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The process of Respiration.

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Respiration Respiration is the process by which human beings and other living things obtain and use oxygen. Except for certain microorganisms, all living things require oxygen to live. Respiration also involves the elimination of carbon dioxide, a gas produced when cells use oxygen. Respiration may be divided into three phases: (1) external respiration, (2) internal respiration, and (3) cellular respiration. In external respiration, or breathing, a plant or animal takes in oxygen from its environment and releases carbon dioxide. In internal respiration, oxygen is carried to the cells of the organism and carbon dioxide is carried away from them. In cellular respiration, oxygen is used in chemical reactions within the cells. These reactions release energy and produce carbon dioxide and water as waste products. Organisms carry out external respiration in various ways, depending on their size and environment. For example, single-celled organisms, such as diatoms, and amoebas, exchange oxygen and carbon dioxide directly with the environment through their cell membranes. In higher plants and animals, however, each cell lacks direct contact with the environment. External respiration in these organisms requires a system of specialized structures or organs. This article deals chiefly with respiration in human beings and other mammals. Respiration in other animals with lungs--such as birds, reptiles, and most adult amphibians--is carried out in similar ways. ...read more.


Between breaths, when the respiratory system is "at rest," the lungs still contain almost half the gas they can hold. This gas provides a reserve so that the exchange of oxygen and carbon dioxide can continue between breaths. Control of breathing. Breathing is regulated by the respiratory centre, groups of nerve cells in the brain stem. Every few seconds, these cells send bursts of impulses to the muscles involved in inspiration. These signals determine the rate and depth of breathing. Another group of special cells, called chemoreceptors, sense the oxygen and carbon dioxide levels in the blood and the acidity of cerebrospinal fluid surrounding the brain. Slight increases or decreases in carbon dioxide cause changes in the acidity of body fluids. These changes may affect various body functions. Chemoreceptors send signals to the respiratory centre to quicken or slow the rate of breathing. In this way, they help maintain normal levels of oxygen and acidity in the body. Internal respiration Internal respiration refers to the process by which oxygen is transported to body tissues and carbon dioxide is carried away from them. Red blood cells play an essential role in this process. They contain haemoglobin, a molecule that can carry large amounts of oxygen. They also contain an enzyme called carbonic anhydrase. This enzyme helps change carbon dioxide into bicarbonate ion, a form that is easily carried in blood. ...read more.


At the same time, carbon dioxide moves from blood to water. Fish take in water through the mouth and force it out over the gills. Other animals that lack lungs also have special ways of breathing. For example, earthworms breathe through their skin. They have a system of capillaries just beneath the skin. Oxygen and carbon dioxide are exchanged between air in the soil and the animal's blood. Insects have a system of tiny air tubes called tracheae for breathing. These tubes carry air from the environment directly to different parts of the body. Some animals, such as amphibians, use more than one organ of respiration during their life. Frogs, for example, breathe through gills while they are tadpoles. Mature frogs breathe chiefly with lungs and also exchange gas with the environment through their skin. Respiration in plants In higher plants, oxygen and carbon dioxide move into and out of the roots and stems through the outer layers of cells. The majority of gas exchange in plants, however, takes place through small openings in the leaves called stomata. Like animal cells, plant cells obtain energy through chemical reactions that break down glucose. Green plants also produce energy through a "reverse respiration" process called photosynthesis. In photosynthesis, the plant uses energy from light to make glucose. During this process, the plant takes in carbon dioxide from the environment and produces oxygen as a waste product. Certain bacteria also perform photosynthesis. ...read more.

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