What is sewage? Explain why it is harmful to discharge untreated
sewage into rivers or seas.
Fill in the blanks:
(a) Cleaning of water is a process of removing ____________.
(b) Wastewater released by houses is called ____________.
(c) Dried ____________ is used as manure.
(d) Drains get blocked by ____________ and ____________.
Study the following statements about ozone:
(a) It is essential for breathing of living organisms.
(b) It is used to disinfect water.
(c) It absorbs ultraviolet rays.
(d) Its proportion in air is about 3%.
Which of these statements are correct?
(i) (a), (b) and (c)
(ii) (b) and (c)
(iii) (a) and (d)
(iv) All four
Micro-organisms act upon the dead plants to produce
(i) sand (ii) mushrooms (iii) humus (iv) wood
Which of the following
statements is not correct?
(i) Forests protect the soil
from erosion.
(ii) Plants and animals in
a forest are not
depedent on one
another.
(iii) Forests influence the
climate and water
cycle.
(iv) Soil helps forests to
grow and regenerate.
Which of the following is not
a forest product?
(i) Gum
(ii) Plywood
(iii) Sealing wax
(iv) Kerosene
Why should we worry about the conditions and issues related to forests
far from us?
Fill in the blanks:
(a) The insects, butterflies, honeybees and birds help flowering plants
in .
(b) A forest is a purifier of and .
(c) Herbs form the layer in the forest.
(d) The decaying leaves and animal droppings in a forest enrich the
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