaker of water tipped over on the lab table — how do we clean it before it reaches the sockets?” •
“How will you lift the hot vessel from the stove without burning your hand?” Adventure: “We are going on a long space journey — what is the one most useful thing you carry?”
(a fun nod to The Hitchhiker’s Guide to the Galaxy, where a towel is the traveller’s most useful object).
Key idea: Observe the tone of an answer too. A calm, confident answer
tells you the question described a small panic or a problem.
Step 4 – Answer. The butterfly flaps its wings 42 times. ✔ (matches the given answer)
The textbook itself says: do not ask an obvious question like “What is 32 + 10?”, and also not
“What is the answer to life, the universe and everything?” (the famous joke answer “42” from the book
The Hitchhiker’s Guide to the Galaxy). So we must invent something more curious.
Other creative questions that fit
Measurement type: “How many seconds does the pendulum of the wall clock take to complete 21 full swings, if one swing takes 2 seconds?” •
“A paper plane travels 6 m in one throw. How many metres will it cover in 7 identical throws?” Counting type: “How many students in our class of 60 said that ‘asking questions’ is their favourite part of science?” •
“How many teeth does an adult human have, if 42 is counted for a dog?” (a dog has 42 teeth!) Data type: “What was the temperature (in °C) recorded in Indore on the hottest day of May?”
Key idea: A number becomes an interesting answer only when the question gives it
a unit and a situation. Great scientists ask amazing questions — remember,
“to be a wise person, you must be a whys person”.
Exercise & Practice Questions (from the chapter)
Chapter 1 is an introductory chapter, so the textbook gives only Activity 1.1 and no printed
exercise list. The questions below are framed directly from the text and the pictures of this
chapter and are the type asked in school tests.
Q1
Why is science called a process and not just a collection of facts?
SOLUTION
Science is called a process because it is a way of thinking, not a finished list of answers.
It welcomes curiosity — it begins when we notice something and wonder about it.
It asks questions — How do things work? Why do events happen the way they do? What patterns do we see in nature?
It is open to the unknown — a scientist is willing to say “I do not know yet, let us find out”.
It is tested by activities and experiments, not accepted just because someone said so.
It is never finished — even an experiment that confirms what we expected can raise new questions needing new experiments.
That is exactly why the chapter is called “The Ever-Evolving World of Science” — our
understanding keeps growing and changing.
Q2
What is special about the page numbers of this book, and what does it teach us?
SOLUTION
The page numbers follow the playful flight of a butterfly and the soaring of a paper plane.
Meaning
A butterfly flutters freely → learning should be free, playful and curious.
A paper plane soars into the sky → learning “takes flight” when curiosity leads the way.
Something as simple as a paper plane actually inspired real scientific exploration of flight:
early inventors studied bird wings, and modern engineers design aircraft.
So the dream of flying began with simple observations and experiments — exactly what this book wants you to do.
Q3
“Different chapters of science are all interconnected.” Explain with the help of a diagram.
SOLUTION
Although the book has separate chapters on physics, chemistry, biology and earth sciences,
they are not separate worlds. A scientific idea in one area inspires discoveries in another, or at
least allows us to ask new questions in another area.
Fig. 2 — The branches of science are connected to one another.
Example from this chapter
Heat is studied in physics; the same heat ripens fruits (biology) and melts a glacier
and evaporates sea water (earth science), and it also speeds up chemical changes in materials
(chemistry). One idea — four subjects.
Q4
Look at the picture given in the chapter. Which everyday questions about materials does the book ask us to explore?
SOLUTIONFig. 3 — Why are some fruits sour? (from the chapter)Fig. 4 — What happens when we wash a haldi stain on our school uniform? (from the chapter)
The book begins with the properties of materials around us — things we experience daily but
never ask questions about:
Why are some fruits sour? (lemon, raw mango, tamarind, tomato) — this leads to the study of
acids and bases.
