4

Respiration in Organisms
Expected Learning Outcomes

Knowledge to be gained: •Aerobic and anaerobic respiration •Breathing •Respiration in humans

•Respiration in various animals •Respiration in plants
Skill to be developed: •Explaining the breathing process by showing a working model of lungs
with the help of a simple activity.
Attitude to be inculcated: •Value the importance of oxygen.
Our body is like a machine. ere are many respiration involves taking in oxygen (from
processes in our body which start at birth and air) into the cells, using it for releasing energy
end at death. Respiration is one of them. We by burning food, and then eliminating the
respire to get energy. waste products (carbon dioxide and water)
If food is the fuel for our human body, from the body. e food that is fully digested in
respiration is the process of burning that fuel to the small intestine is absorbed by the blood and
release energy to run our body. A human being transported to all the cells of the body. e
cannot survive for more than a few minutes assimilation (breakdown) of glucose (digested
without breathing. food), to release energy, takes place with the
help of respiration. Most living things need
RESPIRATION
oxygen to obtain energy from food. is
Respiration is a fundamental process by oxygen reacts with the food (like glucose)
which energy is released/obtained by the present in the body cells and burns them to
breakdown of digested food. Respiration release energy. is energy is used by the living
occurs in all the living cells. e process of organisms. e process of respiration can be
46 Exploring Science-7
 written in the form of a word equation as as glucose and fructose called respiratory
follows: substrates) is changed into water and carbon
Glucose + Oxygen
Respiration
Carbon dioxide+Water+Energy
dioxide, accompanied by the release of usable
(food) (form air) (in body energy (ATP or Adenosine Triphosphate).
cells)

In fact, respiration is a kind of slow-burning of TYPES OF RESPIRATION: AEROBIC

food at the body’s temperature to produce AND ANAEROBIC RESPIRATION
energy. During respiration, oxygen is taken in Respiration usually takes place in the presence
and carbon dioxide is given out. us, the of oxygen. Respiration can, however, also take
process of respiration involves the exchange place in the absence of oxygen, though it is very
of gases: oxygen and carbon dioxide. e rare. Based on whether oxygen is used up or not,
process of respiration is the reverse of there are two types of respiration: aerobic
photosynthesis. is is because, photosynthesis respiration and anaerobic respiration.
is the making of food (like glucose) by ese two types of respirations are discussed
absorbing sunlight energy, whereas respiration below:
is the breaking down of food (like glucose) to
Aerobic Respiration
release energy.
e breakdown of food (glucose) into carbon
ere are two main steps in the process of
dioxide and water to release energy using
respiration:
oxygen is called aerobic respiration. It is called
u External respiration (Breathing):
aerobic respiration because it uses ‘air’ which
Breathing is taking in oxygen from air and
contains oxygen (aerobic means with air). In
releasing carbon dioxide.
aerobic respiration, glucose is completely
u Internal respiration (Cellular broken down into carbon dioxide and water
respiration): It uses oxygen in the cells of with the use of oxygen, to release energy. It can
the organism to release energy from food be represented by the word equation as follows:
(like glucose).
Oxygen
Glucose Carbon dioxide+Water+Energy
e air which we ‘breathe in’ is transported to all (Aerobic
(food) Respiration)
parts of the body, and ultimately to each cell of
the body. In the cells, oxygen (from air) brings e energ y released during aerobic
about the breakdown of glucose (food). Since respiration is used by the organism. Most
the process of respiration takes place inside living organisms carr y out aerobic
the cells of the body, it is also called cellular respiration (by using oxygen of air), and
respiration. e process of cellular respiration such organisms are called aerobes. For
is common to all living organisms (humans, example, humans, dogs, cats, lions,
other animals and plants). It takes place in all elephants, cows, buffaloes, goats, deer, birds,
the cells of an organism. lizards, snakes, earthworms, frogs, sh and
During respiration, the energy-rich food (such insects (such as cockroaches, grasshopper,
Respiration in Organisms 47
house ies, mosquitoes), etc. Humans and extra energy is needed), anaerobic respiration
most plants carry out aerobic respiration by can take place in our muscles for a short period
using oxygen from air. Aerobic respiration of time.
produces much more energy in comparison You might have noticed that when you go out
to anaerobic respiration because the for a quick sprint, sometimes you get muscle
complete breakdown of glucose (food) cramps (pain in the muscles). is happens
occurs during aerobic respiration. because when we push our body to run very fast,
Anaerobic Respiration we use a lot more energy than our body muscles
can produce aerobically. e supply of oxygen
When glucose is broken down in the absence
to produce the energy required is low. In such
of oxygen, it is called anaerobic respiration.
circumstances, our muscles start anaerobic
e animals and plants that can survive and
respiration to ful l the demand for energy. e
obtain energy in the absence of oxygen are
cramps occur because of anaerobic respiration,
called anaerobes. which leads to the building up of lactic acid in
Anaerobic respiration occurs in micro- the muscles. Lactic acid is a bi-product of
organisms like yeast, some bacteria and some anaerobic respiration in the muscles.
parasitic atworms. In the absence of oxygen,
Absence of
glucose breaks down into ethyl alcohol and Glucose
oxygen
Lactic acid + Energy
(Anaerobic
carbon dioxide, and releases energy. (in muscle Respiration)
cells)
Absence of
oxygen
Glucose Alcohol + Carbon dioxide + Energy
(food) (Anaerobic When the oxygen supplied by the blood is used
Respiration)
up faster in our muscle cells than that can be
e organisms which obtain energy by the supplied by the blood, then a temporary
process of anaerobic respiration (without using de ciency of oxygen occurs in the muscle cells.
oxygen), are called anaerobes. Yeast is an In other words, during heavy exercise, the
anaerobe. Hence, yeast can survive in the demand of energy is greater but the supply of
absence of oxygen. energy is less. To ful l the demand of extra
energy, anaerobic respiration takes place in
Knowledge Booster our muscle cells in the absence of oxygen.
Yeast is a single-celled organism. It respires During anaerobic respiration, the food breaks
anaerobically and converts glucose into ethyl
alcohol. The yeast cells are therefore used to down into lactic acid and releases some energy.
make wine and beer. They are also used in the is extra energy helps us to continue doing
baking industry. hard physical exercise.
Anaerobic respiration in muscles Absence of
oxygen
Glucose Lactic acid + Energy
Generally, we humans obtain energy by aerobic (in muscle
(Anaerobic
Respiration)
respiration, but under certain conditions (when cells)

