PREFACE CHAPTER GASEOUS EXCHANGE Concept Map 7 Gaseous Exchange Gaseous exchange in human Breathing cycle Structures involved Trachea Stomata Bronchus Bronchiole Alveolus Structure of haemoglobin Transport of O2 and CO2 O2 dissociation curves Bohr’s effect Foetal haemoglobin Myoglobin Gaseous exchange in plants Mechanism of breathing control Lung volumes Mechanism of opening and closing Structure and functions Haemoglobin Tidal volume Inspiratory reserve volume Expiratory reserve volume Vital capacity Residual volume Total lung capacity Bilingual Keywords Exchange – Pertukaran Breathing – Pernafasan Inhalation – Tarik nafas Exhalation – Hembus nafas Lung – Peparu Saturated – Ketepuan Lateral – Sisi Diaphragm – Diafragma Relaxation – Pengenduran Turgid – Segah vi STPM Scheme of Assessment Term of Study Paper Code and Name Theme / Title Type of Test Mark (Weighting) Duration Administration First Term 964/1 Biology Paper 1 Biological Molecules and Metabolism Written test Section A 15 compulsory multiple-choice questions to be answered. Section B 2 compulsory short structured questins to be answered. Section C 2 out of 3 essay questions to be answered. All questions are based on topics 1 to 6. 60 (26.67%) 15 15 30 1—1 2 hours Central assessment Second Term 964/2 Biology Paper 2 Physiology Written test Section A 15 compulsory multiple-choice questions to be answered. Section B 2 compulsory short structured questins to be answered. Section C 2 out of 3 essay questions to be answered. All questions are based on topics 7 to 13. 60 (26.67%) 15 15 30 1—1 2 hours Central assessment vi Learning Outcomes CHAPTER 13 Biology Term 2 STPM Chapter 13 Infectious Diseases Students should be able to: (a) describe the causes and symptoms of cholera; (b) explain the transmission of cholera; (c) discuss the roles of social, economical and biological factors in the prevention of cholera. Figure 13.4 Vibrio cholerae as observed under electron microscope 4. For the general public, the primary method of controlling A. aegypti is by eliminating its habitats where the mosquito lays her eggs within and outside buildings. This is done by emptying containers of water or by adding Abate larvicide or biological control agents e.g. predators of larvae to stagnated water after raining. 5. Spraying insecticide to kill the adult females is also effective. This is done by the ministry of health immediately after case of outbreak being reported. This is more effective when water-based pyrethroid insecticide fogging formulations such as Resigen or Aqua-resigen is used when people may be more willing to open their houses to be sprayed compared with diesel-based insecticide. 6. People can prevent mosquito bites by wearing clothing that fully covers the skin, using mosquito netting while resting, and/or the application of insect repellent (DEET being the most effective). Mosquito bite is the only way the dengue virus can enter our body. 13.3 Cholera 13.3 Cholera 1. Cholera is an infection in the small intestine caused by the bacterium Vibrio cholerae which causes profuse, watery diarrhoea and vomiting. 2. It is endemic in parts of Asia, particularly India. In 1991 more than 16 000 people died worldwide from half a million cases of cholera. Improved treatment has reduced the death rate dramatically, but it is still a serious disease. The Causes and Symptoms of Cholera Causes 1. Cholera is caused by bacterium Vibrio cholerae (Figure 13.4). This comma-shaped motile bacterium can live in the gut of animals and also any natural environment. 2. The main source of infection is contaminated drinking water by faeces from a sufferer of the disease or a ‘carrier’. A carrier is an individual infected with vibrios who does not develop the typical symptoms of cholera. 3. Vibrio cholera multiplies in the intestine, releasing a powerful toxin called choleragen, which disrupts the functions of the epithelium so that salts and water leave the blood causing severe diarrhoea. The organisms can only multiply and flourish in the human intestine, although they can survive outside of the body. 2013/P2/Q15 2014/P2/Q20(b) STPM MM Pre-U STPM Text Biology Term 2 is written based on the latest syllabus made by the Malaysian Examinations Council (MEC). The book is well designed and organised with the following features to help students understand the concepts taught. Concept Map Provides an overall view of the concepts learnt in the chapter Bilingual Keywords A list of bilingual terms is provided STPM Scheme of Assessment Latest STPM scheme of Assessment starting 2012 Learning Outcomes A list of subtopics that students will learn in each chapter Past-year Questions tagging Enables students to know the topics of frequently tested in the exam
CHAPTER 10 166 Biology Term 2 STPM Chapter 10 Reproduction, Development and Growth Quick Check 1 1. Absolute growth rate = Final measurement – initial measurement —————————————————————— initial measurement = unit time Relative growth rate = Final measurement – initial measurement —————————————————————— initial measurement = unit time or = Final measurement – initial measurement —————————————————————— initial measurement = 100% Quick Check 2 1. This is because of the body of arthropods such as crab is completely covered by the shell and growth can only occur after ecdysis when the shell is soft. The body then increases in size, followed by gain in weight. After some time, the process is repeated, especially during metamorphosis. This will produce intermittent growth. After the arthropod becomes adult, ecdysis stops and it finally dies, producing limited growth. On the other hand, the shell of molluscs such as snail does not completely cover the whole body. The mantle that produces the shell adds in new substances to the shell at the growing periphery. It produces a continuous and unlimited growth. 2. Allometric growth produces a change in the form of the body compared to isometric growth. This change in form allows flexibility in adaptation to the environment as the young develops or metamorphosises. The larva and adult may feed on different food, thus lessen competition between the young and adult. Revision Exercise 10 Objective Questions 1. D 2. B 3. C 4. A 5. A 6. C 7. B 8. B 9. A 10. B 11. D 12. A 13. D 14. A 15. D 16. C 17. D 18. A Structured Questions 1. (a) Cotyledon, plumule, radicle and embryo. (b) The outer coat of maize grain is the pericarp formed from fusion of the ovary wall and integuments. (c) Maize grain has endosperm whereas soya bean has no endosperm. Maize grain has one cotyledon whereas soya bean has two cotyledons. Maize grain has coleoptile and coleorhiza whereas soya bean has no such structures. Maize grain has aleurone layer whereas soya bean has no such layer. (d) Seed is formed after the triploid endosperm primary nucleus divides repeatedly to form many nuclei and then cells to supply food for the embryo. The zygote divides first, forming a row of cells, then forms the cotyledon. The embryo is protected by the integument, forming the testa and the seed. Fruit is formed when the ovary wall thickened and later becomes fleshy or fibrous to protect the seed. 2. (a) It is allometric growth. The growth of the head is not proportional to that of the body. In the foetal state, the growth of the head is faster than that of the body. However, the other parts of the body grow faster after birth. (b) It is because human growth occurs before adulthood and stops thereafter. After a period of maximum growth during adolescence, human reproduces and ages and no further growth is observed until death at about 75 years old. (c) Most of them such as corals and molluscs do not stop growing. They do not have a period of maximum growth and continue to grow and reproduce at the same time. (d) Insects. During their development or metamorphosis, they cannot grow continuously as the exoskeleton limits it. Only after ecdysis, when the exoskeleton is still soft can the body grow i.e. expand and increase in dry mass. Essay Questions 1. B J t )VNBOHSPXUIJTBMMPNFUSJDffiUIFHSPXUI of organs is not proportional to that of the body t "OFYBNQMFJTUIFHSPXUIPGUIFIFBEJT very fast during embryonic and infant stages then almost stops after four years old t 4P UIF JODSFBTF JO TJ[F PG UIF CPEZ JT accompanied with the change of shape t ćF JODSFBTF JO TVSGBDF BSFB JT OPU proportional to the square of the increase in length JJ t 'JTIHSPXUIJTJTPNFUSJDffi UIFHSPXUI PG organs is proportional to that of the body t 4P UIFJODSFBTFJOTJ[FPGUIFCPEZJTOPU accompanied with the change of shape t ćF JODSFBTF JO TVSGBDF BSFB JT proportional to the square of the increase in length t ćFJODSFBTFJOWPMVNFJTQSPQPSUJPOBMUP the cube of the increase in length ANSWERS CHAPTER 7 20 Biology Term 2 STPM Chapter 7 Gaseous Exchange Objective Questions 1. What is present in the wall of trachea? Epidermis Elastic fibres Smooth muscle A Present Present Present B Present Present Absent C Absent Present Present D Present Absent Absent 2. Which would be found in a bronchus wall? I cartilage cells II ciliated cells III exocytotic vesicles A I and II only B I and III only C II and III only D I, II and III 3. What is the main function of cilia which line the respiratory surface? A To prevent the lungs from dehydration by providing mucus B Move the mucus away from the lungs C Lubricate the bronchi to ease the air flow into the lungs D Moisten the trachea 4. Which correctly shows the areas of the respiratory tract that contain cartilage, smooth muscle, goblet cells and cilia? Cartilage Smooth muscle Goblet cells Cilia A Bronchus, bronchiole Alveoli, bronchiole Bronchus, alveoli Bronchus, bronchiole B Trachea, bronchus Bronchiole, alveoli Bronchus, bronchiole Trachea, bronchus C Trachea, bronchiole Trachea, bronchus Trachea, alveoli Bronchiole, alveoli D Trachea, bronchus Trachea, bronchus Bronchus, bronchiole Trachea, bronchiole 5. The diagram shows a magnified section through a small part of the lung tissue. 1 2 3 4 What are 1, 2, 3 and 4? 123 4 A Alveolar epithelial cell Macrophage Lumen of alveolus Blood capillary wall B Blood capillary wall Alveolar epithelial cell Blood plasma Phagocyte C Wall of bronchiole Arteriole wall blood Lumen of bronchiole Capillary wall D Alveolar epithelial cell Blood capillary wall Lumen of alveolus Macrophage 6. The diagram shows an alveolus with an associated blood capillary. The arrows indicate the direction of blood flow. A B C D Which part has the lowest oxygen concentration? 7 STPM PRACTICECHAPTER 8 40 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants 4. Prevention of hypertension is the same as in the case of atherosclerosis i.e. by avoiding high calorie and salty food, smoking, alcohol and maintaining a healthy lifestyle through exercise. Myocardial infarction 1. Myocardial infarction is a form of heart attack in which the coronary artery is blocked resulting in the death of a part of heart tissue as no oxygen is sent there. This blockage can be caused by atherosclerosis or embolus. 2. It results in the following: (a) Scar tissue is formed in the heart, the heart is weakened and it is prone to a second attack. (b) The heart cannot function normally and the person is weakened, as supply of blood to the body is not good. (c) Blood clotting called thrombosis tends to occur in the weakened heart. The moving clotted blood called embolus may block artery in the brain, causing stroke, block coronary artery which can result in another myocardial infarction or block any artery, causing ischemia. (d) Severe myocardial infarction causes instant death as too big a part of the heart muscle is without oxygen. 3. Causes and prevention of myocardial infarction are the same as those of atherosclerosis. Most people may show the first sign of impending myocardial infarction. This sign is associated with the gradual blockage of coronary artery or its branches due to atherosclerosis. The usually sign is pain in the chest called angina pectoris due to lack of oxygen in the heart muscle. The other sign is short of breath during exercise. The percentage blockage of the coronary artery and its branches can be determined by C.T. (Computed tomography) or MRI (Magnetic resonance imaging scanning) in the hospital. Knowledge of the percentage of blockage will enable cardiac surgeon to recommend corrective surgery to prevent myocardial infarction. An embolus is most often a piece of a thrombus that has broken free and is carried towards the brain by the bloodstream. In medicine, ‘ischemia’ is a restriction in blood supply to tissues, causing a shortage of oxygen and glucose needed by cellular metabolism (to keep tissue alive). Info Bio Info Bio Quick Check 1 1. Why are the walls of the heart of different thickness? 2. How does the heart of a foetus differ from that of an adult? 3. Why is the age of people getting infected with cardiovascular diseases getting younger? Exam Tips Remember the meaning, causes and prevention of arteriosclerosis, hypertension and myocardial infarction. CHAPTER 7 Biology Term 2 STPM Chapter 7 Gaseous Exchange (b) From the graph above, calculate the normal breathing rate per minute. [3] (c) (i) What is the lung volume that cannot be determined by the spirometer trace? [1] (ii) State a reason why the volume in (c)(i) cannot be determined from the trace. [1] 2. The diagram below shows the oxygen dissociation curves of myoglobin, mother haemoglobin and foetal haemoglobin. Partial pressure of O2/ mm Hg 50 50 X Y Z 100 Saturation of O2 (HbO8) / % 100 (a) Label curves X, Y and Z. [3] (b) Comparing curves X and Y, what is the physiological significance of their difference? [2] (c) Comparing curves Y and Z (d) What is the effect of carbon dioxide on the oxygen dissociation curve of the mother? Explain the effect and its significance. [3] Essay Questions 1. (a) Explain how haemoglobin is adapted for oxygen transport in our body. [7] (b) Explain how carbon dioxide is transported in the blood. [8] 2. (a) Explain the role of abscisic acid and potassium ions in controlling water loss by the stomata under the condition of water stress. [10] (b) Describe what happens to the various forms of carbon dioxide which are transported by the blood in the lungs. [5] MMM STPM Practice A variety of examination-type questions to check students’ understanding of the chapters learnt Answers Complete answers are provided Exam Tips Provides helpful tips for students in answering exam questions Quick Check Provides short questions for students to test their understanding of the concepts learnt in the subtopics Online Quick Quiz Scan QR code for self-assessment at the end of each chapter Info Bio Provides extra information that relates to the subtopics learnt
294 Biology Term 2 STPM Glossary Biology Term 2 Glo Index A Abscisic acid 98 Action potential 68 Aedes aegypti 255 Aldosterone 203 Anopheles 271 Antibody 221 Antigen 220 Antigen-presenting cell 227 Apoplast pathway 46 Arteriosclerosis 37 Atherosclerosis 37 Auxin 94 B B cells 229 C Cardiac cycle 30 Chemoreceptors 13 Corpus luteum 125 Cowper’s gland 127 Curare 87 Cytokinins 98 D Deamination 187 E Ecdysis 159 Epigeal germination 148 Epitope 221 Ethephon 107 Ethylene 99 F Filtration pressure 197 G Gibberellins 96 H Haemoglobin 6 Halophytes 207 Hepatocytes 176 Human Immunodeficiency Virus (HIV) 238 Hydrogen carbonate ions 7 Hypertension 39 Hypogeal germination 148 I Immunoglobulins 222 Indoleacetic acid (IAA) 94 K Kinetin 98 L Lymphocytes 224 M Macrophages 226 Menstrual cycle 130 Metamorphosis 160 Mycobacterium tuberculosis 266 Myocardial infarction 40 N Nephron 195 Neuromuscular junction 76 O Oogenesis 124 Opsonisation 227 Oxygen dissociation curve 8 P Parturition 139 Perforin 231 Photoperiodism 102 Phytochrome 101 Pinocytosis 198 Plasmodium 271 Purkyne tissue 34 S Symplast pathway 46 T T cells 227 Thermoregulation 174 Transamination 185 Transpiration pull 49 Turgor pressure 18 R Resting potential 67 Root pressure 47 S Sarcomere 77 Spermatogenesis 122 V Vacuolar pathway 46 Vas deferens 127 Vibrio cholerae 265 X Xenophytes 208 Z Zeatin 98 292 Agglutination Clumping of bacteria or viruses together to form a bigger aggregate Aldosterone Involves in homeostatic control of sodium ion in the blood Antibody Globular glycoprotein that acts against a particular antigen Antigen A protein in which the body recognizes as foreign or non-self B cells Lymphocytes that mature in the bone marrow and then spread throughout the body. Cardiac cycle Sequence of events which makes up one heartbeat which consists of one systole and one diastole Cerebral ischemia Oxygen deficiency in cerebrum Chemoreceptors Receptor cells that can be stimulated by chemicals Cholera Infection in the small intestine caused by the bacterium Vibrio cholera Deamination Conversion of an amino acid to a keto acid by the removal of the amine functional group Dengue An infectious disease transmitted by a vector, Aedes aegypti mosquito Diastole The event that occurs when the heart muscle relaxes. Double fertilisation A process in the flowering plant life cycle in which there are two fertilisations; one fertilisation results in the formation of zygote, whereas the second results in the formation of endosperm. Epitope A small specific part of a larger antigen, which is capable to bind with a specific antibody. Gluconeogenesis Synthesis of glucose from non-carbohydrate sources such as lactate, glycerol, fatty acids and some amino acids. Glycogenesis Formation of glycogen from glucose. This process is under the control of insulin. Glycogenolysis Breakdown of glycogen to glucose to provide immediate energy and to maintain blood glucose levels. Haemoglobin A respiratory pigment found in red blood cells to transport oxygen from lungs to the tissues Halophytes Plants that can live in soil with more than 0.5% of salt. Hepatomegaly Enlarged liver Incubation period A period of time between exposure and onset of symptoms ffi STPM Model Paper (964/2) Section A [15 marks] Bahagian A [15 markah] Answer all questions in this section. Jawab semua soalan dalam bahagian ini. 1. Which is true about the parts of the gas exchange system? Bahagian manakah adalah benar bagi sistem pertukaran gas? Part Bahagian Cartilage Rawan Cilia Silia Goblet cell Sel labu Smooth muscle Otot licin A Trachea Trakea Present Ada Present Ada Present Ada Absent Tiada B Alveolus Alveolus Absent Tiada Present Ada Absent Tiada Absent Tiada C Bronchiole Bronkiol Absent Tiada Present Ada Present Ada Absent Tiada D Bronchus Bronkus Present Ada Present Ada Present Ada Present Ada 2. Which feature of xylem vessels allows them to have reduced resistance to water movement? Yang manakah ciri salur xilem yang membenarkannya mempunyai rintangan pengaliran air yang kurang? A With companion cells supplying energy Dengan sel rakan bagi pembekalan tenaga B Lignin forms an incomplete secondary wall growth Lignin membentuk dinding sekunder tidak sempurna C There are no cross walls between vessel elements Dengan ketiadaan dinding melintang di antara unsur salur D Vessel elements join to form narrow tubes Unsur salur bergabung menjadi tiub sempit 3. Different substances, such as sucrose and amino acids, can move in different directions in the phloem sieve tubes. Which explanation is correct? Bahan seperti sukrosa dan asid amino dapat bergerak ke arah berlainan dalam tiub tapis floem. Keterangan yang manakah yang betul? A Both active transport and mass flow occur in each individual phloem sieve tube. Kedua-dua pengangkutan aktif dan pengaliran berkelompok berlaku dalam setiap tiub tapis floem individu B Active transport occurs in some phloem sieve tubes and mass flow occurs in other phloem sieve tubes. Pengangkutan aktif berlaku di dalam sesetengah tiub tapis floem dan pengaliran berkelompok di dalam tiub tapis floem yang lain. C Mass flow occurs in both directions at the same time in each individual phloem sieve tube. Pengaliran berkelompok berlaku di keduadua hala dalam setiap tiub tapis floem individu. D Mass flow occurs in different directions in different phloem sieve tubes at the same time. Pengaliran berkelompok berlaku di keduadua hala dalam tiub tapis floem yang berlainan pada masa yang sama. MZ STPM Model Paper (964/2) A model paper that follows the latest STPM exam format is provided for practice Index Provides a list of terms to enable easy and direct access to the subtopics. Glossary Gives a list of important terms to ease the students’ understanding of their meanings.