What happens when we wash a haldi stain on our school uniform? The yellow stain turns
reddish when soap (a base) touches it — turmeric acts as a natural indicator.
Both questions show the same big idea: ordinary things at home are full of science, if we
are willing to ask.
Q5
Using batteries, lamps and wires, what do we try to find out? How does it lead to metals and non-metals?
SOLUTIONFig. 5 — Testing a material in a simple circuit (from the chapter)
Step 1 – Make a simple circuit. Connect a battery, a lamp (bulb) and wires, and
leave a gap in the circuit.
Step 2 – Place the test material in the gap — for example the steel spoon shown in
the picture, then a plastic scale, a piece of wood, a pencil lead, a coin, etc.
Step 3 – Observe the lamp.
If the lamp glows → the material lets electricity pass → it is a conductor (usually a metal, like the spoon).
If the lamp does not glow → it is an insulator / poor conductor (usually a non-metal, like plastic or wood).
Step 4 – Classify. By testing many materials we classify them on the basis of their
properties, and this is how we enter the world of metals and non-metals.
Q6
Classify the changes mentioned in the chapter into reversible and irreversible changes: a torch battery running out, ice melting into water, fruits ripening, rocks breaking into pebbles.
SOLUTION
Change
Type
Reason
Ice melts into water
Reversible
On cooling, the water freezes back into ice. No new substance is formed.
A torch battery runs out
Irreversible
The chemicals inside are used up; the cell cannot be used again.
Fruits ripen
Irreversible
A ripe fruit can never be turned back into a raw fruit.
Rocks break into pebbles
Irreversible
The pebbles cannot be joined back into the original rock.
Fig. 6 — Reversible vs irreversible changes.
Many of these changes happen — or happen faster — when things are heated.
Q7
Describe the journey of water shown in the chapter. Which force / agent drives it?
SOLUTIONFig. 7 — Water is everywhere: the never-ending journey of water (from the chapter)
Step 1 – Heating. The heat of the Sun falls on the seas, lakes and rivers.
Step 2 – Evaporation. Water changes into water vapour and rises up.
Step 3 – Condensation. High above, the vapour cools and forms clouds.
Step 4 – Precipitation. The water falls back as rain (or snow on the mountains).
Step 5 – Infiltration. Some rain water trickles down into the ground and
travels underground, coming out somewhere far away.
The Sun’s heat is the engine of this whole journey — which again shows how heat
(physics) and water (earth science) are connected.
Q8
What are life processes? Name the questions the chapter raises about plants.
SOLUTIONFig. 8 — Plants also need food to grow (from the chapter)
Life processes are the basic activities that are essential for the survival of all living
things. The chapter mentions:
Nutrition — we have to eat to grow.
Respiration — we have to breathe.
Transport / circulation — blood circulates the nutrients from food all over the body.
Along with growth (our bodies change rapidly around the middle-school years).
The questions asked about plants
Don’t plants also need food to grow?
How do they get their food?
Do they also breathe? How?
Over the long time that life has evolved on Earth, it has worked all this out in a
beautiful and carefully balanced way.
Q9
How did early humans measure time, long before clocks and digital watches? Draw/identify the device.
SOLUTIONFig. 9 — A sundial (from the chapter)
Early humans observed the shadows of objects in the Sun and used the position of the shadow
to tell the time.
How a sundial works
Step 1. A slanting pointer (called the gnomon) is fixed on a flat dial marked with hours.
Step 2. As the Earth rotates, the Sun appears to move across the sky, so the direction and length of the shadow keeps changing.
Step 3. The mark on which the shadow falls tells us the time of day.
Today we use pendulum clocks and wrist watches (see the wall clock shown in the chapter),
but the idea began with a simple observation of a shadow.
Fig. 10 — A modern pendulum wall clock (from the chapter)
Q10
Apart from telling time, what else do light and shadows help us understand?
SOLUTION
Light and shadows are used for shadow puppets and for telling the time (sundial).
