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Chapter 10 | Respiratory System | Breathing

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10 O Respiration in Organisms Therefore, all living organisms respire to get energy from food. During breathing, we breathe in air. You know that air contains oxygen. We breathe out air which is rich in carbon dioxide. The air we breathe in is transported to all parts of the body and ultimately to each cell. In the cells, oxygen in the air helps in the breakdown of food. The process of breakdown of food in the cell with the release of energy is called cellular respiration. respiration Cellular
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  SSSSS CIENCECIENCECIENCECIENCECIENCE 108108108108108 Respiration in OrganismsRespiration in OrganismsRespiration in OrganismsRespiration in OrganismsRespiration in Organisms 1010101010 O ne day Boojho was eagerly  waiting to meet hisgrandparents who were comingto the town after a year. He was in a realhurry as he wanted to receive them at the bus-stop. He ran fast and reached the bus-stop in a few minutes. He was breathing rapidly. His grandmother askedhim why he was breathing so fast. Boojhotold her that he came running all the way.But the question got stuck in his mind.He wondered why running makes a person breathe faster. The answer toBoojho’s question lies in understanding why we breathe. Breathing is a part of respiration. Let us learn about respiration. 10.1 W 10.1 W 10.1 W 10.1 W 10.1 W  HY HY HY HY HY    DODODODODO W  W  W  W  W  EEEEE R R R R R  ESPIREESPIREESPIREESPIREESPIRE ????? In Chapter 2 you learnt that allorganisms are made of smallmicroscopic units called cells. A cell isthe smallest structural and functionalunit of an organism. Each cell of anorganism performs certain functionssuch as nutrition, transport, excretionand reproduction. To perform thesefunctions, the cell needs energy. Even when we are eating, sleeping or reading we require energy. But, where does thisenergy come from? Can you say why  your parents insist that you should eat regularly? The food has stored energy, which is released during respiration. Therefore, all living organisms respireto get energy from food. During breathing, we breathe in air. You know that air contains oxygen. We breathe out air which is rich in carbon dioxide. Theair we breathe in is transported to allparts of the body and ultimately to eachcell. In the cells, oxygen in the air helpsin the breakdown of food. The processof breakdown of food in the cell with therelease of energy is calledcellular cellular cellular cellular cellular respirationrespirationrespirationrespirationrespiration. Cellular respiration takesplace in thecells of all organismscells of all organismscells of all organismscells of all organismscells of all organisms.In the cell, the food (glucose) is brokendown into carbon dioxide and water usingoxygen. When breakdown of glucoseoccurs with the use of oxygen it is calledaerobicaerobicaerobicaerobicaerobicrespirationrespirationrespirationrespirationrespiration. Food can also be broken down, without using oxygen. Thisis calledanaerobic respirationanaerobic respirationanaerobic respirationanaerobic respirationanaerobic respiration.Breakdown of food releases energy.  With the use of oxygen Glucose   carbon dioxide + water + energy  You should know that there are someorganisms such as yeast that can survivein the absence of air. They are calledanaerobesanaerobesanaerobesanaerobesanaerobes. They get energy throughanaerobic respiration. In the absence of oxygen, glucose breaks down into alcoholand carbon dioxide, as given below:    Without the use of oxygen Glucose alcohol + carbon dioxide + energy   R R R R R  ESPIRATIONESPIRATIONESPIRATIONESPIRATIONESPIRATION   INININININ OOOOO RGANISMSRGANISMSRGANISMSRGANISMSRGANISMS 109109109109109 Our muscle cells can also respireanaerobically, but only for a short time, when there is a temporary deficiency of oxygen. During heavy exercise, fast running (Fig. 10.1), cycling, walking for many hours or heavy weight lifting, thedemand for energy is high. But thesupply of oxygen to produce the energy is limited. Then anaerobic respirationtakes places in the muscle cells to fulfilthe demand of energy:   (in muscle) in the absence of oxygen Glucose lactic acid + energy  Fig. 10.1Fig. 10.1Fig. 10.1Fig. 10.1Fig. 10.1 During exercise, some muscles may respire anaerobically  Have you ever wondered why you get muscle cramps after heavy exercise? Thecramps occur when muscle cells respireanaerobically. The partial breakdown of glucose produces lactic acid. Theaccumulation of lactic acid causes musclecramps. We get relief from cramps after a hot water bath or a massage. Can youguess why it is so? Hot water bath or massage improves circulation of blood. As a result, the supply of oxygen to themuscle cells increases. The increase inthe supply of oxygen results in thecomplete breakdown of lactic acid intocarbon dioxide and water. 