Analysis of STPM Papers (2015 – 2017) Chapter 2015 2016 2017 A B C A B C A B C 7 Gaseous Exchange 21–2––3–1 8 Transport in Animals and Plants 3 1 – 1 1 0.5 1 – 1 9 Control and Regulation 3––3–13–1 10 Reproduction, Development and Growth 3 1 2 3 – 1.5 2 1 – 11 Homeostasis 1––2––3–1 12 Immunity 1––21–1–– 13 Infectious Diseases 2–12––11– Total 15 3 3 15 2 3 14 2 4 Z
vi STPM Scheme of Assessment Term of Study Paper Code and Name Theme / Title Type of Test Mark (Weighting) Duration Administration First Term 964/1 Biology Paper 1 Biological Molecules and Metabolism Written test Section A 15 compulsory multiple-choice questions to be answered. Section B 2 compulsory short structured questins to be answered. Section C 2 out of 3 essay questions to be answered. All questions are based on topics 1 to 6. 60 (26.67%) 15 15 30 1—1 2 hours Central assessment Second Term 964/2 Biology Paper 2 Physiology Written test Section A 15 compulsory multiple-choice questions to be answered. Section B 2 compulsory short structured questins to be answered. Section C 2 out of 3 essay questions to be answered. All questions are based on topics 7 to 13. 60 (26.67%) 15 15 30 1—1 2 hours Central assessment vi
vii Term of Study Paper Code and Name Theme / Title Type of Test Mark (Weighting) Duration Administration Third Term 964/3 Biology Paper 3 Ecology and Genetics Written test Section A 15 compulsory multiple-choice questions to be answered. Section B 2 compulsory short structured questions to be answered. Section C 2 out of 3 essay questions to be answered. All questions are based on topics 14 to 19. 60 (26.67%) 15 15 30 1—1 2 hours Central assessment 964/5 Biology Paper 5 Written Practical Test 3 structured questions with diagram/graph/ table to be answered. 45 (20%) 1—1 2 hours Central assessment First, Second and Third Terms 964/4 Biology Paper 4 Biology Practical School-based Assessment of Practical 15 compulsory experiments to be carried out. 25 (20%) Throughout the three terms School-based assessment vii
CONTENTS &KDSWHU ttttttttttttttttttttttttttttttttttttttttttttt t 7 Gaseous Exchange 1 7.1 Gaseous Exchange in Humans 2 7.2 Breathing cycle 13 7.3 Gaseous Exchange in Plants 16 STPM Practice 7 20 QQ 24 Answers 24 &KDSWHU ttttttttttttttttttttttttttttttttttttttttttttt t 8 Transport in Animals and Plants 27 8.1 Transport System in Mammals 28 8.2 Transport System in Vascular Plants 44 STPM Practice 8 55 QQ 59 Answers 59 &KDSWHU ttttttttttttttttttttttttttttttttttttttttttttt t 9 Control and Regulation 62 9.1 Nervous System 63 9.2 Hormones 89 STPM Practice 9 108 QQ 113 Answers 113 &KDSWHU ttttttttttttttttttttttttttttttttttttttttttttt t Reproduction, Development 10 and Growth 120 10.1 Sexual Reproduction in Humans 121 10.2 Sexual Reproduction in Flowering Plants 141 10.3 Seed Germination 147 10.4 Growth Curves and Patterns of Growth 151 STPM Practice 10 162 QQ 165 Answers 166 &KDSWHU ttttttttttttttttttttttttttttttttttttttttttttt t 11 Homeostasis 168 11.1 Importance of Homeostasis 169 11.2 Liver 175 11.3 Osmoregulation in Mammals 194 11.4 Osmoregulation in Plants 205 STPM Practice 11 211 QQ 214 Answers 214 &KDSWHU ttttttttttttttttttttttttttttttttttttttttttttt t 12 Immunity 218 12.1 Immunity 219 12.2 Development of Immunity 230 12.3 Concept of Self and Non-self 235 12.4 Immune Disorder 242 STPM Practice 12 245 QQ 248 Answers 248 &KDSWHU ttttttttttttttttttttttttttttttttttttttttttttt t 13 Infectious Diseases 252 13.1 Infectious Disease 253 13.2 Dengue 256 13.3 Cholera 264 13.4 Tuberculosis (TB) 267 13.5 Malaria 272 STPM Practice 13 278 QQ 281 Answers 281 STPM Model Paper (964/2) 283 Answers 289 Glossary 292 Index 294 ZMMM
CHAPTER GASEOUS EXCHANGE Concept Map 7 Gaseous Exchange Gaseous exchange in human Breathing cycle Structures involved Trachea Stomata Bronchus Bronchiole Alveolus Structure of haemoglobin Transport of O2 and CO2 O2 dissociation curves Bohr’s effect Foetal haemoglobin Myoglobin Gaseous exchange in plants Mechanism of breathing control Lung volumes Mechanism of opening and closing Structure and functions Haemoglobin Tidal volume Inspiratory reserve volume Expiratory reserve volume Vital capacity Residual volume Total lung capacity Bilingual Keywords Exchange – Pertukaran Breathing – Pernafasan Inhalation – Tarik nafas Exhalation – Hembus nafas Lung – Peparu Saturated – Ketepuan Lateral – Sisi Diaphragm – Diafragma Relaxation – Pengenduran Turgid – Segah
Learning Outcomes CHAPTER 7 2 Biology Term 2 STPM Chapter 7 Gaseous Exchange Language Check Gaseous Exchange 1. Gaseous exchange occurs in all respiring cells. During cell respiration, oxygen enters the cell and carbon dioxide is released from the cell. 2. Humans, like many land animals, use a pair of lungs for gaseous exchange. The lungs are efficient gaseous exchange organs to absorb oxygen and release carbon dioxide. 3. Plants obtain the gases they need through their leaves. Plants require carbon dioxide for photosynthesis and oxygen for respiration. During the day, carbon dioxide diffuses into the plant leaves for photosynthesis and oxygen produced from photosynthesis diffuses out of the plant leaves. At night, oxygen diffuses into the plant leaves for respiration and carbon dioxide produced from respiration diffuses out of the plant leaves. 7.1 Gaseous Exchange in Humans 7.1 Gaseous Exchange in Humans The Structure of Human Respiratory System 1. The structures for gaseous exchange in a human are lungs, as well as trachea, bronchi, bronchioles and alveoli (Figure 7.1). The most important are the two lungs. Each lung is filled with many tiny air spaces called alveoli or air sacs. Nasal cavity Oral cavity Pharynx Larynx Trachea Bronchiole Lung Diaphragm Ribs Bronchi Figure 7.1 The human respiratory system ( YVUJO\Z¶ZPUN\SHY Bronchi – plural ) S]LVS\Z¶ZPUN\SHY (S]LVSP¶WS\YHS :[\KLU[ZZOV\SKILHISL[V! H V\[SPUL[OLZ[Y\J[\YL VMO\THUYLZWPYH[VY` Z`Z[LTPUJS\KPUN[OL TPJYVZJVWPJZ[Y\J[\YLVM [OL^HSSVMHUHS]LVS\Z" I KLZJYPIL[OLZ[Y\J[\YLVM OHLTVNSVIPU" J L_WSHPU[OL[YHUZWVY[ VMV_`NLUHUKJHYIVU KPV_PKLPUISVVK" K L_WSHPU[OLV_`NLU KPZZVJPH[PVUJ\Y]LZVM OHLTVNSVIPUT`VNSVIPU HUKMVL[HSOHLTVNSVIPU" L L_WSHPU[OL)VOYLɈLJ[ and relate it to the V_`NLUKPZZVJPH[PVU J\Y]L
CHAPTER 7 3 Biology Term 2 STPM Chapter 7 Gaseous Exchange 2. Air can enter the body either through the nose or mouth. It is better to breathe through the nose because the structure of the nose allows the air to become warm, moist and filtered before it gets into the lungs. Inside the nasal cavity are some thin bones called turbinal bones which are covered with a moist and thin layer of cells. Some of these cells make liquid containing water and mucus which evaporates into the air in the nose and moistens it. Other cells have very tiny hairs called cilia to prevent large particles from entering the lungs. 3. From nasal cavity, the air then passes into the throat or pharynx. The pharynx is at the entrance of the trachea. Food is prevented from entering the larynx by epiglottis which bends to close the entrance when food passes through. Just below the epiglottis is the voice box or larynx. This contains the vocal cords. The vocal cords can be tightened by muscles to make sounds when air passes over them. 4. The air passes through the larynx into the windpipe or trachea. The trachea has C-shaped rings of cartilage, dorsally incomplete, to keep it hollow for unhindered passage of air. The innermost layer is lined by pseudo-stratified cilliated epithelium, which has cilia and mucussecreting goblet cells. It has mucous glands beneath the epithelium. The mucus traps bacteria and airborne particles. The cilia sweep the debris-laden mucus toward the mouth which then is expelled or swallowed. The trachea wall also contains layers of smooth muscles, collagen and elastic tissues. Connective tissue Smooth muscle Sub-mucosa + mucous glands Ciliated epithelium Lumen Cartilage Trachea 5. At the end of the trachea, it branches into two, right and left bronchi going into each lung. The bronchi also have cartilage rings which are diminishing in sizes as they branch out into smaller bronchi. Similarly, the bronchi have ciliated epithelium, layers of smooth muscles, collagen and elastic tissues. 6. From the end of each smallest bronchus, it is further branched into smaller bronchioles with no cartilage. The bronchioles have ciliated epithelium, smooth muscles and elastic tissues. The wall of the ;OLPUULYTVZ[SH`LYVM[YHJOLH PZSPULK^P[OJPSPH[LKWZL\KV Z[YH[PÄLKJVS\TUHYLWP[OLSP\T ;OLLWP[OLSP\THSZVJVU[HPU NVISL[JLSSZ[OH[WYVK\JL HUKYLSLHZLT\J\Z;OL T\J\ZOLSWZ[V[YHWK\Z[HUK TPJYVVYNHUPZTZ Info Bio INFO /\THU9LZWPYH[VY` :`Z[LT
CHAPTER 7 4 Biology Term 2 STPM Chapter 7 Gaseous Exchange bronchioles can expand and contract. Each bronchiole ends up with an air sac, the alveolus, whose outer wall is attached to each other. Connective tissue Smooth muscle Ciliated epithelium Bronchus Cartilage Connective tissue Smooth muscle Bronchiole Ciliated epithelium 7. The walls of the alveoli are the respiratory surface which is surrounded by a network of capillaries (Figure 7.2). Oxygen diffuses across the walls of the alveoli into the blood and carbon dioxide diffuses from the blood into the walls of the alveoli. Capillaries Alveoli Bronchiole Pulmonary venule Oxygenated blood to the heart Deoxygenated blood from the heart Pulmonary arteriole Oxygenated blood to the heart Interior of alveolus CO2 O2 Deoxygenated blood from the heart Blood plasma Blood cell Cells of alveolus Figure 7.2 The structure of alveoli and gaseous exchange in an alveolus
CHAPTER 7 5 Biology Term 2 STPM Chapter 7 Gaseous Exchange 6. The alveolar wall is made up of very thin squamous epithelial cell of about 1.0 μm thick. The thinness cuts down diffusion distance and ensures that oxygen and carbon dioxide molecules can diffuse very easily across it. 7. The alveolar walls have a large surface area. The total surface area of the alveolar walls in both lungs comprises an area of 50-100 m² (about as large as a tennis court and 50 times larger than the body surface). The large surface area makes the total volume of air that can get into the alveoli bigger. For example, the total volume of air that can get into the alveoli of a young man is around 4.6 litres. 8. The alveolar walls have elastic fibres found beneath the squamous epithelium. These fibres are produced by fibrocytes to keep the walls elastic. This enables the alveoli to recoil during exhalation so that the alveoli are always supplied with fresh air. 9. The alveolar wall cells produce water and phospholipid to keep the surface moist. This enables both oxygen and carbon dioxide to dissolve in the liquid before diffusing across the wall. Phospholipid acts as surfactant to prevent the wall from collapsing due to high surface tension of water. 10. The alveolar wall contains macrophages. Macrophages come out of the capillaries especially when the alveoli are infected with viruses or bacteria. The macrophages also engulf dust beside microorganisms on the inner surfaces of the alveoli. Alveolar air space Alveolar wall Capillary Fibre-secreting cell Elastic fibres Red blood cell Figure 7.3 Section through an alveolus The structure of system human respiratory 1. Trachea – with ciliated epithelium, goblet cells & mucous glands [V[YHWIHJ[LYPH sweep them out – with cartilage, smooth muscles, collagen & elastic tissue MVYHPY[VÅV^PU[V bronchi from throat 2. Bronchus – with ciliated epithelium, cartilage, smooth muscles, collagen & elastic tissue MVYHPY[VÅV^PU[V bronchioles from trachea 3. Bronchiole – with ciliated epithelium, smooth muscles & elastic tissue MVYHPY[VÅV^PU[V alveoli from bronchioles 4. Alveolus – thin wall of simple squamous epithelium, – with many capillaries around – large surface area ¶ ^P[OLSHZ[PJÄIYLZ – surfactant + macrophage MVYNHZLV\ZL_JOHUNL Summary
Exam Tips CHAPTER 7 6 Biology Term 2 STPM Chapter 7 Gaseous Exchange The Structure of Haemoglobin 1. Haemoglobin is a respiratory pigment, which is found in the red blood cells to transport oxygen from the lungs to the tissues. The respiratory pigment combines with oxygen and greatly increases the capacity of blood to transport oxygen. 2. Haemoglobin is a globular protein. It is made up of four polypeptides chains. Two of these polypetides chains make an identical pair, and are called _ chains containing 141 amino acids each. The other two make a different identical pair and are called ` chains containing 146 amino acids each. Each chain has a tertiary structure. 9LTLTILY[OLZ[Y\J[\YL VMOHLTVNSVIPU[OH[PZH JVUQ\NH[LKNSVI\SHYWYV[LPU HUKOHZHX\H[LYUHY` Z[Y\J[\YL Fe2+ N N O2 N N Bound to the chain on one side Haem group chain chain Can bind with O2 on the other side Fe Fe Fe Fe chain chain Figure 7.4 Components of a haemoglobin molecule 3. The haemoglobin molecule is nearly spherical. The four polypeptide chains pack closely together, where their hydrophobic R groups pointing in towards the centre of the molecule and their hydrophilic ones pointing outwards. The bonds involved in its tertiary and quarternary structures are disulfide, ionic, hydrophobic and hydrogen bonds. The outward-pointing hydrophilic R groups on the surface of the molecule are important in maintaining its solubility. 4. Each polypeptide chain is bonded to a haem group. Each haem group contains an iron ion, Fe2+. One oxygen molecule, O2 , can bind with each iron ion. So, a complete haemoglobin molecule, with four haem groups, can bind with four oxygen molecules at a time. This forms a molecule called oxyhaemoglobin, which is bright red in colour. This occurs in the lungs. Hb + 4O2 ±A HbO8 Haemoglobin Oxygen Oxyhaemoglobin 5. In the tissues, oxyhaemoglobin releases its oxygen to the cells. Haemoglobin without oxygen is purplish red. Deoxgenated blood is returned to the right side of the heart to be pumped into the lungs for oxygenation. Haemoglobin structure 1. 4 small units, 2 _– and 2 `-polypeptides 2. Spherical globular protein 3. Soluble in water with hydrophilic groups outside, hydrophobic inside 4. Bonded together as quaternary structure 5. )VUKZPU]VS]LKHYLKPZ\SÄKL ionic, hydrophobic & H 6. Each unit with haem as prosthetic group 7. Haem has Fe2+ ion to bind with O2 8. Each molecule carries 4 O2 9. Oxyhaemoglobin is bright red Summary INFO 7O`ZPVSVN`VM /HLTVNSVIPU