48 Exploring Science-7
 Similarities Between Aerobic and Anaerobic Respiration.
Aerobic Respiration Anaerobic Respiration
1. In aerobic respiration, energy is produced 1. In anaerobic respiration also energy is
by the breakdown of food (like glucose). produced by the breakdown of food (like
glucose).
2. Aerobic respiration takes place in the cells 2. Anaerobic respiration also takes place in
of the organism. the cells of the organism.

Differences between Aerobic and Anaerobic Respiration

Aerobic Respiration Anaerobic Respiration
1. Aerobic respiration takes place in the 1. Anaerobic respiration takes place in the
presence of oxygen. absence of oxygen.
2. Complete breakdown of food occurs in 2. Partial breakdown of food occurs in
aerobic respiration. anaerobic respiration.
3. e end products in aerobic respiration are 3. Along with energy, the end products in
carbon dioxide and water, along with anaerobic respiration may be alcohol or
energy. lactic acid.
4. A e r o b i c r e s p i r a t i o n p r o d u c e s a 4. Much less energy is produced in anaerobic
considerable amount of energy. respiration.

Checkpoint-1
Write True or False
1. Human beings cannot survive for more than a few minutes without breathing. ______________
2. Respiration occurs in all living cells. ______________
3. Humans and most of the plants carry out aerobic respiration. ______________
4. Much more energy is produced in anaerobic respiration. ______________

BREATHING e breathing in human beings takes place

through an organ called the ‘lungs’. e taking
Breathing can be de ned as the process by
in of air, rich in oxygen, into the body during
which air, rich in oxygen, is taken inside the
breathing is called inhalation and the giving
body of an organism and air, rich in carbon
out (expelling) of air, rich in carbon dioxide,
dioxide, is expelled from the body (with the
is called exhalation. Both, inhalation and
help of breathing organs). Different organisms exhalation, take place regularly during breathing.
have different organs for breathing, depending A breath means ‘one inhalation plus one
on their structure and requirements of oxygen. exhalation’.

Respiration in Organisms 49
 Differences between Breathing and Cellular Respiration
Breathing Cellular respiration
1. Breathing is a physical process in which exchange 1. Cellular respiration is a chemical process in which
of gases take place. Oxygen is absorbed and carbon the oxygen absorbed during breathing is used to
dioxide is released. break down food particles (glucose) to release
energy.

