Because a gas is being made inside the dough and cannot get out. The gas collects in thousands of tiny bubbles, each bubble pushes the dough outward, and the whole lump swells. Where the gas comes from depends on how the dough was made: Fermented dough (bread, bhatura , idli and dosa batter): tiny living things — yeasts and certain bacteria — feed on the sugars and starch in the flour and give out carbon dioxide gas as they respire. This is why such dough is left in a warm place for hours. Dough raised with baking soda: no living thing is involved. The soda releases carbon dioxide the moment it meets an acid such as curd or lemon juice. That is why a soda-and- dahi bhatura batter starts bubbling straight away. Why it happens: the gas is only half the story — the dough must also be able to hold it. Kneading wheat flour with water develops gluten into a stretchy, springy network. Gas cannot slip out through it, so each bubble stretches the dough instead of escaping. Un-kneaded flour and water would just fizz and go flat. When the dough is finally baked or fried, the stretched walls set hard around the bubbles — that is why bread is spongy. Try this: take two identical balls of fermented dough. Keep one in a warm corner of the kitchen and one in the fridge. Measure the height of each after 2 hours. You changed only the temperature , so any difference in rising must be caused by temperature — living things work faster when it is warm.

NCERT Solutions Curiosity Chapter 1 Entering the Investigative World of Science — In-text Questions

Book page 2 Updated on2026-09-05

Q1.

Why does dough rise?

Answer

Because a gas is being made inside the dough and cannot get out. The gas collects in thousands of tiny bubbles, each bubble pushes the dough outward, and the whole lump swells.

Where the gas comes from depends on how the dough was made:

Fermented dough (bread, bhatura, idli and dosa batter): tiny living things — yeasts and certain bacteria — feed on the sugars and starch in the flour and give out carbon dioxide gas as they respire. This is why such dough is left in a warm place for hours.
Dough raised with baking soda: no living thing is involved. The soda releases carbon dioxide the moment it meets an acid such as curd or lemon juice. That is why a soda-and-dahi bhatura batter starts bubbling straight away.

Why it happens: the gas is only half the story — the dough must also be able to hold it. Kneading wheat flour with water develops gluten into a stretchy, springy network. Gas cannot slip out through it, so each bubble stretches the dough instead of escaping. Un-kneaded flour and water would just fizz and go flat. When the dough is finally baked or fried, the stretched walls set hard around the bubbles — that is why bread is spongy.

Try this: take two identical balls of fermented dough. Keep one in a warm corner of the kitchen and one in the fridge. Measure the height of each after 2 hours. You changed only the temperature, so any difference in rising must be caused by temperature — living things work faster when it is warm.

Q2.

Is the world getting warmer?

Answer

Yes. Records from thousands of thermometers on land, from ships and buoys at sea, and now from satellites all agree: the average temperature of the Earth’s surface has risen by roughly 1.1 °C to 1.3 °C since about 1850.

Why it happens: burning coal, petrol, diesel and natural gas releases carbon dioxide into the air. Sunlight passes through carbon dioxide easily, but the heat the warm Earth sends back out is partly absorbed by it and returned downward — the gas acts like a blanket. Put more of the blanket in the air and less heat leaves, so the average temperature settles at a higher value.

One degree sounds tiny — why does it matter? Because it is an average over the whole planet and the whole year. Shifting an average shifts the extremes with it: heatwaves become longer and more frequent, the monsoon becomes more erratic, and glaciers that were in slow balance begin to lose more ice than they gain.

How do we know it is not just a hot summer? A single hot day is weather; a rise in the average that holds for more than a century is climate. And separate lines of evidence agree with the thermometers — Himalayan glaciers are retreating, sea level is rising as ocean water warms and expands, and the oceans themselves are measurably warmer.

Tip: the last chapter of this book comes back to this question in full. Notice that the answer rests on a trend measured over time, not on any one observation — that is the difference between a scientific claim and an opinion.

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