NCERT Solutions Curiosity Chapter 2 Science · Society · Interdisciplinary Projects — Discover, design, and debate

Book page 27 Updated on2026-09-05

Q1.

India has a long history of biogas production. One of our oldest biogas plant was set up in late 1850s. Find out about the Biogas Program initiated by the Ministry of New and Renewable Energy, Government of India.

Answer

Start from what the chapter already told you, then look up the programme. Biogas is the mixture of gases released when certain bacteria decompose plant and animal waste, or household wastewater, in an oxygen-free environment. It is mainly methane with carbon dioxide, and has been used as a fuel for cooking, heating, generating electricity and even running vehicles.

Where to look: the website and annual report of the Ministry of New and Renewable Energy (MNRE), Government of India; your district's agriculture or rural development office; a nearby village that has a working plant.

What to find out and record:

The name of the current national biogas programme and the year it began.
What size of plant a family gets, what it is fed with (cattle dung, kitchen waste, farm waste), and how much gas it gives in a day.
What financial help the government gives towards building a plant, and who is eligible.
How many plants have been installed in your state, and the trend over the last few years.
What happens to the slurry left behind after the gas is taken out.

Why a biogas plant solves two problems at once: the waste that goes in would otherwise rot in the open and be a nuisance. Inside the sealed plant the same rotting is done by bacteria that live without oxygen, and the gas they release is collected instead of being lost. The material left over is already decomposed — it is manure. So the plant gives fuel and fertiliser from the same waste, which is why it suits a village household so well.

Tip for the report: add one local fact — the number of plants in your own block, or a photograph of a plant near you — and one clear diagram of how the dung goes in, the gas comes off the top and the slurry comes out at the other end.

Q2.

Fermented food items like fermented soya bean and fermented bamboo shoots are consumed as traditional food in some parts of India. With the help of your parents and teachers, list some traditional food items from your area that utilise the process of fermentation. Investigate the ingredients used in the preparation of these fermented food items; the method of preparing them; the microorganism responsible for the fermentation of the food, and the cultural and nutritional importance of the fermented food.

Answer

Make the list first, and for each food record the four things the question asks: ingredients, method, microorganism, and cultural or nutritional importance.

Sample list (add your own local dishes):

Food	Main ingredients	Method in short	Microorganism mainly responsible
Curd (dahi)	Milk + a spoon of old curd	Warm milk, add starter, keep in a warm place overnight	Lactobacillus and other bacteria
Idli and dosa	Rice and urad dal, salt	Soak, grind, keep the batter in a warm place until it rises	Lactobacillus, with yeasts
Bhatura	Maida, curd or yeast	Knead and keep the dough covered in a warm place	Lactobacillus or yeast
Bread, cake, pastry	Flour, sugar, yeast	Knead with warm water and let the dough rise	Yeast (a fungus)
Kanji	Black carrot or beetroot, mustard, salt, water	Keep the jar in the sun for a few days until it turns sour	Lactic acid bacteria
Fermented bamboo shoots (soibum, and pickles of bamboo shoot)	Tender bamboo shoots, salt	Shred, pack tightly in a covered container, leave for weeks	Lactic acid bacteria
Fermented soya bean (kinema, tungrymbai, axone)	Boiled soya beans	Wrap the warm boiled beans and keep them in a warm place for one to three days	Bacteria of the Bacillus group
Fermented leafy greens and radish (gundruk, sinki)	Mustard or radish leaves, radish	Wilt, press into a container without air, ferment, then dry	Lactic acid bacteria

Cultural and nutritional importance to write about: fermented foods keep far longer than the fresh material, which mattered greatly before refrigeration and still matters in hill areas in winter; they are easier to digest; fermentation gives them their characteristic sour taste and smell; and each of these dishes belongs to a particular community and season, so the recipe is passed down in families.

What is actually happening in every one of these: the microorganism is feeding on the sugars or starch in the food. As it does so it leaves behind a by-product — lactic acid in curd, kanji and bamboo shoots, carbon dioxide in idli batter and bread dough. The acid gives the sour taste and, because most spoilage organisms cannot grow in an acidic food, it also preserves it. That is why fermenting is both a way of cooking and a way of storing.

