• Respiration is defi ned as a conversion of chemical bond energy of various organic molecules into energy of usable form within living cells (i.e., ATP).
• The phenomenon of breaking of the C–C bond of complex organic molecules occurs through oxidation. The compounds that are oxidized, are known as respiratory substrates.
The breakdown of respiratory substrates provide carbon skeleton for the synthesis of a large number of other essential plant products, such as polysaccharides, proteins, fats, nucleic acids, pigments, cytochromes etc.
• The specific organelle in a cell where most of the respiration occurs is the mitochondria.
• During the process of respiration, oxygen is utilized and carbon dioxide, water and energy are released as products. This energy is utilized in various energy requiring processes of the organisms.
• The reaction that occurs in common respiration of glucose can be summed up as –
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy
• The mechanism of breakdown of food materials within the cell to release and trapping this energy for ATP synthesis is known as cellular respiration. Hence, cellular respiration is an enzyme controlled process of biological oxidation of food materials in a living cell, using molecular oxygen (O2), producing CO2 & H2O and releasing energy in a small steps and storing it in biologically useful forms generally ATP.
• Hence, Respiration is a catabolic, exothermic and oxidative process.
• Only green plants and cyanobacteria can prepare their own food by the process of photosynthesis. They trap light energy and convert it into chemical energy that is stored in the bonds of carbohydrates like glucose, sucrose and starch. They are called autotrophs.
Animals are heterotrophic, i.e., they obtain food from plants directly (herbivores) or indirectly (carnivores). Saprophytes, like fungi, are dependent on dead and decaying matter.
DO PLANTS BREATHE?
• Plants require O2 for respiration to occur and they also give out CO2. Hence, plants have systems in place that ensure the availability of O2. Plants, unlike animals, have no specialized organs for gaseous exchange but they have stomata and lenticels for this purpose.
• Plant get along without respiratory organ because each plant part take care of its own gas exchange. There is little transport of gases from one part to another.
• Roots, stems and leaves respire at rates far lower than animals do. Only during photosynthesis, large volumes of gases exchanged and, each leaf is well adapted to take care of its own needs during these periods.
• According to Lavosier, cell respiration resembles the combustion (e.g. burning of coal, wood, oil etc.) in the breakdown of complex organic compounds in the presence of oxygen & production of carbon dioxide and energy, but there are certain fundamental differences between cell respiration & combustion (Refer table 14.1
