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12 Respiration in
Animals and Plants
Learning Objectives KNOWTHESE PoINTS BEFORE YouSTART
The students will be able to Breathing is a mechanical process of pumping air into and out ofthe lungs.
learn the
necessity of
respiration.
Respiration is a chemical process of exchange of oxygen and carbon dioxide
between outside air and the cells.
distinguish between
breathing and respiration. In external respiration, there is an exchange ofoxygen and carbon dioxide
between air and blood. External respiration takes place in the lungs at the
alveoli.
understand aerobic and
anaerobic respiration.
learn breathing in human
beings and in other
Haemoglobinofblood transports oxygen from lungs to the bodycells
Insects are peculiar in having air tubes or trachea for respiration.
Aquatic animals like fishes have gills. They obtain oxygen dissolved in water.
animals.
Comprehend respiration
in plants. Earthworms breathe through their moist skin.
Now, study the chapter in detail.
RESPIRATION
We eat food to get energy. The energy stored in food molecules is
released by their oxidation, i.e., combining of food molecules with
oxygen. Hence, oxidation occurs in the presence of oxygen. The
processof taking oxygen into the body and then oxidation of food
with this oxygen and release of carbon dioxide and energy is called
respiration.
Respiration can be defined as a biochemical process thatinvolves:
intake ofoxygen from the environment.
f food (glucose) with the help Anaerobic respiration
Oxidationof
ofoxygen taken
se of energy and carbon dioxide.
respiration
When glucose is broken down in the absence
of oxygen, it is called anaerobic respiration.
The animals and plants that can survive and
obtain energy in the absence of oxYgen are
in.
r e l e a s e
imination of carbon dioxide.eliminati
whydo we respire
needs energy to run. We fill petrol in
called anaerobes.
A car.The petrol burns, using oxygen from Anaerobic respiration occurs in yeast, some
a r
the air
he air and gves energy to the car to run. bacteria and parasitic flatworms. In the
and gives
ilarly, he food reacts with oxygen of absence of oxygen, glucose breaks down into
thehe air releasing energy and carbon dioxide. ethyl alcohol and carbon dioxide.
Hence, energy is released during oxidation
intheabsence Ethyl Carbon+ Energy
of oxygen
offood. Every body cell needs energy and
Glucose
alcohol dioxide
theretore,
needs food and oxygen. To get
need to respire, i..,oxygen we
hreathe fresh air rich in oxygen through
Do animals also respire anaerobically?
respiratory organs. Parasitic animals that live in the
alimentary canal (like roundworms and
flatworms) respire anaerobically. They
do not get oxygen in the alimentary canal.
transport oxygen fror respiratory organs
to every body cell.
Breathing and respiration
Breathing and respiration are two different
processes. Breathing is a mechanical process
of pumping air into and out of the lungs.
Respiration is a chemical process ofexchange
of oxygen and carbon dioxide between the
Sonething More
In anaerobic respiration, breakdown ofglucose is
incomplete.
Very little energy is produced in anaerobic
respiration.
Yeast is a single-celled organism. It respires
anaerobically and yields ethyl alcohol. The yeast
cells are, therefore, used to make wine and beer.
They are also used in baking industry.
The anaerobic breakdown of sugars into alcohol
is called fermentation.
outside air and cells.
During respiration, glucose produces carbon
dioxide, water and energy.
Aerobic and anaerobic respiration
Aerobic respiration
When glucose breaks into carbon dioxide and
warer using oxygen inside the body cells, it is
called aerobic respiration.
Can we respire anaerobically?
We cannot respire anaerobically, our
skeletal muscles can but only for a
short period.
Glucose
in the
Carbon Water + Energy
presence of
Oxygen dioxide
During vigorous muscular activities, like fast
Anumals that use oxygen for respiration are running, brisk walk1ng or heavy exercise,
called aerobes. Majority of animals and more energy is needed. Therefore, demand
plants have aerobic respiration. for oxygen also increases, but oxygen supply
to muscles remains unchanged. Under
shortage of oxygen, skeletal muscles respire
anaerobically and glucose breaks down to Lungs
lactic acid releasing energy.
BREATHING IN HUMAN BEINGS
Lungs are the main respiratory organs in
our body. They are a pair of spongy, high
elastic and bag-like structures. They enclose
thin-walled and tiny air-sacs called alveolk
The surface of alveoli is covered with
network of blood capillaries. When we
breathe in, these alveoli are filled with fresh
air. Oxygen from this air enters the blood
capillaries and carbon dioxide from blood
Glucose theshortageof
Oxygen in musclecells Lactic acid + Energy
Something More
When muscles respire anaerobically, the glucosebreaks down into lactic acid. The accumulationof lactic acid causes muscle cramps. We get relief
from cramps after a hot bath or a gentle massage
with lukewarm oil. This increases the blood circulation Comes out.
and consequently the oxygen supply to the muscles
increases. This causes oxidation of lactic acid into
carbon dioxide and water.
