Cellular Respiration in Plants

Cellular respiration, also referred to as oxidative metabolism, is a set of metabolic processes and reactions executed within the cell of an organism in order to convert the biochemical energy, derived from the nutrients, to adenosine triphosphate (ATP). ATP is a nucleotide which is the major source of energy for cellular reactions. The process revolves around catabolic reactions which facilitate oxidation of one molecule, with the reduction of the other. There are two types of cellular respiration, aerobic cellular respiration and anaerobic cellular respiration. Both, animals as well as plants, execute cellular respiration to produce energy. They use nutrients such as glucose, amino acids, and fatty acids to produce the energy. The common oxidizing agent in this process is molecular oxygen.

What is Cellular Respiration in Plants?

It sounds confusing, as we already know that plants produce energy through the process of photosynthesis. It's true indeed, but that's not the only means of energy generation for plants. Cellular reaction in plants is totally opposite to photosynthesis, and more importantly, it does exist in plant life. There are four stages of cellular reaction in plants - glycolysis, transition reaction, the Krebs cycle, and electron transport chain. In order to understand how does cellular respiration occur in plants, we will have to get into the details of each of its stages.

Glycolysis
The first stage of cellular respiration in plants, glycolysis, is the process wherein the glucose obtained from the food is chemically modified to form compound pyruvate. This process, which occurs in the cytosol of the cell, is carried out in the absence of oxygen. During this process, energy is released from glucose compounds in the form of 2 NADH molecules and 2 ATP molecules.

Transition Reaction
Transition reaction, also known as pyruvate decarboxylation, is the second stage of cellular respiration in plants, wherein pyruvate is decarboxylated and added to Coenzyme A (CoA) in order to form Acetyl CoA. It is an important stage in the cellular respiration process as it forms a link between the metabolic pathways of glycolysis and the Krebs cycle.

The Krebs Cycle
The next stage of cellular respiration in plants, the Krebs cycle, comprises a series of steps which oxidize the Aceytl CoA molecule. Unlike glycolysis, the Krebs cycle requires oxygen for functioning. This aerobic process is catalyzed by enzymes. 2 complete turns of the Krebs cycle produce

• 4 carbon dioxide molecules
• 6 NADH molecules
• 2 ATP molecules
• 2 FADH2 molecules

Electron Transport Chain
The last stage of cellular respiration in plants is the electron transport chain, which produces the remaining 32-34 ATP. The chain is made up of electron-carrying proteins, based at the membrane of the mitochondrian. These proteins transfer electrons from one self to another. These electrons are finally added to oxygen, which is the final electron acceptor, along with the protons which leads to formation of water. In this process, ATP is produced by proton motive force, a store of potential energy created by the gradient that is formed when the protons move across the biological membrane. In simple words, electron transport chain triggers a gradient though which ATP is produced in a process known as chemiosmosis.

During photosynthesis the plant utilizes the energy from the sun and stores it in the form of bonds of glucose molecules, whereas during cellular respiration in plants, the glucose molecules stored in the plants are broken down to obtain the energy, in the presence of oxygen. Similarly, the plant can produce ATP in the absence of oxygen as well. This process is known as fermentation, but it's not as efficient as cellular respiration, and hence not so important.