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Know Your Flora: What Is Plant Respiration?

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During photosynthesis, light energy is converted into chemical energy. The energy is stored in carbohydrate molecules including glucose and starch.

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How Plants Breathe
Plants make energy by oxidizing carbohydrate molecules into simple low-energy molecules. Respiration includes the reactions involved in the oxidation process. Plant respiration is the process of breaking down high-energy complex molecules into simple low-energy molecules. The energy released as a result of this process is made available for cell activities through intermediate compounds known as adenosine triphosphate.

During respiration, the energy contained in the respiratory substrates is not released all at once; the energy is slowly released through a series of reactions controlled by enzymes. Respiration occurs in all plant cells and is generally referred to as cellular respiration. Respiration utilizes oxygen with carbon dioxide and water released as products. Some of the most critical life processes such as synthesis of fats, proteins and carbohydrates require energy. Respiration ensures that the energy is made available to plant living cells.

Some of the most important factors involved in respiration include: consumption of oxygen, oxidation and decomposition of food leading to loss of dry weight, liberation of carbon dioxide and water, and release of energy.

Types of Respiration
The two main types of respiration are aerobic and anaerobic. Aerobic respiration leads to the complete oxidation of stored foods. This type of respiration occurs in higher organisms. Anaerobic respiration occurs in the complete absence of oxygen. Plants such as cacti, tissues of higher plants and fleshy fruits and succulent plants may temporarily utilize this type of respiration. Little energy is released by this process.

Mechanism of Respiration
Respiration occurs in two major phases including glycolysis and the Krebs cycle. These processes convert carbohydrates into pyruvic acid through a series of enzymatic reactions. These reactions are known as glycolysis and they often take place in the cytosol. The pyruvic acid is transported into the mitochondria where it is converted into carbon dioxide and water through the actions of several enzymes. The series of enzymatic reactions involved in this process is known as glycolysis.

Glycolysis
This term is used to describe a series of reactions that occur in a wide variety of tissues. The reactions start with hexose sugar and end with pyruvic acid. The term glycolysis was coined from two Greek words: Glycos and lysis meaning sugar and splitting respectively.

The first stage in the breakdown of glucose is known as glycolysis. This process is a common feature of both aerobic and anaerobic respiration. Plants derive glucose from sucrose, which is the end product of photosynthesis. The enzyme invertase converts sucrose into glucose and fructose, which are used in the process of glycolysis.

Main Steps in the Glycolytic Pathway
Phosphorylation is the process of breaking down sugar into glucose and fructose through the actions of the enzyme hexokinase. The by-products of this process then isomerize to produce fructose-6-phosphate. Isomerization is facilitated by the enzyme phosphohexose isomerase. The next step in the glycolysis process is the phosphorylation of fructose-6-phosphate.

Once the phosphorylation of fructose-6-phosphate is complete, the fructose is split into two molecules: triose phosphate and dihydroxyacetone. The next steps involve the formation of ATP, isomerization, dehydration and generation of ATP.

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