Respiration & Its Types

1.0Respiration

All living organisms need energy for carrying out daily life activities be it absorption, transportation, movement, reproduction or even breathing. Where does all this energy come from?

All the energy required for ‘life’ processes is obtained by oxidation of some macromolecules that we call ‘Food’.

The breaking of the C-C bonds of complex compounds through oxidation within the cells, leading to release of considerable amount of energy is called respiration. The compounds that are oxidised during this process are known as respiratory substrates. Usually carbohydrates are oxidised to release energy; but proteins, fats and even organic acids can be used as respiratory substances in some plants, under certain conditions. During oxidation within a cell, all the energy contained in respiratory substrates is not released free into the cell, or in a single step. It is released in a series of slow step-wise reactions controlled by enzymes, and it is trapped as chemical energy in the form of ATP. Hence, it is important to understand that the energy released by oxidation in respiration is not (or rather cannot be) used directly but is used to synthesise ATP, which is broken down whenever (and wherever) energy needs to be utilised. Hence, ATP acts as the energy currency of the cell.

The Sequence of Use of Respiratory Substrates

(i) Carbohydrate

(ii) Fat

(iii) Protein

Organic acids such as malic acid etc. can be used as respiratory substrates in some plants, under certain conditions.

Cellular respiration

Respiration is the process by which the food taken through nutrition gets oxidized to release energy for various activities within the cell.

2.0Features of Cellular Respiration

(i) Cellular respiration is an amphibolic process.

Reason: The carbon skeleton (intermediates of respiration) produced during respiration is used as precursors for biosynthesis of other molecules in the cell.

(ii) Cellular respiration is an exergonic process.

Reason: The breaking of C–C bonds of complex compounds through oxidation within the cells, leading to release of considerable amount of energy.

Do Plants Breathe?

Plants, unlike animals, have no specialised organs for gaseous exchange but they have stomata and lenticels for this purpose. 

• There are several reasons why plants can get along without respiratory organs. 

(i) Each plant part takes care of its own gas-exchange needs. There is very little transport of gases from one plant part to another. 

(ii) Plants do not present great demands for gaseous exchange. Roots, stems and leaves respire at rates far lower than animals do. Only during photosynthesis, large volumes of gases are exchanged and each leaf is well adapted to take care of its own needs during these periods. When cells photosynthesize, availability of O₂ is not a problem in these cells since O₂ is released within the cell. 

(iii) The distance that gases must diffuse even in large, bulky plants is not great. Each living cell in a plant is located quite close to the surface of the plant. In stems, the ‘living’ cells are organised in thin layers inside and beneath the bark. They also have openings called lenticels. Many cells in the interior are dead and provide only mechanical support. Thus, most cells of a plant have at least a part of their surface in contact with air. This is also facilitated by the loose packing of parenchyma cells in leaves, stems and roots, which provide an interconnected network of air spaces.

3.0Types of Respiration

On The Basis Of Presence Or Absence Of O2

(1) Aerobic respiration

It is a process in which complete breakdown of food (glucose) into carbon dioxide and water in the presence of oxygen and energy is released.

(2) Anaerobic

It is partial breakdown of food (glucose) without using molecular oxygen, to either lactic acid or ethanol and CO₂. 

4.0Also Read