2. is activity takes place in special breathing organs 2. It takes place within all the cells of our body.
like lungs and gills.

3. ere is no release of energy. 3. ere is a release of energy.

altitudes is much less than that is available on

the ground.
Breathing Rate
We have just learnt that a breath means ‘one
inhalation plus one exhalation’. e number of
times a person breathes in one minute is
called his/her breathing rate. On an average,
an adult human being at rest, breathes in and
out 15 to 18 times in a minute. So, the average
Fig.1 Human beings breathe through their lungs
breathing rate of an adult human being at rest
We know that air contains oxygen, so, when we is 15-18 times per minute. is breathing rate
breathe in air, oxygen is absorbed by our body changes when we are involved in doing different
(in order to breakdown food and produce kinds of work. You would have noticed that you
energy). breathe faster while playing any sports. Why do
We breathe air through our nose (or you think this happens?
sometimes even through the mouth). Now, if e breathing rate of a person changes
we close our nostrils and mouth tightly, we start according to the oxygen requirements of the
feeling uneasy soon and cannot hold our breath body. For example, the breathing rate of a
even for one minute. is shows how essential person is the slowest when he/she is sleeping
breathing of air is to keep us alive. because minimum energy is required by the
Breathing is a continuous process which goes body during sleep. is energy can be supplied
on all the time and throughout our life and that by a slow rate of breathing. e breathing rate of
of other animals as well as plants. e a person increases with increased physical
mountaineers carry oxygen cylinders with activity (like exercise, running, weight-liing,
them for breathing because the amount of air etc.) When the breathing rate increases, a
available to a person for breathing at high greater amount of air goes into the lungs and
50 Exploring Science-7
 the blood can absorb oxygen at a faster rate. the bottom of the chest cavity is a curved sheet
us, faster breathing supplies more oxygen to of muscle called diaphragm. e diaphragm
the body cells for producing more energy. forms the oor of the chest cavity. Breathing
During heavy physical exercise, the breathing involves the movements of the rib cage and
rate is about 25 per minute (or even more). the diaphragm. is happens as follows:
Inhalation
Knowledge Booster
During inhalation, the ribs move upwards and
Women breathe slightly faster than men. The
breathing rate of a person is not always constant. outwards and the diaphragm moves
downwards. is increases the volume of the
chest cavity. e lungs being elastic also
increases volume. e air already present in the
Nostril
lungs expands and creates space for more air to
Ribs come into the lungs. Air from the atmosphere
Le and right having higher pressure rushes into the lungs
bronchus through nostrils and air passages and the lungs
Right lung Le lung
get lled with fresh air, rich in oxygen.
Exhalation
Diaphragm
Fig.2 Human respiratory system During exhalation, the ribs move downwards
and inwards and the diaphragm moves
BREATHING MECHANISM upwards.
When we inhale air, it enters our nostrils, passes e volume of the chest cavity decreases, and so
through our nasal passage and windpipe, and does the volume of the lungs. e air already
reaches our lungs. Our two lungs hang in an present inside the lungs contracts and is ready
airtight space in our body called the chest to move out of the lungs. is increases the air
cavity. Around the sides of the chest cavity is the pressure inside the lungs and the air from the
rib cage with sheets of muscles between the ribs lungs is pushed out. e air exhaled by the lungs
(Fig.2). e rib cage encloses the lungs in it. At is richer in carbon dioxide.
Inhalation Exhalation

Carbon
Oxygen dioxide Chest wall and Chest wall and
rib cage expand rib cage contract
Lungs
Lungs
Lungs expand contract
Diaphragm
Diaphragm