- Larynx
Trachea
Check PeINT 1.
1. Define respiration.
2. Which substrate is used by cells for producing
energy?
3. Give the overall reaction of respiration.
4. Why do we feel muscle cramps after a fast
running?
5. Give one example of an anaerobic plant and an
anaerobic animal.
Right lun8 Bronchus
- Left lung
Fig. 12.1 Human lungs
6. What is the end product of anaerobic respiration
in skeletal muscles? Bronchiole
Pulmonary
vein
TABLE 12.1 DIFFERENCESBETWEENAEROBIC AND Alveolar
Pulmonary
ANAEROBIC RESPIRATION duct
artery
Aerobic respiration Anaerobic respiration Alveolar
1. Occurs in the presence of 1. Occurs in the absence of cavity
oxygen.Oxygen.
2. Glucose is completely 2. Glucose is oxidised
incompletelyoxidised.
3. End products are carbon 3. End products are either
ethyl alcohol and carbondioxide and water.
dioxide or lactic acid.
Venule4. More energy is produced
(38 ATP from one molecule
4. Very little energy is
produced (2 ATP from one
molecule of glucose).
Arteriole
Alveolus
ofglucose).
5. Occurs in most of the plants 5. Occurs in few organisms
and animals.
Fig. 12.2 Lung alveoli associated with
a bronchiole and having a network of
blood capillaries on the surface
like yeast, some bacteria
and some parasitic worms.
There
a r e
about 750
are about 750 million alveoli in the bronchi (singular: bronchus) which enter
dioxide between the air in alveoli and blood Breathing and breathing rate
Lungs
are connected with the external air and giving out of carbon dioxide from the
J u n g s .
the lungs of their respective side. Inside the
ThetoThe total surface area of
these alveoli is lungs, the bronchi divide and redivide into
bout 100100 square metres. This is a large bronchioles which further divide and finally
efor exchange of oxygen and carbonfor excl
a r e a
end into air sacs or alveoli.
in the
in the alveolar capillaries.
Breathing is a mechanical process. It involves
taking in of air rich in oxygen into the lungsOrgans of breathing
throughrough nose, nasal passages, pharynx, lungs.
rachea, bronchi and bronchioles.t r a c
Taking in of air rich in oxygen into the lungs
is called inhalation and giving out air rich in
carbon dioxide is known as exhalation.
Nasal cavity
Inhalation and exhalation occur continuously
and alternately. One breathe means one
inhalation and one exhalation. The number ofNasal passage
times a person breathes in a minute is termed
as breathing rate.
Air
Tongue
Pharynx
Something More
Normally we breathe16-18 times/minute.
Breathing rate may increase up to 25 times per
minute during fast running or heavy exercise.
During brisk walking, fast running or exercising we
breathe fast and take deep breath. This provides
more oxygen and more energy. It means more
food is burnt and we feel hungry after exercising,
running or playing.
Trachea
Fig. 12.3 Breathing passage in man
Nose and nasal passages
We breathe air through nose or nostrils.
In the nasal passages, the air gets filtered
Warmed and moistened before entering the
lungs. Therefore, we should always breathe
through nose and not through mouth.
Pharynx
Sneezing: Airaround us is polluted with pollen,
smoke particles, dust, etc. Normally when we
inhale, these unwanted particles are trapped in the
hair presentin the nasal passages. Sometimes
these particles are not trapped in the hair and
irritate the lining of the passage. This causes
sneezing. As a result of sneezing, unwanted
particles are thrown out and only clean air enters
the lungs.
The air from nas passages reaches trachea
through pharynx.
Trachea orWindpipe
The air from pharynx reaches the lungs
hrough windpipe. It is divided into two
When you sneeze, cover your nose so that the
particles you sneeze out do not fall on others and
are not inhaled by them.
cavity. The lungs being elastic also increase
in size and the air pressure in the lunoe
decreases. Air from the atmosphere having
higher pressure rushes into lungs through
nostrils and air passages and the lungs get
filled with fresh air.
Activity
To find out breathing rate under different conditions
Under normal condition: Breathe in and out
gs
normally and count the number of times you
breathe in and breathe out in one minute. The
number of breaths per minute is your breathing
rate.
After brisk walking and running: Count the
number of times you breathe after a briskwalk
after running and after a complete rest. Record
your breathing rates and that of your classmates
in a tabular form as given here.