CHAPTER 7 7 Biology Term 2 STPM Chapter 7 Gaseous Exchange Transport of Oxygen and Carbon Dioxide in Blood (a) Transport of oxygen 1. About 98.5% of oxygen is transported by red blood cells in blood. Only a small amount is carried as a physical solution (0.31 ml per 100 ml) because oxygen dissolves in the plasma. The amount of oxygen in the plasma is easily affected by other solutes such as glucose and mineral ions. 2. Red blood cells contain the pigment haemoglobin which carries the oxygen. This pigment makes the blood red in colour. 3. In the lungs, oxygen diffuses from the alveoli into the blood in the capillaries because the blood has a lower partial pressure of oxygen. The oxygen diffuses into the red blood cells, where it binds to each of the Fe(II) ion in the four haem groups in the haemoglobin (Hb) to form oxyhaemoglobin (HbO8 ). So, each haemoglobin can carry four oxygen molecules. 4. The oxygenated blood is transported into the heart from the lungs by pulmonary veins and pumped out of the heart through the aorta and arteries to supply all parts of the body with oxygenated blood. 5. When it reaches a tissue which needs oxygen, the oxyhaemoglobin releases its oxygen to the tissue due to lower partial pressure of oxygen in that tissue. This is due to the hydrogen ions released when carbon dioxide is converted into carbonic acid (Figure 7.5). The hydrogen ions react with oxyhaemoglobin thus releasing the oxygen. 6. The oxyhaemoglobin then becomes haemoglobinic acid. The blood is said to be deoxygenated. The deoxygenated blood returns to the right side of the heart before it is pumped into the lungs for oxygenation. (b) Transport of carbon dioxide 2010, 2016 1. About 85% of the carbon dioxide transported by the blood is carried as hydrogencarbonate ions, HCO3 – . 2008 (a) Carbon dioxide can be converted into hydrogencarbonate ion as shown in Figure 7.5. CO2 H2CO3 Carbonic anhydrase Plasma H2O H+ HbO2 Erythrocyte + HCO3 – CI– HHb + O2 O2 HCO3 – Figure 7.5 How CO2 is converted into HCO3 – in an erythrocyte
CHAPTER 7 8 Biology Term 2 STPM Chapter 7 Gaseous Exchange (b) Carbon dioxide diffuses into the red blood cells and reacts with water to form hydrogen carbonate or carbonic acid. This process is catalysed by carbonic anhydrase. Hydrogen carbonate ionises easily to form hydrogen ion and hydrogen carbonate ion. The hydrogencarbonate ions then diffuse out of the red blood cell into the blood plasma, where they are carried in plasma solution. (c) The change in the charge within the red blood cells is balanced by chloride ions that diffuse in. This is known as the chloride shift. The hydrogen ions react with oxyhaemoglobin to release the oxygen and form haemoglobinic acid. (d) When blood reaches the lungs, the process is reversed and carbon dioxide diffuses into the air in the alveoli. The hydrogencarbonate ions and hydrogen ions recombine to form carbon dioxide molecules once more also catalysed by carbonic anhydrase. 2. About 5% of carbon dioxide simply dissolve in the blood plasma and is carried as carbon dioxide molecules. 3. About 10% of carbon dioxide is carried as carbaminohaemoglobin. (a) Carbon dioxide can combine directly with the terminal amine groups (–NH2 ) of the haemoglobin polypeptides, forming a compound called carbaminohaemoglobin. HHbNH2 + CO2 ±±A HHbNHCOOH Haemoglobin carbaminohaemoglobin (b) The amount of carbon dioxide which can be carried this way depends on the amount of oxygen already being carried by the haemoglobin. The lesser the amount of oxygen that is being carried by the haemoglobin, the more carbon dioxide can be carried by the haemoglobin. (c) When blood reaches the lungs, the reactions described above go into reverse. The relatively low concentration of carbon dioxide in the alveoli compared with that in the blood causes carbon dioxide to diffuse from the blood into the air in the alveoli, stimulating the carbon dioxide of carbaminohaemoglobin to leave the red blood cell. Oxygen Dissociation Curves of Haemoglobin, Myoglobin and Foetal Haemoglobin 2010 (a) Oxygen Dissociation Curve of Haemoglobin 1. The curve shows the percentage saturation of oxygen plotted against partial pressure of oxygen. It indicates the varying percentage of oxyhaemoglobin at different concentration of oxygen as partial pressure from 0 kPa to 13.3 kPa as in lungs with high vapour pressure. 2. The curve indicates the affinity of haemoglobin to oxygen. Loading up with oxygen when partial pressure of oxygen increases and unloading oxygen when partial pressure of oxygen decreases. 7HY[PHSWYLZZ\YLVMHU`NHZ$[V P[ZJVUJLU[YH[PVUPUHTP_[\YL VMNHZLZ^OPJOPUKP]PK\HSS` JVU[YPI\[LZWHY[PHSS`[VV]LYHSS WYLZZ\YL-VYL_HTWSL62 at ZLHSL]LSPZ ZVWHY[PHS WYLZZ\YLVM62 PZ—1 5 VMfffflTT /N$ffiTT/N fffflTT/N$R7HRPSVWHZJHS R7H$ffffiTT/N Info Bio 2013/P2/Q2 STPM
CHAPTER 7 9 Biology Term 2 STPM Chapter 7 Gaseous Exchange 3. When the first oxygen molecule is bound to a haemoglobin molecule, it changes the conformation of the haemoglobin molecule and facilitates the second and third oxygen to bind. The binding of the fourth oxygen is not facilitated so there is a slight delay. This is also called molecule cooperation. 4. The facilitation of one molecule of oxygen for the binding of the second and third oxygen gives rise to the S-shape sigmoid curve of the oxygen dissociation curve as shown in Figure 7.6. Percentage saturation of haemoglobin with oxygen 100 90 80 70 60 50 40 30 20 10 0 0246 Partial pressure of oxygen / kPa 8 10 12 14 13 Part of the circulation Partial pressure of oxygen / kPa Percentage saturation of haemoglobin Capillaries in the lungs 98 Capillaries in muscle tissue at rest 5 70 Capillaries in muscle during strenuous exercise 2.0 20 Figure 7.6 Dissociation curve of haemoglobin (a) The curve shows that at low partial pressure of oxygen (2 kPa), the percentage saturation of haemoglobin is very low (20%), but when there is an increase from 2 kPa to 5 kPa, the saturation increase steeply from 20% to 70%. From partial pressures of oxygen 5 kPa to 13 kPa, the percentage saturation of haemoglobin increases from 70% to 98%. This shows the saturation is leveling off. A maximum of 98% is achieved in the lungs because the partial pressure of vapour is high. (b) Up to an oxygen partial pressure of around 2 kPa, an average of only one oxygen molecule is combined with each haemoglobin molecule. Once this oxygen molecule is combined, the whole haemoglobin molecule is slightly distorted. The distortion makes it easier for a second oxygen to combine with a second haem group on the haemoglobin. This in turn makes it easier for a third oxygen molecule to combine with a third haem group. It is then not so easy for the fourth. So, the curve rises not so steeply but forms a plateau. (c) Over this steep gradient part of the curve, a small change in the partial pressure of oxygen causes a very large change in the amount of oxygen which is carried by the haemoglobin. Exam Tips 9LTLTILYOV^ OHLTVNSVIPUPZHKHW[LK[V [YHUZWVY[62
CHAPTER 7 10 Biology Term 2 STPM Chapter 7 Gaseous Exchange 5. The sigmoid shape of the curve provides a physiological advantage for haemoglobin to transport oxygen. During physical exercise when the partial pressure of oxygen changes from 6 to 3 kPa, almost 40% of oxygen is released for the active muscle tissue. (b) Oxygen Dissociation Curve of Myoglobin 2008 1. Myoglobin, like haemoglobin, is a red pigment which combines reversibly with oxygen. It is not found in the blood, but inside the muscle cells. 2. Myoglobin is a monomeric globular protein and it gives red colour to the muscles or meat. It is soluble in the cytoplasm of the muscle fit cells or fibres. 3. Each myoglobin molecule is made up of only one polypepetide, rather than the four as in a haemoglobin molecule. It has just one haem group, and can combine with just one oxygen molecule. The primary structure of the polypeptide is different from that of haemoglobin. However, once combined, the oxymyoglobin molecule formed is very stable, and will not release its oxygen unless the partial pressure of oxygen around it is very low indeed. 4. The oxygen dissociation curve of myoglobin (Figure 7.7) is on the extreme left of haemoglobin. It shows a higher percentage saturation with oxygen than haemoglobin at low partial pressure of oxygen. At partial pressure of 2 kPa of oxygen, its saturation is almost 95%. It only releases its oxygen when partial pressure of oxygen is less than 1 kPa of oxygen. 5. It also shows the steepest gradient compared with curves of adult and foetal haemoglobin when partial pressure of oxygen increases. Therefore, its affinity for oxygen is highest compared to that of foetal or adult haemoglobin. 6. This is due to the function of myoglobin to store oxygen in muscles. It only gives out its oxygen under extreme low partial pressure of oxygen in the active contracting muscle. This helps to supply oxygen to the flight muscles of birds when they fly into high altitude. % saturation of haemoglobin Myoglobin Foetal haemoglobin Normal haemoglobin 100 80 60 40 20 2 0 4 6 Partial pressure of oxygen / kPa 8 10 12 14 Figure 7.7 Dissociation curves of various respiratory pigments 4`VNSVIPUVUS`NP]LZV\[P[Z V_`NLUH[H]LY`low partial WYLZZ\YLVMV_`NLUHZPU[OL JHZLVMIPYKÅ`PUNPUOPNO HS[P[\KLVY[OLT\ZJSLZ\ZPUN \WV_`NLUTVYL[OHU[OL OHLTVNSVIPUJHUZ\WWS` Info Bio 2014/P2/Q1 STPM
Summary STPM 2013/P2/Q1 CHAPTER 7 11 Biology Term 2 STPM Chapter 7 Gaseous Exchange (c) Oxygen Dissociation Curve of Foetal Haemoglobin 1. A developing foetus has to get all its oxygen from its mother’s blood through the placenta. The placenta is a place where oxygen can diffuse across from mother’s blood into the foetal blood. Oxygen arrives at the placenta in combination with haemoglobin. Oxygen is released as the partial pressure in the placenta is low (5 kPa). 2. The partial pressure of oxygen in the foetus’s blood is lower than that in the placenta and the adult’s blood. The oxygen diffuses from the mother's capilaries into the blood of the foetus at the placenta across a short diffusion distance. 3. Foetal haemoglobin combines more readily with oxygen than adult haemoglobin. Thus, foetal haemoglobin is said to have a higher affinity for oxygen than the adult haemoglobin. 4. A dissociation curve for foetal haemoglobin (Figure 7.8) shows that foetal haemoglobin always has higher saturation than adult haemoglobin at any oxygen partial pressure before getting fully saturated. The curve lies above the curve for adult haemoglobin. In the uterus where the partial pressure of oxygen is around 5 kPa, the foetal haemoglobin is almost saturated and supplies all the oxygen need of the foetus. It also means that the foetal haemoglobin would not easily lose its oxygen and it can transport oxygen efficiently for the foetal need. Percentage saturation Foetal haemoglobin Normal haemoglobin 100 80 60 40 20 0 2 4 6 Partial pressure of oxygen / kPa 8 10 12 14 Figure 7.8 Dissociation curves of adult haemoglobin and foetal haemoglobin The Bohr Effect 1. Bohr effect is the effect when the haemoglobin is exposed to higher carbon dioxide concentration and the dissociation curve is shifted to the right as shown in Figure 7.9. O2 dissociation curves of adult haemoglobin (a), foetal haemoglobin (b) and myoglobin (c) (a) (b) (c) 1.Gradient Steep Steeper Steepest 2.% saturation High Higher Higest 3. 98% saturation at 13.3 kPa 5 kPa 2 kPa 4.$IÀQLW\ for O2 High Higher Highest 5.Function VXSSO\ O2 from lungs to tissues Obtain O2 from placenta Store O2 in muscles Exam Tips 9LTLTILY[OLKPɈLYLUJLZ IL[^LLU[OL62 KPZZVJPH[PVU J\Y]LZVMMVL[\ZHUK TV[OLYHUKP[ZWO`ZPVSVNPJHS PTWVY[HUJL
CHAPTER 7 12 Biology Term 2 STPM Chapter 7 Gaseous Exchange The Bohr Effect 1) High pCO2 – Low pH 1 2) Normal pCO2 – Normal pH 3) Low pCO2 – High pH 100 80 60 40 20 90 70 50 30 10 2 0 4 6 pO2 (kPa) % saturation of blood with O2 8 10 2 3 Figure 7.9 +PZZVJPH[PVUJ\Y]LZVMOHLTVNSVIPUZOV^PUN[OLLɈLJ[VM*62 concentration 2. Bohr effect is caused by the carbon dioxide given out by active respiring cells. The carbon dioxide diffuses from the cells into blood plasma, then it diffuses into the red blood cells. 3. In the cytoplasm of the red blood cells, there is an enzyme, carbonic anhydrase. This enzyme catalyses the formation of carbonic acid which dissociates to form hydrogen ion and hydrogencarbonate ion. Carbonic anhydrase CO2 + H2 O H2 CO3 Carbon dioxide water carbonic acid H2 CO3 H+ + HCO3 – Carbonic acid hydrogen ion hydrogencarbonate ion 4. The hydrogen ions readily combine with oxyhaemoglobin, releases the oxygen which it is carrying and forming haemoglobinic acid, HHb. Hydrogen ions weaken the bonds between oxygen and haemoglobin, and lower the affinity of haemoglobin to oxygen. 5. The presence of a high partial pressure of carbon dioxide causes haemoglobin to release more oxygen. This is called the Bohr effect, after Christian Bohr who discovered it in 1904. 6. This is an adaptation as it has a physiological advantage. Cells that produce a lot of carbon dioxide are actively respiring and also requires the greatest amount of oxygen. 7. Bohr effect ensures that haemoglobin supplies enough oxygen to active respiring cells. 8. A high concentration of hydrogen ions means having a low pH. By removing the hydrogen ions from solution, haemoglobin is acting as buffer to maintain the pH of the blood close to neutral. So, Bohr effect ensures excess carbon dioxide or hydrogen ions are removed. Quick Check 1 1. Why do higher animals have haemoglobin in the erythrocytes instead of dissolved in the plasma? 2. Can oxygen and carbon dioxide be carried at the same time in the blood?
