All living things in the world including plants require energy in order to function. This energy is obtained from the food we eat. The cells break down the energy stored in the food through a unique system known as cellular respiration. In plain language, cellular respiration means the procedure through which the food is broken down by the cells of living beings in order to produce the energy which is in the form of ATP molecules (also known as the Adenosine Tri Phosphate molecules). Plants use a part of this ATP energy during photosynthesis for producing sugar. The sugars are then broken down during cellular respiration. This cycle is continued again and again as long as the plant lives.
In cellular respiration there are three stages, which are known as (a) Glycolysis (b) Krebs Cycle and (c) Electron Transport Chain (Etc). Every cell of all living creatures, which includes plants, carries cellular respiration, as it is very essential for life. However, there is no fixed time or point in the timing of the respiration. Cells, which are neighbors, also involve itself in cellular respiration at different stages. The reaction that occurs during cellular respiration produces the energy. During this process, the polymers are broken down in more small and manageable pieces. The carbohydrate that is obtained during the respiration is disassembled into molecules of glucose, which in turn is used to produce ATP molecules, which are rich in energy. In plain terms, we can say that during cellular respiration, one glucose molecules and six oxygen molecules will produce six carbon dioxide and six water molecules and in between 36 to 38 ATP molecules.
There are three stages of cellular respiration, which are as follows:
- (a) Glycolysis
This process breaks down the molecules of glucose from the carbohydrates and converts it into pyruvate. The procedure occurs in the cytosol, inside the cell and can carry its work without the requirement of oxygen. At the first stage of glycolysis, the phosphate is drawn from the ATP and added to the molecule of the glucose, which makes the molecule to become chemically reactive. This reaction changes the molecule into isomer and fructose.
- (b) Krebs cycle
By Krebs cycle we mean a series of procedures, which gets catalyzed by the enzymes, and oxidize the molecule of Acetyl-coA. It is actually an aerobic procedure, which actually means that it requires oxygen for functioning. Krebs cycle must complete two complete turns for producing 4 molecules of carbon dioxide, 6 molecules of NADH, 2 molecules of ATP and 2 molecules of FADH2 which is an energy giving molecule.
- (c) Electron Transport Chain
During the process of glycolysis and Krebs cycle, very little energy is produced. The energy that remains inside the original molecule of glucose gets released through the electron transport chain. This chain is actually a widespread network of electron carrying proteins, which are found inside the inner membrane of the mitochondrion. The work of these proteins is to transfer the electrons from one to another and finally adds itself with the protons to the oxygen, which is known as the final electron acceptor. Though water is produced during this procedure, no ATP is produced. ATP is produced later through a proton. Thus the work of the electron transport chain is only to produce an ingredient from which ATP can be produced.
We should remember that cellular respiration could occur only if oxygen is available. There are some organisms that live in anaerobic conditions. In such cases, full cellular respiration is not possible for those organisms that are living in anaerobic conditions. Glycolysis is the one and only cellular respiration process for such type of organisms.
Thus we can safely say that all organisms use the sugar, which is available in their food to turn it into energy in order to be able to live and perform the necessary actions that are made by all living creatures.