Class 6 Science Notes for Air Around Us

NOTES

CLASS 6
SCIENCE

Study Material

DOWNLOAD PDF

AIR AROUND US

Atmosphere: The thin blanket of air surrounding the surface of the Earth is called the
atmosphere.
The atmosphere is divided into five distinct layers on the basis of variations in
temperature that changes due to increasing altitude. Air gets scant as we move up in the
atmosphere. These are as follows:

 Troposphere: This is the first layer to the atmosphere which is nearest to the surface
and is responsible for weather conditions. The troposphere itself is said to contain
about more than 75% of the atmosphere!
 Stratosphere: This is the layer just above the troposphere which contains the ozone
layer and where the aeroplanes fly and is also home to most of the clouds!
 Mesosphere: This is the third and the coldest layer of our atmosphere and extends to a
good 80 km above the surface of the Earth.

 Thermosphere: This is the fourth and one of the hottest layers of Earth where
temperatures go to a 1500 o this is where the space shuttles go to study Earth from
space! The air in this layer is very thin and about 99.9% of the atmosphere is said to
lie below this particular layer.
 Exosphere: This is the outermost layer of the atmosphere where molecules and atoms
escape into space. Beginning at 480 km above the Earth, this layer then extends into
the space.

Constituents of Air
Air is a mixture of a number of gases and some other particles such as:
1. Water Vapour: Air contains water vapour which helps maintain the water cycle. When
air comes in contact with cold surfaces, it is these vapours that turn into or condense into
droplets of water. The amount of water vapours in the air from place to place and
time to time. At a normal 30°C for instance can contain say up to 4% of water vapour.
2. Oxygen: It is the oxygen in the air that helps humans and animals carry out the
respiration process. Oxygen is also required for fire to keep burning. If we were to keep
an inverted tumbler covering a burning candle, the candle will go off in a few seconds
because of the lack of oxygen-containing air due to the tumbler. Dry air is said contain
about 21% of oxygen.
3. Nitrogen: Dry air is said to contain about 78% of nitrogen. This component of air helps
plants in their growth process.
4. Carbon dioxide: Carbon dioxide is a very small (only 0.04%) component of air and is a
byproduct of respiration by humans and animals. Fire also uses up oxygen to burn and
then produces carbon dioxide and a few other gases upon burning. This is why we feel
suffocated if there is something burning inside a room. This happens due to an excess of
carbon dioxide as the fire continues to burn in the room, choking out oxygen in the air.
5. Dust and Smoke: Smoke is another component given out when fire burns. It is very
harmful and adds fine dust particles and a few other gases to the air.

6.
The composition of the components of air
As we can see from the Figure above, Oxygen and nitrogen together make up 99% of
air while the other components come up to a mere 1% of all air in our environment.

Availability of Oxygen in Water and Soil
It is often asked how animals under the soil and in water are able to breathe. The answer
is that both soil and water have air dissolved in them.
 When we heat or boil water, we often notice that bubbles start to form. These bubbles
are in fact, an indication that air molecules are present in the water. When water is
heated, the air dissolved in it escapes first followed by water itself getting converted
into vapour. This is how animals living underwater are able to respire.

Air bubbles can be seen when water is heated
 To see the presence of water in the soil, we take a small lump of it in a beaker and add
water to it. We see bubbles coming out of it which as we discussed, is proof of the
existence of air molecules in the soil. As water is added, it displaces the water
molecules in the soil which we see in the form of bubbles. Animals make use of this
air to breathe under the soil. Some animals make holes and burrows in the soil to help
make pathways for air to enter the soil. When it rains heavily, earthworms and other
animals come out of the soil because these pathways get blocked by the water and they
need to come outside to find the air to breathe.

Air particles present in soil

Balance of Oxygen in the Atmosphere
It is common knowledge that humans and animals can‘t survive without plants because
they produce oxygen via photosynthesis. The balance of oxygen in the environment is
thus maintained through the respiratory processes of plants and animals.
The importance of Air
Air has a number of uses:
 The air which is in motion is known as wind. The wind is important for the rotation of
windmills which help in drawing water from tube wells.
 They also help in running flour mills.
 Windmills are also used to produce electricity.
 Insects and birds are only able to fly because of the presence of air
 Boats, yachts, aeroplanes and parachutes also need air to sail and glide
 Air has a very important role to play in the water cycle as well.
 It also helps in distributing the pollen and seeds from flowers of various plants.