Naturally, light helps us see. Today we have developed many ways to generate light, so we
can read a book at night even when the Sun does not shine.
More importantly, asking questions about the nature of light has given us a very
deep understanding of the universe.
Light also shows us the behaviour of mirrors — multiple images are formed when mirrors are
placed at an angle to each other.
Even the Earth and the Moon cast shadows, which produce the fascinating phenomena of
eclipses.
Fig. 11 — Multiple images formed by mirrors placed at an angle (from the chapter)Fig. 12 — A beam of light travelling through a glass — a simple experiment that raises new questions (from the chapter)
Q11
Which movements of the Earth and the Moon must we understand, and what do they cause?
SOLUTIONFig. 13 — An eclipse (from the chapter)Fig. 14 — Day and night depend on receiving light from the Sun (from the chapter)
Movement
What it causes
The Earth rotates about its axis
Day and night — the half facing the Sun has day, the other half has night.
The Moon revolves around the Earth
Shadows of the Earth and Moon → lunar and solar eclipses.
The Earth revolves around the Sun
The long-term cycle that affects life on our planet.
All of this happens only because the Earth and Moon receive light from the Sun and can
cast shadows. Isn’t it amazing that we humans can wonder about the wonderful world we live in?
Q12
The chapter says science is not just about discovery but also about responsibility. Explain.
SOLUTIONFig. 15 — Young explorers observing, discussing and questioning together (from the chapter)
As young science explorers we soon see that human activities are linked to what happens in the
natural world, and are also connected to the society we live in.
So whatever we do — burning fuel, wasting water, cutting trees, throwing plastic — has an effect
on nature and on other people.
Science can play a big role in addressing environmental challenges (pollution, melting
glaciers, shortage of water) and in creating a more sustainable world.
Therefore knowledge brings responsibility: we must use what we learn to protect the
environment, not to harm it.
Q13
Rocks breaking into pebbles is shown in the chapter. Suppose a big rock of mass 24 kg breaks into pebbles of 400 g each. How many pebbles are formed? (Numerical)
SOLUTIONFig. 16 — Rocks break into pebbles — an irreversible change (from the chapter)
Step 1 – Given.
Mass of rock, \(M = 24\ \text{kg}\); Mass of one pebble, \(m = 400\ \text{g}\)
Step 2 – Make the units the same.
$$M = 24\ \text{kg} = 24 \times 1000\ \text{g} = 24000\ \text{g}$$
Step 3 – Use the relation.
$$\text{Number of pebbles},\; n = \frac{M}{m}$$
Step 5 – Answer.60 pebbles are formed.
Note that the total mass stays the same (24 kg) even though the rock has broken — only the
shape and size changed, and the change is irreversible.
Q14
In a race, a student runs 100 m in 20 s (see the picture of the runners). Find her speed. (Numerical — “how fast does something happen?”)
SOLUTIONFig. 17 — How fast does something happen? (from the chapter)
Step 4 – Convert to km/h (optional).
$$v = 5 \times \frac{18}{5} = 18\ \text{km/h}$$
Answer: Her speed is 5 m/s, i.e. 18 km/h.
Measuring time is what lets us answer “how fast does something happen?” — which is
why the chapter moves from clocks and sundials straight to speed.
Q15
“To be a wise person, you must be a whys person.” What does this sentence mean for a student of science?
SOLUTION
The sentence is a pun — “wise” and “whys” sound the same.
It means that wisdom comes from asking “Why?” again and again, instead of accepting things
silently.
Great scientists don’t just answer questions — they ask amazing ones. A good question can open
up an entirely new field of science.
For a student it means: be curious, question the ordinary (why is a lemon sour? why does a battery
die? why does a shadow move?), test your ideas by experiment, and be ready for the answer to lead
to even more questions.
That is the real message of this chapter — let your imagination take flight:
explore new ideas, discover wonders, and reach for the skies!
