Q47. How do the cockroaches breathe?
A cockroach has small openings on the sides of its body. These openings are
called spiracles. They have a network of air tubes called tracheae for gas
exchange. Oxygen rich air rushes through spiracles into the tracheal tubes,
diffuses into the body tissue, and reaches every cell of the body. Similarly,
carbon dioxide from the cells goes into the tracheal tubes and moves out
Q48. Why does an athlete breathe faster and deeper than usual
after finishing the race?
fast running the demand for energy is high. But the supply of oxygen
to produce the energy is limited. Our muscle cells can also
respire anaerobically, but only for a short time, when there is a temporary
deficiency of oxygen. Thus, an athlete breathes faster and deeper than usual
after finishing the race so that more oxygen is supplied to the cells. This
speed up the breakdown of food and more energy is released.
Q49. Why do we respire?
All organisms are made of small microscopic units called cells. A cell is the
smallest structural and functional unit of an organism. Each cell of an organism
performs certain functions such as nutrition, transport, excretion and
reproduction. To perform these functions, the cell needs energy. Even when we are
eating, sleeping or reading we require energy. The food has stored energy, which
is released during respiration. Therefore, we respire to get energy from food.
Q50. List the similarities and differences between aerobic and
Both aerobic and anaerobic respirations are
types of cellular respiration.
Both generate energy by breaking down
glucose and produces byproducts.
It occurs in the presence of oxygen.
It occurs in the absence of oxygen.
Large amount of energy is released.
Small amount of energy is released.
Glucose breaks down into water and carbon dioxide.
Glucose breaks down into alcohol and carbon dioxide.
It is a slow process.
It is a fast process.
It occurs in most of the plants and animals.
It occurs in human muscles cells, yeast, bacteria etc.
Q51. How do we breathe?
Normally we take in air through our nostrils. When we inhale air, it passes
through our nostrils into the nasal cavity. From the nasal cavity, the air
reaches our lungs through the windpipe. Lungs are present in the chest cavity.
This cavity is surrounded by ribs on the sides. A large, muscular sheet called
diaphragm forms the floor of the chest cavity. Breathing involves the movement
of the diaphragm and the rib cage. During inhalation, ribs
move up and outwards and diaphragm moves down. This movement increases space in
our chest cavity and air rushes into the lungs. The lungs get filled with air. During
exhalation, ribs move down and inwards, while diaphragm moves up to its former
position. This reduces the size of the chest cavity and air is pushed out of
Q52. Take three test-tubes. Fill ¾ th of each with water. Label
them A, B and C. Keep a snail in test-tube A, a water plant in test-tube B and
in C, keep snail and plant both. Which test-tube would have the highest concentration
Snail breathes in oxygen and breathes out carbon dioxide. Hence concentration
of CO2 increases in the test tube. Therefore, Test tube A will have high concentration of carbon dioxide.
test tube B water plant uses carbon dioxide for synthesizing food and hence
there will be less concentration of carbon dioxide compared to test tube A.
test tube C, carbon dioxide produced by snail is utilized by plant for
synthesis of food and oxygen released by plant is utilized by snail for
respiration. Hence, concentration of carbon dioxide is least in test tube C.
Q53. Write one word for the following:
The air tubes of insects - Trachea
surrounding chest cavity - Ribs
Muscular floor of chest
cavity - Diaphragm
Tiny pores on the surface of
leaf - Stomata
Small openings on the sides
of the body of an insect - Spiracles
The respiratory organs of
human beings - Lungs
The openings through which we
inhale - Nostrils
An anaerobic organism - Yeast
An organism with tracheal
system - Ant
Q54. Whales and dolphins often come up to the water surface.
They even release a fountain of water sometimes while moving upwards. Why do they
Whales and dolphins are mammals and breathe air into their lungs, just like we
do. They cannot breathe under water like fish can as they do not have gills. They
breathe through a nostril, called a blowhole, located right on top of their
heads. This allows them to take breaths by exposing just the top of their heads
to the air while they are swimming or resting under the water. After each
breath, the blowhole is sealed tightly by strong muscles that surround it, so
that water cannot get into the dolphin’s lungs.
they surfaces for air, they breathes out (exhales) first and then breathes in
(inhales) fresh air. The water spray is not coming from theirs lungs; it is
just water sitting on top of their head around the blowhole being blown away
before they inhale.
Q55. Explain the mechanism of breathing with the help of an
Ans. Take a wide plastic
bottle. Remove the bottom. Get a Y-shaped glass or plastic tube. Make a hole in
the lid so that the tube may pass through it. To the forked end of the tube fix
two deflated balloons. Introduce the tube into the bottle. Now cap the bottle. Seal
it to make it airtight. To the open base of the bottle tie a thin rubber or plastic
sheet using a large rubber band. To understand the
expansion of the lungs, pull the rubber sheet from the base downwards. The
volume of the cavity increases. This causes the pressure to decrease. Air
rushes in to equalize the pressure, causing the balloons to inflate. Next, push
the rubber/plastic sheet up. The volume of the cavity decreases. This causes an
increase in pressure within the bottle, the air rushes out of the balloons
causing them to deflate.
Image from NCERT