Air rushing into the lungs
Pleural Trachea
membranes
Ribsraised LungName of Breathing rate
expandedthe class-
Under After After Aftera
mate
normal a brisk running complete
condition walkfor for 100 m rest Rib
Contracted10 min or more
Diaphragm
pulled down
muscles of
Yourself
diaphragm
Fig. 12.4 Inhalation
Observe and compare your observations. Exhalation
Conclusion
During exhalation, the ribs move downward
The breathing rate does not remain the same under
all conditions. It increases when we need more
energy, i.e., while walking, running or exercising. It
slows down when we are at complete rest doing
no work. When breathing rate slows down to the
extent that we do not get sufficient oxygen, we feel
sleepy or drowsy.
and inward and the diaphragm moves up.
When the ribs and diaphragm return to
their original position, the volume of thoracic
cavity decreases and so also ofthe lungs.This
increases the air pressure inside the lungs and
the air from the lungs is pushed out.
Mechanism of breathing Air moving out from the lungs
Lungs are spongy structures. They are placed
inside an air-tight thoracic cavity enclosed
in the ribcage. A large muscular diaphragm
forms its floor. The diaphragm separates
thoracic cavity from abdominal cavity. The
rib muscles and muscles of diaphragm work
Ribs returned
to normal
position Vertebral
column
together to aid in breathing
Diaphragm
Inhalation returned to
its normal Relaxed
During inhalation, the ribs move upwards
and outwards and the diaphragm moves
down. This increases the volume of thoracic
shape
muscles of
diaphragm
Fig. 12.5 Exhalation
18
Eventsthatoccur during breathing
ze of the thorad cavity changes. It
expands(when are raised upward and outwardand the
aphragm flattens during inhalation.
Something More
Activity 3
To measure the change in the size of chest cavity
with a measuring tape, measure the size of chest
of your friend as shown in the figure.
The volume of oracic cavity reduces when
move down and inward and the diaphragm
ribs
heComes dome-shaped during exhalation.
Air pressure in the lungs changes. Air press
be low when lungs expand and becomes
Airmoves in and out of lungs due to a change in
becol
m
high when lungs are reduced in size.
air pressure in the lungs.
Activity
To demonstrate breathing process
Remove the bottom of a wide plastic bottle. Make a
hole in the cork and insert a Y-shaped glass tube in it.
Ex two deflated balloons to the two free ends of glass
tube. Now insert the cork in the mouth of the bottle
from inside. Finally attach a sheet of rubber over the
open bottom of the bottle as shown in the figure.
Seal the cork with modelling clay or wax.
Ask him to take a deep breath and measure the
chest size again.
Repeat the experiment with other friends and record
your observations as shown in the table.
CHANGE IN THE SIZE OF CHEST CAVITY
DURING BREATHING
Name ofthe When Difference inWhen
friend expanded relaxed size
(during (during
Plastic
bottle
inhalation)| exhalation)
Y-tube
Balloons
Volume
(decreases)
Process ofrespiration
Respiration takes place in following steps:
Exchange of gases between air and
blood - External respiration.
Exchange ofgases between blood and body
cells Internal respiration.
Break down of glucose in body cells-
Cellular respiration.
Oxygen that enters the blood from alveoli
during external respiration combines with
haemoglobin - the respiratory pigment
in Red Blood Cells (RBCs). They form a
temporary compound called oxyhaemoglobin.
Volume
(increases)
Rubber
sheets
Working
Gently pull the rubber sheet down. Observe the change
in balloons, which gradually increase in size. Gently
release the rubber sheet and observe what happens.
In this experiment,
balloons are equivalent to.
rubber sheet is equivalentto.
plastic bottlerepresents
What is the effect when rubber sheet is pulled down?
Why deflated balloons become reflated when
rubber sheet is pulled down?
What happens to balloons when rubber sheet is
released?
11
On reaching the tissue cells, oxyhaemoglobinbreaks to release the trapped oxygen. The
released oxygen enters the cells. This is called
internal respiration.
How much air can a person hold in
his lungs?
An adult can take in a maximum of
about 5 litres air. During normal or
relaxed breathing, only 500 cm3 (half
litre) air in the lungs is replaced at
each breathe. During exercise or
running, i.e., in forced breathing, about
3 litres of air is replaced in lungs
at each breathe. Therefore, running,
playing and jumping are good and very
much needed for good health.
During cellular respiration, breakdown of
glucose takes place to release carbon dioxide
and energy.
TABLE 12.2 DIFFERENCES BETWEEN EXTERNAL
AND INTERNAL RESPIRATION
External respiration Internal respiration
1. It is an exchange of gases 1. It involves an exchange of
between air and blood. gases between blood and
body cells.
TABLE 12.3 DiFFERENCES BETWEEN THE
2. It occurs at the level of 2. It occurs at the level of
cOMPOSITION OF INHALED AND EXHALED AIR
alveoli body cells.
