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NCERT Solutions Curiosity Chapter 2 In-text Questions — How Are We Connected to Microbes?

Book page 18 Updated on2026-09-05

Q1.
Can we find microorganisms in other places, too?
Answer

Yes — microorganisms can be found everywhere.

  • In water, soil and air, and even in some food items.
  • On the surfaces of leaves, stems, roots or any other part of a plant — you can explore these with a microscope.
  • In extreme climatic conditions such as hot water springs and snow cold zones, as well as at moderate temperatures.
  • Inside our own bodies, especially in our gut. As you studied in ‘Life Processes in Animals’ in Curiosity, Grade 7, our intestine has many bacteria that help in digestion.
Why they are everywhere: microorganisms are extremely small and extremely varied. Like plants and animals they differ in shape, size and structure — spherical, rod-shaped, spiral, comma-shaped or irregular — and this diversity means that for almost any set of conditions on Earth, hot or cold, wet or dry, there is some microbe that can live in it.
Q2.
Have you ever seen a lemon, tomato, orange, or any other food item rot after being left outside for some time? If yes, you may have noticed a powdery or cotton-like growth on them (Fig. 2.9). This happens because they have been infected by microbes. But where did these microbes come from? How did they come in contact with the food?
Answer

They came from the surroundings — from the air, from the surface the fruit was kept on, from the water it was washed in and from the hands that touched it. Microorganisms are present everywhere: in water, soil and air, so a fruit lying in the open is never actually in a microbe-free place.

What then happens on the fruit itself:

  1. Very small fungal and bacterial forms settle on the fruit's skin from the air and from whatever it rests on.
  2. A ripe fruit gives them everything they need — it is moist, it is full of sugar, and the room is warm. These are exactly the conditions in which microorganisms grow.
  3. A bruise or a cut in the skin lets them reach the soft flesh inside.
  4. They multiply. The fungus grows as branched filaments, which is why you see a cotton-like or powdery patch — you are looking at a colony large enough for the naked eye, not at one organism.
Why it looks like rotting: the microbes are feeding. They break down the complex substances of the fruit into simpler ones — the same process by which they turn fallen leaves into manure. The fruit softens, darkens and smells because its material is being decomposed.
Check it yourself: keep two identical slices of the same fruit, one in the open and one in the refrigerator. The cold one stays fresh far longer, because low temperature slows the growth of these organisms — it does not remove them.
Q3.
But why do microorganisms not infect the pickles and murabbas?
Answer

Because of what is added to them. The book's own answer: you add many spices with salt or sugar, which act as preservatives. A high concentration of salt or sugar does not allow these organisms to grow on them.

Why a strong salt or sugar solution stops them: a microorganism can only grow where there is water it can use. In a pickle almost all the water is locked up in a very strong salt solution, and in a murabba in a very strong sugar syrup, so almost no free water is left for the microbe. Worse for the microbe, such a strong solution outside its cell draws water out through its cell membrane, so the cell shrinks and cannot multiply. The oil layer on top of a pickle helps further by keeping the surface away from moist air.
Did you know? This is why our grandmothers always insisted on a dry spoon for the pickle jar. A drop of water lowers the salt concentration just at that spot — and that is exactly where the fungus appears first.
Q4.
How does the diversity of microorganisms play a role in our daily life? How do they help clean the environment?
Answer

Different kinds of microbes do different jobs for us, and the most important of these jobs is breaking down waste.

WhereWhich microbeWhat it does for us
Soil and compost pitFungi and bacteriaAct on plant waste and dead animal bodies and break the complex substances down into simpler, nutrient-rich manure — decomposition. The nutrients go back to the soil.
Oxygen-free surroundings, wastewaterCertain bacteriaDecompose plant and animal waste and release biogas — mainly methane with carbon dioxide — used for cooking, heating, electricity and even vehicles.
Root nodules of legumesRhizobiumTraps nitrogen from the air and makes it useful to the plant, so crops grow well without chemical fertilisers.
KitchenYeast, LactobacillusMakes bread, cakes and bhaturas rise; ferments idli and dosa batter; turns milk into curd.
Our gutBacteriaHelp in digestion.
Water bodiesMicroalgaeMake their own food using sunlight and release oxygen — more than half of Earth's oxygen supply; feed aquatic animals; help clean water and are used to make biofuel.
Polluted sitesSpecially developed bacteriaBreak down oil spills — the bacterium developed by Ananda Mohan Chakrabarty in 1971.
Why decomposition is the key service: the nutrients in a fallen leaf or a dead animal are locked inside complex substances that a plant cannot take up. Microbes break those substances into simple, nutrient-rich ones that dissolve and return to the soil. Without this step the waste would pile up and the nutrients would never come back into use — so microbes both clean the environment and recycle it.
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