Learning Outcomes CHAPTER 7 13 Biology Term 2 STPM Chapter 7 Gaseous Exchange :[\KLU[ZZOV\SKILHISL[V! (a) explain the control of IYLH[OPUNTLJOHUPZT including the role of JOLTVYLJLW[VY" I KLÄUL[PKHS]VS\TL ]P[HSJHWHJP[`[V[HSS\UN JHWHJP[`PUZWPYH[VY` YLZLY]L]VS\TL L_WPYH[VY`YLZLY]L ]VS\TLHUKYLZPK\HS ]VS\TL 7.2 Breathing Cycle 7.2 Breathing Cycle Breathing cycle is a repetitive event, which involves an inhalation (inspiration) followed by an exhalation (expiration). The main stimulus that controls the rate of the cycle is carbon dioxide, which can be detected by chemoreceptors. Control of Breathing 1. Chemoreptors are receptor cells that can be stimulated by chemicals including hydrogen ion concentration caused by carbon dioxide. (a) These chemoreceptors are stimulated by the increase in hydrogen ion concentration (low pH) and they can produce impulses that are sent to the breathing control centre in the brain by sensory neurones. (b) There are two types of chemoreceptors that detect hydrogen ion concentration i.e. the peripheral and central chemoreceptors. (c) Peripheral chemoreptors are found in the aortic and carotid bodies that are found near to the bases of aorta and carotid artery respectively. They are responsible for the immediate stimulation of breathing when the partial pressure of carbon dioxide in the blood increases but this only accounts for 30% of increased rate of breathing. (d) Central chemoreceptors are found in the brain. They detect increase in hydrogen ion concentration in the cerebrospinal fluid. Therefore, partial pressure of carbon dioxide that is too high in the blood also affects the pH of the cerebrospinal fluid. The central chemoreceptors are responsible for sustained increase in breathing rate until the pH is normal. (e) Chemoreceptors sensitive to oxygen concentration are located in the medulla, aortic and carotid bodies. As oxygen is abundance under normal circumstance, the effect of oxygen on breathing rate is relatively minor. 2. The breathing rate is controlled involuntarily by breathing centre, which is located in the medulla of the brain. This is part of the autonomic nervous system. (a) The breathing centre is divided into inspiratory centre and expiratory centre. (b) The inspiratory centre increases the rate and depth of inspiration and is found at the ventral part of the breathing centre. The inspiratory breathing centre sends impulse to the intercostal muscles through intercostal nerve and to the diaphragm through the phrenic nerve. (c) The expiratory centre stimulates expiration but inhibits inspiration and is found at the dorsal and lateral parts of the breathing centre. This centre is connected to stretch receptors in bronchi and bronchioles through vagus nerve. INFO 4LJOHUPZTVM Breathing
Summary CHAPTER 7 14 Biology Term 2 STPM Chapter 7 Gaseous Exchange 3. The sequence of events that occurs in the process of an involuntarily controlled breathing is as shown in Figure 7.10. (a) Carbon dioxide from respiration is detected by chemoreceptors and the impulses generated are sent to the breathing centre that controls the rate of breathing. (b) From the inspiratory centre, impulse is sent through phrenic and intercostal nerves to the diaphragm and external intercostal muscle respectively. (c) Both muscles contract resulting in the expansion of thoracic cavity, which causes the lung to inflate. Inspiration occurs and air is inhaled. (d) When the lungs expand, stretch receptors within the walls of bronchioles and bronchi are stimulated. (e) Inhibitory impulses are sent to inspiratory centre, which cut off inspiratory activity. (f) Such action results in the relaxation of the respiratory muscles i.e. the external intercostal muscles and diaphragm. (g) The thoracic cavity contracts and deflates the lungs, resulting in expiration and air is exhaled. (h) The walls of the bronchiole and bronchi contract and no inhibitory impulse is sent to the inspiratory centre. The cycle then begins again. Control of breathing mechanism 1. Peripheral receptors in aortic and carotid bodies, central receptors in brain – detect H+ concentration. 2. Receptors send impulse to LQVSLUDWRU\FHQWUH 3. Centre sends impulse to diaphragm through phrenic nerve 4. Lungs expand, inspiration occurs 5. Stretch receptors in lungs VHQGLQKLELWRU\LPSXOVHWR LQVSLUDWRU\FHQWUH 6. No impulse is sent to diaphragm 7. Diaphragm relaxes and expiration occurs 8. &HUHEUXPFDQYROXQWDU\ contract diaphragms & intercostal muscle Lungs contract Lungs expand Cerebrum Breathing centre Inhibitory impulse fired from stretch receptors in lungs Inhibitory impulses not fired Diaphragm and intercostal muscles relax CO2 from respiration (g) Expiration (h) Stretch receptor not stimulated (i) Step (a) begins again (f) Impulse not sent (a) Stimulus (e) Impulse inhibited (b) Impulse fired (d) Stretch receptor stimulated (c) Inspiration Voluntary control Intercostal muscle and diaphragm contract Figure 7.10 The control of breathing rate
Summary CHAPTER 7 15 Biology Term 2 STPM Chapter 7 Gaseous Exchange 4. The rate of breathing to a certain extent, can be controlled voluntarily. This is done through the motor centre of the cerebrum that generates impulse, which is sent to the breathing centre and then to the diaphragm and external intercostal muscle to contract and to expand the muscle thoracic cavity. Voluntary contraction of internal costal muscles is possible after the lungs are inflated to force out the air. Definitions of Lung Volumes and Capacities The following terms describe various lung (respiratory) volumes: 1. Tidal volume (0.45 dm3 ) is the volume of air that is breathed in and out during one breath. The volume is about 450 cm3 at rest. The tidal volume can be increased when we are exercising to a maximum about 3 dm3 . 2. Inspiratory reserve volume (1.5 dm3 ) is the extra volume of air taken in voluntarily after the normal inhalation. Women normally have smaller inspiratory reserve volume. 3. Expiratory reserve volume (1.5 dm3 ) is the volume of air that can be further breathed out after the normal exhalation. 4. Vital capacity (4.5 dm3 ) is the maximum volume of air that can be exchanged during one breath in and out. This is equal to the volume of air breathed out after a forced inspiration followed by a forced expiration. Vital capacity is about 4, 500 cm3 for normal people but athletes have a higher vital capacity through training. We may breathe in the vital capacity amount of air when exercising. 5. People suffering from emphysema have a vital capacity which is greatly reduced. In serious conditions, holes may appear in the alveoli that further reduce the expansion of the lungs. 6. Residual volume (1.5 dm3 ) is the volume of air still remains in the lung after a maximal forced exhalation. This volume includes the air left in the trachea, bronchi and bronchioles, which cannot be contracted to expel the air. 7. Total lung capacity (5 dm3 ) is the maximum volume of air in the lungs after a forced inhalation. This is the same as the vital capacity plus the residual volume. The total lung capacity of men is usually bigger than that of women. 8. The relationship between the volumes mentioned above is as shown in Figure 7.11. Exam Tips 9LTLTILYOV^IYLH[OPUNPZ ILPUNYLN\SH[LK +LÄUP[PVUZ 1. Tidal volume – volume of air breathed in 2. Inspiratory reserve volume – volume of air taken in by forced breath in after normal breath in 3. Expiratory reserve volume – volume of air exhaled out by forced breath out after normal breath out 4. Vital capacity – maximum tidal volume, = (1 + 2 + 3) 5. Residual volume – volume of air left after maximal forced breath out 6. Total lung capacity = (1 + 2 + 3 + 5) or (4 + 5)
Learning Outcomes CHAPTER 7 16 Biology Term 2 STPM Chapter 7 Gaseous Exchange Language Check 1.5 3 4 Residual volume Time / s 3 Expiratory reserve volume 5 Vital capacity 6 Total lung volume 1 Tidal volume 2 Inspiratory reserve volume 3.45 5 Lung volume / dm3 Figure 7.11 Various lung volumes 2011 Quick Check 2 1. How do singers control their breathing during singing? 2. What are other chemoreceptors located in our body? 3. How can frequent diving enable a person to adapt to stay under water longer? 7.3 Gaseous Exchange in Plants 7.3 Gaseous Exchange in Plants 1. Plants obtain the gases they need through their leaves. They require oxygen for respiration and carbon dioxide for photosynthesis. 2. Gas exchange occurs during photosynthesis. During this process, carbon dioxide diffuses into plant leaves and oxygen diffuses out from the plant leaves. Gas exchange also occurs during respiration. During this process, oxygen diffuses into plant leaves and carbon dioxide diffuses out of plant leaves. 3. The gases diffuse into the intercellular spaces of the leaf through pores, which are normally on the underside of the leaf called stomata. From these spaces they will diffuse into the cells that require them. The Structure and Functions of Stomata 1. The gases move into and out of the plants through specialised stomata. These stomata are of optimum size, shape, and distribution for the efficient diffusion of gases. Each stoma is surrounded by two specialised structures called guard cells. These two cells are attached together at their ends. :[\KLU[ZZOV\SKILHISL[V! H KLZJYPIL[OLZ[Y\J[\YL HUKM\UJ[PVUZVM Z[VTH[H" I KLZJYPIL[OLTLJOHUPZT of opening and JSVZPUNVMZ[VTH[H IHZLKVUWV[HZZP\T ion accumulation O`WV[OLZPZ ]: VTH¶ZPUN\SHY Stomata – plural
CHAPTER 7 17 Biology Term 2 STPM Chapter 7 Gaseous Exchange 2. The structure of a stoma is as shown in Figure 7.12. Outer thin wall Inner thick wall Stoma pore Chloroplast Nucleus Nucleus Vacuole Guard cell Figure 7.12 The structure of a stoma (a) A stoma is formed from two guard cells, which are shaped like two curved sausages. The two guard cells are fused at their ends allowing the cells to bend as they expand. (b) The guard cells are living cells with protoplast, nucleus, chloroplasts and sap vacuole. (c) The orientation of cytoskeleton within the guard cells is special especially in plants that follow circadian rhythm of opening and closing of stomata like legumes. The microtubules orientate in radial pattern when guard cells expand and become fragmented when the guard cells collapse. Thus, microtubules can influence the orientation of microfibrils in the cell wall. (d) The inner wall of guard cells lining the pore is thick and the outer wall is thin. Cellulose microfibrils are orientated radially rather than longitudinally in the wall of guard cells. There are more longitudinal microfibrils at the inner wall. Thus, when the guard cells expand, they bend to elongate. (e) The structure of the guard cells causes the stoma to open when the guard cells become turgid as the curved cells leave a pore in between them. (f) The pore is closed when the guard cells are flaccid as the cells soften and contracted leaving no pore in between them. The two guard cells collapse onto each other. 2. The functions of the stomata are as follows: (a) Stomata allow exchange of gases between the inside and outside of the leaves. During the day, carbon dioxide diffuses into the leaves to be used for photosynthesis and oxygen produced from photosynthesis diffuses out. During the night, oxygen diffuses into the leaves for respiration and carbon dioxide produced from respiration diffuses out. Thus, stomata can regulate the exchange of gases especially carbon dioxide uptake during the day. So, stomata regulate the rate of photosynthesis in response to a large number of external and internal signals. Summary ;OLM\UJ[PVUZVMZ[VTH[H 1. For gaseous exchange 2. Allow transpiration for lifting water 3. Allow transpiration for cooling leaves 4. Reduce excessive loss of water when pores close 5. Open during the day (stimulated by light) 6. Close at night INFO .HZLV\Z,_JOHUNL PU7SHU[Z VIDEO Stomata
CHAPTER 7 18 Biology Term 2 STPM Chapter 7 Gaseous Exchange (b) Stomata allow transpiration to occur. During transpiration, water vapour diffuses out through stomata due to water vapour concentration gradient i.e. higher in the air spaces of the leaf and lower in the atmosphere. The diffusion of water vapour out of the stoma creates a transpiration pull in the xylem so that water is transported up to the leaves for photosynthesis. As a variety of mineral ions are found in the soil and dissolved in water, this transpiration pull also helps to transport them up into the leaves for metabolic functions. Thus, stomata can regulate the rate of transpiration, as well as uptake of water and mineral ions. (c) Allowing water vapour to escape from plant leaves, the stomata also help to lowers the temperature of the leaves. This is so especially in the hot afternoon when the leaves have to be exposed to direct sunlight for photosynthesis. The monkey plants of California are reputed to open the stomata at certain temperature and able to control the temperature of the leaves, even when the temperature of the environment rises to a dangerous level. (d) Stomata can reduce excessive loss of water. This is done physically as when water is lost from the guard cells, the cells become flaccid. That automatically closes the stomata. Mechanism of Opening and Closing of Stomata 2011 Guard cells Nucleus Nucleus Vacuol Thick internal wall Thin external wall Chloroplasts Open stoma Closed stoma The opening of stoma The closing of stoma Figure 7.13 The opening and closing of stoma 1. Stomata open when the guard cells become turgid. When water flows into the guard cells by osmosis, the internal fluid pressure is exerted on the outer thin walls. An internal fluid pressure that is osmotically induced builds up against cell walls is called turgor pressure. This makes the guard cells expand. Due to the relatively inelastic thicker wall of the pore, the guard cells bend and draw away from each other, so the pores open. 2013/P2/10, Q19(b) STPM
