Respiration involves:
(i) Gaseous exchange (Breathing) : Intake of oxygen from the
atmosphere and release of CO2.
(ii) Cellular respiration: Breakdown of simple food in order to
release energy inside the cell.
• Breakdown of Glucose by Various Pathways
→ The first step is the break-down of glucose (a six-carbon
molecule) into a three-carbon molecule called pyruvate which
takes place in the cytoplasm.
→ The pyruvate may be converted into ethanol and carbon
dioxide which takes place in yeast during fermentation. Since
this process takes place in the absence of air (oxygen), it is
called anaerobic respiration.
→ The pyruvate is broken down into three-carbon pyruvate
molecule in the presence of oxygen to give three molecules of
carbon dioxide and water. This process takes place in
mitochondria. Since this process takes place in the presence of
air (oxygen), it is called aerobic respiration.
→ The pyruvate is converted into lactic acid when there is a
lack of oxygen in our muscle cells, which is also a three-carbon
molecule. This build-up of lactic acid in our muscles during
sudden activity causes cramps.
The whole process of break down of glucose is shown below:
The energy released during cellular respiration is immediately
used to synthesise a molecule called ATP which is used to fuel
all other activities in the cell. In these processes, ATP is broken
down giving rise to a fixed amount of energy which can drive
the endothermic reactions taking place in the cell.
→ The rate of breathing in aquatic organisms is much faster
than that seen in terrestrial organisms because the amount of
dissolved oxygen is fairly low compared to the amount of
oxygen in the air.
aerobic Respiration Anaerobic Respiration
Takes place in the presence Takes place in the absence of
of oxygen. oxygen.
Occurs in mitochondria. Occurs in cytoplasm.
End products are CO2 and End products are alcohol or
H2O. lactic acid.
More amount of energy is Less amount of energy is
released. released.
Passage of air through the respiratory system:
→ Nostril: Air is taken into the body.
→ Nasal Passage: It is a channel for airflow through the nose.
→ Nasal Cavity: It is lined with hairs and mucus membrane. It
warms, moisturize, and filter air before it reaches the lungs.
→ Pharynx: It contains rings of cartilage which ensure that the
air-passage does not collapse.
Mechanism of Breathing
Inhalation Exhalation
During inhalation the
thoracic cavity (chest cavity)
expands. Thoracic cavity contracts.
Ribs lift up. Ribs move downwards.
Diaphragm become flat in Diaphragm becomes dome
shape. shaped.
Volume of lungs
Volume of lungs increases decreases and air exits from
and air enters the lungs. the lungs.
Exchange of gases between alveoli, blood and tissues
(i) Air (rich in O2) reaches blood which combines with
haemoglobin in RBC and O2 is released in
alveoli tissues (through blood vessels).
(ii) CO2 is released in blood and dissolved into it and carried by
blood vessels. The carbon dioxide is released in alveolar sac
which is sent out through nostrils.
→ Terrestial organisms: Use atmospheric oxygen for respiration.
→ Aquatic organisms: Use dissolved oxygen for respiration.
Respiration in plants
Respiration in plants is simpler than the respiration in animals.
Gaseous exchange occur through :
(a) Stomata in leaves
(b) Lenticels in stems
(c) General surface of the root
→ Larynx: It houses the vocal cords and manipulates pitch and
volume, which is essential for phonation. It is also known as
voice box.
→ Trachea: Pharynx splits into trachea and esophagus. It
connects the larynx (or voice box) to the bronchi of the lungs. It
provides air flow to and from the lungs for respiration.
→ Bronchi: They are the main passageway into the lungs. They
are the extensions of the windpipe that shuttle air to and from
the lungs. The oxygen goes to the lungs and carbon dioxide
leave the lungs through them.
→ Bronchioles: Bronchi get smaller when they reaches closer to
lungs tissues and are called Bronchioles. They are the
passageways by which air passes through the nose or mouth to
the alveoli of the lungs
→ Alveoli: They are smaller tubes which finally terminate in
balloon-like structures which are called alveoli. They allow
oxygen and carbon dioxide to move between the lungs and
bloodstream.
→ Blood capillaries: They are the sites of the transfer of oxygen
and other nutrients from the bloodstream to other tissues in the
body. They also collect carbon dioxide and waste materials and
return it to the veins.