Tip: interview one elder in your family for the method — ask especially about the time and the place they keep it, and you will find they are describing exactly the warmth and moisture the microbe needs.

Q3.

Study the different parts of a macro fungus mushroom using a magnifying glass and microscope. Take the help of students from senior classes and explore the internal structure of different parts of mushrooms under the microscope in your school laboratory.

Answer

What to look at, in order:

Part	With the naked eye and magnifying glass	Under the microscope
Cap	The umbrella-shaped top; note its colour, and whether the surface is smooth or scaly	A dense mass of fine threads packed together
Gills (under the cap)	Thin plates running from the stalk to the rim like the spokes of a wheel	The surface carries tiny spores; a piece mounted in water shows them clearly
Stalk	The stem that holds the cap up; break it and see that it is not hollow like a plant stem	Long threads running lengthwise
Base / mycelium	Fine white cottony threads at the bottom, spreading into the material it grew on	Branched filaments without chlorophyll — exactly the description of fungi in Table 2.2

Spore print — worth doing: cut off the stalk, place the cap gills-down on a sheet of white paper, cover it with a bowl and leave it overnight. In the morning lift the cap and you will find a pattern of fine powder on the paper, in the shape of the gills. That powder is the spores. Look at a little of it under the microscope.

Why the mushroom has no green in it: a mushroom is a fungus. Fungal cells have a cell wall but no chloroplasts, so a mushroom cannot make its own food through photosynthesis. It has to grow on straw, wood or decaying matter and feed on it by breaking it down — which is why you find mushrooms on rotting logs and in damp compost, and why they are decomposers like the moulds in Table 2.2.

Tip: study a mushroom bought from the market or one your teacher gives you, and handle it with a spoon or gloves as the book advises for soil, washing your hands afterwards.

Q4.

Interact with an entrepreneur and learn the steps for cultivation of mushroom.

Answer

Go with a written list of questions, and note the steps in the order the grower actually does them.

The usual steps of oyster-mushroom cultivation, so that you can follow what you are shown:

Prepare the substrate. Paddy straw or wheat straw is chopped and soaked in water.
Pasteurise it. The wet straw is treated with hot water or steam at a controlled temperature for a few hours, then cooled and drained.
Mix in the spawn. Spawn is grain already carrying the growing mushroom fungus. It is mixed through the cooled straw in layers.
Fill the bags. The mixture is packed into polythene bags with small holes punched for air, and the bags are stacked in a dark room.
Maintain the room. Moderate temperature, high humidity kept up by spraying water, and some fresh air. In two to three weeks the bags turn white as the fungal threads spread through the straw.
Fruiting and harvest. The bags are opened to light and air; small pinheads appear and grow into mushrooms in a few days. They are picked by twisting them off, and two or three more flushes follow.
After the crop. The spent straw is not thrown away — it is already partly decomposed and makes good manure.

Why the straw is pasteurised — the key step: straw is not sterile. It already carries the moulds and bacteria you saw in Table 2.2, and those would grow much faster than the mushroom and take the food first. Heating the wet straw to a controlled temperature kills most of these unwanted microorganisms, without destroying the straw itself. The mushroom spawn is then added into a substrate where it has almost no competition, so it can spread through the straw undisturbed. Note that pasteurisation does not kill everything — it only reduces the unwanted microbes enough to give the mushroom a clear head start, which is why the grower still keeps the room and the bags clean.

Questions worth asking the entrepreneur: where the spawn is bought and how it is stored; what the room temperature and humidity are kept at; how many days from spawning to first harvest; what a bag yields; what the biggest cause of crop failure is; where the mushrooms are sold and at what price; what the cost of starting up was.

Link it back: mushroom growing, Spirulina farming and biogas are all the same idea turned into a livelihood — give a chosen microorganism the conditions it needs, keep the unwanted ones out, and harvest what it produces.

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