Inhaled air Exhaled air
What do we inhale and exhale 1. Oxygen 21% | 1. Oxygen 16.4%
We inhale and exhale air. But the composition 0.03% 2. Carbon dioxide 4.4%2. Carbon dioxide
ofair inhaled and air exhaled is different. The
air inhaled has more oxygen and less carbon Check PeINT 2 -
dioxide, while the percentage of oxygen is Fill in the blanks.
less and that of carbon dioxide is more in 1. The diaphragm is lowered during
the air we exhale. This difference is given in 2. Breathing is a -
Table 12.3.
process.
3. Carbon dioxide turns. milky.
4. Exhaled air has. %ofcarbon dioxide
and % of oxygen.
Activity 5. Thoracic cavity is also calledTo show that we exhale carbon dioxide
Take a clean and transparent 6. Duringr we take fresh air into
plastic bottle with narrow
opening. Pour some freshly
prepared lime water in it.
Make a hole in the cork RESPIRATION
IN OTHER ANIMALSand insert a plastic straw
in it. Fix the cork in the
We have lungs for respiration. But all
animals do not have lungs. Frogs, snakes,
crocodiles, birds and mammals possess
lungs. They have nostrils (not the
nose) to
inhale air. However, animals like earthworm,
cockroach, mosquito, snail and fish are without
lungs. Their respiratory organs are much
bottle and make it airtight.
Make sure that the end of
straw dips in lime water
Blow gently through the
straw into lime water several times and observe the
change in its colour.
Observation and inference
Lime water turns milky in the bottle. Why?
Carbon dioxide turns lime water milky. It means
different.exhaled air contains carbon dioxide.
vorm (Cutaneous respiration)
nAnd leeches breathe only through (Aquatic respiration)
Farth Respiration in fishes
Earthwo
Earkin. Their skin is moist and slimy Fishes and other animals living in water are
skin. Thei
numerous blood capillaries. Skinandha.
rge
mber of capillaries is called dissolved in water. Their respiratory organs
called aquatic animals. They obtain oxygen
a
highlyvascular. The exchange of oxygen are gills.
bon dioxide occurs between air and
bloodin tid in the skin. Frogs have lungs just like us
but they
c a n
alsocan also breathe through their skin
when
in water. That is why frog's skin is
Gills
sippery.
Respiration in cockroach and
other insects (Tracheal respiration)
airtubes
called tracheae. The air tubes form
The respiratory organs in insects are branched Fig. 12.7 Gills in fish
fne network inside the body and are in
contact with the cells. They open on the body
surface by spiracles. The spiracles open and
close to allow respiratory gases to move in
Gills are projections of skin. They have a
network of fine blood capillaries. The oxygen
dissolved in water enters the blood capillaries.
Carbon dioxide present in capillary blood is
released into water. The oxygenated blood
from capillaries is taken to heart and pumped
to different parts of the body and blood from
body tissues which has carbon dioxide is taken
to gills for the exchange of respiratory gases.
and out of the air tubes.
Spiracles
Can we survive under water just
like whales?Tracheae
We c�nnot live in water for long. Our
breath is short and so we will have to
come to water surface for breathing
very frequently. We can, however
stay under water with an oxygen
cylinder. You might have seen divers
with oxygen cylinders at their back.Fig. 12.6 Tracheal system in cockroach
Containing oxygen enters the tracheal
uDes through spiracles and diffuses into every
cell of the body.
Sotnething More
rachea or air tubes are found exclusively in insects
and do not occur in any other animal group.
Transport of gases in plants takes place by
diffusion only.
Different parts ofa plant have different
methods of obtaining oxygen and
releasing
carbon dioxide.
Do whales and dolphins have gills for
respiration?
Whales and dolphins live in water but
they are mammals. All mammals have
lungs for respiration and breathing air.
Whales and dolphins also have lungs.They often come to the surface ofwater for inhaling and exhaling air.
When they exhale, they release a
fountain of water.
In leaves
The leaves have tiny pores called stomata.
The exchange of gases in leaves occurs
through these pores.
RESPIRATION IN PLANTS In stems
Plants respire like all other organisms. Each Young stems have stomata as in leaves. In
plant cell uses glucose and oxygen and old woody stems, lenticels develop below the
releases carbon dioxide, water and energy.
bark to ensure gaseous exchange.
But during daytime carbon dioxide released
by respiration is used for photosynthesis and
Oxygen produced during photosynthesis is
utilised for respiration. So plants do not take
oxygen during day. But at night, plants also
take oxygen from the atmosphere and give
out carbon dioxide.
Stomatal
pore
Guard cell
Epidermal
cells
Why are we asked not to sleep under
the tree at night?
Fig. 12.8 Stomata on leaf surface
Plants use oxygen and give out
carbon dioxide at night. Therefore,
concentration or amount of Co,
(carbon dioxide) under the tree goes
up and may prove to be harmful.
However, this CO, Soon diffuses in
the atmospheric air.
