Page 145 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key
P. 145
16 Water : A Valuable Resource
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Chapter in a Nutshell
v Water is essential for the existence of all forms of life.
v Conservation of water is important for our survival.
v According to statistics, a person needs 50 litres of clean and fresh water per day for various
reasons.
v Of all the water available, about 97% is present in the oceans. It is saline and not fit for
human consumption, in any form.
v Only 3% of water is fresh and present in the form of icecaps, glaciers, underground reservoirs,
rivers and lakes.
v Of all the freshwater, only about 1% is easily accessible and the rest is trapped in glaciers
and icecaps.
v Water exists in three different forms: solid, liquid and gas.
v When ice is heated, it is converted into water which in turn changes into water vapour on
further heating.
v When water vapour cools down, it is converted into water which again freezes into ice upon
further cooling.
v The continuous movement of water from the atmosphere to the Earth and back to the
atmosphere through various processes is called the water cycle.
v Water on the surface of the Earth turns into water vapour by absorbing heat from the
atmosphere. This process is called evaporation.
v As the water vapour rises higher, it cools down and changes into tiny droplets of water due
to low temperature at high altitudes. This process is called condensation.
v When water droplets in the clouds grow large and become heavy, they fall down as rain.
This is called precipitation.
v Transpiration is the process of evaporation of excess water from the leaves of plants.
v Surface runoff is the flow of water occurring on the ground surface when excess rainwater,
stormwater, melted water or other sources, can no longer sufficiently rapidly infiltrate in
the soil. Only some amount of rainwater is absorbed by the soil called groundwater.
v The main sources of water on Earth are: surface water, ground water and rainwater.
v Surface water is any body of water found on the Earth’s surface, including the saltwater in
the oceans and the freshwater in the streams, rivers and lakes, in which water gets collected
from rain and melted glaciers.
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