CIE IGCSE Biology Revision Notes - Excretion in Humans PDF

CIE IGCSE Biology Revision Notes savemyexams.co.uk 13 EXCRETION 2 ORGANISATION OFIN HUMANS THE ORGANISM...

CIE IGCSE Biology Revision Notes savemyexams.co.uk 13 EXCRETION 2 ORGANISATION OFIN HUMANS THE ORGANISM YOUR NOTES CONTENTS: 13.1 THE EXCRETORY SYSTEM 13.2 THE URINARY SYSTEM 13.3 THE KIDNEY (EXTENDED ONLY) 13.4 KIDNEY FAILURE (EXTENDED ONLY) VIEW EXAM QUESTIONS 13.1 THE EXCRETORY SYSTEM Excretory Products Unlike plants, humans have organs which are specialised for the removal of certain excretory products They include the lungs and kidneys The liver also has a vital role in excretion Organs involved in excretion ORGAN MAINLY EXPLANATION EXCRETES LUNGS CARBON DIOXIDE THE LUNGS EXCRETE CARBON DIOXIDE (A WASTE PRODUCT OF AEROBIC RESPIRATION) DURING EXHALATION KIDNEYS EXCESS WATER, THE KIDNEYS EXCRETE EXCESS WATER, EXCESS SALTS AND UREA SALTS AND UREA (FORMED IN THE LIVER FROM EXCESS AMINO ACIDS) BY PRODUCING URINE CIE IGCSE Biology Resources © copyright Save My Exams Page 1 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Biology Revision Notes savemyexams.co.uk 13 EXCRETION IN HUMANS YOUR NOTES 13.1 THE EXCRETORY SYSTEM cont... EXTENDED ONLY The Need for Excretion Excretion is the removal of the waste substances of metabolic reactions (the chemical reactions that take place inside cells), toxic materials and substances in excess of requirements Carbon dioxide must be excreted as it dissolves in water easily to form an acidic solution which can lower the pH of cells This can reduce the activity of enzymes in the body which are essential for controlling the rate of metabolic reactions For this reason, too much carbon dioxide in the body is toxic Urea is also toxic to the body in higher concentrations and so must be excreted The Role of the Liver Many digested food molecules absorbed into the blood in the small intestine are carried to the liver for assimilation (when food molecules are converted to other molecules that the body needs) These include amino acids, which are used to build proteins such as fibrinogen, a protein found in blood plasma that is important in blood clotting Excess amino acids absorbed in the blood that are not needed to make proteins cannot be stored, so they are broken down in a process called deamination Enzymes in the liver split up the amino acid molecules The part of the molecule which contains carbon is turned into glycogen and stored The other part, which contains nitrogen, is turned into ammonia, which is highly toxic, and so is immediately converted into urea, which is less toxic The urea dissolves in the blood and is taken to the kidney to be excreted A small amount is also excreted in sweat CIE IGCSE Biology Resources © copyright Save My Exams Page 2 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Biology Revision Notes savemyexams.co.uk 13 EXCRETION 2 ORGANISATION OFIN HUMANS THE ORGANISM YOUR NOTES 13.1 THE EXCRETORY SYSTEM cont... EXTENDED ONLY cont... Amino acid groups In deamination, the nitrogen-containing amino group is removed and converted into ammonia and then urea to be excreted EXAM TIP Excretion and egestion are two terms that often get confused: Excretion is the removal from the body of waste products of metabolic reactions, toxic substances and substances in excess of requirements Egestion is the expulsion of undigested food waste from the anus CIE IGCSE Biology Resources © copyright Save My Exams Page 3 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Biology Revision Notes savemyexams.co.uk 13 EXCRETION IN HUMANS YOUR NOTES 13.2 THE URINARY SYSTEM Structure The urinary system in humans Main structures involved: STRUCTURE EXPLANATION KIDNEY TWO BEAN-SHAPED ORGANS THAT FILTER THE BLOOD URETER TUBE CONNECTING THE KIDNEY TO THE BLADDER BLADDER ORGAN THAT STORES URINE (EXCESS WATER, SALTS AND UREA) AS IT IS PRODUCED BY THE KIDNEY URETHRA TUBE THAT CONNECTS THE BLADDER TO THE EXTERIOR; WHERE URINE IS RELEASED CIE IGCSE Biology Resources © copyright Save My Exams Page 4 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Biology Revision Notes savemyexams.co.uk 13 EXCRETION 2 ORGANISATION OFIN HUMANS THE ORGANISM YOUR NOTES 13.2 THE