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NCERT Solutions Curiosity Chapter 1 Life processes in animals and plants; time and speed — In-text Questions

Book page 4 Updated on2026-09-05

Q1.
Especially around the middle-school years, our bodies are changing rapidly! Why?
Answer

Because this is the age at which the body begins to grow up into an adult body. Chemical messengers called hormones, released by glands inside the body, switch on a burst of growth and other changes.

  • A growth spurt — height and weight increase faster now than at any time since you were a baby. Bones lengthen, so hands and feet often grow first.
  • Body proportions change — shoulders, hips and muscles develop, and the voice deepens in boys.
  • Feelings change too — mood swings and new interests are a normal part of the same process.
Why it happens: growth is one of the life processes. To build new bone and muscle so quickly the body needs a lot of raw material and energy, which is why appetite rises at this age. All of it is normal, it happens to everyone, and it happens at a different pace for each person — there is no “right” speed.
Tip: Rapid growth needs a balanced diet (dal, milk or curd, green vegetables, fruit, eggs or nuts), 8–9 hours of sleep and daily physical activity. Skipping meals during these years costs more than at any other age.
Q2.
But why animals alone?
Answer

They are not alone — and that is exactly the point the book is making. The paragraph has just listed the life processes of animals (eating, breathing, blood carrying nutrients), and then it stops you short: plants are living too, so plants must be doing all of this as well.

Life processIn animalsIn plants
NutritionEat food made by othersMake their own food in green leaves
RespirationLungs, gills, skin, air tubesStomata, lenticels, root surface
TransportBlood carried by the heartWater and food carried in tubes inside the stem
ExcretionUrine, sweat, breathing outGases through stomata; wastes stored in old leaves and bark
Growth and reproductionYoung ones grow into adultsSeeds germinate and plants grow, flower and seed again
Why it happens: a life process is any process a body must run to stay alive. Every living thing — an elephant, a mango tree, a mushroom, a bacterium — has to take in materials, release energy, move things about and grow. Only the machinery differs, never the need.
Q3.
Don’t plants also need food to grow?
Answer

Yes, of course they do. Food does two jobs for every living thing, and a plant needs both.

  • Energy — released from food during respiration, and used for growing, repairing and moving materials about.
  • Building material — the new leaves, roots, stem, flowers and seeds of a plant are all built out of substances made from its food.

The proof is easy to see. A gram seed on wet cotton in a dark cupboard sprouts, grows pale and thin, and then dies. A second seed kept in sunlight grows green and strong. The first one used up the food stored in the seed and could make no more.

Why we miss it: we do not see a plant eating, so it feels as if it lives on nothing but water. In fact a plant is doing something far cleverer than eating — it is manufacturing its food out of air, water and sunlight, right where it stands.
Q4.
How do they get their food?
Answer

Green plants make their own food by the process of photosynthesis, which happens mainly in the leaves.

Carbon dioxide + Water  —sunlight, chlorophyll→  Food (glucose) + Oxygen

Where each ingredient comes from:

  • Carbon dioxide — from the air, through tiny pores in the leaf called stomata.
  • Water and minerals — pulled up from the soil by the roots and carried to the leaves through tubes in the stem.
  • Sunlight — the energy source.
  • Chlorophyll — the green colouring matter of the leaf, which traps the sunlight. This is why the leaf is the “food factory” of the plant.

A few plants cannot do this and get food in other ways: amarbel (Cuscuta), the yellow thread-like plant, sucks food from the plant it twines around; the pitcher plant traps insects to make up for poor soil.

Why it matters to us: photosynthesis is where nearly all the food on Earth begins. Whether you eat rice or fish, the energy in your meal was first captured from sunlight by some green leaf. The oxygen you are breathing right now came from the same process.
Q5.
Do they also breathe? How?
Answer

Yes. Plants respire all day and all night, in every living cell. They simply have no lungs and no nose, so the exchange of gases happens through small openings spread over the plant body.