CHAPTER 7 19 Biology Term 2 STPM Chapter 7 Gaseous Exchange 2. Stomata close when the guard cells become flaccid. This is because when water leaves the guard cells, there is no turgor pressure. When the internal fluid pressure drops, the cells collapse against each other and close the pores. 3. The opening and closing of stomata based on potassium ion (K+) accumulation hypothesis. (a) Levitt (1974) proposed active potassium theory. He observed that when there is light, especially blue light, it stimulates the proton H+ pumps in the membrane of the guard cells. This causes fast release of proton (H+) from guard cells. This requires energy in the form of ATP which is supplied by the chloroplasts in the guard cells. This leads to increase in value of pH in guard cells. Rise in pH converts starch into organic acid (like malic acid). Malic acid further dissociates to form H+ and malate anion. (b) This in turn stimulates the potassium pumps to actively pump in K+ (potassium) ions to compensate the negative electrical potential. (c) An increase in K+ concentration lowers the water potential that causes the water to diffuse in by osmosis, increasing the turgor pressure and opens the stomata. (d) The accumulation of positive charges (K+) in the guard cells is balanced by cloride ion (Cl– ) or the formation of organic acid such as malate, depending on species of the plant. (e) At night, the reverse process takes place when there is no light. K+ ions are pumped out, increasing the water potential. The guard cells become flaccid and close the stomata. 4. Abscisic acid, which is a plant hormone, plays an important role in the closing of stomata in response to stress i.e. drought or high temperature. It is produced in the chloroplasts of the leaf mesophyll cells. It diffuses and binds to specific receptors of the plasma membrane of the guard cells, stimulating the potassium pumps that pump the K+ ions out. Water diffuses out of guard cells causing the cells to become flaccid and close the stomata. Abscisic acid also stimulates the enzymes that cause depolymerisation of microfibrils in the wall causing the guard cells to become flaccid. Cytokinin, another hormone, stimulates the opening of the stomata in some plants. ;OL[YHKP[PVUHSO`WV[OLZPZ PZIHZLKVUZ\NHYZ[HYJO PU[LYJVU]LYZPVU H >OLU[OLYLPZSPNO[ WOV[VZ`U[OLZPZ[HRLZWSHJL PU[OLJOSVYVWSHZ[ZVM[OL N\HYKJLSSZYLZ\S[PUNPUHU HJJ\T\SH[PVUVMZ\NHYPU [OLN\HYKJLSSZ I ;OLZ\NHYYLK\JLZthe ^H[LYWV[LU[PHSVM[OLJLSSZ HUK^H[LYKPɈ\ZLZPUMYVT ULPNOIV\YPUNJLSSZ;O\Z [OLN\HYKJLSSZILJVTL [\YNPKHUK[OLZ[VTH VWLUZ J ([UPNO[[OLYLPZUV WOV[VZ`U[OLZPZHUK[OL Z\NHYPZJOHUNLK[VZ[HYJO The water potential of the N\HYKJLSSZYL]LYZLZHUK [OLZ[VTHJSVZLZ Info Bio Exam Tips 9LTLTILY[OLTLJOHUPZT VMVWLUPUNHUKJSVZPUNVM Z[VTH 2011 Quick Check 3 1. Why are the sizes of stomata different in different plants? STPM 2014/P2/Q2
CHAPTER 7 20 Biology Term 2 STPM Chapter 7 Gaseous Exchange Objective Questions 1. What is present in the wall of trachea? Epidermis Elastic fibres Smooth muscle A Present Present Present B Present Present Absent C Absent Present Present D Present Absent Absent 2. Which would be found in a bronchus wall? I cartilage cells II ciliated cells III exocytotic vesicles A I and II only B I and III only C II and III only D I, II and III 3. What is the main function of cilia which line the respiratory surface? A To prevent the lungs from dehydration by providing mucus B Move the mucus away from the lungs C Lubricate the bronchi to ease the air flow into the lungs D Moisten the trachea 4. Which correctly shows the areas of the respiratory tract that contain cartilage, smooth muscle, goblet cells and cilia? Cartilage Smooth muscle Goblet cells Cilia A Bronchus, bronchiole Alveoli, bronchiole Bronchus, alveoli Bronchus, bronchiole B Trachea, bronchus Bronchiole, alveoli Bronchus, bronchiole Trachea, bronchus C Trachea, bronchiole Trachea, bronchus Trachea, alveoli Bronchiole, alveoli D Trachea, bronchus Trachea, bronchus Bronchus, bronchiole Trachea, bronchiole 5. The diagram shows a magnified section through a small part of the lung tissue. 1 2 3 4 What are 1, 2, 3 and 4? 1234 A Alveolar epithelial cell Macrophage Lumen of alveolus Blood capillary wall B Blood capillary wall Alveolar epithelial cell Blood plasma Phagocyte C Wall of bronchiole Arteriole wall blood Lumen of bronchiole Capillary wall D Alveolar epithelial cell Blood capillary wall Lumen of alveolus Macrophage 6. The diagram shows an alveolus with an associated blood capillary. The arrows indicate the direction of blood flow. A B C D Which part has the lowest oxygen concentration? STPM PRACTICE 7
CHAPTER 7 21 Biology Term 2 STPM Chapter 7 Gaseous Exchange 7. What happens to the reaction shown below when carbon dioxide concentration in blood increases? Hb + 4O2 AHbO8 A The reaction shifts to the left B The reaction shifts to the right C Carboxyhaemoglobin complex is formed D Oxyhaemoglobin-carbon dioxide complex is formed 8. An individual has oxygen dissociation curve for haemoglobin to the left compared to that of a normal individual. Which statement is correct? I The individual has migrated from low altitude to high altitude II The individual has migrated from high altitude to low altitude III The total haemoglobin in red blood cell of the individual increases IV The total haemoglobin in red blood cell of the individual decreases A I and III B I and IV C II and III D II and IV 9. Chloride shift occurs when A the water potential in the red blood cells is maintained B the pH in the red blood cells is maintained C Cl– ions in the plasma diffuse into the red blood cells to replace the HCO3 – ions that are diffusing out D Cl– ions in the plasma diffuse into the red blood cells to replace the CO3 2– ions that are diffusing out 10. The diagram shows the effect of three different partial pressures of carbon dioxide on the oxygen dissociation curve for human haemoglobin. X = Partial pressure of carbon dioxide: 3.0 kPa X Y = Partial pressure of carbon dioxide: 5.0 kPa Z = Partial pressure of carbon dioxide: 7.0 kPa 100 Partial pressure of oxygen / kPa Percentage saturation of haemoglobin with oxygen 0 12 0 Y Z What effect does carbon dioxide have on haemoglobin? A It makes it more efficient at taking up oxygen and also more efficient at releasing it. B It makes it more efficient at taking up oxygen and less efficient at releasing it. C It makes it less efficient at taking up oxygen and more efficient at releasing it. D It makes it less efficient at taking up oxygen and also less efficient at releasing it. 11. The graph shows the dissociation of oxygen of haemoglobin at two different pHs. Curve 1 Curve 2 100 Oxygen partial pressure Percentage saturation of haemoglobin with oxygen 0 0 Which combination is correct? Lower pH Tissue A Curve 1 Resting muscle B Curve 1 Active muscle C Curve 2 Resting muscle D Curve 2 Active muscle
CHAPTER 7 22 Biology Term 2 STPM Chapter 7 Gaseous Exchange 12. An increase in carbon dioxide in human blood shifts the oxyhaemoglobin dissociation curve to the right. What is the explanation for this effect? A Carbon dioxide is more soluble than oxygen and displaces it B An increase in carbon dioxide concentration increases the ventilation rate C Diffusion of carbon dioxide between the alveoli and the blood is more rapid D Increasing the H+ concentration decreases haemoglobin affinity for oxygen 13. Which combination about human myoglobin is correct? I Myoglobin has a low affinity towards carbon dioxide II Myoglobin only releases its oxygen when the supply of oxyhaemoglobin is insufficient III Myoglobin retains its oxygen in resting cells IV Myoglobin releases oxygen easily to muscle cells A I and II C II and III B I and IV D III and IV 14. Which form of carbon dioxide is transported in the red blood cell? A Carbaminohaemoglobin B Carboxyhaemoglobin C Haemoglobinic acid D Hydrogencarbonate 15. The diagram shows the Bohr effect. X Y 100 Partial pressure of oxygen / kPa Percentage saturation of haemoglobin with oxygen 0 0 2 4 6 8 10 80 60 40 20 What causes the shift from X to Y? A Decreased concentration of carbon dioxide and high pH B Decreased concentration of carbon dioxide and low pH C Increased concentration of carbon dioxide and high pH D Increased concentration of carbon dioxide and low pH 16. The oxygen dissociation curves X and Y of haemoglobin for humans are shown in the graph below. Oxygen saturation of haemoglobin / % 50 100 Partial pressure of oxygen / mmHg 50 Y X 100 Which is true of the following descriptions? A Oxygen is released more readily in X than in Y. B X occurs in the respiring tissue while Y occurs in the lung. C Affinity of haemoglobin for oxygen in X is higher than in Y. D The partial pressure of CO2 is higher in X while the partial pressure of O2 is higher in Y. 17. Why there is presence of myoglobin in active tissues? A It enhances the supply of oxygen. B It has four haem molecules. C It binds both carbon dioxide and oxygen. D It helps maintain the steepness of the pressure gradient in tissues. 18. The breathing rate is controlled by A Cerebellum B Hypothalamus C Medulla Oblongata D Thalamus
CHAPTER 7 23 Biology Term 2 STPM Chapter 7 Gaseous Exchange 19. Which of the following is not true about transport in plants? A In the apoplast pathway, water diffuses into the roots between the walls of the root epidermal cells. B When the root pressure is very high, it forces water into the leaves and causes guttation. C The Casparian strip forms a barrier that forces water to pass by the simplest pathway. D The high root pressure will cause transpirational pull. 21. What causes the opening of a stoma? A The decrease in the concentration of potassium ions in the guard cells. B The increase in the concentration of glucose in the guard cells. C The increase in the concentration of the abscisic acid when plants are exposed to stress. D The increase in the concentration of carbon dioxide in the guard cells. 20. The diagram shows the condition of stomata in the morning. W X Y Z What do W, X, Y and Z represent? WX Y Z A Passive transport of K+ Active transport of Cl– H2 O by osmosis O2 by simple diffusion B Active transport of K+ H2 O by osmosis O2 by simple diffusion Active transport of Cl– C Active transport of Cl– CO2 by simple diffusion Active transport of H+ Active transport of K+ D Active transport of Cl– Active transport of H+ CO2 by simple diffusion Passive transport of K+ Structured Questions 1. The graph below shows a spirometer trace of lung volumes taken during a breathing cycle of a healthy female adult. A peak on the graph represents one breath. 10 seconds Forced breathing Time Normal breathing Lung volume 1 dm3 Forced breathing Inspiration Expiration (a) From the graph above, determine the [3] (i) tidal volume (ii) expiratory reserve volume (iii) vital capacity
CHAPTER 7 24 Biology Term 2 STPM Chapter 7 Gaseous Exchange (b) From the graph above, calculate the normal breathing rate per minute. [3] (c) (i) What is the lung volume that cannot be determined by the spirometer trace? [1] (ii) State a reason why the volume in (c)(i) cannot be determined from the trace. [1] 2. The diagram below shows the oxygen dissociation curves of myoglobin, mother haemoglobin and foetal haemoglobin. 2/ mm Hg 50 50 X Y Z 100 Saturation of O2 (Hb O8) / % 100 (a) Label curves X, Y and Z. [3] (b) Comparing curves X and Y, what is the physiological significance of their difference? [2] (c) Comparing curves Y and Z, what is the physiological significance of their difference? [2] (d) What is the effect of carbon dioxide on the oxygen dissociation curve of the mother? Explain the effect and its significance. [3] Essay Questions 1. (a) Explain how haemoglobin is adapted for oxygen transport in our body. [7] (b) Explain how carbon dioxide is transported in the blood. [8] 2. (a) Explain the role of abscisic acid and potassium ions in controlling water loss by the stomata under the condition of water stress. [10] (b) Describe what happens to the various forms of carbon dioxide which are transported by the blood in the lungs. [5]
CHAPTER 7 25 Biology Term 2 STPM Chapter 7 Gaseous Exchange Quick Check 1 1. It is more efficient as the plasma membrane of the erythrocytes prevents substances from influencing the transport of oxygen by haemoglobin. The erythrocytes are specialised cell adapted with enzymes specifically for the function. 2. Yes, though little oxygen is carried in the blood if there is more carbon dioxide in it. A small concentration of carbon dioxide dissolves in the plasma and diffuses into the red blood cell to bind with the haemoglobin side chain amino groups. Quick Check 2 1. The motor centre of the cerebrum consciously can withhold the diaphragm muscle when the lung is expanded. The air is then released. 2. Other chemoreceptors include osmoreceptors in the hypothalamus, taste receptors in the tongue and smell receptors in the nasal chamber. 3. The diver is adapted to control his lung. The lung can expand bigger through practice. Frequent practice cause the lung to adapt with more blood vessels and better absorption. Quick Check 3 1. They are adapted to live in different climatic conditions. Those that are adapted to live in dry environment have fewer and smaller stoma pores to cut down water loss. STPM Practice 7 Objective Questions 1. C 2. D 3 C 4. D 5. D 6. A 7. A 8. A 9. C 10. C 11. D 12. D 13. A 14. D 15. D 16. C 17. A 18. C 19. D 20. B 21. B Structured Questions 1. (a) (i) 0.5 dm3 (ii) 0.75 dm3 (iii) 3.25 dm3 (0.75 + 0.50 + 2.00) (b) 12 breaths per minute (c) (i) Residual volume (ii) Because the trace does not show the total lung volume/the spirometer can only measure volume of air moved (d) Exercise (e) Inspiratory reserve volume (or vital capacity) 2. (a) X is the oxygen dissociation curve of myoglobin, Y is that of foetal haemoglobin and Z is that of mother haemoglobin. (b) The dissociation curve of X, myoglobin is to the left of that of foetal haemoglobin, indicating that it has a higher affinity for oxygen than that of foetus. This enables oxygen to be stored in the developing muscles of the foetus and to be used when partial pressure of oxygen runs low. (c) The dissociation curve of Y, foetal haemoglobin is to the left of that of the mother’s haemoglobin, indicating that it has a higher affinity for oxygen than that of the mother. This enables the foetal haemoglobin to obtain oxygen from the mother’s haemoglobin at the placenta where the partial pressure of oxygen is low. (d) Carbon dioxide shifts the oxygen dissociation curve to the right, allowing oxyhaemoglobin to dissociate its oxygen even at high partial pressure of oxygen. The effect is caused by the carbon dioxide dissolved in the blood, forming H+ that allow oxyhaemoglobin to release its oxygen. The significance is that oxyhaemoglobin releases its oxygen in the area with high carbon dioxide concentration where the cells are most active and require oxygen the most. Essay Questions 1. B t )BFNPHMPCJOJTBEBQUFE UP USBOTQPSUPYZHFO by its molecular structure that has four haem groups to bind with four molecules of oxygen to form oxyhaemoglobin. t *UT BEBQUBUJPO UP USBOTQPSU PYZHFO JT CFTU illustrated by its sigmoid shape dissociation curve of percentage saturation plotted against partial pressure of oxygen. t 8IFOJUUSBOTQPSUTPYZHFOGSPNUIFMVOHCBDL to the heart and from the heart through the arteries, very little oxygen is released. t ćJTJTCFDBVTFUIFDIBOHFJOQBSUJBMQSFTTVSF of oxygen in the arteries is little. It can still maintain an 80% saturation of oxygen in the haemoglobin. t )PXFWFS UIFSFJTBTIBSQESPQPGTBUVSBUJPOPG oxygen when the blood arrives at the tissues, therefore releasing the oxygen exactly where the tissues require it for respiration. t 'VSUIFS ESPQ JO QBSUJBM QSFTTVSF POMZ DBVTF a slow release of oxygen, as haemoglobin is adapted not to deprive the tissues of sudden loss of oxygen. ANSWERS