SOME IMPORTANT QUESTIONS

1. Fill in the Blanks-
i.) Plants absorb ____ to make their own food.

ii.) Oxygen is returned to the atmosphere by the process of ____.

iii.) Combustion cannot take place without ____ gas.

iv.) ____ gas maintains the temperature of the earth.

v.) Carbon dioxide is ____ than air.

Answer.
i.) Carbon dioxide ii.) Photosynthesis. iii.) Oxygen gas. iv.) Carbon dioxide v.) Carbon dioxide

State True or False
i.) Plants use oxygen during photosynthesis.

ii.) The only elements in the air are nitrogen and oxygen.

iii.) Water vapour is present in the air.

iv.) Air exerts pressure.

v.) The composition of air is constant in the atmosphere.
Answer.
i.) True ii.) False iii.) True iv.) True v.) False
Match the Following-
Column A Column B

a.) Respiration i.) Process of preparing food by plants.

b.) Air ii.) It is moving air.

c.) Photosynthesis iii.) Process of burning food to get energy.

d.) Nitrogen iv.) It is a gaseous mixture

e.) Wind v.) The major component of air.
Answer.

Column A Column B

a.) Respiration iii.) Process of burning food to get energy.

b.) Air iv.) It is a gaseous mixture

c.) Photosynthesis i.) Process of preparing food by plants.

d.) Nitrogen v.) The major component of air.

e.) Wind ii.) It is moving air.

Very Short Answer Questions-
Q1. Name the main component of air.
Answer. Nitrogen.
Q2. What is the percentage of oxygen in the air?
Answer. 20.9%
Q3. What is the source of carbon dioxide in the atmosphere?
Answer. Animal and plant respiration, as well as fuel combustion.
Q4. Which gas in the air is necessary for combustion?
Answer. Oxygen.
Q5. Define humidity.
Answer. The amount of water vapour present in the air is humidity.

Q6. Which gas is given out during respiration by humans?
Answer. Carbon dioxide.
Q7. Can you see the air?
Answer. No, we cannot see air. We can only feel it.
Q8. Name some musical instruments in which air plays an important role.
Answer. Flute, saxophone, trumpet, horn, etc.
Q9. Which gas in the air is essential for breathing?
Answer. Oxygen.
Q10. Which gases in the air are not a supporter of combustion?
Answer. Nitrogen and carbon dioxide.

Short Answer Questions-
Q1. Why is air considered a mixture?
Answer. Air is made up primarily of oxygen and nitrogen, as well as carbon dioxide and other
gases. In the air, these gases retain their properties. As a result, the air is referred to as a mixture.
Q2. Why do you think mountaineers bring oxygen cylinders when climbing high mountains?
Answer. The amount of air decreases as we ascend higher into the atmosphere. The air at the
summits of extremely high mountains is so thin that people cannot breathe properly.
Mountaineers, or people who climb mountains, carry ―oxygen gas‖ cylinders with them. They
breathe in oxygen from these cylinders to survive on high mountains.

Q3. List the properties of air.
Answer. The following are the properties of air:

 It is colourless
 It is transparent
 It can be compressed.
 It occupies space
 It has mass
Q4. Define atmosphere.

Answer. The atmosphere is a gaseous blanket that surrounds the earth and contains the air we
breathe. The planet‘s gravitational attraction keeps it close to the planet‘s surface.

Q5. Why do you feel suffocation in a closed room, where some material is burning?

Answer. In a closed room where some material is burning, we feel suffocated because the smoke
contains few gases and harmful fine dust particles.

Q6. How does oxygen reach animals living in soil and water?

Answer. Air fills the space between the soil particles. The air between soil particles supplies
oxygen to the animals that live there.

Aquatic animals and plants use dissolved oxygen in the water.

