Respiration

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  • May 1, 2023
9th Biology Ch#07 Bioenergetics Respiration

Respiration

Definition:

A chemical process in which oxygen is used to make energy from carbohydrates (sugars).

Chemical Equation:

Glucose + Oxygen → Carbon dioxide + water + Energy
C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP

Cellular Respiration:

Definition:

It is the oxidation of food taking place within the cells by the help of oxidative enzymes resulting in the release of energy.Cellular respiration also called tissue respiration takes place within the cell. It isthe actual process which liberates energy.

Types of Respiration:

There are two types of respiration found in living organisms for the production of energy.

i Aerobic Respiration

ii Anaerobic Respiration

Anaerobic Respiration:

Definition:

Anaerobic respiration also called “Fermentation”. It takes place in the absence of oxygen, hence the food is oxidised partially, releasing a small amount of energy. Only (5%to 10%) as compared to aerobic respiration. It takes place in some bacteria, fungi, yeast and endoparasites.

 In anaerobic respiration, glucose is not broken down completely so less energy is released but it can sustain life even in the absence of oxygen.

There are two types of anaerobic respiration

i)Alcoholic Fermentation

ii)Acidic Fermentation

Alcoholic Fermentation:

Alcoholic Fermentation is a type of cellular respiration which does not require oxygen (anaerobic respiration), and involves the breaking down of glucose to pyruvic acid and then finally ethanol. It happens when bacteria and fungi deprived of oxygen start respiring anaerobically and produce ethyl alcohol with CO2 .

Chemical Equation:

Glucose → Ethanol + CO2 + Some energy
C6H12O6 → 2C2H5OH + 2CO2 + Some ATP

Acidic Fermentation:

Acidic Fermentation is a type of cellular respiration which does not require oxygen (anaerobic respiration), and involves the breakdown of glucose to lactic acid. During glucose breaks down into a substance called lactic acid. In acidic Fermentation a limited amount of energy is produced as compared to aerobic respiration.

Chemical Equation:

Glucose → Lactic acid + Some energy
C6H12O6 → 2C3H6O3

Importance of Anaerobic Respiration (Fermentation):

The following points explain the economic importance of the process of fermentation:

  1. It is a source of various products such as ethyl alcohol, lactic acid, propionic acid and butanol etc.
  2. The process is used in brewing industries for the production of wine.
  3. Dairy industries use this process for the production of various dairy products such as cheese, yoghurt etc.
  4. In baking process the yeast fermentation is utilised
  5. Several industrially important solvents such as acetone are the by-products of fermentation.
  1. Lactic acid and acetic are the products of Fermentation which are used in various fields.
  2. The soya sauce is made through fermentation by a fungus Aspergillus.
  3. Humans can also provide energy to their skeletal muscle cells through anaerobic respiration.

2.Aerobic Respiration:

Definition:

It takes place in the presence of free oxygen, oxidising the food completely and releasing the maximum energy, 2827 kj/mole of glucose. The end products are carbon dioxide and water.

Chemical Equation:

Glucose + oxygen → Carbon dioxide + water + Energy (36 ATP)
C6H12O6 + 6O2 → 6CO2 + 6H2O + 36 ATP

Mechanism of Aerobic Respiration:

Aerobic respiration takes place in three steps at different places in the cell

  •  Glycolysis
  •  Kreb’s Cycle
  • Electron Transport Chain (ETC)

a) Glycolysis:

     Gr: Glyco = Sugar

    Lysis = Break down 

“The process in which a glucose molecule (six carbon sugar ) is broken down into two molecules of Pyruvic acid (3C acid)”.

  Glycolysis occurs in cytoplasm and oxygen is not involved at this stage, so it occurs in both aerobic and anaerobic respiration. This splitting of glucose releases a small amount of energy of glucose which is enough to generate 2 molecules of ATP. Glycolysis is a complex sequence of reactions all occurring in cytosol.

b)Kreb’s Cycle:

A British biochemist, Sir Hans Krebs discovered this series of reactions that is why it is called the Kreb cycle.In the Kreb cycle, pyruvic acid molecules are completely oxidised along with the formation of ATP, NADH and FADH2. Before entering in krebs cycle, pyruvic acid is changed into 2-carbo
compound called acetyl CoA.

c) Electron Transport Chain (ECT):

It is the last stage of cellular respiration. It is the transfer of electrons in an electron transport chain. In this step

  • NADH and FADH2 release electrons and hydrogen ions.
  • These electrons are taken up by a series of electron carriers.
  • When electrons move, through the series of electron carriers they lose energy, which is used to synthesise ATP.
  •  At the end of the chain, electrons and hydrogen ions combine with molecular oxygen and form water compound called acetyl CoA.

Use of Respiration Energy in Body of an Organism:

  • Plants and animals need energy to stay alive. Following are some processes which utilise respiration energy.
  • Energy is used by all organism to build up large molecules from smaller ones (for example, 
  • building up proteins from amino acids or making starch from glucose needs energy.)
  • Energy is used by animals to contract muscles during movement.
  • Energy is used by mammals and birds to keep their body temperature steady in colder surroundings.
  • Organisms use energy for their growth and repair of cells.
  • Respiratory energy is used in movement of ions and molecules from low concentration to high.
  • During cell division formation of large molecules (DNA and protein) and movement of chromosomes require energy.
  • Energy is used in conduction of nerve impulses ( Electrical signals of neurons) which takes place in the active transport of ions.
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