Warning: We should never sleep in a
closed room with an oil lamp burning
because this reduces oxygen and
increases carbon dioxide in air.
In roots
Root hair arising from different regions of
root extend into air spaces present between
the soil particles and take up oxygen from
there.
Check PeINT 3
Fill in the blanks.
1. Insects have. as respiratory organs.
Plants do not have respiratory organs to
obtain oxygen from atmosphere.
Each part of a plant can independently 3. Fishes have
take in oxygen from the surrounding air
and give out carbon dioxide.
2. For respiration in earthworm, IS
moist and
for breathing.
4. Gills are an extension of.
122

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Class 7 Respiration

  • 1. 12 Respiration in Animals and Plants Learning Objectives KNOWTHESE PoINTS BEFORE YouSTART The students will be able to Breathing is a mechanical process of pumping air into and out ofthe lungs. learn the necessity of respiration. Respiration is a chemical process of exchange of oxygen and carbon dioxide between outside air and the cells. distinguish between breathing and respiration. In external respiration, there is an exchange ofoxygen and carbon dioxide between air and blood. External respiration takes place in the lungs at the alveoli. understand aerobic and anaerobic respiration. learn breathing in human beings and in other Haemoglobinofblood transports oxygen from lungs to the bodycells Insects are peculiar in having air tubes or trachea for respiration. Aquatic animals like fishes have gills. They obtain oxygen dissolved in water. animals. Comprehend respiration in plants. Earthworms breathe through their moist skin. Now, study the chapter in detail. RESPIRATION We eat food to get energy. The energy stored in food molecules is released by their oxidation, i.e., combining of food molecules with oxygen. Hence, oxidation occurs in the presence of oxygen. The processof taking oxygen into the body and then oxidation of food with this oxygen and release of carbon dioxide and energy is called respiration. Respiration can be defined as a biochemical process thatinvolves: intake ofoxygen from the environment.
  • 2. f food (glucose) with the help Anaerobic respiration Oxidationof ofoxygen taken se of energy and carbon dioxide. respiration When glucose is broken down in the absence of oxygen, it is called anaerobic respiration. The animals and plants that can survive and obtain energy in the absence of oxYgen are in. r e l e a s e imination of carbon dioxide.eliminati whydo we respire needs energy to run. We fill petrol in called anaerobes. A car.The petrol burns, using oxygen from Anaerobic respiration occurs in yeast, some a r the air he air and gves energy to the car to run. bacteria and parasitic flatworms. In the and gives ilarly, he food reacts with oxygen of absence of oxygen, glucose breaks down into thehe air releasing energy and carbon dioxide. ethyl alcohol and carbon dioxide. Hence, energy is released during oxidation intheabsence Ethyl Carbon+ Energy of oxygen offood. Every body cell needs energy and Glucose alcohol dioxide theretore, needs food and oxygen. To get need to respire, i..,oxygen we hreathe fresh air rich in oxygen through Do animals also respire anaerobically? respiratory organs. Parasitic animals that live in the alimentary canal (like roundworms and flatworms) respire anaerobically. They do not get oxygen in the alimentary canal. transport oxygen fror respiratory organs to every body cell. Breathing and respiration Breathing and respiration are two different processes. Breathing is a mechanical process of pumping air into and out of the lungs. Respiration is a chemical process ofexchange of oxygen and carbon dioxide between the Sonething More In anaerobic respiration, breakdown ofglucose is incomplete. Very little energy is produced in anaerobic respiration. Yeast is a single-celled organism. It respires anaerobically and yields ethyl alcohol. The yeast cells are, therefore, used to make wine and beer. They are also used in baking industry. The anaerobic breakdown of sugars into alcohol is called fermentation. outside air and cells. During respiration, glucose produces carbon dioxide, water and energy. Aerobic and anaerobic respiration Aerobic respiration When glucose breaks into carbon dioxide and warer using oxygen inside the body cells, it is called aerobic respiration. Can we respire anaerobically? We cannot respire anaerobically, our skeletal muscles can but only for a short period. Glucose in the Carbon Water + Energy presence of Oxygen dioxide During vigorous muscular activities, like fast Anumals that use oxygen for respiration are running, brisk walk1ng or heavy exercise, called aerobes. Majority of animals and more energy is needed. Therefore, demand plants have aerobic respiration. for oxygen also increases, but oxygen supply