URINARY SYSTEM cont... EXAM TIP Note the difference between the ‘ureter’ and the ‘urethra’. These two names are commonly confused by students so take care to learn them and know which tube is which – they are NOT interchangeable! Changes in Urine The colour and quantity of urine produced in the body can change quickly Large quantities of urine are usually pale yellow in colour because it contains a lot of water and so the urea is less concentrated Small quantities of urine are usually darker yellow / orange in colour because it contains little water and so the urea is more concentrated There are various reasons why the concentration of urine will change, including: Water intake – the more fluids drunk, the more water will be removed from the body and so a large quantity of pale yellow, dilute urine will be produced Temperature – the higher the temperature the more water is lost in sweat and so less will appear in urine, meaning a smaller quantity of dark yellow, concentrated urine will be produced Exercise – the more exercise done, the more water is lost in sweat and so less will appear in urine, meaning a smaller quantity of dark yellow, concentrated urine will be produced 13.3 THE KIDNEY EXTENDED ONLY The Kidney The kidneys are located in the back of the abdomen and have two important functions in the body: they regulate the water content in the blood they excrete the toxic waste products of metabolism (such as urea) and substances in excess of requirements (such as salts) CIE IGCSE Biology Resources © copyright Save My Exams Page 5 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Biology Revision Notes savemyexams.co.uk 13 EXCRETION IN HUMANS YOUR NOTES 13.3 THE KIDNEY EXTENDED ONLY cont... The structure of a human kidney Waste substances CIE IGCSE Biology Resources © copyright Save My Exams Page 6 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Biology Revision Notes savemyexams.co.uk 13 EXCRETION 2 ORGANISATION OFIN HUMANS THE ORGANISM YOUR NOTES 13.3 THE KIDNEY cont... EXTENDED ONLY cont... Each kidney contains around a million tiny structures called nephrons, also known as kidney tubules or renal tubules The nephrons start in the cortex of the kidney, loop down into the medulla and back up to the cortex The contents of the nephrons drain into the innermost part of the kidney and the urine collects there before it flows into the ureter to be carried to the bladder for storage Structure of a nephron CIE IGCSE Biology Resources © copyright Save My Exams Page 7 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Biology Revision Notes savemyexams.co.uk 13 EXCRETION IN HUMANS YOUR NOTES 13.3 THE KIDNEY EXTENDED ONLY cont... The Nephron 1. Ultrafiltration Diagram showing the process of ultrafiltration CIE IGCSE Biology Resources © copyright Save My Exams Page 8 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Biology Revision Notes savemyexams.co.uk 13 EXCRETION 2 ORGANISATION OFIN HUMANS THE ORGANISM YOUR NOTES 13.3 THE KIDNEY cont... EXTENDED ONLY cont... Arterioles branch off the renal artery and lead to each nephron, where they form a knot of capillaries (the glomerulus) sitting inside the cup-shaped Bowman’s capsule The capillaries get narrower as they get further into the glomerulus which increases the pressure on the blood moving through them (which is already at high pressure because it is coming directly from the renal artery which is connected to the aorta) This eventually causes the smaller molecules being carried in the blood to be forced out of the capillaries and into the Bowman’s capsule, where they form what is known as the filtrate This process is known as ultrafiltration The substances forced out of the capillaries are: glucose, water, urea, salts Some of these are useful and will be reabsorbed back into the blood further down the nephron COMPONENT REABSORBED AT WATER LOOP OF HENLE AND COLLECTING DUCT SALTS LOOP OF HENLE GLUCOSE PROXIMAL (FIRST) CONVOLUTED UREA NOT REABSORBED Components of filtrate CIE IGCSE Biology Resources © copyright Save My Exams Page 9 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Biology Revision Notes savemyexams.co.uk 13 EXCRETION IN HUMANS YOUR NOTES 13.3 THE KIDNEY EXTENDED ONLY cont... 