Diaphragm pulls downwards Diaphragm moves upwards Diaphragm contracts Diaphragm relaxes
helping lungs to take in oxygen forcing lungs to expel carbon dioxide
Fig.3 Inhalation and exhalation
51
 Observation:
Activity-1
(i) When you pull the rubber sheet downwards,
To demonstrate the mechanism of breathing. the space inside the bottle increases,
Materials Required: Transparent plastic bottle, lowering the air pressure inside the bottle.
Y-shaped glass or plastic tube, 2 balloons, e air from outside rushes in through a Y-
plasticine, rubber sheet, rubber band. shaped tube into balloons, due to which the
Method: balloons get in ated (i.e., their size
u Take a wide transparent plastic bottle (a so increases). is is how you inhale air during
drink plastic bottle will do) and get breathing.
someone to cut off its bottom (Fig.4). (ii) When you push the rubber sheet up, the
u Make a hole through the bottle’s cap. space inside the bottle decreases. is
u Fix and tie two de ated balloons at the two pushes out the air inside the balloons
forked ends of a Y-shaped glass or plastic tube. through the tube, due to which, the
u Introduce the tube tted with the two balloons get de ated (their size decreases).
de ated balloons from the cut end of the is is how you exhale air during
bottle and pass the tube through the hole in breathing.
the cap. Use plasticine to seal the cap and Conclusion: e action of the rubber sheet in
make it airtight. this activity shows how we inhale and exhale
u Fix a thin rubber sheet by tying it around air during breathing with the help of the
the open base of the bottle using a large downward and upward movement of the
rubber band. Your apparatus is ready. diaphragm in our body.

1 2 During the process of respiration, when glucose

is broken down to release energy, then some of
the oxygen from inhaled air is used up, and
carbon dioxide and water are produced as
byproducts. is is why, the exhaled air contains
less oxygen and more carbon dioxide and water
3 4 vapour. e amount of oxygen, carbon dioxide
and water vapour in inhaled air and exhaled air
is given below:
Inhaled Air Exhaled Air
Fig.4
Oxygen: 21% Oxygen: 16.4%
u In this apparatus, the space inside the bottle
represents the chest cavity, the balloons Carbon dioxide: 0.04% Carbon dioxide: 4.4%
represent the lungs, whereas the rubber
Water vapour: little Water vapour: A lot
sheet represents the diaphragm.
52 Exploring Science-7
 Nasal cavity
Activity-2 Nostril Pharynx
Aim: To show that carbon dioxide is produced
Larynx
during respiration. Trachea
Materials Required: Glass or plastic bottle, Right Le
lime water, straw. bronchus bronchus
Method: Right Le
lung lung
1. Take a slender, clean glass or plastic bottle.
Make a hole in its lid and x it on the bottle.
2. Pour some freshly prepared lime water into Diaphragm
the glass or plastic bottle. Insert a plastic Fig.6 Human respiratory system
straw through the hole in the lid in such a
Nose: Nose encloses the nasal cavity which
way that it dips in lime water.
opens to the outside through two nostrils. e
3. Blow gently through the straw a few times.
nose has ne hair and it secretes a sticky liquid,
Observation: e lime water in the glass or mucus, produced by the inner lining of the
plastic bottle turns milky. nose.
Conclusion: e exhaled air contains carbon u Fine hair and mucus present in the nose
dioxide gas because carbon dioxide gas turns prevent the entry of dust particles and germs
lime water milky. So, we conclude that carbon
into the respiratory system.
dioxide gas is released during exhalation.
u Mucus moistens the air in the nasal cavity.
u Blood circulation in the nose warms the air.
From the nasal cavity, air passes into the
Blow air Straw pharynx which has two openings in its lower
part. One opens into the oesophagus (food
Straw
pipe) and the other into the windpipe or
trachea. e opening of the pharynx into the
trachea is called the glottis.
Trachea: Trachea or windpipe is a long
Lime water
Lime water turns milky cylindrical tube supported by cartilaginous
rings (rings made of cartilage), which prevent it
Fig.5 Carbon dioxide is released during respiration from collapsing. e upper part of the trachea is
connected to a box-like organ called larynx.
RESPIRATION IN HUMANS Larynx is also called the voice box. Larynx
e respiratory system in human beings produces vocal sounds and prevents the
consists of the following organs: Nose, pharynx, passage of food or other foreign particles
trachea, bronchi and lungs. down into the respiratory system.
Respiration in Organisms 53
 Alveoli
Carbon dioxided
Bronchioles Windpipe Oxygen
(trachea)