  • Leaves — through stomata, tiny pores on the leaf surface that open and close.
  • Stems — through lenticels, small breaks in the bark of woody stems.
  • Roots — the root surface takes in air from the spaces between soil particles.
RespirationPhotosynthesis
WhenAll the time, day and nightOnly in light
WhereEvery living cellOnly in green parts
Gas taken inOxygenCarbon dioxide
Gas given outCarbon dioxideOxygen
Why plants seem not to breathe: in bright daylight a green leaf uses up carbon dioxide for photosynthesis much faster than its respiration produces it, so from outside it looks as though the leaf only gives out oxygen. Respiration has not stopped — it is simply hidden behind the larger process.
Check it yourself: Over-water a potted plant for a few days and it wilts. The water has filled the air spaces in the soil, so the roots cannot get oxygen. Proof that roots really do need to breathe.
Q6.
Ah, but what is time?
Answer

Time is what we measure between two events. It answers two different questions: which event came first, and how long something lasted.

Time is not a thing you can hold, weigh or put in a box — but it can be measured, and that is enough for science. We measure it exactly the way we measure length: by choosing a fixed unit and counting how many of them fit in.

1 minute = 60 seconds
1 hour = 60 minutes = 3600 seconds
1 day = 24 hours = 24 × 3600 = 86 400 seconds

The second (s) is the SI unit of time. Notice that our everyday units all come from repeating events in the sky — a day is one spin of the Earth, a month is roughly one round of the Moon, a year is one round of the Earth about the Sun.

Why it happens: a clock is possible only because some events repeat with the same duration every time. If sunrise came after a short gap one day and a long gap the next, no calendar could ever have been made.
Q7.
…but have you thought about how we measure time?
Answer

By counting a repeating event. Any event that repeats after exactly the same interval can be turned into a clock; the whole history of timekeeping is a hunt for events that repeat more and more reliably.

DeviceThe repeating event it counts
Sundial (shadow clock)The Sun’s daily journey moving the shadow across a dial
Water clock, sand clock (hourglass)A steady trickle of water or sand emptying a fixed vessel
Pendulum clockThe to-and-fro swing of a pendulum
Quartz watch, mobile phoneThe vibrations of a tiny quartz crystal
Atomic clockVibrations inside atoms — the most reliable of all

The oldest method is the one mentioned on this page of your book: long before electric clocks, people watched the shadow of an object in the Sun and read the time from where the shadow fell. The Jantar Mantar observatories at Jaipur and Delhi still carry giant stone sundials built on exactly this idea.

Why a pendulum works so well: for a given length, a pendulum takes the same time for every swing, whether the swing is wide or narrow. Count 60 such equal swings and you have a fixed interval you can trust — which is why pendulum clocks ruled for nearly 300 years.
Try This: Tie a small stone to a 1-metre thread and let it swing. Count the time for 20 complete swings and divide by 20 to get the time for one. Repeat with a half-metre thread. The shorter pendulum swings faster — you have just built and tested a clock.
Q8.
And how fast does something happen?
Answer

“How fast” is a question about rate — how much of something happens in one unit of time. For a moving object we call it speed.

Speed = Distance travelled ÷ Time taken

A runner covers 100 m in 20 s
Speed = 100 ÷ 20 = 5 m/s
In km/h: 5 × 3600 ÷ 1000 = 18 km/h

Comparing speeds is what makes a race meaningful. Of two runners, the faster one is the one who covers the same distance in less time, or a greater distance in the same time.

“How fast” applies to changes too, not only to motion:

  • A matchstick burns in a few seconds — a fast change.
  • An iron gate rusts over months — a slow change.
  • A rock crumbles into pebbles over thousands of years — an extremely slow change.
Why it happens: to say how fast, you must always divide by the time taken. That is why “fast” is meaningless on its own: a bus covering 60 km is neither fast nor slow until you are told whether it took one hour or one day.
Check it yourself: Time a friend walking the length of your school corridor and measure the corridor with a metre scale. Divide length by time — that is your friend’s speed in metres per second. Ordinary walking works out to about 1.2–1.5 m/s.
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