Notes_Respiration 2024.doc.pdf

Temasek Junior College Think Cycle ✓ Know IP Year 3 Biology RESPIRATION NOTES Learning out...

Temasek Junior College Think Cycle ✓ Know IP Year 3 Biology RESPIRATION NOTES Learning outcomes: By the end of the topic, you should be able to: (a) identify on diagrams and name the larynx, trachea, bronchi, bronchioles, alveoli and associated capillaries (b) explain how the structure of alveolus is suited for its function of gas exchange (c) describe the removal of carbon dioxide from the lungs, including the role of the carbonic anhydrase enzyme (d) describe the process of breathing and the role of cilia, diaphragm, ribs and intercostal muscles (e) define and state the equation, in words and symbols, for aerobic respiration in humans (f) define and state the equation, in words only, for anaerobic respiration in humans (g) explain why cells respire anaerobically during vigorous exercise resulting in oxygen debt that is removed by rapid, deep breathing after exercise (h) describe the respiratory diseases (i.e. chronic bronchitis, emphysema and lung cancer) caused by smoking Use the knowledge gained in this section in new situations or to solve related problems. 1  Introduction 1. WHY DO LIVING ORGANISMS RESPIRE? Living organisms need energy to move, excrete, grow, reproduce and maintain themselves. The ultimate source of energy is light from the Sun. During photosynthesis, green plants convert light into chemical energy which they store in the form of organic molecules. This energy is transferred to other organism through feeding. To use the energy stored in food, living organisms break down the food molecules through a process called oxidation. The oxidation of food molecules to release energy is called respiration (or cellular respiration). Photosynthetic organisms also respire. They oxidise the glucose made during photosynthesis to release energy for the cells to use. Note: energy is released NOT produced/ manufactured. It is released. Cellular respiration can be aerobic (oxygen present) or anaerobic (oxygen absent). Examples of the processes driven by energy released from respiration are: - anabolic reactions (e.g. synthesis of proteins) - active transport (e.g. absorption of glucose in the small intestines, absorption of mineral ions from the soil solution by root hair cells) - movement (e.g. contraction and relaxation of muscles) - maintenance of body temperature 2. AEROBIC RESPIRATION Aerobic respiration is the oxidation of glucose in the presence of oxygen with the release of a large amount of energy. Carbon dioxide and water are released as waste products. Glucose is the preferred respiratory substrate. In eukaryotic cells, most of the process of respiration occurs in the mitochondria. word equation for aerobic respiration: glucose + oxygen large amount of energy + carbon dioxide + water chemical equation for aerobic respiration: 2 C6H12O6 + 6O2 large amount of energy + 6CO2 + 6H2O 3. ANAEROBIC RESPIRATION Anaerobic respiration is the breakdown of food substances in the absence of oxygen, with the release of a relatively small amount of energy. Anaerobic respiration occurs in certain body cells (muscles) and microorganisms. 3.1. Anaerobic respiration in Yeasts: Anaerobic respiration in yeast (unicellular fungi) is called alcoholic fermentation. Equation for anaerobic respiration in yeast: glucose ethanol + carbon dioxide + small amount of energy o The ethanol produced may accumulate in the medium around the cells until its concentration rises to a level which prevents further fermentation, so killing the yeast. 3  3.2 Anaerobic Respiration in Skeletal Muscles: During strenuous exercises, the muscles contract more vigorously for faster movement. This increases energy demand in the muscles. Both breathing and heart rate increase to increase rate of respiration so that more energy can be released. Increased breathing and heart rate to enable: o increased rate of oxygenation of blood at the lungs o increased rate of transport of oxygen and glucose to the muscles o increased rate of removal of the carbon dioxide produced If the increased in oxygen uptake is unable to meet the oxygen demand in the muscles, anaerobic respiration occurs. Anaerobic respiration releases the additional energy required for the increased muscular contraction. Anaerobic respiration causes the accumulation of lactic acid in the muscles that can lead to fatigue. After the exercise has ended, the breathing and heart rate remain high because o lactic acid is sent to the liver to be oxidised into carbon dioxide and water. Some lactic acid is converted to glucose and later glycogen for storage in the liver and muscles. The additional oxygen required to oxidise the lactic acid in the liver is termed oxygen debt. Heart rate and breathing rate returns to norm when all the lactic acid has been oxidised – oxygen debt is paid. NOTE: When anaerobic respiration is occurring, so is aerobic respiration. Aerobic respiration does not stop because anaerobic respiration is occurring 3.3. Differences between Aerobic Respiration and Anaerobic Respiration. Aerobic respiration Anaerobic respiration Availability of Oxygen presence of oxygen absence of oxygen Energy released releases all available energy releases less energy lactic acid in mammals produces carbon dioxide and Other by-products ethanol and carbon dioxide water in yeast. ❖ Strict anaerobes (e.g. some groups of bacteria) - these cannot survive in the presence of oxygen ❖ Facultative anaerobes (e.g. yeasts, many groups of bacteria) - these can release energy either by fermentation or aerobic respiration, depending on whether oxygen is available. - at a cellular level, the muscle cells of animals behave like facultative anaerobes. 