Bronchi Air
Lung Blood vessel carrying
CO₂ and water vapour CO₂ O₂
Diaphragm rich blood
Air sacs (alveoli) Blood vessel
carrying
Fig.7 Lungs contain millions of alveoli O₂ rich blood
Fig.8 Gaseous exchange in alveoli
Bronchi: Trachea branches into two tubes
O₂ (oxygen) CO₂ (carbon dioxide)
called bronchi, one of which enters each lung.
Inside the lung, bronchi branch into ne
branches called bronchioles.
Lungs
Lungs: A pair of lungs is the organ for gaseous
exchange in human beings. Finest branches of Organs

bronchioles end in tiny sacs called alveoli or air

Red
sacs. Alveoli have a very thin wall and are blood cells
surrounded by a network of ne blood
capillaries. e exchange of gases between the
Fig.9 Respiration in humans
alveoli and the blood capillaries takes place
through their thin walls. is process occurs by
Knowledge Booster
the diffusion of air through the cell membranes High up in the mountains, the air is thinner than
of the alveoli. us, alveoli are the structures at sea level. People who live in places with a high
responsible for gaseous exchange. Oxygen al tude have larger lungs so that they can take in
more air with each breath and get the right
present inside the alveoli diffuses across the amount of oxygen.
walls of the alveoli and into the blood in the
capillaries. SNEEZING
Blood carries the oxygen received from the e air around us may be polluted with pollen,
lungs to different parts of the body. Blood smoke particles, dust, etc. Normally when we
contains Red Blood Cells (RBC) which contain inhale, these unwanted particles are trapped by
t he re d pi g me nt c a l l e d ha e mog lobin. the hair present in the nasal passages. Sometimes,
Haemoglobin gives the blood its red colour. these particles are not trapped and irritate the
Haemoglobin combines with the oxygen and lining of the passage. is causes sneezing. As a
carries it to all the cells. Similarly, haemoglobin result of sneezing, unwanted particles are thrown
combines with the carbon dioxide diffused out and only clean air enters our lungs. When you
from the cells and carries it to the lungs. Here, sneeze, cover your nose so that the particles you
the carbon dioxide diffuses into the alveoli and sneeze out do not fall on others, and are not
is breathed out through the nose (Fig.9). inhaled by them.
54 Exploring Science-7
 Checkpoint-2
Answer the following
1. Where is the glottis present?
2. What are alveoli responsible for?
3. What is the function of haemoglobin? Where is it found?
4. Which organs can be used to breathe air?
5. Our lungs hang in an air-tight space called ______________.
6. ______________ forms the oor of the chest cavity.

RESPIRATION IN ANIMALS Respiration in Fish

Different animals respire through different Fish have special organs of breathing, called
parts of their body. Respiration in some gills, found on both sides of their head (Fig.11).
common animals is described below: e sh breathes by taking in water through its
Respiration in Earthworms and Frogs mouth and sending it through the gills. Gills are
e earthworms breathe through their skin. well supplied with blood vessels.
e skin of an earthworm is thin and moist. e blood vessels of the gills extract dissolved
Gases can easily be exchanged through the oxygen from the water and send it to all parts
earthworm’s skin, by the process of diffusion. of the body. is oxygen is utilised in
e earthworm absorbs oxygen (of air) respiration to produce energy and carbon
required for respiration through its thin and dioxide. is carbon dioxide is brought back by
moist skin. the blood into the gills for expelling into the
Frogs have lungs for breathing. They can also surrounding water. Some other aquatic animals
breathe through their moist skin. us, a frog is like prawns, crabs and freshwater mussels also
an animal which can breathe through its respire through gills or similar structures.
lungs as well as through its moist skin. ey
Gills
breathe through the lungs when on land and
through the skin when in water. Fig.11 Fish breathe
through gills

Glottis opens to let

air into the lungs Water in

Water out
Lungs ere are, however, some sea animals, like
dolphins and whales, which live in water but do
Fig.10 Frogs breathe through lungs not have gills. Dolphins and whales breathe in
as well as through their skin
Respiration in Organisms 55
air through their nostrils (called blowholes) So, plants do not take oxygen during the day.
which are located on the upper parts of their During the daytime, both respiration and
heads. ey come to the surface of seawater photosynthesis take place in plants. e
from time to time to breathe in air. oxygen produced during photosynthesis is
Respiration in Insects generally much more than the amount of
oxygen released by the plant for its respiration.
Insects like grasshoppers and cockroaches
e unutilised oxygen is released back into the
have a respiratory system, consisting of a
air. is way, during the daytime, plants act as
network of thin air tubes called trachea that
a net supplier of oxygen rather than a net
spread throughout the body. ese air tubes
consumer of oxygen. But at night, plants also
have tiny openings, called spiracles, on the sides
take oxygen from the atmosphere and give out
of their body.
carbon dioxide.
For example, a cockroach has spiracles (tiny
u Plants do not have respiratory organs to
holes) on the sides of its body and tracheae (air-
obtain oxygen from the atmosphere.
tubes) throughout the inside its body to help in
the process of breathing and respiration. Insects u Each part of a plant can independently take

