com www.GOALias.blogspot.com www.GOALias ... - fun learning

www.GOALias.blogspot.comthe mouth of the funnel on your chestnear the heart. Now try to listencarefully. Do you hear a regularthumping sound ? The sound is that ofheartbeats. How many times did yourheartbeat in a minute ? Count againafter running for 4–5 minutes. Compareyour observations.Record your own pulse rate andheartbeat and that of your friends whileresting and after running and record inTable 11.2. Do you find any relationshipbetween your heartbeat and pulse rate?Each heart beat generates one pulse inthe arteries and the pulse rate perminute indicates the rate of heartbeat.The rhythmic beating of the variouschambers of the heart maintaincirculation of blood and transport ofsubstances to the different parts of thebody.Boojho wonders if sponges andhydra also have blood? Animals suchas sponges and Hydra do not posses anycirculatory system. The water in whichthey live brings food and oxygen as itThe English physician, William Harvey(A.D.1578–1657), discovered thecirculation of blood. The currentopinion in those days was that bloodoscillates in the vessels of the body.For his views, Harvey was ridiculedand was called “circulator”. He lostmost of his patients. However, beforehe died, Harvey’s idea aboutcirculation was generally accepted asa biological fact.enters their bodies. The water carriesaway waste materials and carbon dioxideas it moves out. Thus, these animals donot need a circulatory fluid like theblood.Let us now learn about the removalof waste other than carbon dioxide.11.2 EXCRETIONIN ANIMALSRecall how carbon dioxide is removedas waste from the body through thelungs during exhalation. Also recall thatthe undigested food is removed duringegestion. Let us now find out how theother waste materials are removed fromthe body. You may wonder where theseunwanted materials come from!When our cells perform theirfunctions, certain waste products arereleased. These are toxic and hence needto be removed from the body. Theprocess of removal of wastes producedin the cells of the living organisms iscalled excretion. The parts involved inexcretion forms the excretory system.Excretory system in humansThe waste which is present in the bloodhas to be removed from the body. Howcan this be done? A mechanism to filterthe blood is required. This is done bythe blood capillaries in the kidneys.When the blood reaches the two kidneys,it contains both useful and harmfulsubstances. The useful substances areabsorbed back into the blood. Thewastes dissolved in water are removedas urine. From the kidneys, the urinegoes into the urinary bladder through126SCIENCE