How Respiration Takes Place in Plants
Plant respiration is a biochemical process where the plant will absorb oxygen and use it to drive the breakdown of organic molecules (e.g., glucose) into energy (in the form of adenosine triphosphate, or ATP), carbon dioxide and water. The energy is used to facilitate metabolic activity, such as the growth and formation of new plant tissue. Enzymes are found throughout the entire process, as they work to increase the rate of the reaction. Does this Spark an idea?
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Significance
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Respiration is a biochemical process that harnesses glucose and oxygen to provide ATP for metabolic function. However, it must be highlighted that the plant is responsible for the production of its own "food," i.e., glucose. The glucose is then stored in the form of starch granules. The starch molecule is a large number of glucose units bonded together via a glycosidic link. This is photosynthesis. It uses carbon dioxide, water and sunlight to produce glucose (with oxygen as its by-product). Thus, the plant then breaks down the starch to produce glucose for respiration.
Structure & Function
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Unlike animals, plants do not inhale or exhale air. The plant has its own dedicated routes to absorb oxygen and release the products, but this is not considered "breathing." The plant leaf and stem epidermis possess minute openings called stomata. It is through these openings that oxygen, carbon dioxide and water vapor diffuse into and out of the plant cell along a concentration gradient. The stoma is essentially the site for gaseous exchange.
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Types
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Respiration can occur in the presence and absence of oxygen. Aerobic respiration occurs in the presence of oxygen, while anaerobic respiration occurs in the absence. Remember that the aim is to produce energy for metabolism. The plant can do this even in the absence of oxygen; however, the energy yields will be quite low. Overall, one glucose molecule will yield 2 units of ATP anaerobically, compared to 38 units in aerobic conditions.
In aerobic respiration, glucose will produce carbon dioxide, water and energy. On the other hand, anaerobic respiration will produce carbon dioxide, ethanol and energy.
Stages
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The process of respiration occurs in stages. Glycolysis occurs in the cytoplasm of the cell. The glucose is broken down to produce pyruvate, releasing ATP. The pyruvate then enters the citrate cycle, or Krebs cycle, which occurs in the matrix of the mitochondrion. This is a enzyme-fueled metabolic pathway that acts to release ATP and additional energy to molecules called nicotinamide dinucleotide (NAD) and flavin adenine dinucleotide (FAD).
The final stage is the electron transport chain, which occurs in the cristae of the mitochondrion. This generates more energy by converting the FAD and NAD molecules into ATP, while water is produced as its by-product.
Limitations of Respiration
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Because it is a biochemical reaction, respiration can be inhibited by physical or chemical factors such as temperature, water, enzyme concentrations, pH and soil composition (e.g., availability of minerals, oxygen/carbon dioxide and surface area). Factors such as these can inhibit or slow down the rate at which glucose is broken down and converted into energy. Factors like as temperature and pH, if not at optimum levels, can denature proteins such as enzymes, rendering many essential processes useless.
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References
- Photo Credit Plant image by Platinum Pictures from Fotolia.com