  • 3. to muscles remains unchanged. Under shortage of oxygen, skeletal muscles respire anaerobically and glucose breaks down to Lungs lactic acid releasing energy. BREATHING IN HUMAN BEINGS Lungs are the main respiratory organs in our body. They are a pair of spongy, high elastic and bag-like structures. They enclose thin-walled and tiny air-sacs called alveolk The surface of alveoli is covered with network of blood capillaries. When we breathe in, these alveoli are filled with fresh air. Oxygen from this air enters the blood capillaries and carbon dioxide from blood Glucose theshortageof Oxygen in musclecells Lactic acid + Energy Something More When muscles respire anaerobically, the glucosebreaks down into lactic acid. The accumulationof lactic acid causes muscle cramps. We get relief from cramps after a hot bath or a gentle massage with lukewarm oil. This increases the blood circulation Comes out. and consequently the oxygen supply to the muscles increases. This causes oxidation of lactic acid into carbon dioxide and water. - Larynx Trachea Check PeINT 1. 1. Define respiration. 2. Which substrate is used by cells for producing energy? 3. Give the overall reaction of respiration. 4. Why do we feel muscle cramps after a fast running? 5. Give one example of an anaerobic plant and an anaerobic animal. Right lun8 Bronchus - Left lung Fig. 12.1 Human lungs 6. What is the end product of anaerobic respiration in skeletal muscles? Bronchiole Pulmonary vein TABLE 12.1 DIFFERENCESBETWEENAEROBIC AND Alveolar Pulmonary ANAEROBIC RESPIRATION duct artery Aerobic respiration Anaerobic respiration Alveolar 1. Occurs in the presence of 1. Occurs in the absence of cavity oxygen.Oxygen. 2. Glucose is completely 2. Glucose is oxidised incompletelyoxidised. 3. End products are carbon 3. End products are either ethyl alcohol and carbondioxide and water. dioxide or lactic acid. Venule4. More energy is produced (38 ATP from one molecule 4. Very little energy is produced (2 ATP from one molecule of glucose). Arteriole Alveolus ofglucose). 5. Occurs in most of the plants 5. Occurs in few organisms and animals. Fig. 12.2 Lung alveoli associated with a bronchiole and having a network of blood capillaries on the surface like yeast, some bacteria and some parasitic worms.
  • 4. There a r e about 750 are about 750 million alveoli in the bronchi (singular: bronchus) which enter dioxide between the air in alveoli and blood Breathing and breathing rate Lungs are connected with the external air and giving out of carbon dioxide from the J u n g s . the lungs of their respective side. Inside the ThetoThe total surface area of these alveoli is lungs, the bronchi divide and redivide into bout 100100 square metres. This is a large bronchioles which further divide and finally efor exchange of oxygen and carbonfor excl a r e a end into air sacs or alveoli. in the in the alveolar capillaries. Breathing is a mechanical process. It involves taking in of air rich in oxygen into the lungsOrgans of breathing throughrough nose, nasal passages, pharynx, lungs. rachea, bronchi and bronchioles.t r a c Taking in of air rich in oxygen into the lungs is called inhalation and giving out air rich in carbon dioxide is known as exhalation. Nasal cavity Inhalation and exhalation occur continuously and alternately. One breathe means one inhalation and one exhalation. The number ofNasal passage times a person breathes in a minute is termed as breathing rate. Air Tongue Pharynx Something More Normally we breathe16-18 times/minute. Breathing rate may increase up to 25 times per minute during fast running or heavy exercise. During brisk walking, fast running or exercising we breathe fast and take deep breath. This provides more oxygen and more energy. It means more food is burnt and we feel hungry after exercising, running or playing. Trachea Fig. 12.3 Breathing passage in man Nose and nasal passages We breathe air through nose or nostrils. In the nasal passages, the air gets filtered Warmed and moistened before entering the lungs. Therefore, we should always breathe through nose and not through mouth. Pharynx Sneezing: Airaround us is polluted with pollen, smoke particles, dust, etc. Normally when we inhale, these unwanted particles are trapped in the hair presentin the nasal passages. Sometimes these particles are not trapped in the hair and irritate the lining of the passage. This causes sneezing. As a result of sneezing, unwanted particles are thrown out and only clean air enters the lungs. The air from nas passages reaches trachea through pharynx. Trachea orWindpipe The air from pharynx reaches the lungs hrough windpipe. It is divided into two When you sneeze, cover your nose so that the particles you sneeze out do not fall on others and are not inhaled by them.
