Respiration in

Organisms
National Science Olympiad
Class 7
TABLE OF
CONTENTS

01 02
Human
03
Respiration
Respiration
& its Types Respiratory in other
System organisms
Respiration &
its Types
01
Respiration
Respiration is the process of gaseous exchange in an organism. Respiration at a cellular level,
however, refers to the burning of food to obtain energy. Its Chemical Formula is: C6H12O6 + 6O2 →
6CO2 + 6H2O + Energy. There are 2 main life process of respiration:
 Breathing/External Respiration: It means taking in air rich in oxygen and giving out air rich in
carbon dioxide with the help of respiratory organs. The taking in of air rich in oxygen into the
body is called inhalation and giving out of air rich in carbon dioxide is known as exhalation.
 Cellular/Internal Respiration: When the cells obtain oxygen from the blood, they use up this
oxygen to burn the food. Burning of food releases energy which is stored in the form of Energy.
Thus respiration at the cellular level is the burning of food using oxygen to get energy.
Aerobic Respiration
Aerobic respiration is the respiration where glucose is broken down by oxygen to
release energy along with carbon dioxide and water being produced as by-products of
the reaction. C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy. The energy produced in this
type of respiration is more. Organisms that use this type of respiration is called
aerobes. The glucose is completely broken down into water and carbon dioxide. It
takes place in animals and plants. Examples for aerobic respiration are all
multicellular organisms like birds, animals, insects, humans etc.
Anaerobic Respiration
Anaerobic respiration is the respiration which occurs in the absence of oxygen to produce the
energy. It occurs in yeast cells in which alcohol is produced. It also occurs in muscles of our
body when we do excess workout which causes the temporary lack of the oxygen for muscles.
There is partial breakdown of glucose into carbon dioxide and ethyl alcohol. Its formula is:
C6H12O6 In absence of oxygen Ethanol + Carbon dioxide + Energy. The muscle cells then start doing
anaerobic respiration and produce lactic acid, which reduces after rest and deeply breath
oxygen. Its formula is: Glucose In absence of oxygen Lactic acid + Energy (in muscles). The energy
produced in this type of respiration is less. Organisms that use this type of respiration is
called anaerobes. Yeast, multicellular neried, protozoans bacteria are some organisms that
respire through anaerobic respiration.
Human Respiratory
System
02
 Human Respiratory System
As defined above, the human respiratory
system consists of a group of organs and
tissues that help us to breathe. Aside from
the lungs, there are also muscles and a vast
network of blood vessels that facilitate the
process of respiration. Our respiratory
system comprises of the nose, nasal
passages, pharynx, larynx, trachea,
bronchi, and lungs.
The respiratory system is the network of
organs and tissues that help with
breathing.
 Nostrils & Nasal Cavities
Pair of slit like openings that open into the nasal cavities are called
nostrils. The nasal cavities possess hair, which trap dust particles and
germs in the air and filter them. The nasal cavities are richly supplied
with blood vessels that warm the incoming air. The sticky mucus
lining of the nasal cavities moistens the air and filter dust particles.

Pharynx
The air enters the pharynx after passing through the nasal cavities. It
is a common passage at the back of the mouth for both air and food.
Larynx
The upper part of trachea contains larynx with the vocal
cords which help in sound production. It is also called the
voice box. The entrance of the larynx is guarded by a stiff flap-
like structure, the epiglottis. It opens during breathing, but
closes the passage of windpipe while swallowing or drinking,
thus preventing the food from entering the lungs.