CHAPTER 7 26 Biology Term 2 STPM Chapter 7 Gaseous Exchange t )BFNPHMPCJOJTBMTPBEBQUFE UPSFMFBTFNPSF oxygen when there is a higher concentration of H+ caused by higher carbon dioxide concentration. This is to supply more oxygen to the tissues that produce most CO2 and active in respiration. t 'PFUBM IBFNPHMPCJO IBT B IJHIFS BďOJUZ GPS oxygen as the foetus has to get 100% of its oxygen from the blood of the mother’s placenta. (b) t 7FSZMJUUMFDBSCPOEJPYJEFJTUSBOTQPSUFEBTHBT dissolved in the plasma of the blood. t &WFO TNBMMFS QFSDFOUBHF PG DBSCPO EJPYJEF form carbonic acid and transported as such in the plasma. t " HPPE QFSDFOUBHF PG DBSCPO EJPYJEF DBO diffuse into the red blood cells and bind to the haemoglobin, forming carbaminohaemoglobin. t ćFDBSCPOEJPYJEFBDUVBMMZCJOETUPUIFBNJOP side chains of haemoglobin temporarily, to be released later. t ćF BNPVOU PG DBSCPO EJPYJEF CPVOE UP UIF side chains depends on the amount of oxygen being carried i.e. more carbon dioxide can be bound if there is a lesser amount of oxygen. t .PTU PG UIF DBSCPO EJPYJEF JT DBSSJFE JO UIF plasma in the form of hydrogen carbonate ions. t ćF DBSCPO EJPYJEF IBT UP EJČVTF JOUP UIF red blood cells where the enzyme carbonic anhydrase changes it very fast to carbonic acid. t $BSCPOJD BDJE JPOJTFT JOUP )+ and HCO3 – . The plasma membrane of the red blood cell is very permeable to HCO3 – and the ions are transported in the plasma as such. t )PXFWFS UIF USBOTQPSU PG DBSCPO EJPYJEF BT HCO3 – is helped by chloride ions in the plasma that diffuse into the red blood cells to balance off the negative HCO3 – that diffuse out. 2. B t "CTJDJTJD BDJE "#" JT UIF QSJNBSZ JOUFSOBM signal that enables plants to withstand drought. t "#"JTQSPEVDFEJONFTPQIZMMDFMMTBOEHVBSE cells in the leaf. t 8IFOBQMBOUCFHJOTUPXJMU "#"BDDVNVMBUFT in the leaves. t "#" DBVTFT UIF TUPNBUB UP DMPTF SBQJEMZ reducing transpiration and preventing further water loss. t "#" DBO CJOE UP SFDFQUPST PO UIF QMBTNB membrane of guard cells. t ćJTDBVTFTUSBOTEVDUJPOXJUIUIFBDUJWFJOUBLF of calcium ions as second messenger. t $BMDJVNJPOTDBVTFUIFPQFOJOHPGPVUXBSEMZ directed potassium ion channels. t ćJTDBVTFTUIFQPUBTTJVNJPOTUPEJČVTFPVU lowering the water potential of the guard cells. t 8BUFSEJČVTFTPVUPGUIFHVBSEDFMMCZPTNPTJT t -PTTPGXBUFSDBVTFTUIFHVBSEDFMMTUPCFDPNF flaccid thus closing the stoma. t "#"JTBMTPQSPEVDFEJOUIFSPPUTXIFOUIFSF is a water shortage in the soil. t "#" JT UIFO USBOTQPSUFE JOUP UIF MFBWFT CZ the xylem to cause wilting and closing of the stomata. t "#" DBO EJSFDUMZ DBVTF EFQPMZNFSJTBUJPO PG actin filament in the guard cells, closing the stomata. (b) t *OUIFMVOHT $02 diffuses out from the blood into the alveolar sac down concentration gradient. t ćJT $02 may come from soluble form, hydrogen carbonic form, carbonic acid form or carbaminohaemoglobin form. t )ZESPHFODBSCPOBUFJPOTEJČVTFJOUP UIFSFE blood cells from the plasma to combine with hydrogen ions forming carbonic acid. t ćJT JT DBVTFE CZ DBSCPOJD BOIZESBTF UIBU catalyses the conversion of carbonic acid to CO2 and water in the red blood cell. t ćF DBSCBNJOPIBFNPHMPCJO JO UIF SFE blood cell also release the CO2 in the lungs as haemoglobin binds with oxygen to form oxyhaemoglobin.
CHAPTER TRANSPORT IN ANIMALS AND PLANTS Concept Map 8 Transport in Animals and Plants Transport system in animals Structure of a mammalian heart Transport system in plants Cardiac cycle Systole Root pressure Mass flow Electro-osmosis Cytoplasmic streaming Peristaltic waves Cohesion – tension theory Relation to blood circulatory system Apoplast Symplast Vacuolar Diastole Sequence of events Initiation of heartbeat Regulation of heartbeat Arteriosclerosis Atherosclerosis Hypertension Out at arteriole end In at venule end Myocardial infarction Lymphatic system Fluid movement out and into capillaries Control of heartbeat Uptake of water and mineral ions Pathways through root tissues Water movement from root to leaves Translocation of organic substances Concept of source and sink Loading and unloading Cardiovascular diseases (causes and preventions) Changes in pressure and volume Bilingual Keywords Cardiac – Kardium Semilunar valve – Injap sabit Valve – Injap Heartbeat – Denyutan jantung Distend – Mengembang Pronounced – Nyata Pacemaker – Perentak Excitation – Ujaan Cardiovascular – Kardiovaskular Disease – Penyakit Obesity – Kegendutan Tension – Tegangan 4HZZÅV^¶Pengaliran jisim Critical – Genting
Learning Outcomes CHAPTER 8 ffi Biology Term 2 STPM Chapter 8 Transport in Animals and Plants Language Check ([YP\T¶ZPUN\SHY ([YPH¶WS\YHS =LU[YPJSL¶ZPUN\SHY =LU[YPJSLZ¶WS\YHS Students should be able to: (a) describe the structure of a mammalian heart; I KLÄULZ`Z[VSLHUK KPHZ[VSLHUKL_WSHPU[OL sequence of events in a JHYKPHJJ`JSLPUJS\KPUN JOHUNLZPUWYLZZ\YL and volume in aorta, left atrium and left ventricle; (c) describe the initiation HUKYLN\SH[PVUVM heartbeat; K L_WSHPUO`WLY[LUZPVU atherosclerosis, arteriosclerosis and myocardial infarction, and state their causes HUKWYL]LU[PVUZ" L KLZJYPIL[OLS`TWOH[PJ system in relation to the blood circulatory system; (f) determine the direction VMÅ\PKTV]LTLU[H[ the arterial and venous LUKZVM[OLJHWPSSHYPLZ I`JHSJ\SH[PUN[OL KPɈLYLUJLZIL[^LLU VZTV[PJWYLZZ\YL ZVS\[LWV[LU[PHSHUK O`KYVZ[H[PJWYLZZ\YLZ 8.1 Transport System in Mammals 8.1 Transport System in Mammals The Structure of a Mammalian Heart 1. The mammalian heart is a hollow muscular organ and has a mass of around 300 g. The muscle of which the heart is made is called cardiac muscle. 2. The cardiac muscle is made of interconnecting cells, whose plasma membranes are very tightly joined together. 3. This close contact between the muscle cells allows waves of electrical excitation to pass easily between them, which is a very important feature of cardiac muscle. 4. On the surface of the heart, the right and left coronary arteries can be seen (Figure 8.1). The coronary arteries branch from the aorta and deliver oxygenated blood to the heart muscles. 5. The human heart is divided into right and left sides by the septum. Each side has an upper chamber called atrium (or sometimes auricle) and a lower chamber called ventricle. Thus, the heart has four chambers as shown in Figure 8.2. 6. Blood flows into the ventricles from the atria, and is then squeezed out through the arteries. Blood from the left ventricle flows into the aorta, while blood from the right ventricle flows into the pulmonary arteries. Aorta Left pulmonary arteries Left subclavian artery Left common carotid artery Brachiocephalic trunk Superior vena cava Right pulmonary arteries Pulmonary trunk Left coronary artery Left ventricle Left atrium Right pulmonary veins Right atrium Right coronary artery Right ventricle Inferior vena cava Figure 8.1 External structure of the heart INFO /LHY[(UH[VT`
CHAPTER 8 ffl Biology Term 2 STPM Chapter 8 Transport in Animals and Plants Aorta (to body) Pulmonary artery Left pulmonary veins (from left lung) Left atrium Semilunar valve Cardiac muscle Left ventricle Septum Superior vena cava Right pulmonary artery (to right lung) Right pulmonary vein (from right lung) Semilunar valve Right atrium Tricuspid valve Right ventricle Inferior vena cava Chordae tendinae Bicuspid valve/ mitral valve Figure 8.2 The internal structure of the heart 8. The superior vena cava and inferior vena cava return deoxygenated blood from the head, neck and arms to the right atrium. The inferior vena cava returns blood from the body posterior to the heart. 9. Then, the pulmonary artery carries deoxygenated blood to the lungs through the right and left pulmonary arteries. Blood is oxygenated in the lungs. 10. Oxygenated blood returns to the left atrium through two right and two left pulmonary veins. Therefore, pulmonary veins are the few veins that carry oxygenated blood. 11. Then, the largest artery, the aorta distributes blood to the head and to the rest of the body. The aorta begins as a short ascending aorta, curves to the left to form the aortic arch, descends posteriorly and continues as the descending aorta. 12. The atria are separated from the ventricles by atrioventricular (AV) valves that control the one-way flow of blood. The one on the left is the mitral or bicuspid valve, and the one on the right is the tricuspid valve. 13. String-like cords called chordae tendineae (tendinous strands) attach and secure the cusps of the AV valves to enlarged papillary muscles that project from the ventricular walls. Chordae tendinae allow the AV valves to close during ventricular contraction, but prevent their cusps from getting pushed up into the atria. The papillary muscles are stimulated to contract as the ventricles contract to ensure the AV valves do not invert into the atria. The human heart has two atria and two ventricles. Blood enters the heart by the atria and leaves from the ventricles. A septum separates the right and left side of the heart. 7. Figure 8.2 shows the blood vessels which carry blood into and out of the heart. Summary
Exam Tips Summary CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants 14. Semilunar valve is present each at the base of pulmonary artery and aorta allowing blood to exit the heart one way from the ventricle. Blood in the right ventricle goes through the pulmonary valve to enter the pulmonary artery. The aortic valve is located at the base of the aorta. 15. The walls of the atria are thinner compared to the walls of the ventricles. This is due to atria contraction is less powerful by sending the blood only in a short distance down into ventricle. Ventricles have thicker wall to send blood out of the heart. The left ventricle has a thicker wall compared to the right ventricle as the right ventricle sends blood into the lungs while the left ventricle sends blood all over the body. Cardiac Cycle 2011, 2014/P2/Q16 1. Cardiac cycle is the sequence of events which makes up one heartbeat which consists of one systole and one diastole. 2. Systole is the event that occurs when the heart muscle contracts. Systole can be divided into two types i.e. atrial systole and ventricular systole. 3. Diastole is the event that occurs when the heart muscle relaxes. Similarly, diastole can also be divided into two types i.e. atrial diastole and ventricular diastole. Tricuspid valve opens Biscupid valve opens Atrial systole Atrial wall contracted Ventricular systole Semilunar valves open Pulmonary artery Aorta Ventricles contracted Ventricular diastole Biscupid valve Semilunar valves close Blood is Blood is filling atria moving away Triscupid valve still close Ventricles relax Atrial diastole Blood is filling ventricles Figure 8.3 Events of the heartbeat 9LTLTILY[OLKPɈLYLUJLZ IL[^LLU[YHUZWVY[Z`Z[LT VMWSHU[ZHUKHUPTHSZ Cardiac cycle 1. Atrial systole occurs after sinoatrial node (SAN) has sent excitation to atria 2. Blood is forced into ventricles through open atrioventricular (AV) valves 3. Ventricular systole occurs after AV node has sent excitation to ventricles when [OL`HYLÄSSLK^P[OISVVK 4. AV valves close producing “lub” sound and blood is forced out of heart 5. Diastole occurs, heart muscle relaxes and semilunar valves close to WYL]LU[IHJRÅV^WYVK\JPUN “dub” sound 6. )SVVKÅV^ZPU[V[OLOLHY[ MYVTV\[ZPKLÄSSPUNH[YPH[OLU ventricles Semilunar valves in the veins and in the entrances to the HVY[H HUKW\STVUHY` HY[LY` and atrioventricular valves, WYL]LU[IHJRÅV^VMISVVK Info Bio
CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants 4. The sequence of events in a cardiac cycle are shown in Figure 8.3. As the cycle is continuous, a description of it could begin anywhere. For easy description, cardiac cycle starts as atrial systole. (a) Atrial systole starts when the atria receive excitation from the sinoatrial node. (b) The left and right atria contract together, forcing blood within them into the ventricles through the atrioventricular valves, which are already open. (c) The pressure is not very great as the walls of the atria are thin but all the blood within the atria is forced down into the ventricles, which are already 70% full. (d) The blood from the atria does not go back into the pulmonary veins or the vena cavae, because they have semilunar valves to prevent backflow. 5. Then, it is followed by ventricular systole. 2008 (a) About 0.1 second after atria contract and when the ventricles are filled, the ventricles contract together after receiving excitation from the atrioventricular node. (b) The thick muscular walls of the ventricles squeeze inwards on the blood, increasing its pressure and forcing it out of the heart. (c) As soon as the pressure in the ventricles becomes greater than the pressure in the atria, pressures are exerted on bicuspid and tricuspid valves, forcing them to shut producing the first sound ‘lub’. (d) The pressure is great because of the thick ventricular wall. Atrioventricular valves prevent backflow into the atria. (e) The high pressure forces the oxygenated blood into aorta from the left ventricle and deoxygenated blood into pulmonary artery from the right ventricle, through semilunar valves at their bases. 6. It is followed by ventricular diastole. (a) About 0.3 second after the start of ventricular systole, both ventricular walls relax, the pressure in the ventricles drops. (b) The high pressure in the aorta and pulmonary arteries forces backflow of blood shutting the semilunar valves at their bases, producing the second heart sound, the ‘dub’. (c) As soon as the pressure in the ventricles is lower than that of the atria, the atrioventricular valves open and blood flows down from the atria. (d) The blood keeps on filling the ventricles for 0.5 second until 70% of the heart’s total volume before atrial systole that forces another 30% blood into them. 7. Finally, it is atrial diastole. (a) Atrial diastole starts immediately after systole but the atrial pressure is affected by the ventricular systole, when atrioventricular valves bulge up.
