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Introduction |
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All living creatures need food. The food is consumed so that energy is obtained. The energy is utilised by the body for various purposes like locomotion, conduction of impulses, repair of damaged tissues, building of cell materials, etc. |
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Respiration and Breathing |
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In most cases, glucose is oxidised in the presence of oxygen to give carbon dioxide. Thus, for respiration, an organism has to take in oxygen and give out carbon dioxide. This is called gaseous exchange. The oxygen taken in is used to break down the respiratory substrate (e.g., glucose) and energy is released along with carbon dioxide. This whole process is called respiration. |
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Respiration - Meaning |
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Respiration can be broadly defined as the breakdown of organic compounds into simpler compounds accompanied by the release of energy. |
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Types of Respiration - Aerobic and Anaerobic |
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Most of plants and animal cells respire aerobically, that is, in the presence of oxygen. However, there are certain microbes that respire in the absence of free oxygen. This respiration is called anaerobic respiration. It is also called fermentation. |
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Stages of Respiration |
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As mentioned in the above section, for energy to be released from food, there has to be an exchange of gases - oxygen and carbon dioxide. |
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Gaseous Exchange in Plants |
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In lower plants (and also protozoans) exchange of gases takes place through the general body surface as they are not highly modified or specialised. Also, the body surface allows the diffusion of gases. In higher plants the exchange of gases takes place through stomata. |
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Gaseous Exchange in Earthworm |
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Earthworm has a segmented cylindrical body covered by a thin cuticle below which is the epidermis. This skin is always kept very moist by the secretion of mucus from the epidermis and body fluids from the excretory pores. It always lives in moist soil especially during the day. This prevents their skin from drying or desiccation. |
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Gaseous Exchange in Fish |
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The region between the buccal cavity (mouth) and the oesophagus is called the pharynx. In the pharyngeal region, the wall on either side shows slits which open to the exterior. These slits are called the gill slits. The gill slits are separated by a tissue called the gill arch or the branchial arch. There are four pairs of gill arches separating five pairs of gill slits. |
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Gaseous Exchange in Frog |
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Frogs respire through skin as well as the lungs. The oxygen rich air enters the skin or lungs. From here the blood picks up the oxygen and transports it to the tissues of various organs. From the tissues the blood picks up carbon dioxide and transports it back to the skin or the lungs from where it is expired into the outer atmosphere. |
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Gaseous Exchange in Grasshopper |
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The respiratory system in insects is called the tracheal system. It involves the diffusion of oxygen directly from the atmosphere into the air-filled tubes. Thus, the diffusion is through air and hence, is more efficient than the diffusion through water (300,000 times more) or tissues (1,000,000 times more). |
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Gaseous Exchange in Human Beings |
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There are a pair of lungs in the thoracic cavity - the left lung and the right lung. The left lung is slightly smaller (because of the heart which is slightly to the left of the body) and has two lobes and the right lung is bigger with three lobes. They are spongy and elastic organs that are broad at the bottom and taper at the top. |
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Transport of Gases |
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Some of the carbon dioxide is transported in haemoglobin. However, most of the carbon dioxide is transported as bicarbonate ions. Carbon dioxide first combines with water to form carboxylic acid. This then splits into hydrogen ions and bicarbonate ions. The hydrogen ions are absorbed by the haemoglobin. |
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Breathing Mechanism |
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The physical movements associated with the gaseous exchange are called breathing. They are controlled by the respiratory centre of the medulla oblongata in the human brain. Thus, the breathing movements are involuntary to a large extent. |
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Respiratory Volumes |
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There are totally about 700 million alveoli in the two lungs of an adult human being. This increases the surface area enormously. The total surface area of the lungs is 70 square metres which is almost the size of the tennis court. It is nearly 100 times the surface of the human body (skin). |
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Cellular Respiration |
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Glucose is a carbohydrate - a compound of carbon and hydrogen. The bonds between the carbon and the hydrogen atoms are very strong. In the cells, the substrate, often glucose, is broken down into carbon dioxide and water in the presence of oxygen. This process breaks the bonds between carbon and hydrogen and thus releases energy. This is called respiration. |
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Electron Transport Chain (ETC) |
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It takes place in the mitochondrial membranes. During this step, the hydrogen ions (or a pair of electrons) are transported from one carrier to another and they are finally used to reduce oxygen to water. During this transfer of electrons, lot of energy is released which is in the form of ATP. ATP is thus an energy rich molecule and can be called the energy currency of the cell. |
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Respiratory Quotient |
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If one observes the equation of respiration, the number of moles of oxygen needed is equal to the number of moles of carbon dioxide produced. This CO2:O2 ratio is called the "respiratory quotient". |
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Significance of Respiration |
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Respiration is an important process in nature. It is a process by which the solar energy trapped by the plants in the food can be utilised. The organic compounds are broken down to release energy. This energy is in the form of ATP molecules and is made available for all the vital activities of the organism. ATP can also be stored. |
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Experiments on Respiration |
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The apparatus shown is called the respiroscope that is used to demonstrate respiration. Few germinating seeds are taken in the bulb of the respirometer. The tube is inserted into a beaker containing mercury. A pellet of KOH is introduced into the set-up. |
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Summary |
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Respiration is defined as the catabolic biochemical process during which organic compounds break down in order to release energy. The organic compounds that are broken down are called the substrates. Glucose is the most common substrate. |
