Respiration

Introduction

     All living organisms require a continuous supply of energy for carrying out various functions. The main source of energy for all the functions, in all living organisms is cellular respiration.

Types of Respiration

     Cellular respiration is of 2 types according to its dependence on oxygen.

Respiratory Quotient

     During aerobic respiration oxygen is consumed and carbon dioxide is evolved.

Mechanism of Respiration

     Human cellular respiration can be divided into 2 main phases.

Kreb's Cycle

     The oxidation of pyruvic acid into CO₂ and water is called Krebs cycle.

Electron Transport System

     The metabolic pathway through which the electron passes from one carrier to another, is called the electron transport system.

Pentose Phosphate Pathway

     In some microorganisms, biological oxidation of glucose follows a different pathway. It is known as pentose phosphate pathway or hexose mono phosphate shunt or direct oxidation of glucose.

Experiments on Respiration

     Put some germinating seeds in a conical flask. With the help of a thread suspend a small tube containing KOH in the flask. Through the hole of the cork pass a glass tube bent twice at right angles. One end of the tube is in the flask while the other end is in the beaker filled with water. Make the apparatus air tight. Note the level of water in the tube. Keep the apparatus for sometime and note the position of water.

Compensation Point

     At a given low concentration of CO₂ and non-limiting light intensity, the photosynthetic rate of a given plant will be equal to the total amount of respiration. The atmospheric concentration of CO₂ at which photosynthesis just compensates for respiration is referred to as the CO₂ compensation point.

Summary

     In anaerobic respiration, molecular oxygen is not needed. The electrons removed from the substrate are transferred by the oxidoreductases to electron acceptors other than oxygen. Its end products are lactic acid or ethanol.