Exam Tips CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants (b) Only after the ventricular diastole starts, then the pressure in the atria drops when the whole heart muscle relaxes. (c) Oxygenated blood from the pulmonary vein enters the left atrium and the deoxygenated blood from the vena cavae enters the right atrium. (d) The atrial pressure increases when the blood is filling while the ventricular pressure decreases during diastole. Blood flows down into the ventricles pushing the atrioventricular valves open when enough blood fills the atria. (e) The whole cardiac cycle lasts about 0.8 second and all the events repeat. Changes in the pressure and volume of the left atrium 1. The changes in pressure and volume of the left atrium are slight but goes up and down in 3 waves during the cardiac cycle as shown in Figure 8.4. 2. In the first wave, when the left atrium contracts, its pressure increases and volume decreases. Blood is forced into the ventricles. 3. The second wave is caused by the bicuspid valve shutting and its upward bulge increases its pressure and decreases its volume. At that moment, the left atrium is relaxing. 4. The third wave is caused by the filling of blood from the pulmonary vein but its pressure drops suddenly due to the opening of bicuspid valve when the pressure of the left ventricle falls below the atrial pressure. 5. Then, its pressure increases slowly as its volume also increases because of the continual filling of blood before the cycle repeats. Changes in the pressure and volume of the left ventricle 1. The changes in the pressure and volume of the left ventricle are more pronounced as shown in the graph of the cardiac cycle (Figure 8.4). 2. In the first wave, there is a slight increase in the pressure and volume of the left ventricle due to systole of the atria. Its volume is filled to maximum. 3. The second wave is very strong due to its own systole. Its volume is squeezed to zero when its pressure increases to a maximum of 16 kPa. 4. When its muscle relaxes during diastole, its pressure drops to zero and its volume starts to increase when the blood is filling from the left atrium. 5. Then, the pressure hardly increases and its volume is gradually filled to full volume before the cycle repeats. 9LTLTILY[OL^OVSL JHYKPHJJ`JSLPUKL[HPSZ
Exam Tips Summary CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants Changes in the pressure and volume of aorta 1. The changes in the pressure and volume of the aorta are slight as shown in the graph of the cardiac cycle (Figure 8.4). 2. During atrial systole, the aortic pressure is unaffected, the pressure of aorta decreases after the recoil of blood towards the heart and volume decreases slightly. 3. During ventricular systole, blood is forced into the aorta, increasing its pressure and volume to the maximum. 4. During ventricular diastole, the blood pressure in the aorta decreases but there is a notch (called nacrotic notch) due to the shutting of aortic (semilunar) valve at its base. 5. Its pressure then continues to fall but does not fall to zero because it does not dilate too much and there is always blood in it before the next wave comes. The pulsating changes in the aorta continue in the arteries as pulses, which is also equal to the heart rate. Ventricular systole Lub Dup Lub Dup S S Q Q T T P P R R Ventricular diastole Ventricular systole Heart sounds 80 120 160 0 20 40 60 80 100 120 Electrocardiogram Ventricular volume Ventricular pressure Atrial pressure AV valve opens Aortic valve closes Aortic valve opens Aortic pressure 0 0.2 Pressure (mm Hg) Volume (ml) 0.4 0.6 0.8 Time (seconds) 1.0 1.2 1.4 AV valve closes Figure 8.4 Pressure changes in the heart during the cardiac cycle Initiation and Regulation of Heartbeat Initiation of Heartbeat (Intrinsic control) 1. The heart is made of cardiac muscle and is myogenic. It contracts and relaxes naturally, does not need to receive impulses from the central nervous system to make it contract. This means that the heart still can contract rhythmically even if it is removed from the body and kept in a warm nutrient solution. The heartbeat is initiated by the sinoatrial node (SAN) or pacemaker. 9LTLTILY[OLJOHUNLZ VMWYLZZ\YLHUK]VS\TLVM aorta, atrium and ventricle VU[OLSLM[ZPKLHYLNVVK LUV\NO;OL` HYL[OLZHTL PU[OLYPNO[ZPKLL_JLW[[OH[ [OLTHNUP[\KLPZSV^LYHZ YPNO[ZPKLVUS`ZLUKISVVK[V [OLS\UNZ Changes in pressure and volume Left atrium 1. Pressure increases and volume decreases during atrial systole 2. Pressure increases then decreases and remain low but volume remain constant during ventricular systole 3. Pressure and volume remain constant during diastole Left ventricle 1. Pressure increases and volume increases during atrial systole 2. Pressure shoots to maximum, volume decreases to minimum during ventricular systole 3. Pressure decreases to minimum, volume increases during diastole Aorta 1. Pressure and volume decrease during atrial systole 2. Pressure shoots to maximum then decreases during ventricular systole 3. Pressure and volume decrease during diastole
Summary CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants Exam Tips Remember the structure of [OLOLHY[ 2. SAN is located at the dorsal wall of the right atrium, near to where the vena cavae enter the heart as shown in Figure 8.5. Sinoatrial node (SAN) Right ventricle Atrioventricular node (AVN) Conduction myofibers (Purkinje fibers) Atrioventricular (AV) bundle (bundle of His) Left atrium Left ventricle Right and left bundle branches Figure 8.5 Vertical section of the heart to show the positions of the sinoatrial node and the atrioventricular node 3. SAN consists of a small number of special cardiac fibres that have their natural rhythm of contractions. The fibres are connected to all the muscle fibres of the atria. The SAN is also has nerve endings from the brain to control the heart rate. 4. Each time the SAN contracts, it sets up a wave of excitation to all the muscle fibres of the atrial walls. This occurs after the cells of the SAN slowly depolarised during atrial diastole and then action potential produced spreads from SAN. 5. The cardiac muscle in the atrial walls responds to this excitation wave by contracting, at the same rhythm as the SAN. During the contraction, the muscle fibres cannot respond to second stimulus thus the period is called refractory period. The refractory period is long and enables the muscle cells to recover fully without becoming fatigued. 6. There is a band of fibres called the atrioventricular septum between the atria and ventricles that does not conduct the excitation wave. The excitation is not directly passed to the ventricular muscle but to another node called atrioventricular node (AVN). 7. AVN is located in the septum in between the atria and ventricles. It consists of similar specialised tissue as that of the SAN and is connected to the AV bundle (bundle of His), which is the only route for transmission of impulse from atria to ventricles. 8. The AV bundle is divided to the left and right bundles. These are strands of modified cardiac fibres, which give rise to finer branches called Purkyne (Purkinje) tissue that in turns connects to all the muscle fibres of the ventricles. Initiation and regulation of heartbeat Initiation: Heart is myogenic A SAN acts as pacemaker A sends excitation to atria Aatria contract A AVN Adelays impulse Asends excitation A through AV bundle, bundles of His and Purkinje tissue A ventricles contract from bottom up. Regulation: Increases rate by cardiac accelerator centre A after receiving impulse from stretch receptors of vena cavae A through sympathetic nerve to SAN A and adrenaline released by adrenal medulla during exercise or fear A plus thyroxine when cold. Decrease rate by cardiac inhibitory centre A after receiving impulse from stretch receptors of aortic and carotid bodies Athrough parasympathetic vagus nerve to SAN. 2013/P2/Q3 STPM 2017 STPM
CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants 9. The excitation from the AVN is sent to the ventricles through the Purkyne tissues. The Purkyne tissue spreads from the bottom upwards into all parts of ventricular wall. 10. After the AVN receives the excitation from the SAN, it will send out excitation (Q, R and S wave in the electrocardiogram in Figure 8.4) to the ventricular muscles, causing the ventricles to contract from bottom upwards. This only occurs after about 0.1 second after the atria contracted to allow ventricle to be filled with blood. Regulation of Heartbeat (Extrinsic control) 1. The heartbeat is under autonomic control through the cardiac control centre in the medulla. The autonomic nervous system is the involuntary part of our nervous control. It also controls the endocrine system. 2. There are two regions in the centre that affect the rate of heartbeat, the cardiac inhibitory centre and the cardiac accelerator centre (Figure 8.6). The former inhibits whereas the latter increases the rate of heartbeat. Medulla Cardiac inhibitory centre Cardiac accelerator centre Impulses in sympathetic nerves-accelerates Sensory nerve -accelerates Impulses in parasympathetic nerve(vagus) -inhibits SAN AVN Aortic body with chemoreceptors Impulses from aorta and carotid receptors-inhibit Carotid bodies in neck Aortic stretch receptors Nitric Arteries and arterioles around the body Change in volume of venous return Vena cavae stretch receptor Figure 8.6 Nervous control of the rate of heartbeat
CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants 3. The autonomic system is the part of the nervous system that controls all the unconscious activities of the body including the rate of heartbeat. This system is divided into sympathetic and parasympathetic systems. 4. In the sympathetic system, a pair of spinal nerves originates from the cardiac accelerator centre and runs parallel to the spinal cord and enters the SAN. (a) These nerves will stimulate the increase in the rate of heartbeat as a result of receiving impulse from stretch receptors of the vena cavae. (b) This is when the body is under stress or muscles of the body contract actively, more blood is sent back to the heart stretching the receptors in the vena cavae. (c) This happens when we exercise or under stress conditions, such as when we are angry or frightened, the rate of heartbeat increases. The cardiac accelerator centre sends suitable amount of impulse in response to the SAN. (d) At the same time, sympathetic nerves also send impulses to the adrenal medulla to release adrenaline (epirephrine) and noradrenaline (norepinephrine). (e) These two hormones are also part of the ‘flight or fight’ response in which the two hormones directly stimulate SAN to increase the rate of heartbeat. (f) The sympathetic system also indirectly sends chemical signal to the anterior pituitary gland, which in turn stimulates the thyroid gland to release thyroxine. Thyroxine increases the basal metabolic rate of the body, especially when in cold. An increase in metabolic activity requires a greater amount of oxygen and an increase in rate of heartbeat for the purpose. 5. In the parasympathetic nervous system, a pair of cranial nerves from the tenth pairs i.e. the vagus nerves, originates from the cardiac inhibitory centre connects with the SAN. (a) These nerves decreases the rate of heartbeat as a result from stimulation from stretch receptors from aorta and carotid arteries. (b) This occurs after exercise or after emergency conditions when the heartbeat is already increased. (c) This action will decrease or restore the rate of heartbeat to the normal resting rate. (d) The parasympathetic nervous system also inhibits the adrenal medulla directly to stop the release of epinephrine (adrenaline) and norepinephrine (noradrenaline). Cardiovascular Diseases These are diseases of the heart and the circularatory system, including arteriosclerosis, atherosclerosis, hypertension and myocardial infarction. Exam Tips Remember the mechanism and control of the heartbeat (2010 STPM essay X\LZ[PVUZ 2013/P2/Q4 STPM
CHAPTER 8 fl Biology Term 2 STPM Chapter 8 Transport in Animals and Plants Arteriosclerosis and Atherosclerosis 1. Arteriosclerosis is a chronic disease characterised by abnormal hardening and thickening of walls of large and medium-sized arteries resulting in the loss of elasticity. Arteriosclerosis may be used as general hardening of arterial wall or very specific hardening due to calcified plaque formed. The most common form of arteriosclerosis is atherosclerosis. 2. Atherosclerosis is a condition in which an artery wall thickened as a result of the accumulation of fatty materials such as cholesterol. This reduces the flow of blood to the tissues; may also increase the chance of blood clots forming within the artery and obstructing the flow of blood altogether. If blood cannot flow into capillaries, the surrounding tissue does not receive enough nutrients and oxygen, and may die. This build-up of fatty deposits, called atheroma, forms plaques on the inner walls of arteries. These yellowish plaques contain cholesterol, fibres, dead muscle cells and platelets. If the plaques grows and breaks through the lining of the artery, blood clot called thrombus will be formed. This will rapidly slow or stop blood flow, leading to death of the tissues fed by the artery in approximately 5 minutes. When this happens in a coronary artery, heart muscles may die, causing a heart attack. If it happens in an artery in the brain, the results is a stroke. Normal artery Artery narrowed by atherosclerosis Blood flow Plaque Figure 8.7 Changes in arterial wall 3. The process starts gradually. (a) In the beginning, lipids are deposited beneath the endothelium in the muscle cells of the arterial wall. This is the start of arteriosclerosis as the arterial wall becomes not so elastic. (b) Cells in the arterial wall proliferate and the inner lining thickens. (c) More lipids, especially cholesterol from the low-density lipoproteins, accumulate in the wall. (d) Eventually calcium is deposited there, contributing to the slow formation of hard plaque. (e) As the plaque develops, arteries lose their ability to stretch when fill with blood and they become progressively blocked, resulting in atherosclerosis. What is the difference between arteriosclerosis and atherosclerosis? (Y[LYPVZJSLYVZPZPZHU` OHYKLUPUNZ[PɈLUPUNVM HY[LY`^HSSZ6ULVM[OL^H`Z [OPZJHUOHWWLUPZ[OYV\NO H[OLYVZJSLYVZPZ^OPJOPZ^OLU HUH[OLYVTHHI\PSK\WVM KLHKYLKISVVKJLSSZÄIYLZHUK WSH[LSL[ZILNPUZ[VHJJ\T\SH[L ^P[OPUHUHY[LY`^HSSHUKTH` stick out into the lumen or even IYLHR[OYV\NO[OLLUKV[OLSP\T This makes the artery less ÅL_PISL:VZVTLVUL^P[O arteriosclerosis (hardened arteries) may not have H[OLYVZJSLYVZPZWSHX\LI\[ ZVTLVUL^P[OH[OLYVZJSLYVZPZ must have arteriosclerosis, as [OLPYHY[LYPLZOH]LOHYKLULK Info Bio 2013/P2/Q18(a) INFO Cardiovascular Disease VIDEO ([OLYVZJSLYVZPZ