  • 5. cavity. The lungs being elastic also increase in size and the air pressure in the lunoe decreases. Air from the atmosphere having higher pressure rushes into lungs through nostrils and air passages and the lungs get filled with fresh air. Activity To find out breathing rate under different conditions Under normal condition: Breathe in and out gs normally and count the number of times you breathe in and breathe out in one minute. The number of breaths per minute is your breathing rate. After brisk walking and running: Count the number of times you breathe after a briskwalk after running and after a complete rest. Record your breathing rates and that of your classmates in a tabular form as given here. Air rushing into the lungs Pleural Trachea membranes Ribsraised LungName of Breathing rate expandedthe class- Under After After Aftera mate normal a brisk running complete condition walkfor for 100 m rest Rib Contracted10 min or more Diaphragm pulled down muscles of Yourself diaphragm Fig. 12.4 Inhalation Observe and compare your observations. Exhalation Conclusion During exhalation, the ribs move downward The breathing rate does not remain the same under all conditions. It increases when we need more energy, i.e., while walking, running or exercising. It slows down when we are at complete rest doing no work. When breathing rate slows down to the extent that we do not get sufficient oxygen, we feel sleepy or drowsy. and inward and the diaphragm moves up. When the ribs and diaphragm return to their original position, the volume of thoracic cavity decreases and so also ofthe lungs.This increases the air pressure inside the lungs and the air from the lungs is pushed out. Mechanism of breathing Air moving out from the lungs Lungs are spongy structures. They are placed inside an air-tight thoracic cavity enclosed in the ribcage. A large muscular diaphragm forms its floor. The diaphragm separates thoracic cavity from abdominal cavity. The rib muscles and muscles of diaphragm work Ribs returned to normal position Vertebral column together to aid in breathing Diaphragm Inhalation returned to its normal Relaxed During inhalation, the ribs move upwards and outwards and the diaphragm moves down. This increases the volume of thoracic shape muscles of diaphragm Fig. 12.5 Exhalation 18
  • 6. Eventsthatoccur during breathing ze of the thorad cavity changes. It expands(when are raised upward and outwardand the aphragm flattens during inhalation. Something More Activity 3 To measure the change in the size of chest cavity with a measuring tape, measure the size of chest of your friend as shown in the figure. The volume of oracic cavity reduces when move down and inward and the diaphragm ribs heComes dome-shaped during exhalation. Air pressure in the lungs changes. Air press be low when lungs expand and becomes Airmoves in and out of lungs due to a change in becol m high when lungs are reduced in size. air pressure in the lungs. Activity To demonstrate breathing process Remove the bottom of a wide plastic bottle. Make a hole in the cork and insert a Y-shaped glass tube in it. Ex two deflated balloons to the two free ends of glass tube. Now insert the cork in the mouth of the bottle from inside. Finally attach a sheet of rubber over the open bottom of the bottle as shown in the figure. Seal the cork with modelling clay or wax. Ask him to take a deep breath and measure the chest size again. Repeat the experiment with other friends and record your observations as shown in the table. CHANGE IN THE SIZE OF CHEST CAVITY DURING BREATHING Name ofthe When Difference inWhen friend expanded relaxed size (during (during Plastic bottle inhalation)| exhalation) Y-tube Balloons Volume (decreases) Process ofrespiration Respiration takes place in following steps: Exchange of gases between air and blood - External respiration. Exchange ofgases between blood and body cells Internal respiration. Break down of glucose in body cells- Cellular respiration. Oxygen that enters the blood from alveoli during external respiration combines with haemoglobin - the respiratory pigment in Red Blood Cells (RBCs). They form a temporary compound called oxyhaemoglobin. Volume (increases) Rubber sheets Working Gently pull the rubber sheet down. Observe the change in balloons, which gradually increase in size. Gently release the rubber sheet and observe what happens. In this experiment, balloons are equivalent to. rubber sheet is equivalentto. plastic bottlerepresents What is the effect when rubber sheet is pulled down? Why deflated balloons become reflated when rubber sheet is pulled down? What happens to balloons when rubber sheet is released? 11
  • 7. On reaching the tissue cells, oxyhaemoglobinbreaks to release the trapped oxygen. The released oxygen enters the cells. This is called internal respiration. How much air can a person hold in his lungs? An adult can take in a maximum of about 5 litres air. During normal or relaxed breathing, only 500 cm3 (half litre) air in the lungs is replaced at each breathe. During exercise or running, i.e., in forced breathing, about 3 litres of air is replaced in lungs at each breathe. Therefore, running, playing and jumping are good and very much needed for good health. During cellular respiration, breakdown of glucose takes place to release carbon dioxide and energy. TABLE 12.2 DIFFERENCES BETWEEN EXTERNAL AND INTERNAL RESPIRATION External respiration Internal respiration 1. It is an exchange of gases 1. It involves an exchange of between air and blood. gases between blood and body cells. TABLE 12.3 DiFFERENCES BETWEEN THE 2. It occurs at the level of 2. It occurs at the level of cOMPOSITION OF INHALED AND EXHALED AIR alveoli body cells. Inhaled air Exhaled air What do we inhale and exhale 1. Oxygen 21% | 1. Oxygen 16.4% We inhale and exhale air. But the composition 0.03% 2. Carbon dioxide 4.4%2. Carbon dioxide ofair inhaled and air exhaled is different. The air inhaled has more oxygen and less carbon Check PeINT 2 - dioxide, while the percentage of oxygen is Fill in the blanks. less and that of carbon dioxide is more in 1. The diaphragm is lowered during the air we exhale. This difference is given in 2. Breathing is a - Table 12.3. process. 3. Carbon dioxide turns. milky. 4. Exhaled air has. %ofcarbon dioxide and % of oxygen. Activity 5. Thoracic cavity is also calledTo show that we exhale carbon dioxide Take a clean and transparent 6. Duringr we take fresh air into plastic bottle with narrow opening. Pour some freshly prepared lime water in it. Make a hole in the cork RESPIRATION IN OTHER ANIMALSand insert a plastic straw in it. Fix the cork in the We have lungs for respiration. But all animals do not have lungs. Frogs, snakes, crocodiles, birds and mammals possess lungs. They have nostrils (not the nose) to inhale air. However, animals like earthworm, cockroach, mosquito, snail and fish are without lungs. Their respiratory organs are much bottle and make it airtight. Make sure that the end of straw dips in lime water Blow gently through the straw into lime water several times and observe the change in its colour. Observation and inference Lime water turns milky in the bottle. Why? Carbon dioxide turns lime water milky. It means different.exhaled air contains carbon dioxide.
