Std 5 EVS 1 · Chapter 18

18. The Environment and Us

Complete solutions to the Exercise. Maharashtra State Board (Balbharati), Standard 5 EVS 1.

Exercises

1What’s the solution? Rivers and lakes are filled with water hyacinth.

Remove it physically — the plants can be pulled out using boats or machines made for the purpose.

Use living things that feed on it — certain insects and animals eat water hyacinth and keep it in check naturally.

Use the least possible chemicals — weedkillers poured into a lake harm the fish and other living things in it, so they must be avoided as far as possible.

Take the help of local people — the villagers or townsfolk living beside the water body can join in the work of clearing it.

Stop it at the source — water hyacinth spreads fast in water carrying sewage and waste. Treating the waste water before letting it in checks the growth.

Why it matters: a thick mat of water hyacinth cuts off sunlight and air from the water below, so the fish and other water animals cannot live in it.

2Use your brain power! What would happen if no kites (birds) are left in a particular region? Which living things would increase in number? Which would decrease?

The kite is a link in the food chain of that region. If it disappears, the balance in nature is upset.

Effect	Living things
Would increase	The small animals the kite feeds on — rats, mice, squirrels, small snakes, insects and small birds
Would decrease	The plants and crops eaten by those animals, and other scavengers that share the flesh of dead animals with the kite

Kites also feed on the bodies of dead animals. Without them such bodies would lie about and rot, spreading disease. So the loss of one bird affects the whole living world of that place.

3Answer the following questions.

(a) What is meant by migration?

The movement of people or animals from one place to another is called migration.

(b) Describe the life-cycle of birds.

Egg — the mother bird lays eggs in a nest and keeps them warm.

Chick — the egg hatches and a young chick comes out, which the parents feed.

Growing up — feathers grow, and the young bird slowly learns to fly and to find its own food.

Adult — the grown bird builds a nest of its own and lays eggs, and the cycle begins again.

(1) Burning fuels releases very large quantities of carbon dioxide into the air, and vehicles give out poisonous gases along with smoke.

(2) Industries let out poisonous gases into the air, which pollutes it on a very large scale.

(d) For what purpose do we use land obtained by clearing forests?

The cleared land is used for farming and for building roads, railways, houses and other buildings, bridges and dams.

4Give reasons.

(a) It is important to conserve the living components of the environment.

Every plant and animal is a link in some food chain. If different kinds of plants and animals become extinct one by one, many of these links are lost. That would affect the whole living world on the earth and the balance in nature would collapse. This is why the living components of the environment must be conserved.

(b) The numbers of wild animals are falling day by day.

Wild animals live in the forests and find their food there. But the forests are becoming smaller as land is cleared for farming, roads and settlements. The animals lose both their homes and their food, and so their numbers keep falling.

5True or false?

(a) Dead plants and animals are abiotic components.

False. Dead plants and animals were once living, so they are counted among the biotic components. Soil, water, air and sunlight are the abiotic components.

(b) It is necessary to conserve biodiversity.

True. The variety of living things keeps the food chains complete and nature in balance.

6Classify the following as natural or man-made — soil, horse, stone, water hyacinth, book, sunlight, dolphin, pen, chair, water, cottonwool, table, trees, brick.

Natural	Man-made
Soil	Book
Horse	Pen
Stone	Chair
Water hyacinth	Table
Sunlight	Brick
Dolphin	—
Water	—
Cottonwool	—
Trees	—

Note: cottonwool comes from the cotton plant, so it is natural. A brick is made by man out of natural soil — the soil is natural, but the brick is man-made.

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