such as grasshoppers, house ies, bees and in oxygen from the surrounding air and give
wasps also have spiracles and tracheae for out carbon dioxide.
breathing and respiration. u Transport of gases in plants takes place only
Air sac by diffusion.
u Different parts of a plant have different
methods of obtaining oxygen and releasing
carbon dioxide.
oracic
spiracles Respiration in Leaves
Tracheae e exchange of gases (oxygen and carbon
Abdominal dioxide) in the leaves during respiration takes
spiracle place through stomata. Stomata are tiny pores
present on the surface of the leaves of a plant.
Fig.12 Grasshopper breathes through a
network of spiracles When stomata opens up, oxygen from air enters
into the leaf through them and reaches all the
RESPIRATION IN PLANTS
cells by the process of diffusion (Fig.13). is
Plants respire like all other organisms. Each
oxygen is used in respiration in the cells of the
plant cell uses glucose and oxygen and releases
leaf. e carbon dioxide produced during
carbon dioxide, water and energy. But during
respiration diffuses out from the leaf into the air
the daytime, the carbon dioxide released by
through the same stomata.
respiration is used for photosynthesis and
oxygen produced during photosynthesis is So, we can also say that the plants breathe through
utilised for respiration. the tiny pores in their leaves called stomata.
56 Exploring Science-7
 Open stomata
Carbon dioxide

Oxygen

Closed stomata

Fig.13 Open and closed stomata Fig.14 Aerial roots found in mangroves

Respiration in Roots If a potted plant is over-watered for a long time,

e roots of a plant have a very large number of then the plant may ultimately die. Too much
tiny hair on them called root hair. Air is present water expels all the air from in between the soil
in between the particles of soil. e root hair particles. Due to this reason, oxygen is not
available to the roots for respiration. This causes
use the air present in between soil particles to
suffocation, and the plant may die.
breathe.
Plants that grow in areas where the land is
Oxygen from air in soil particles diffuses into the
root hair and reaches all the cells of the root, submerged in water for many months of a year,
where it is utilised in respiration. Carbon dioxide develop special roots which come out into the
produced during respiration goes out through open in order to respire. Such aerial roots are
the root hair by the process of diffusion. mostly found in mangroves (Fig.14).

Keywords
Respiration : The process of breakdown of food in the cells of the body for the release
of energy.
Aerobic Respiration : Respiration that takes place in the presence of oxygen.
Anaerobic Respiration : Respiration that takes place in the absence of oxygen.
Breathing : The process by which air rich in oxygen is taken inside the body of an
organism and the air rich in carbon dioxide is expelled from the body,
with the help of breathing organs.
Breathing Rate : The number of times a person breathes in one minute.
Larynx : Voice box present in the upper part of trachea.
Lungs : The organ where gaseous exchange takes place in the human body.
Alveoli : The structure responsible for gaseous exchange inside the lungs.
Spiracles : Tiny air tubes present on the sides of the bodies of insects, which help
them to breathe.
Stomata : Tiny pores present on the underside of leaves, which allow for exchange
of gases.

Respiration in Organisms 57
 Points to Remember
u Living organisms need a constant supply of energy to function.
u Respiration is the process by which energy is released from food. It involves two steps: external
respiration and internal respiration.
u In animals, two types of respiration occur. Aerobic respiration, which occurs in the presence
of oxygen; Anerobic respiration, which occurs in the absence of oxygen.
u Breathing is a part of the process of respiration during which an organism takes in air, rich in
oxygen, and gives out air, rich in carbon dioxide.
u e organs responsible for breathing vary in different organisms.
u Our lungs expand during inhalation and come back to their original state during exhalation.
u Air enters our body through the nostrils and passes into the nasal cavity. From there it travels
through the pharynx, trachea, bronchi and bronchioles, into alveoli. Alveoli are tiny air sacs.
u e exchange of gases during respiration in animals occurs through diffusion.
u In humans, the exchange of gases takes place in the alveoli which are surrounded by blood
vessels.
u In earthworms, the exchange of gases takes place through its thin moist skin. In sh, it takes
place through gills, and in insects, it takes place through tracheae and spiracles.
u e stomata of leaves are the windows of the plants for free access to respiratory gases.

