NCERT Solutions Curiosity Chapter 11 – 229Chapter exercise — Let us enhance our learning

Step 1 — unjumble the names.

Step 2 — match each picture with its name. In Fig. 11.9 the picture in the last row is a rock, so it matches ocrk. Match the remaining three pictures in your book — trees growing together, something being blown or turned by moving air, and flowing or stored water — with refost, ndiw and atwre.

Step 3 — the new table, with the classification.

(i) A fuel that is commonly used in two wheelers like scooters or bikes is (b) Petrol.

• (a) Kerosene — used in lamps and stoves, not in two-wheeler engines.
• (c) Diesel — used in trucks, buses and tractors, which have a different kind of engine.
• (d) LPG — a cooking gas; a few vehicles use gas, but as CNG, not as the usual two-wheeler fuel.

(ii) An example of a renewable resource is (b) Water.

• (a) Coal, (c) Natural gas and (d) Petrol (from petroleum) are all fossil fuels — non-renewable.
• Water is renewed by nature through the water cycle, so it is renewable.

Because it takes millions of years to form, is present in limited quantity, and is not replenished within a reasonable period of time — once used, it is gone.

• How it formed: petroleum was formed from the remains of microorganisms and plants that got buried deep inside the Earth long ago and were slowly changed into petroleum, natural gas and coal.
• How long it took: millions of years — not years or centuries.
• How much there is: it is found only in certain places and in limited quantity — in India at Mumbai High, in Gujarat, Assam and Barmer in Rajasthan.
• What happens when we use it: the petrol or diesel is burnt and turns into smoke and gases. Nothing is left behind that can become petroleum again.

A forest is not just a crowd of trees — it is a whole community of plants, animals, soil and micro-organisms built up over a very long time. Trees can be planted; a forest has to grow.

• Trees take decades. A sal, teak or deodar tree needs 30 to 60 years to reach full size. It takes many years to grow a new forest or restore a lost one.
• The soil is lost first. Once the trees are gone, the roots no longer hold the soil, and rain washes the fertile topsoil away. New saplings then have poor soil to grow in.
• The undergrowth and humus are gone. The layer of decaying leaves that enriches the soil takes years to build up again.
• The animals leave. Birds, bats, bees and insects that pollinate flowers and scatter seeds move away, so natural regrowth becomes slow. Ajji’s village leaves fallen fruit for animals precisely so that their droppings sow new trees.
• Only a few species get replanted. A natural forest has hundreds of kinds of plants; a plantation usually has one or two, so the variety of life is not restored.
• Weeds take over the cleared land and choke the new saplings.

Four (with more to spare):

1. Breathing and respiration — we and almost all living beings take in oxygen from the air; without it we cannot survive even a few minutes.
2. Burning of fuel — the gas stove, the chulha and every vehicle engine need the oxygen of the air to burn fuel and give heat.
3. Generating electricity from wind — moving air turns the wings of a windmill, as at Muppandal in Tamil Nadu and the Jaisalmer Wind Park in Rajasthan; the same wind turns a firki.
4. Drying of wet clothes and grain — moving air carries away the water vapour, so wet things dry faster on a windy day.

Other correct answers:

• Flying a kite, and the flying of birds and aeroplanes.
• Sailing a boat with the wind, and winnowing grain to separate the husk.
• Speaking and hearing — sound travels through air.
• Pollination and scattering of seeds by the wind.

Actions I can take (in order of what a Class 6 student can actually do):

1. Plant saplings at home, in school and along the colony road — and choose native trees such as neem, peepal, banyan, gulmohar, amla, jamun, mango and moringa rather than only decorative ones.
2. Look after them, not just plant them — water each sapling, put a tree guard around it, and add dry leaves at the base. A sapling that dies is not green cover.
3. Adopt a tree — let each child in the class take charge of one tree for the whole year and keep a record of its growth.
4. Grow a kitchen garden — tulsi, curry leaf, mint, chillies and tomatoes in pots on the balcony or terrace.
5. Make compost from kitchen and garden waste and use it instead of buying fertiliser.
6. Celebrate Van Mahotsav — the week-long forest festival held across the country in July — and organise a plantation drive with your teacher.
7. Protect what already exists — do not pluck branches or carve names on trunks; report anyone cutting a tree without permission; save the old trees of the neighbourhood.
8. Spread the word — posters, a wall magazine, a street play, and gifting saplings on birthdays instead of plastic gifts.
9. Join the school eco-club and keep a simple survey of how many trees your street has, so the increase can be measured.

The picture shows a large shining dish facing the sky with a vessel placed in front of it, outside a village hut — this is a solar cooker (a dish-type solar cooker).

(i) The energy used is solar energy — heat and light from the Sun. The curved dish gathers the Sun’s rays and concentrates them on the vessel, which becomes hot enough to cook the food. No fuel is burnt at all.

(ii) One benefit and one drawback

More benefits: no fuel bill, no danger of fire or gas leak, the food does not burn, and it keeps its nutrients.
More drawbacks: the cooker is costly to buy, needs open space, must be turned every hour to face the Sun, and cannot be used for frying or making chapatis.

Because the trees are what keep the soil in place and keep it fertile. Take them away and the soil is damaged in four different ways.

1. The soil is washed away (erosion). The roots of plants hold on to the soil and prevent it from being washed away. With no roots, rain water carries the fertile topsoil into streams and rivers, and wind blows away the dry surface.
2. The soil loses its nutrients. Leaves that fall from trees decay and enrich the soil with nutrients, which new plants then use. No trees means no leaf-fall, no decay, and a soil that grows poorer every year.
3. The soil dries out and hardens. Without the shade of the trees, the Sun beats directly on the ground; moisture evaporates, and the soil bakes hard and cracks.
4. The life inside the soil dies out. Earthworms — natural agents that turn and loosen the soil — insects and tiny organisms need moisture and dead leaves. Without them the soil stops being loosened and mixed.

Two ways human activities pollute the air:

1. Burning fossil fuels in vehicles. When petrol and diesel burn in engines, smoke and carbon dioxide are produced. Over-dependence on fossil fuels for transportation has caused large-scale air pollution — which is exactly what Bhoomi and Surya smell when they reach the city.
2. Burning fuels in factories and power plants, and burning waste. Coal burnt to produce electricity, and the smoke from brick kilns, chimneys, burning garbage and crop stubble, fill the air with soot, ash and harmful gases. Cooking on coal, wood and dung cakes pollutes the air inside homes too.

Other ways: dust from construction, mining and quarrying; chemical fumes and pesticide sprays; burning of plastic waste.

One action to reduce air pollution:

One bus carries as many people as forty scooters, so it produces a fraction of the smoke per person. Other good actions: shift to CNG or electric vehicles, use LPG or a solar cooker at home instead of coal or dung cakes, switch off the engine at red lights, and plant more trees, which take in carbon dioxide and trap dust.

Take the three devices one by one.

The rest of the household would also feel it: clothes would not dry, food and chillies could not be sun-dried, a solar water heater would give no hot water, plants would grow poorly, and the days would be dark and cold.

The completed chart:

Position: the demand is real, but felling natural forests on a large scale to meet it is not justified. The need can be met in ways that do not destroy forests.

How this helps the environment:

• Less water drawn from the borewell or the municipal supply means less groundwater pumped out, so the water table falls more slowly.
• Rainwater harvesting recharges the ground instead of letting rain run off into drains.
• Pumping water uses electricity, most of which comes from coal — so saving water also saves coal and cuts air pollution.
• More water is left in the rivers and ponds for farmers, animals and the fish that live there.
• Students carry the habit home, so the saving multiplies across the whole neighbourhood.