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MHT-CET : Biology Entrance Exam

MHT - CET : Biology - Respiration Know More

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Respiratory substrate is the organic food material which is used for respiratory breakdown. It can be carbohydrates, organic acids, proteins, fats or oils.

Glucose is the readily available energy source for the cells.

Oxidation of the substrate during anaerobic respiration is incomplete. The by products are ethyl alcohol, CO2 and energy released.

Mitochondria are the cell organelles concerned with aerobic respiration and are present in eukaryotic cells only. They are called power houses of the cell.

Yeast, i.e. Saccharomyces, is the unicellular fungus that releases enzyme zymase that brings about alcoholic fermentation.

Lactic acid fermentation is due to microorganisms like lactic acid bacteria. During lactic acid fermentation lactose is broken down to lactic acid. CO2 is not evolved in this process.

ATP is adenosine triphosphate. Each ATP molecule is composed of pentose sugar ribose, purine base adenine and three phosphate groups. Adenine and ribose form adenosine. The three phosphate groups attached to adenosine in a chain form ATP. Of the three phosphate bonds, maximum energy is stored in the third or last phosphate bond. The third phosphate bond breaks on hydrolysis of ATP and releases approximately 7.3 kcal of energy.

ATP ADP + 7.3 kcal + iP

Respiratory quotient, i.e. R.Q, is a respiratory ratio of the volume of CO2 liberated to the volume of O2 absorbed during respiration.


Volume of Co2 released

Volume of O2 absorbed

It is measured by using respirometer.

The R.Q. value differs depending on the type of respiration, complete or incomplete oxidation of substrate and nature of respiratory substrate.

For carbohydrates, the R.Q. is one because the volume of CO2 released during respiration is equal to volume of O2 absorbed. Example: Seeds of rice, wheat, oat, pea, etc.

For oils and fats the R.Q. is less than one because the oxygen content of fats and oils and is very less. Thus, they need more oxygen during respiration, while the CO2 released is less. Thus the R.Q. is less than oneand is mostly around 0.7. Example: Mustard seeds, castor seeds, etc.

R.Q. for proteins is also less than one approximately 0.8 or 0.9.

For organic acids like oxalic acid, the R.Q. is more than one because the oxygen content of organic acids is higher. Thus, oxygen required for respiration is less and the volume of CO2 released is more.

During anaerobic respiration, the value of R.Q. is infinity because it takes place without oxygen but CO2 is released.

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