Exercise
A. Tick (3) the Correct Option
1. During heavy exercise, we get cramps in the muscles due to the accumulation of:
(a) carbon dioxide (b) lactic acid
(c) alcohol (d) water
2. e normal range of breathing rate per minute of an average adult person at rest is:
(a) 15 - 18 (b) 9 - 12
(c) 30 - 33 (d) 21 - 24
3. During exhalation, the ribs:
(a) move downwards (b) move outwards
(c) do not move at all (d) move upwards

58 Exploring Science-7
 4. During respiration in humans, the exchange of gases takes place in the:
(a) bronchi (b) alveoli
(c) bronchioles (d) trachea
5. e animal which can breathe through the lungs as well as through skin:
(a) sh (b) dolphin
(c) frog (d) crocodile
6. Which of the following is not associated with respiration?
(a) Kidney (b) Gills
(c) Lungs (d) Trachea
B. Fill in the Blanks with Suitable Words
1. ________________ in the blood combines with oxygen and carries it to all the cells.
2. e skin of the earthworm is ____________ and ____________.
3. Fish have ________________ for breathing.
4. Insects have ________________ as respiratory organs.
5. Oxygen from air enters into a leaf through ________________.
C. Very-Short-Answer-Type Questions
1. De ne respiration.
2. Respiration is a kind of quick burning of food at high temperatures to release energy.
True or False?
3. Name the two broad steps in the process of respiration.
4. Complete breakdown of food occurs only in anaerobic respiration. True or False?
5. Write a word equation to represent anaerobic respiration in yeasts.
6. De ne breathing.
7. What is the breathing rate of an adult human being at rest?
8. Exhaled air contains less carbon dioxide than inhaled air. True or False?
9. Plants do not respire during the daytime. True or False?
10. Plants can respire even through their roots. True or False?
D. Short-Answer-Type Questions
1. How is respiration opposite to photosynthesis with regard to the exchange of gases?
2. Describe the two main steps in the process of respiration.
3. Differentiate between aerobic and anaerobic respiration. Write a word equation to
represent each.
Respiration in Organisms 59
 4. When does anaerobic respiration take place in muscles? Write a word equation to show
its end products.
5. What does a 'breath' mean? What is inhalation and exhalation?
6. Why do mountaineers carry oxygen gas cylinders with them?
7. Why is the breathing rate of a person slowest when he/she is sleeping?
8. Write three functions of the nose.
9. Describe the process of respiration in the following animals:
(a) Earthworm (b) Frog (c) Fish
10. Differentiate between breathing and cellular respiration.
E. Long-Answer-Type Questions
1. With the help of a labelled diagram, describe the mechanism of breathing in the human
body.
2. Explain the respiratory system of human beings with the help of a diagram. Also, explain
the role of different organs of the respiratory system.
3. Describe how respiration takes place in plants.

HOTS
1. We should breathe only through our nose and not through our mouth. Why?
2. Why is it advised not to sleep under a tree at night?
3. Why does a sh die when brought out of water?

Activity Zone

Project Work

A. Measure the breathing rate of the members of your family. Find out:
1. If the breathing rate of children is different from that of adults.
2. If the breathing rate of males is different from that of females.
Write down your observations in your notebook and share it with the class.

B. Arti cial respiration is a life-saving method by which victims of heart attack, electric shocks,
drowning, choking, etc., are given external support to bring their normal breathing back. With
the help of your parents and the internet, gather more information about arti cial respiration
and make a presentation to the class.

60 Exploring Science-7
Science Excursion
C. Visit a doctor’s clinic along with two of your friends. Request the doctor for an interview. Ask
him about the harmful effects of smoking. Learn about its effect on our lungs. Find out how
smoking is linked to cancer. You can also collect material on this topic from other sources.
Find out the general percentage of people who smoke. If you have a smoker in the family,
confront them with the material that you have collected.

Memory Map

RESPIRATION

type

Aerobic respiration Anaerobic respiration

Through skin Through gills Through lungs Through stomata

Earthworms Fish Birds in mammals Reptiles Plants

Humans
parts of respiratory system

Nose Nostrils Trachea Bronchi Lungs

(wind pipe)
Alveoli
(air sacs)

e-Resources
Please visit the link given below or scan the QR code for more resources on
this chapter:
https://www.megamindpublication.com/s-3-science/b-3-exploring-science-7/c-30/respiration-in-organisms.html

Respiration in Organisms 61