Adenosine triphosphate

Adenosine Triphosphate Definition

ATP stands for adenosine triphosphate. Energy is stored in ATPs which is used by the cell, for every energy-consuming process.

Adenosine Triphosphate Structure

ATP is synthesized in mitochondria of a cell. Chemically each ATP molecule is made up of an organic compound “ribose” to form “adenosine”. This adenosine is attached to a chain of three inorganic phosphate groups, in this way a complex compound ATP is formed.


Hydrolysis of ATP to ADP

Chemically ATP is hydrolyzed to ADP, (adenosine diphosphate) with the help of an enzyme named ATPase.  During the process a phosphate ion and 30.6KJ or 7,3Kcal are released.

Conversion of ADP to ATP

During the oxidation of food, energy is released. This energy is used to convert ADP into ATP again. This ATP becomes charged again to give ADP on hydrolysis. In this way, the ATP-ADP cycle is formed.

Absorption of energy in ATP

A mole of glucose release 2827KJ on Kcal, energy is stored in ATPs whereas the rest is lost as heat energy.


The human respiratory system consists of a pair of lungs and an associated system of tubes. Intake in the removal of air takes through the nose.


Following are the breathing or respiratory organs of human being:

  • External nostrils
  • The nasal passage
  • Internal nostrils
  • Pharynx
  • Trachea
  • Glottis
  • Larynx
  • Bronchi
  • Lungs


Lungs are situated in the thorax, surrounded by a rib cage. The walls of the rib cage are made up of the ribs attached anteriorly to the sternum and posteriorly to the vertebral column with intercostal muscles in between. The floor is made up by the diaphragm.

Adenosine triphosphate Function

  • External nostrils: air enters through a pair of nostrils into the nasal cavity.
  • Nasal cavity : air entering the nasal cavity is humidified and warmed to body temperature. All kinds of dust and germs are trapped here to purify the air.
  • Internal nostrils: the internal opening of the nasal cavity is known as internal nostrils.
  • Pharynx: it is the way of passage of air from internal nostrils to the larynx. It is a muscular tube.
  • Larynx:  the larynx or voice box is a cavity at the top of the trachea. Glottis is the opening of larynx, which is guarded by the valve called the “epiglottis”
  • Trachea:  it is a tube running from the pharynx to the lungs. It is also called the windpipe. The walls of trachea are made up of rings of cartilage. These rings keep the trachea open at all times. Ciliated cells present in the lining of the trachea secrete mucously.
  • Bronchi: The trachea is divided into two short tubs called the “BRONCHI” each bronchus enters the lungs and divides again and again to form a mass of very fine branches called “bronchioles”, which open into alveoli.”
  • Alveoli: at the end of each bronchiole there is a bunch of tiny air sacs called “alveoli” here the exchange of gases takes place between air and the blood, present in blood capillaries of alveoli.
  • Lungs: there is a pair of two spongy lungs situate in the rib cage. Alveoli are present in the lungs.


  • The air enters through the pair of external nostrils.
  • Air enters the nasal cavity.
  • Then it enters the pharynx in the throat.
  • From the pharynx, air passes into the larynx.
  • Through larynx, it passes to the trachea.
  • From the trachea, it goes to the bronchus of each side.
  • Then it enters the bronchioles.
  • From bronchioles, air enters the alveoli where gaseous exchange takes place.


There are two types of cellular respiration

  • Aerobic respiration
  • Anaerobic respiration

Aerobic respiration takes place in the presence of oxygen.


Sometimes cellular respiration takes place in the absence of oxygen. This type of respiration is known as “anaerobic respiration”


Aerobic respiration is the usual mode of respiration in which oxygen is necessary. In this process, food is completely oxidized to release the maximum energy 2827KJ/ mole of glucose. Carbon dioxide and water produced in this process. It is a catabolic process.

Chemical equation

Glucose + oxygen      →   water + carbon dioxide +energy (2827KJ)

Anaerobic respiration

An-aerobic respiration oxygen is not necessary. It is also called “fermentation”. It occurs in some plants e.g. yeast. In this type of respiration, food is partially oxidized so a very small amount of energy is released. In animal lactic acid is produced while in bacteria and fungi alcohol and carbon dioxide are produced at the end of the process.

Chemical equation

  • In bacteria and fungi

Glucose    →     ethanol+ carbon dioxide +energy (210KJ)

  • Animals

Glucose → lactic acid +  energy  (210KJ)


In aerobic respiration due to the absence of oxygen of food is oxidized partially, resulting in the formation of ethanol (alcohol) and CO2 in bacteria and fungi whereas lactic acid is produced in animals.  Ethanol and lactic acid are harmful to the organism because they are toxic compounds.

Advantages of anaerobic respiration

  • Easy survival

 Organisms in which anaerobic respiration takes place has the advantage to survive without oxygen.

  • Alcoholic fermentation

Alcoholic fermentation is commercially used to make alcoholic products like beer, wine, vinegar, etc.

  • Formation of ATP in human muscles

Human muscle cell makes ATP by lactic fermentation when oxygen is deficient. This lactic acid, later on, is converted back into energy-releasing compounds pyruvic acid and glycogen by the liver cells.


  1. Absorption of oxygen

Hemoglobin in the red cells of blood absorbs and oxygen gives it to all the body tissues. This absorption of oxygen in hemoglobin occurred through alveoli.

As alveoli thin-walled and richly supplied with blood capillaries from these thin walls of alveoli blood is easily diffused into the hemoglobin of blood in blood capillaries.

  1. Release of carbon dioxide

Carbon dioxide from the body tissues is absorbed into the blood. This carbon dioxide from the blood diffuses into the air in the alveoli sacs, and is removed from the lungs expiration or exhalation of


In case of a prolonged exercise, muscles cells may require a lot of oxygen supply very quickly., that is why breathing becomes deeper and faster to inhale more and and more oxygen.

Mechanism of deep breathing during exercise

During continuous exercise heart beat and blood circulation become faster. Eventually a limit is reached when the heart and lungs cannot supply oxygen to the muscles any faster, but more energy is still needed for the movement of the muscles.

Extra energy

To provide extra energy by anaerobic respiration, some glucose is broken down producing lactic acid in the absence of oxygen releasing a little extra energy.

Energy dept.

The deposition of lactic acid makes the muscles fatigue. The amount of oxygen needed to remove this lactic acid from the muscles is called the oxygen debt.

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