  • 8. vorm (Cutaneous respiration) nAnd leeches breathe only through (Aquatic respiration) Farth Respiration in fishes Earthwo Earkin. Their skin is moist and slimy Fishes and other animals living in water are skin. Thei numerous blood capillaries. Skinandha. rge mber of capillaries is called dissolved in water. Their respiratory organs called aquatic animals. They obtain oxygen a highlyvascular. The exchange of oxygen are gills. bon dioxide occurs between air and bloodin tid in the skin. Frogs have lungs just like us but they c a n alsocan also breathe through their skin when in water. That is why frog's skin is Gills sippery. Respiration in cockroach and other insects (Tracheal respiration) airtubes called tracheae. The air tubes form The respiratory organs in insects are branched Fig. 12.7 Gills in fish fne network inside the body and are in contact with the cells. They open on the body surface by spiracles. The spiracles open and close to allow respiratory gases to move in Gills are projections of skin. They have a network of fine blood capillaries. The oxygen dissolved in water enters the blood capillaries. Carbon dioxide present in capillary blood is released into water. The oxygenated blood from capillaries is taken to heart and pumped to different parts of the body and blood from body tissues which has carbon dioxide is taken to gills for the exchange of respiratory gases. and out of the air tubes. Spiracles Can we survive under water just like whales?Tracheae We c�nnot live in water for long. Our breath is short and so we will have to come to water surface for breathing very frequently. We can, however stay under water with an oxygen cylinder. You might have seen divers with oxygen cylinders at their back.Fig. 12.6 Tracheal system in cockroach Containing oxygen enters the tracheal uDes through spiracles and diffuses into every cell of the body. Sotnething More rachea or air tubes are found exclusively in insects and do not occur in any other animal group.
  • 9. Transport of gases in plants takes place by diffusion only. Different parts ofa plant have different methods of obtaining oxygen and releasing carbon dioxide. Do whales and dolphins have gills for respiration? Whales and dolphins live in water but they are mammals. All mammals have lungs for respiration and breathing air. Whales and dolphins also have lungs.They often come to the surface ofwater for inhaling and exhaling air. When they exhale, they release a fountain of water. In leaves The leaves have tiny pores called stomata. The exchange of gases in leaves occurs through these pores. RESPIRATION IN PLANTS In stems Plants respire like all other organisms. Each Young stems have stomata as in leaves. In plant cell uses glucose and oxygen and old woody stems, lenticels develop below the releases carbon dioxide, water and energy. bark to ensure gaseous exchange. But during daytime carbon dioxide released by respiration is used for photosynthesis and Oxygen produced during photosynthesis is utilised for respiration. So plants do not take oxygen during day. But at night, plants also take oxygen from the atmosphere and give out carbon dioxide. Stomatal pore Guard cell Epidermal cells Why are we asked not to sleep under the tree at night? Fig. 12.8 Stomata on leaf surface Plants use oxygen and give out carbon dioxide at night. Therefore, concentration or amount of Co, (carbon dioxide) under the tree goes up and may prove to be harmful. However, this CO, Soon diffuses in the atmospheric air. Warning: We should never sleep in a closed room with an oil lamp burning because this reduces oxygen and increases carbon dioxide in air. In roots Root hair arising from different regions of root extend into air spaces present between the soil particles and take up oxygen from there. Check PeINT 3 Fill in the blanks. 1. Insects have. as respiratory organs. Plants do not have respiratory organs to obtain oxygen from atmosphere. Each part of a plant can independently 3. Fishes have take in oxygen from the surrounding air and give out carbon dioxide. 2. For respiration in earthworm, IS moist and for breathing. 4. Gills are an extension of. 122