2. Selective Reabsorption Reabsorption of Glucose Diagram showing the reabsorption of glucose CIE IGCSE Biology Resources © copyright Save My Exams Page 10 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Biology Revision Notes savemyexams.co.uk 13 EXCRETION 2 ORGANISATION OFIN HUMANS THE ORGANISM YOUR NOTES 13.3 THE KIDNEY cont... EXTENDED ONLY cont... After the glomerular filtrate enters the Bowman’s Capsule, glucose is the first substance to be reabsorbed at the proximal (first) convoluted tubule This takes place by active transport The nephron is adapted for this by having many mitochondria to provide energy for the active transport of glucose molecules Reabsorption of glucose cannot take place anywhere else in the nephron as the gates that facilitate the active transport of glucose are only found in the proximal convoluted tubule In a person with a normal blood glucose level, there are enough gates present to remove all of the glucose from the filtrate back into the blood People with diabetes cannot control their blood glucose levels and they are often very high, meaning that not all of the glucose filtered out can be reabsorbed into the blood in the proximal convoluted tubule As there is nowhere else for the glucose to be reabsorbed, it continues in the filtrate and ends up in urine This is why one of the first tests a doctor may do to check if someone is diabetic is to test their urine for the presence of glucose Reabsorption of Water & Salts As the filtrate drips through the Loop of Henle necessary salts are reabsorbed back into the blood by diffusion As salts are reabsorbed back into the blood, water follows by osmosis Water is also reabsorbed from the collecting duct in different amounts depending on how much water the body needs at that time CIE IGCSE Biology Resources © copyright Save My Exams Page 11 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Biology Revision Notes savemyexams.co.uk 13 EXCRETION IN HUMANS YOUR NOTES 13.4 KIDNEY FAILURE EXTENDED ONLY cont... Causes, Consequences, Treatments The kidneys might not work properly for several reasons, including accidents or disease Humans can survive with one functioning kidney, but if both are damaged then there will quickly be a build-up of toxic wastes in the body which will be fatal if not removed Treatment options for total kidney failure Kidney Dialysis The usual treatment for someone with kidney failure is dialysis This is an artificial method of filtering the blood to remove toxins and excess substances Patients are connected to a dialysis machine which acts as an artificial kidney to remove most of the urea and restore/maintain the water and salt balance of the blood Unfiltered blood is taken from an artery in the arm, pumped into the dialysis machine and then returned to a vein in the arm Inside the machine the blood and dialysis fluid are separated by a partially permeable membrane – the blood flows in the opposite direction to dialysis fluid, allowing exchange to occur between the two where a concentration gradient exists Dialysis fluid contains: a glucose concentration similar to a normal level in blood a concentration of salts similar to a normal level in blood no urea CIE IGCSE Biology Resources © copyright Save My Exams Page 12 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Biology Revision Notes savemyexams.co.uk 13 EXCRETION 2 ORGANISATION OFIN HUMANS THE ORGANISM YOUR NOTES 13.4 KIDNEY FAILURE cont... EXTENDED ONLY cont... How a dialysis machine works to filter the blood CIE IGCSE Biology Resources © copyright Save My Exams Page 13 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Biology Revision Notes savemyexams.co.uk 13 EXCRETION IN HUMANS YOUR NOTES 13.4 KIDNEY FAILURE cont... EXTENDED ONLY cont... As the dialysis fluid has no urea in it, there is a large concentration gradient – meaning that urea diffuses across the partially permeable membrane, from the blood to the dialysis fluid As the dialysis fluid contains a glucose concentration equal to a normal blood sugar level, this prevents the net movement of glucose across the membrane as no concentration gradient exists As the dialysis fluid contains a salt concentration similar to the ideal blood