Page 67 - Science Class 07

breathing, he can take in 3-5 litres of air. The
composi on of exhaled air differs from that of
inhaled air. The amount of carbon dioxide
increases during exhala on while the amount
of oxygen is reduced during exhala on. The
amount of water varies during inhala on and it
is exhaled in saturated condi on. But the
amount of nitrogen remains the same during
inhala on and exhala on because nitrogen
does not diffuse in blood and its quality
remains constant. Besides, the inhaled air takes
the temperature of the body and the
temperature of this air is higher than that of
the air present in the environment.
Have you ever thought why clouds of mist
are formed when we breathe out on a cold
day?
Actually, the air we breathe out is warmer
than the air of the atmosphere. So, when
this warm air which also contains a small
amount of water vapour meets with cold
atmospheric air, it condenses and hence
clouds of mist are formed.
Why do sportspersons get cramps in their
legs?
When a sportsperson run con nuously for a
longer period of me, their legs require
extra amount of energy, but they do not get
sufficient amount of oxygen. In this situa on,
the cells of leg respire anaerobically and
produce lac c acid. When he or she stops
running the lac c acid accumulates in his or
her legs that results in cramps. A er a few
minutes later the lac c acid automa cally
breaks down and the cramps get vanished.
Science-7
1. What is the func on of nasal cavity?
2. What is larynx?
3. Write the structure and func on of
trachea.
4. What is the func on of alveoli?
5. What happens during the process of
respira on?
6. Why does the amount of nitrogen not
change during inhala on and exhala on
of air?
Aim : To show that the air exhaled by us
contains CO .
2
Materials required : Two test tubes, lime
water and piece of rubber pipes.
Method : Fill both the test tube half with
fresh lime water. Adjust the apparatus as
shown in the picture. Breathe out air
through your mouth so that it can reach
inside the test tube. Air which mixes up with
lime water makes it milky, but the breathed
out air in the other test tube does not mixes
up with lime water and hence its colour
remains the same. It shows that breathed
out air contains CO .
2
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