Q7. Why does the transparent glass of windows become hazy if it is not cleaned regularly?

Answer. Dust particles in the air adhere to the clear glass of windows. These particles also attract
other elements, such as pollen, which collects on glass. As a result, if the windows‘ transparent
glass is not wiped regularly, it appears hazy.

Q8. What are the functions of long chimneys in factories?

Answer. When fuel is burned, smoke is produced. Frequent smoke is harmful because it contains
a few gases and fine dust particles. Long chimneys in factories keep harmful gases and smoke
away from the people living near the factory.

Q9. Why do our nostrils have fine hair and mucus? Why is it not recommended to breathe in
through the mouth?

Answer. The air contains dust particles. Inside the nose, fine hair and mucus prevent dust
particles from entering the respiratory system.

Dust particles may enter our respiratory tract if we breathe through our mouth because it lacks
these dust barriers (fine hair and mucus). Hence, breathing through the mouth is not advised.

Q10. Why do animals that live deep in the soil come to the surface during heavy rains?

Answer. Animals that live in the soil obtain oxygen for breathing (or respiration) from the air
that exists between the soil particles. When it rains heavily, water fills the spaces in the soil
occupied by the air. In this situation, the animals living within the soil must emerge from the soil
to breathe. Earthworms, for example, emerge from the soil only during heavy rains.

Long Answer Questions
Q1. Why do animals that live deep within the soil come to the surface during heavy rains? How
can you say that animals and plants are mutually dependent?

Answer. Plants and animals are mutually dependent on survival. Plants cannot survive for long
without animals because they require CO2 for photosynthesis, which is exhaled by animals.
Similarly, animals will have no oxygen to breathe if plants do not exist. As a result, we can say
that both are required to keep the balance of oxygen and carbon dioxide in the atmosphere.

Q2. Are breathing and respiration the same thing?

Answer. No, breathing and respiration are not the same things.
Breathing is a biophysical process in which oxygen is inhaled, and carbon dioxide is exhaled. In
contrast, energy is produced during respiration by breaking down glucose, either in the presence
of oxygen (aerobic respiration) or in the absence of oxygen (anaerobic respiration) (anaerobic
respiration).
Thus, breathing is a physical process, whereas respiration is a chemical process.

Q3. Breathing through your mouth could be dangerous.‖ How?
Answer. The amount of dust particles in the air varies according to time and location. We inhale
air when we breathe through our nostrils. Fine hair and mucus are found inside the nose to keep
dust particles out of the respiratory system. Breathing through our mouths can be harmful
because it allows dust from the air to enter our respiratory system (lungs, etc.) and harm our
health.
Q4. How is oxygen replaced in the atmosphere or air?

Answer. The oxygen in the air is used by animals (and plants) through respiration and is
constantly replaced by plants through photosynthesis.

Plants produce their own food while simultaneously producing oxygen. Plants also use oxygen
for respiration, but they produce more than they consume. Because of this, plants are said to
produce oxygen.

Animals cannot survive without plants. Similarly, plants cannot survive without animals. They
would consume the entire amount of CO2 in the atmosphere. As a result, both are required to
maintain the balance of oxygen and carbon dioxide in the atmosphere.
Q5. What will happen if atmospheric CO2 levels rise?
Answer. Carbon dioxide has the ability to absorb infrared rays, which are heat rays. Nature
maintains a carbon dioxide balance in the atmosphere, which provides optimal warmth.
Increased carbon dioxide concentration in the atmosphere would raise the earth‘s temperature,
causing glaciers to melt and flood, and so on. This is referred to as Global Warming.

******************************************************************************

Study Materials
Notes

Model Papers Class 6 Notes

Sample Papers Class 7 Notes
Half Yearly Sample Papers Class 8 Notes

Class 9 Notes
Important Resources
Class 10 Notes
Periodic Table
Class 11 Notes
Writing Skills / Formats

Maps of India / World Class 12 Notes

Books and Solutions

NCERT Books
NCERT Book Solutions
HC Verma Chapter Wise Solutions
RD Sharma Solutions
CGBSE Solutions