concentration, movement of salts across the membrane only occurs where there is an imbalance (if the blood is too low in salts, they will diffuse into the blood; if the blood is too high in salts, they will diffuse out of the blood) The fluid in the machine is continually refreshed so that concentration gradients are maintained between the dialysis fluids and the blood Dialysis may take 3-4 hours to complete and needs to be done several times a week to prevent damage to the body from the buildup of toxic substances in the blood An anticoagulant is added to blood before it runs through the machine to prevent the blood from clotting and slowing the flow Kidney Transplants vs Dialysis Kidney transplants are a better long term solution to kidney failure than dialysis; however, there are several disadvantages to kidney transplants, including: Donors won’t have the same antigens on cell surfaces so there will be some immune response to the new kidney (risk of rejection is reduced – but not removed – by ‘tissue typing’ the donor and the recipient first) This has to be suppressed by taking immunosupressant drugs for the rest of their lives – these can have long term side effects and leave the patient vulnerable to infections There are not enough donors to cope with demand CIE IGCSE Biology Resources © copyright Save My Exams Page 14 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Biology Revision Notes savemyexams.co.uk 13 EXCRETION 2 ORGANISATION OFIN HUMANS THE ORGANISM YOUR NOTES 13.4 KIDNEY FAILURE cont... EXTENDED ONLY cont... However, if a healthy, close matched kidney is available, then the benefits of a transplant over dialysis include: the patient has much more freedom as they are not tied to having dialysis several times a week in one place their diets can be much less restrictive than they are when on dialysis use of dialysis machines is very expensive and so this cost is removed a kidney transplant is a long term solution whereas dialysis will only work for a limited time EXAM TIP When answering questions about dialysis, the best answers will: refer to differences in concentration gradients between the dialysis fluid and the blood and use this to explain why substances move in certain directions > NOW TRY SOME EXAM QUESTIONS CIE IGCSE Biology Resources © copyright Save My Exams Page 15 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Biology Revision Notes savemyexams.co.uk 13 EXCRETION IN HUMANS YOUR NOTES EXAM QUESTIONS ? QUESTION 1 What is urea produced from? A Fatty acids B Glucose C Amino acids D Glycerol ? QUESTION 2 Which row of the table below correctly displays the correct roles of the following organs in processing waste in the human body? kidneys liver lungs A excretes urea excretes amino acids removes carbon dioxide B removes carbon excretes deamination of amino acids dioxide urea C removes urea from deamination of amino acids removes carbon dioxide blood D excretes urine deamination of urea removes carbon dioxide ? QUESTION 3 To remain healthy, a person must be able to excrete a number of waste products produced as a result of metabolism. A list of excretory products is given below. Which of the following would be lost from both the kidneys and lungs? A Water B Carbon dioxide C Glucose D Urea CIE IGCSE Biology Resources © copyright Save My Exams Page 16 REVISION NOTES TOPIC QUESTIONS PAST PAPERS  CIE IGCSE Biology Revision Notes savemyexams.co.uk 13 EXCRETION 2 ORGANISATION OFIN HUMANS THE ORGANISM YOUR NOTES EXAM QUESTIONS cont... ? QUESTION 4 Which of the following is a correct example of excretion in mammals? A The production of carbon dioxide from aerobic respiration. B The removal of excess salts from the blood. C The removal of undigested food from the anus. D The release of hormones from glands. ? QUESTION 5 Which of the following is not a main function of the kidneys in a healthy person? A To reabsorb all glucose B To regulate blood pressure C To breakdown toxins D To eliminate excess sodium and potassium ions > CHECK YOUR ANSWERS AT SAVEMYEXAMS.CO.UK Head to savemyexams.co.uk for more questions and revision notes CIE IGCSE Biology Resources © copyright Save My Exams Page 17 REVISION NOTES TOPIC QUESTIONS PAST PAPERS