ATP: Adenosine triphoshate. ATP on hydrolysis will be converted to ADP and inorganic phosphate. This process releases energy. 30.6 KJ is produced per mole of ATP.

The enzyme which catalyses this reaction is called ATPase. All cells use ATP as their source of energy when performing their work. So it is called as universal energy carrier or energy currency. Mitochondria: Present in all eukaryotic cells and are the major sites of aerobic respiration with in cells. Each mitochondria is bounded by 2 membranes and the inner membrane is folded in words into a number of shelf-like ‘cristae,’ which increases the surface area providing the space for the components of the respiratory chain which is located into the membrane. Mitochondria contain circular DNA and 70S ribosome’s.

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Organs of breathing in humans: Lungs are the chief organs of breathing. These are elastic structures in the cost cavity. Each lung contains millions of small air chambers, or sacs called ‘Alveoli’. Network of tiny blood vessels called capillar­ies lies within the walls of each alveolus.

Other structures are called chest wall and the diaphragm. Chest wall includes the ribs – which form a protective cage around the chest cavity and the muscles between the ribs. The diaphragm is a dome shaped sheet of muscle that separates the chest cavity front he abdomen. Air enters and leaves the body through the Ross and the mouth. The pharynx (back of nose and mouth), the larynx (voice box) and the trachea (windpipe) are the air passages that connect the rose and mouth with the lungs. Respiration may be divided into 3 phases – (a) External respiration (breathing) oxygen is taken from environment and released as CO, (Lungs).

(b) Internal respiration oxygen is carried to the cells of organism and CO2 is carries away from them. (Red blood cells do this duty with the help of hemoglobin, which can bind reversibly with oxygen). (c) Cellular respiration the actual energy releasing process taking place in mitochondria of the cell. CO2 and water are the waste products here. It occurs in 3 stages –



Where the glucose is converted into pyruvic acid where the energy yield is 2 ATP through substrate level phosphorylation.

II. Krebs cycle:

(Also called citric acid cycle or tricorboxylic acid cycle) Pyruvic acid enters into a series of chemical reactions. At various steps during kreb’s cycle, energy is captured and passed on to a second series of reactions called the electron transport.

III. Electron transport:

The NADH+ and NADPH+ passes through a series of membrane bound electron carriers. As a result of these reactions, C02 and water are formed and a great deal of energy is liberated as ATP.

This is the normal process in aerobic organisms (Animals and plants). However, in the absence of 02 is not the final electron acceptor. Yeasts can obtain energy through alcoholic fermentation where 2 ATP molecules are produced for every molecules of glucose.

Glucose –> 2 ethanol + 2CO2 + 2 ATP In muscle also, due to 02 shortages at the time of fatigue; lactate fermentation occurs releasing 2 ATP Glucose -> 2 lactose + 2 ATP.