Page 82 - Active Science 5 Ebook and Activity

• Chlorination: Germs present in water can also be killed by using chlorine tablets
available in the market.

• Boiling: To purify water, it must be boiled for 15 minutes. Boiling kills micro-
organisms present in water. In monsoons and during floods, there are chances of
infection from water. So, drinking water which is boiled properly is safe for us.

Let’s Pronounce Together
respiration haemoglobin photosynthesis krypton deflated
concentric meteorological decantation distillation tripod
constituent apparatus chlorination aeration

LET’S
REVISE

• Air is a mixture of gases, dust and water vapour.
• Air is invisible, compressible and exerts pressure in all directions.

• The blanket of air around is called atmosphere. Atmosphere is considered as a synonym of air.
• Air is matter. It has weight and occupies space.
• The major gases in the atmosphere are nitrogen, oxygen and carbon dioxide.

• Oxygen is the most important of all gases present in the atmosphere.
• Polluted air is harmful for our health.
• Water contains one oxygen and two hydrogen atoms that are connected by covalent bonds.

• Insoluble substances can be removed from water mainly by three methods– sedimentation,
decantation and filtration.

• Distillation is a process of purifying water by boiling it and condensing its vapour.

Glossary

• Humidity : The amount of water vapour in the air.
• Troposphere : First layer around the earth that is made of gases that we breathe
every day.
• Stratosphere : The second layer of atmosphere where the aircraft fly.

• Thermosphere : Third layer of atmosphere that blocks the meteors or the small rocks.

• Exosphere : It is the last layer of the atmosphere.
• Air pressure : The force exerted by air.

• Evaporation : The process of converting a liquid to vapour is called evaporation.
• Sedimentation : The process of settling of heavier, insoluble substances is called
sedimentation.

82 Active Science-5