Lungs
These are a pair of respiratory organs that are spongy bag-
like structures, lying in the chest cavity on either side of the
heart. The left lung is two lobed and slightly smaller than the
right lung which is three lobed. The two lungs are protected
by the flexible ribcage and sternum on the front and the
vertebral column at the back. Just beneath the lungs, is a
dome-shaped muscular sheet, the diaphragm.
 Trachea
The larynx leads into a long tube known as trachea or windpipe. It
passes through the neck and extends into the chest cavity. The trachea
is lined with cells which release mucus. Walls of trachea are
supported by C-shaped cartilaginous rings. At the lower end, trachea
gets divided into two tubes called bronchi (singular: bronchus) which
enter the two lungs. Inside the lungs, the bronchi divide and redivide
into bronchioles which further divide and finally end into air sacs or
alveoli. It is here that the exchange of gases takes place. Alveoli have
very thin walls and are richly supplied with blood capillaries. The
oxygen we breathe in goes into the blood and carbon dioxide present
in the blood passes out of the blood into the alveoli.
Breathing- Inhalation & Exhalation
Basis of Comparison Inhalation Exhalation
Process of taking air into It’s the process of letting air out
Meaning
the lungs. from the lungs.
Process Active process Exhalation process
Size of Chest Cavity Increases Decreases
Contract during the Relaxes during exhalation and
Role of Diaphragm process and flattens by turns into dome-shaped by
moving down. moving up.
Increases during the Decreases during the process i.e.
Volume of Lungs
process i.e. get inflated get deflated
Oxygen-rich air is taken
Result Carbon dioxide is pushed out
in the blood.
They relax and external They contract and external
Role of Intercostal Muscle
costal muscles contract intercostals muscles relax
Inhaled air is oxygen and Air exhaled is carbon dioxide
Composition of Air
nitrogen mix and nitrogen mix
Rib cage moves upward
Effect of Intercostal Muscles Rib cage moves downward
and outward
Air Pressure Decreases Increases
Oxygen difference 21% 16.4%
Carbon Dioxide difference 0.04% 4.4%
Process of Cellular Respiration
The oxygen inhaled during the breathing process is carried to all
parts of the body through blood. Oxygen binds to a respiratory
pigment called haemoglobin present in the red blood cells of the
blood. They form a temporary compound called oxyhaemoglobin. On
reaching the cells, it dissociates to release the trapped oxygen and the
released oxygen diffuses into the cells. This oxygen is used for the
oxidation of glucose to release energy.
Diseases Associated with Respiratory System
 Bronchitis: It is an inflammation of the bronchi, generally caused
by an infection.
 Bronchial asthma : It is usually due to an allergic reaction to
certain foreign substances that affect the respiratory system.
 Emphysema: It is caused by gradual breakdown of the thin walls
of the alveoli.
 Flu: Flu (influenza) is an infectious viral disease that causes fever,
headache and sneezing. Different kinds of flu are common flu,
swine flu and bird flu.
Respiration in
other organisms
03
Different animals ranging from microorganisms to
higher animals have different organs and mechanisms of Animals
breathing.
Case I
 Respiration Through Cell Membrane (Diffusion): In unicellular organisms such as Amoeba, Paramecium, etc.,
exchange of gases takes place by diffusion through the cell membrane.
 Respiration Through Spiracles (Tracheal): Insects like cockroaches, grasshoppers and bees have special air
holes on their body surface called spiracles. The spiracles are connected to a network of air tubes inside the
body of insects called tracheae. The smaller branches of the tracheae are called tracheoles that allow diffusion
of respiratory gases to the cells and tissues. Air enters an insect body through these spiracles and reach the
entire body through the tracheae and tracheoles. Oxygen is thus, directly absorbed by the body cells through
simple diffusion and carbon dioxide is sent out through the spiracles.
 Respiration Through Skin (Cutaneous): Earthworm and leeches breathe only through their skin. Their skin is
moist and slimy and has numerous blood capillaries. The exchange of oxygen and carbon dioxide occurs
between air and blood in the skin. Frogs breathe through their skin when in water.
Different animals ranging from microorganisms to
higher animals have different organs and mechanisms of Animals
breathing.
Case I

 Respiration Through Gills (Brachial): Aquatic animals such as fishes have special organs called gills,
which are adapted to take up the oxygen dissolved in water. Gills are supported by soft bony structures
called gill arch. The gill arch is made up of a large number of double row of thread-like structures called
filaments. These filaments are richly supplied with blood vessels called capillaries. Water flow over the
gill filaments during which exchange of gases between the capillaries and water takes place. The blood
in the capillaries absorbs oxygen from the water, and gives out carbon dioxide. The oxygen is
transported by blood throughout the body.
 Respiration Through Lungs (Pulmonary): Adult frogs, lizards, birds, etc. breathe through lungs. A
tadpole has gills but as it grows into a frog it develops lungs for gaseous exchange. Birds have air-filled
sacs attached to the lungs and these air sacs make their body lighter, which help them to fly.
 Respiration in plants
Plants carry out various life processes such as growth, movement, transportation of
materials and photosynthesis. For carrying out these activities plants need energy.
Therefore, to obtain energy plants respire. In each plant cell glucose is oxidised to
release carbon dioxide, water and energy. During daytime carbon dioxide released by
respiration is used for photosynthesis. In plants, gas exchange occurs by the diffusion
of oxygen and carbon dioxide. Stomata, lenticels and root surface are three parts of
plants that help in respiration.
 Respiration in plants
Stomata: Stomata are the tiny openings present on the surface of the leaves. Oxygen
and carbon dioxide diffuse in and out through stomata. Transpiration in plants also
occur through stomata. The oxygen diffuses in through the stomata and then enters
the leaf cells. Similarly. the carbon dioxide produced in aerobic respiration diffuses
out through the stomata. Each stoma (plural stomata) is surrounded by two bean-
shaped guard cells. The opening and closing of stomata is carried out by expansion
and shrinking of the guard cells. Guard cells expand and shrink due to the flow of
water in and out of the cell.
Lenticels: Lenticels are the small pores or openings present on the bark of the stems.
Gas exchange between the atmosphere and the cells takes place through these
lenticels. Lenticels are also found on the fruit skin. Lenticels remain open all the time
as compared to stomata that open and close.
Root Surface: Root cells of plants also respire, so they also need oxygen to generate
energy. They get this oxygen from air trapped between soil particles. Plants
growing in salty water possess specialised roots called the pneumatophores. These
roots grow out of the water surface and have numerous pores on their surface. Gas
exchange in these plants takes place through these pores.
Evolution is the fundamental idea in
all of life science - in all of biology.
— Bill Nye