Respiration in Plants
Respiration is the step-wise oxidation of complex organic molecules and release of energy as ATP for various cellular metabolic activities. It involves exchange of gases between the organism and the external environment.
The green as well as non-green plants obtain oxygen from their environment and return carbon dioxide and water vapour into it. This exchange of gases is known as external respiration or breathing in case of animals. It is a physical process.
The biochemical process, which occurs within cells and oxidizes food to obtain energy, is known as cellular respiration. Various enzymes (biocatalysts) catalyze this process. The process by which cells obtain energy from complex food molecules depends upon whether or not oxygen is present in their environment and utilized.
Respiration is termed aerobic when oxygen is utilized and anaerobic when oxygen is not utilized. In anaerobic respiration, organic molecules are incompletely broken down in the cytosol of the cell and only a small fraction of energy is captured as ATP for use by the cell. In aerobic respiration the reactions of anaerobic respiration are followed by an oxygen requiring process that releases much larger quantity of energy in the form of ATP. This occurs in the mitochondria of the eukaryotes and in the folded plasma membrane (mesosome) of the prokaryotes.
Several common processes occur in both, anaerobic and aerobic respiration, such as
- Oxidation reaction to release chemical energy from complex food.
- Use of coenzyme as carriers of hydrogen to remove the hydrogen from the organic molecule leading to reduction of the coenzyme and oxidation of the substrate. Most of the hydrogen carriers are NAD (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide). These are later reoxidized, releasing energy for ATP synthesis.
- Use of high-energy phosphate compounds like ATP for energy transfer.