RESPIRATION IN PLANTS

Light energy is converted into chemical energy in photosynthesis. This energy is stored in the bonds of molecules like carbohydrates e.g, Glucose, Starch. The oxidation of various organic molecules to release energy for cellular use is called as Respiration. It is stepwise process controlled by enzymes. Respiratory Substrates:- Compounds which get oxidized. The reaction during respiration, when glucose acts as a substrate is:- C6H12O6 + 6O2  6CO2 + 6H2O + Energy (2870 kJ). 4.1 TYPES OF RESPIRATION:- Cellular respiration is of two types depending on the availability of oxygen - (a) Aerobic Respiration - Oxygen is present (b) Anaerobic Respiration - Occurs in absence of O2 (a) Aerobic Respiration:- It uses O2. The organic food is completely oxidized to CO2 and H20. Energy is released. Organisms showing this respiration are known as 'aerobes' or 'aerobic organisms'. It occurs in higher organisms (b) Anaerobic Respiration:- It does not use O2. The organic food is incompletely oxidized into carbonic compounds (like ethylalcohol, acetic acid, lactic acid) and CO2. Small amount of energy is released organisms having this type of respiration are called 'anaerobes' or 'anaerobic organisms'. It is seen in lower organisms and higher plants 4.2 RESPIRATORY RATIO / QUOTIENT ('RQ'):- It is the ratio of volume of CO2 produced to the volume of O2 consumed during respiration over a period of time its value can be 1, zero, more than 1 or less than 1 and depends upon the substrate used. The value of RQ for different substrates is:- (i) Carbohydrates:- C6H12O6 + 6O2  6CO2 + 6H20 + Energy RQ = 1 (ii) Fats:- 2C15H98O6 + 145O2  102CO2 + 98H20 + Energy Tripalmitin RQ = 0.7 (iii) Organic acids:- 2(COOH)2 + O2  4CO2 + 2H20 + Energy oxalic acid RQ = 4 (iv) In anaerobic respiration, there is no consumption of O2, CO2 is produced, carbohydrate is the usual substrate CO2 is produced. Carbohydrate is the usual substrate. C6H12O6  2CO2 + 2C2H5OH + Energy RQ = 2CO2/O RQ = Infinity (  ) (v) Succulents do not evolve CO2 during night. They also convert carbohydrates to organic acids during which O2 is used but CO2 is not evolved. 2C6H12O6 + 3O2  3C4H6O5 + 3H20 RQ = Zero