CHAPTER 8 ffi Biology Term 2 STPM Chapter 8 Transport in Animals and Plants 4. There is no single cause of arteriosclerosis and atherosclerosis; several major factors have been identified. (a) High level of cholesterol in the blood is the main cause. It is often associated with diet rich in high levels of saturated fats and cholesterol. The blood cholesterol concentration in the body is not dependent solely on the intake of cholesterol in foods such as meat and eggs; it depends mainly on the saturated fat derived from animal foods. Red meat and dairy products, such as milk and butter, are especially rich in saturated fat. (b) Hypertension is another cause. The higher the blood pressure, the greater is the risk. This is due to the high blood pressure which can cause injuries to the endothelial wall and starts the atherosclerosis. (c) The risk of developing atherosclerosis is two to six times greater in smokers than in non-smokers and is directly proportional to the number of cigarettes smoked daily. This is due to carbon monoxide and nicotine in the tobacco causing damage to the arterial endothelium. Nicotine increases constriction of blood vessels, stickiness of blood, raise blood density level and directly increases blood pressure. (d) A person with diabetes mellitus or high blood glucose level often have higher risk of the disorder, as the blood lipid level is also raised. High blood sugar tends to damage arterial endothelium thus increases risk of atherosclerosis. (e) The risk of developing arteriosclerosis also increases with age as arterioslerosis is part of the aging process. (f) Decrease in oestrogen level, especially after menopause in women, increases the risk too. This is due to the decrease of oestrogen is associated with the increase in low-density lipoprotein (LDL). (g) Genetic predisposition is another factor as if one or two parents have atherosclerosis, the risk of the children having it is greatly increased. This seems to associate with certain genes that stimulates the increase in blood LDL. (h) Stress increases the risk of arteriosclerosis. Emotional and psychological stress always increases the blood adrenaline level. The adrenaline increases the rate of hearbeat and blood sugar that increase the risk of arteriosclerosis. (i) Lack of exercise increase the risk of arteriosclerosis. Exercise promotes healthy functions of cardiovascular system. Lack of exercise causes weakening in heart function and deposition of lipid in blood vessels. (j) Diet high in salts also increase the risk of atherosclerosis. Blood with high salt content tends to damage arterial endothelium directly and increases blood pressure. (k) Obesity always causes atherosclerosis. Lipids are already deposited around in almost every organ in overweight persons. The heart is weakened, blood lipid content is high and deposition of lipid in blood vessel already started. All these increases the risk of atherosclerosis.
Summary CHAPTER 8 ffl Biology Term 2 STPM Chapter 8 Transport in Animals and Plants 5. Among the most important tips to help prevent atherosclerosis include the following: (a) Intake of food rich in calories including sugar, saturated fats and cholesterol should be lowered. High fibre diet of vegetables and fruits will lower the risk of atherosclerosis. Lipids including cholesterol bind to cellulose and less are absorbed. (b) Exercise at least twice a week, each time not less than half an hour is advisable. This will promote healthy functioning of the heart and flow of blood in the blood vessels. (c) Avoidance of smoking decreases the risk. Without the burden of carbon monoxide and nicotine, the cardiovascular system is healthier. (d) Consumption of food or supplement high in antioxidants and omega 3 also lower the risk. Antioxidants reduce damage of chemicals to the cardiovascular system. A balance amount of omega 3 and omega 6 promotes better metabolism of lipids so that they are not deposited in arteries. Hypertension 1. Hypertension is a disorder of high blood pressure. Normal blood pressure is when your blood pressure is 120/80 mm Hg most of the time. High blood pressure (hypertension) is when your blood pressure is 140/90 mm Hg or above most of the time. If your blood pressure numbers are 120/90 or higher, but below 140/90. It is called pre-hypertension. 2. When blood pressure is too high: (a) there is a higher risk of getting stroke (b) over-straining the heart results in heart attack. (c) there is a higher risk of getting atherosclerosis, accompanied by ischemic diseases. 3. The following are the causes of hypertension. (a) In short term, it occurs because of contraction of smooth muscles in the wall of small arteries and arterioles. This may happen because of an increase in the concentration of the hormone adrenaline in the blood that stimulates the arterioles to contract. (b) It is also associated with moderate and excessive intake of alcohol. Alcohol directly affects the vasomotor centre of the medulla in most people to increase blood pressure. (c) Smoking causes hypertension as nicotine of tobacco constricts arterioles and makes the blood sticky. (d) Obesity burdens the heart as fats within and outside the blood vessel hinders the flow of blood. (e) Salt in the diet results in higher density in the blood that slows down the blood circulation. (f) Genetic factors or predisposition are inborn. The heart contracts more forcefully or the arterial wall is less elastic. Cardiovascular diseases Disease Meanings 1. Arteriosclerosis *HSJPÄJH[PVU of plaque occurs causing hardening and even rupturing of arterial wall 2. Atherosclerosis Atheroma (plaque) of fat and cholesterol are deposited beneath endothelium of artery 3. Hypertension High blood pressure more than 140/90 mm Hg 4. Myocardial infarction Death of heart muscle tissue caused by blocking of blood sent to the tissue Causes of cardiovascular diseases: 1. High cholesterol level in blood especially from food intake 2. Inborn hypertension or genetic factor 3. Smoking and heavy drinking 4. Old age and diabetes 5. Obese and lack of exercise Preventions: 1. Reduce food with high calorie and cholesterol 2. Stop smoking and excessive intake of alcohol 3. Exercise at least twice a week of 30 minutes 4. Intake of antioxidant such as vitamins A, C and E VIDEO /`WLY[LUZPVU
CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants 4. Prevention of hypertension is the same as in the case of atherosclerosis i.e. by avoiding high calorie and salty food, smoking, alcohol and maintaining a healthy lifestyle through exercise. Myocardial infarction 1. Myocardial infarction is a form of heart attack in which the coronary artery is blocked resulting in the death of a part of heart tissue as no oxygen is sent there. This blockage can be caused by atherosclerosis or embolus. 2. It results in the following: (a) Scar tissue is formed in the heart, the heart is weakened and it is prone to a second attack. (b) The heart cannot function normally and the person is weakened, as supply of blood to the body is not good. (c) Blood clotting called thrombosis tends to occur in the weakened heart. The moving clotted blood called embolus may block artery in the brain, causing stroke, block coronary artery which can result in another myocardial infarction or block any artery, causing ischemia. (d) Severe myocardial infarction causes instant death as too big a part of the heart muscle is without oxygen. 3. Causes and prevention of myocardial infarction are the same as those of atherosclerosis. Most people may show the first sign of impending myocardial infarction. This sign is associated with the gradual blockage of coronary artery or its branches due to atherosclerosis. The usually sign is pain in the chest called angina pectoris due to lack of oxygen in the heart muscle. The other sign is short of breath during exercise. The percentage blockage of the coronary artery and its branches can be determined by C.T. (Computed tomography) or MRI (Magnetic resonance imaging scanning) in the hospital. Knowledge of the percentage of blockage will enable cardiac surgeon to recommend corrective surgery to prevent myocardial infarction. (ULTIVS\ZPZTVZ[VM[LUH WPLJLVMH[OYVTI\Z[OH[OHZ broken free and is carried [V^HYKZ[OLIYHPUI`[OL ISVVKZ[YLHT In medicine, ‘ischemia’ is a YLZ[YPJ[PVUPUISVVKZ\WWS`[V [PZZ\LZJH\ZPUNHZOVY[HNLVM V_`NLUHUKNS\JVZLULLKLK I`JLSS\SHYTL[HIVSPZT[VRLLW [PZZ\LHSP]L Info Bio Info Bio Quick Check 1 1. Why are the walls of the heart of different thickness? 2. How does the heart of a foetus differ from that of an adult? 3. Why is the age of people getting infected with cardiovascular diseases getting younger? Exam Tips 9LTLTILY[OLTLHUPUN JH\ZLZHUKWYL]LU[PVU of arteriosclerosis, O`WLY[LUZPVUHUK T`VJHYKPHSPUMHYJ[PVU
CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants Lymphatic System in Relation to the Blood Circulatory System 2017 1. The lymphatic system is a supplementary transport system to channel a portion (10%) of the tissue fluid back to the blood circulatory system. It is also the major part of the immune system. It plays an important role in immune response as the production of lymphocytes and their actions in getting rid of pathogens occur within it. 2. Its organisation consists of the lymph, lymphatic vessels and lymphoid tissues that include lymph nodes, mucosa-associated lymphoid tissues, spleen and thymus gland. The bone marrow together with the lymphocytes and other lymphoid cells that are originated from its stem cells are also parts of the lymphatic system. 3. The human lymphatic system is as shown in Figure 8.8. Adenoids and tonsil Filter antigens from air and food Left lymphatic duct Drains lymph from left arm, head and lower part of the body Left thoracic duct Thymus gland Maturation of cells Spleen Filters antigens from blood Bone marrow Production of blood cells Lymph nodes Filters antigens from lymph Peyer patch Filters antigens from small intestine Thoracic duct Drains most lymph to vein Right lymphatic duct Drains lymph from right arm and head Figure 8.8 Organisation of the human lymphatic system 4. Lymph is the tissue fluid that has flowed into the lymphatic vessels and is essentially recycled blood plasma. Its component is almost the same as tissue fluid and differs from blood by having no blood cells, INFO (UH[VT`VM[OL 3`TWOH[PJHUK Immune System
CHAPTER 8 Biology Term 2 STPM Chapter 8 Transport in Animals and Plants platelets and lesser amount of plasma proteins. Tissue fluid is plasma squeezed out from blood capillaries. 5. Lymph contains more than 95% of water, lymphocytes, little proteins, glucose, amino acids, fat and mineral ions. The proteins found in the lymph are antibodies or immunoglobulins and complement proteins produced by the lymphocytes. It has little fibrinogen, prothrombin and plasma proteins produced by the liver. It contains histamines produced by granulocytes and heparin produced by mast cells found in the tissues. 6. The lymphatic vessels are the system of fine and bigger vessels that return part of the tissue fluid to the blood circulatory system. They are divided into capillaries and ducts. 7. Lymphatic capillaries are the smallest of the lymphatic vessels and can be found in all tissues except in the spleen. They have one layer of thin squamous epithelium called endothelium, same as that of blood capillaries. Unlike blood capillaries, they have closed ends where the endothelium cells are overlapping each other, forming small pores with valves only to allow small molecules to go in. From such capillaries, they collect to form slightly bigger venules, which then become bigger lymphatic ducts. 8. Special lymphatic capillary is found in each villus of the small intestine called lacteal. The lacteals form a special lymphatic system in the small intestine that absorbs glycerol, fatty acids and lipids. They transport the lipids into the thoracic duct and empties into the circulatory system. The lymphatic capillaries in the liver collect secretions including plasma proteins, nutrients, hormones and urea. 9. Lymphatic ducts have the same structures as the venules or veins of the blood circulatory system. Their walls compose of inner layer of endothelium, with a layer of collagen and a small amount of smooth muscle in the bigger ducts. The bigger ducts have valves to ensure unidirectional flow like those of veins. The flow of lymph is aided by the contraction of the skeletal muscles and a weak suction pressure from the heart. Unlike the veins, the lymphatic ducts does not carry red blood cells, with lymph flowing through lymph nodes and are not symmetrical between left and right sides of the body. There is only one thoracic duct collecting lymph from the legs and abdomen. The thoracic duct joins to the duct from the left side of the head and arm before the lymph is emptied into the left anterior vena cava. On the right side, a duct from the right side of the head and right arm are joined to empty the lymph into the right anterior vena cava. 10. Lymph nodes are bean-shaped structures at specific parts of the body notably in the groins, armpits and beneath the lower jaw where lymphocytes divide and pathogens are filtered. 3`TWOLKLTHPZHK`ZM\UJ[PVU VMS`TWOH[PJZ`Z[LT 0[TH`ILPUIVYU^P[O Å\PKUV[ILPUNHISL[VIL HIZVYILKI`[OLS`TWOH[PJ JHWPSSHYPLZ It may be caused by PUMLJ[PVUZ^OPJO^PSSYLZ\S[PU ^H[LYYL[LU[PVUPU[OLSPTIZ LZWLJPHSS`[OLSLNZ;OLSLNZ usually become oversized PULX\HSS` Info Bio