NCERT Class X Science Class: Chapter –16. Management of Natural Resources – Part-6

Download PDF of This Page (Size: 164K)

Question 24:

It is important to make small check dams across the flooded gullies because they

(i) Hold water for irrigation

(ii) Hold water and prevent soil erosion

(iii) Recharge ground water

(iv) Hold water permanently

(a) (i) and (iv)

(b) (ii) and (iii)

(c) (iii) and (iv)

(d) (ii) and (iv)

Answer: B

Short Answer Questions

Question 25:

Prepare a list of five items that you use daily in the school. Identify from the list such items that can be recycled.

Answer:

Paper, rexin bag, blade, pen, plastic box, scale, eraser, compassand dividers (metallic), steel lunch box, steel spoon.

Paper, blade, plastic box, eraser, compass, steel lunch box and steel spoon can be recycled.

Question 26:

List two advantages associated with water harvesting at thecommunity level.

Answer:

(a) The ground water level increases due to rechargingof wells.

(b) Ground water keeps the layers of soil above it moist andprevents loss of water by evaporation.

(c) The water can be stored during rainy season and can be usedwhen required

Question 27:

In a village in Karnataka, people started cultivating crops all arounda lake which was always filled with water. They added fertilizers to their field in order to enhance the yield. Soon they discovered thatthe waterbody was completely covered with green floating plantsand fishes started dying in large numbers.

Analyse the situation and give reasons for excessive growth of plants and death of fish in the lake.

Answer:

Since people used excessive fertilisers in the fields, they were carried down to the lake during rains. As many fertilisers containphosphates and nitrates, the water body became enriched withthese chemicals. These chemicals promote excessive growth of aquatic plants and the surface of water was completely covered with plants. (Eutrophication)

Depletion of light in the water body and insufficient availability of dissolved oxygen and nutrients resulted in the death of fish.

Image Eutrophication process

Image Eutrophication Process

Image Eutrophication process

Developed by: