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.
During aerobic respiration oxygen is consumed and carbon dioxide is evolved.
Human cellular respiration can be divided into 2 main phases.
The oxidation of pyruvic acid into CO2 and water is called Krebs cycle.
The metabolic pathway through which the electron passes from one carrier to another, is called the electron transport system.
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.
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.
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.