10.2 B10.2 B10.2 B10.2 B10.2 B REATHINGREATHINGREATHINGREATHINGREATHING  Activity 10.1 Activity 10.1 Activity 10.1 Activity 10.1 Activity 10.1  Yeasts are single-celled organisms. They respire anaerobically and duringthis process yield alcohol. They are,therefore, used to make wine and beer.CAUTIONCAUTIONCAUTIONCAUTIONCAUTIONDo this activity under the supervisionof your teacher.Close your nostrils and mouthtightly and look at a watch. What did you feel after some time? How long were you able to keep both of them closed?Note down the time for which you couldhold your breath (Fig. 10.2).So, now you know that you cannot survive for long without breathing. You must have seen the movement of the abdomen of dogs, cats and cows,as they breathe. Breathing means takingin air rich in oxygen and giving out air rich in carbon dioxide with the help of respiratory organs. The taking in of air rich in oxygen   into the body is calledinhalationinhalationinhalationinhalationinhalation and giving out of air rich in  SSSSS CIENCECIENCECIENCECIENCECIENCE 110110110110110 one inhalation plus one exhalation. Would you like to find out your  breathing rate? Do you want to know  whether it is constant or it changesaccording to the requirement of oxygen by the body? Let us find out by doingthe following activity.  Activity 10.2 Activity 10.2 Activity 10.2 Activity 10.2 Activity 10.2 Generally we are not aware that we are breathing. However, if you try you cancount your rate of breathing. Breathein and out normally. Find out how many times you breathe in and breathe out in a minute? Did you inhale the samenumber of times as you exhaled? Now count your breathing rate (number of  breaths/minute) after brisk walk andafter running. Record your breathingrate as soon as you finish and also after complete rest. Tabulate your findingsand compare your breathing rates under different conditions with those of your classmates.From the above activity, you must have realised that whenever a personneeds extra energy, he/she breathesfaster. As a result more oxygen isBoojho noticed that when hereleased his breath after holdingit for some time, he had to breathe heavily. Can you tellhim why it was so? Fig. 10.2 Fig. 10.2 Fig. 10.2 Fig. 10.2 Fig. 10.2 Holding breath carbon dioxide   is known asexhalationexhalationexhalationexhalationexhalation.It is a continuous process which goeson all the time and throughout the lifeof an organism. The number of times a person breathes in a minute is termed as the breathing rate breathing rate breathing rate breathing rate breathing rate. Both inhalation andexhalation take place. A breath means Table 10.1 Changes in breathing rate under different conditions Table 10.1 Changes in breathing rate under different conditions Table 10.1 Changes in breathing rate under different conditions Table 10.1 Changes in breathing rate under different conditions Table 10.1 Changes in breathing rate under different conditions Name of the classmateName of the classmateName of the classmateName of the classmateName of the classmateBreathing rateBreathing rateBreathing rateBreathing rateBreathing rateNormalNormalNormalNormalNormal After a brisk  After a brisk  After a brisk  After a brisk  After a brisk  After running After running After running After running After running At rest  At rest  At rest  At rest  At rest  walk for 10 walk for 10 walk for 10 walk for 10 walk for 10fast 100 mfast 100 mfast 100 mfast 100 mfast 100 m minutesminutesminutesminutesminutes Self   R R R R R  ESPIRATIONESPIRATIONESPIRATIONESPIRATIONESPIRATION   INININININ OOOOO RGANISMSRGANISMSRGANISMSRGANISMSRGANISMS 111111111111111 Fig. 10.3 Fig. 10.3 Fig. 10.3 Fig. 10.3 Fig. 10.3 Variation in the breathing rate during different activities  supplied to our cells. It speeds upthe breakdown of food and moreenergy is released. Does this explain why we feel hungry after a physicalactivity? When you feel drowsy, does your  breathing rate slow down? Does your  body receive sufficient oxygen?  Activity 10.3 Activity 10.3 Activity 10.3 Activity 10.3 Activity 10.3 Figure 10.3 shows the various activitiescarried out by a person during a normalday. Can you say in which activity, therate of breathing will be the slowest andin which it will be the fastest? Assignnumbers to the pictures in the order of increasing rate of breathing accordingto your experience. 10.3 H10.3 H10.3 H10.3 H10.3 H OW OW OW OW OW    DODODODODO W  W  W  W  W  EEEEE BBBBB REATHEREATHEREATHEREATHEREATHE ????? Let us now learn about the mechanismof breathing. Normally we take in air through our nostrils. When we inhaleair, it passes through our nostrils intothenasal cavity nasal cavity nasal cavity nasal cavity nasal cavity. From the nasal cavity,the air reaches our lungslungslungslungslungs through the windpipe. Lungs are present in thechest cavity chest cavity chest cavity chest cavity chest cavity (Fig. 10.4). This cavity issurrounded by ribs on the sides. A large,muscular sheet calleddiaphragmdiaphragmdiaphragmdiaphragmdiaphragm formsthe floor of the chest cavity (Fig. 10.4).Breathing involves the movement of thediaphragm and the rib cage.During inhalation, ribs move up andoutwards and diaphragm moves down. This movement increases space in our chest cavity and air rushes into thelungs. The lungs get filled with air.During exhalation, ribs move down andinwards, while diaphragm moves up toits former position. This reduces the sizeof the chest cavity and air is pushed out of the lungs (Fig. 10.5). Thesemovements in our body can be felt On an average, an adult human beingat rest breathes in and out 15–18times in a minute. During heavy exercise, the breathing rate canincrease upto 25 times per minute. While we exercise, not only do we breathe fast, we also take deep breathsand thus inhale more oxygen.Paheli wants to know why  we yawn when we aresleepy or drowsy.
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