Respiration 😮‍💨

I. Introduction to Respiration
Respiration is a vital life process by which living organisms obtain energy from food. It is an
oxidation reaction where carbohydrates are oxidized to produce energy. This released energy is
stored in the form of ATP (adenosine triphosphate). The primary site of this energy production
(cellular respiration) is the mitochondria.
Respiration involves two key aspects:
1.​ Gaseous Exchange: This is the physical process of breathing, involving the intake of
oxygen from the atmosphere and the release of carbon dioxide.
2.​ Cellular Respiration: This refers to the breakdown of simple food molecules inside the
cell to release energy.

II. Steps of Respiration

The initial step of respiration, regardless of oxygen availability, is the breakdown of glucose.
●​ Glucose Breakdown: Glucose, a 6-carbon molecule, is broken down into pyruvate, a
3-carbon molecule. This step occurs in the cytoplasm.
●​ Fate of Pyruvic Acid: The subsequent pathway of pyruvic acid depends on the type of
organism and the presence or absence of oxygen.

III. Types of Respiration

There are two main types of respiration:

A. Aerobic Respiration
●​ Definition: This is a process in which glucose is completely broken down in the presence
of oxygen to release a large amount of energy (ATP), along with carbon dioxide and water
as by-products.
●​ Oxygen Requirement: It explicitly requires oxygen.
●​ Energy Production: Aerobic respiration is highly efficient, producing a large amount of
energy, specifically 38 ATP molecules.
●​ Location: This process primarily takes place in the mitochondria.
●​ Chemical Equation:

●​ Example: Our cells use aerobic respiration to get energy from food, for instance, when
we run.

B. Anaerobic Respiration
●​ Definition: This is the process of breaking down glucose without oxygen to release a
 smaller amount of energy (ATP).
●​ Oxygen Requirement: It occurs in the absence or lack of oxygen.
●​ Energy Production: It releases less energy than aerobic respiration, typically 2 ATP
molecules.
●​ By-products: The by-products include lactic acid or ethanol and carbon dioxide.
●​ Occurs In: This type of respiration happens in organisms like yeast, some bacteria, and
in muscle cells during heavy exercise.

Types of Anaerobic Respiration:

1.​ Alcoholic Fermentation

○​ Description: It is the incomplete breakdown of sugar into ethanol and carbon
dioxide to release energy.
○​ Occurrence: This process mainly occurs in yeast.
○​ Applications: It is utilized in the production of alcoholic beverages like beer and
wine.
○​ Equation: Glucose → Pyruvate + Energy → Ethanol + CO_{2} + 2 ATP.
2.​ Lactic Acid Fermentation
○​ Description: It is the incomplete breakdown of sugar into lactic acid and energy.
○​ Occurrence: This occurs in some bacteria and in our muscle cells.
○​ Muscle Cramps: During intense exercise, muscles rapidly convert glucose to lactic
acid for quick energy. This lactic acid buildup causes fatigue and cramps.

IV. Breathing Mechanism

Breathing is the process of exchanging gases—mainly oxygen and carbon dioxide—between
our body and the environment. Our body requires oxygen to produce energy, and carbon
dioxide is a waste product of cellular energy production. Breathing in brings oxygen into the
body, while breathing out removes carbon dioxide, which helps in keeping our body working
efficiently.

A. Steps of Breathing
1.​ Inhalation: Taking air into the body.
○​ The thoracic (chest) cavity expands.
○​ The ribs lift up, and the diaphragm becomes flat.
○​ The volume of the lungs increases, allowing air to enter the lungs.
2.​ Exhalation: Releasing air out of the body.
○​ The thoracic cavity contracts.
○​ The ribs move downwards, and the diaphragm becomes dome-shaped.
○​ The volume of the lungs decreases, forcing air out of the lungs.

V. Human Respiratory System

The human respiratory system is the biological system responsible for taking in oxygen and
removing carbon dioxide from the body. It is essential for breathing and cellular respiration,
which produces the energy our body needs to function.

A. Passage of Air through the Respiratory System

1.​ Nostrils: Air first enters the body through the nostrils.
2.​ Nasal Passage: This serves as a pathway for air to move through the nose.
3.​ Nasal Cavity: Lined with hair and mucus, it filters, humidifies, and warms the air before it
travels to the lungs.
4.​ Pharynx: A tube-like structure that connects the nasal cavity and mouth to the larynx and
esophagus. It is composed of cartilaginous rings that keep the airway open and prevent
collapse.
5.​ Larynx (Voice Box): Contains vocal cords and helps control voice pitch and volume,
aiding speech.
6.​ Trachea (Windpipe): A continuation of the pharynx that divides into the bronchi. It links
the voice box to the lungs, enabling air movement in and out. It is supported by rings of
cartilage to prevent its collapse when there is no air.
7.​ Bronchi: Major airways that branch from the trachea and transport air in and out of the
lungs. They are involved in gas exchange.
8.​ Bronchioles: Smaller branches of the bronchi that lead deeper into lung tissue. They
direct air from the nose/mouth to the alveoli.
9.​ Alveoli: These are tiny, balloon-like sacs at the end of the bronchioles. They create a vast
surface area for gaseous exchange. Their walls have a rich network of blood vessels
where oxygen mixes with blood, and carbon dioxide is removed based on pressure
differences.

B. Exchange of Gases in Human Body

Oxygen-rich air from the environment passes through the nasal cavities, pharynx, trachea,
bronchi, and bronchioles to reach the alveoli. At the alveoli, oxygen and carbon dioxide are
exchanged between the lungs and the blood. Carbon dioxide-rich air from the body then follows
the reverse path (alveoli, bronchioles, bronchi, trachea, pharynx, nasal cavities) to be released
into the environment.

VI. Respiration in Other Organisms

●​ Unicellular Organisms: Respire through diffusion across their cell surface.
●​ Fish: Respire through gills.
○​ Mechanism: Fish open and close their mouths to take in water. This water is then
forced over the gills, which are located behind their eyes and covered by an
operculum. The gill-slits (or operculum) also open and close in a coordinated
manner to facilitate this flow.
○​ Gas Exchange: The gills have a rich blood supply and a large surface area for
efficient exchange of dissolved oxygen from the water into the blood, and carbon
dioxide from the blood into the water.
○​ Breathing Rate: Since the availability of dissolved oxygen in water is much lower
than oxygen in the air, aquatic organisms like fish have a significantly faster
breathing rate to obtain sufficient oxygen for their metabolic needs.
●​ Earthworm: Respire through their moist skin.
●​ Frogs: Respire through both their moist skin and lungs.
●​ Insects: Respire through a network of tracheal tubes that open to the outside via small
openings called spiracles.
●​ Terrestrial Organisms: Primarily respire through lungs.
●​ Plants: Gaseous exchange occurs through:
○​ Stomata in leaves.
○​ Lenticels in woody stems.
○​ The general surface of the root.
○​ In plants, diffusion is utilized for the exchange of gases. Carbon dioxide is
eliminated at night, while oxygen release is more prominent during the day due to
photosynthesis.