4 3.4 Measuring the Rate of Respiration A respirometer can be set up to measure the rate of respiration by measuring the rate of oxygen used. The soda lime (sodium hydroxide) absorbs both the carbon dioxide present in the test-tube and that produced by the living organisms. When the small organisms respire, they take in oxygen and release carbon dioxide. The carbon dioxide is absorbed by the soda lime. This results in a decrease in the volume (and pressure) of the air in the test-tube. Hence the colour liquid moves towards the living organisms. The volume of oxygen used can then be calculated using the distance moved by the colour liquid in a fixed period of time. 5  4. Parts of the Respiratory System Upper respiratory tract Internal intercostal muscle Lower External intercostal respiratory muscle tract Diaphragm Fig. 4.1: Parts of the respiratory system Organ Description of Organ Function Larynx Also known as voice box Contains vocal cords. Air passage for sound production. Trachea Windpipe – 12 cm long The cartilage reinforces the front and sides Supported by C-shaped rings of of the trachea to prevent the collapse of the cartilage airways. Refer to Fig. 4.2 for more information. Bronchi The trachea is branched into 2 Air passage to the lungs. (singular tubes, the bronchi, one to each lung bronchus) Refer to Fig. 4.2 for more information. 6 The epithelium of the airways (trachea and bronchi) is lined with ciliated cells and mucus secreting cells (goblet cells). Fig. 4.2 Mucus: a sticky substance produced by the goblet cells. It traps dust and bacteria that were inhaled. Cilia: Cilia are hair-like structures that are found on the ciliated cells. The cilia sweep mucus containing dust and bacteria upwards towards the pharynx to be swallowed. Bronchioles Each bronchus divides repeatedly Air passage (singular and ends in very fine bronchioles. bronchiole) Alveoli At the end of the bronchioles are Walls of the alveoli form the respiratory (singular clusters of air sacs (alveoli). surfaces for gaseous exchange alveolus) and associated capillaries Diaphragm A sheet of muscular tissue with Changes the volume of the thoracic cavity circumference attached to the for breathing. thoracic cavity. 5. Breathing Also known as ventilation, is a physical exchange of air between the environment and the lungs. It involves inhalation (inspiration; taking in of air) and exhalation (expiration; breathing out of air). 7  5.1 Breathing Mechanism INHALATION EXHALATION 1. Diaphragm contracts and flattens. 1. Diaphragm relaxes and arches upwards. 2. External intercostal muscles contract while 2. Internal intercostal muscles contract while internal intercostal muscles relax. external intercostal muscles relax. 3. Ribs move upwards and outwards. 3. Ribs move downwards and inwards. 4. Volume of thoracic cavity increases. 4. Volume of thoracic cavity decreases. 5. Expansion in the lungs causes air pressure 5. Lungs are compressed. inside to decrease. 6. Air pressure inside the lungs increase. 6. Atmospheric pressure is higher than the 7. Air pressure in the lungs is higher than the pressure in the lungs. atmospheric pressure 7. Air rushes into the lungs. 8. Air is forced out of the lungs to the exterior. The stimulus for breathing is the concentration of carbon dioxide in blood. Concentration of oxygen in the blood does not affect the breathing rate. 5.2 Composition of inhaled and exhaled air Inhaled Air Exhaled Oxygen 21 % 16 % Carbon dioxide 0.03 % 4% Nitrogen 78 % 78 % water variable Saturated temperature variable Body temperature 8 5.3. Gaseous Exchange at the alveoli The site of gaseous exchange is at the alveoli. 4) one-cell thick epithelium 5) one-cell thick capillary wall Fig. 5.1 Structure of a Alveolus and its associated blood capillary Structure of alveoli Function Provides a large surface area to volume ratio Numerous alveoli in the lungs for efficient gaseous exchange Wall of the alveolus is only one cell Reduces the diffusion distance hence allows thick a faster rate of diffusion of gases through it Well supplied by blood capillaries Maintains a steep concentration gradient Thin film of moisture lining the inner Allows oxygen to dissolve in it surface of the alveolus. exhaled carbon inhaled dioxide oxygen oxygenated epithelium of alveolus blood to (one cell thick) pulmonary vein deoxygenated blood from pulmonary artery oxygen rich red blood cells carbon dioxide oxygen poor red diffuses out blood cells of blood into alveolus one cell thick oxygen binds to capillary walls haemoglobin in red blood cell Fig. 5.2 Gaseous exchange in the alveolus 9 The oxygen and carbon dioxide concentration gradients between the alveolar air and the blood are maintained by: A continuous flow of blood through the capillaries Breathing air in and out of the alveoli The alveolar air has a higher concentration of oxygen and lower concentration of carbon dioxide compared to blood in the capillary. Oxygen molecules diffuse from the alveolar air into the red blood cells in the blood capillary. Carbon dioxide molecules diffuse from the blood into the alveolar air space. 5.4. Transport of Oxygen Alveolus→ Capillary → Blood plasma → Red blood cell. Oxygen dissolves in the moisture lining the alveolar walls and then diffuses into the blood capillaries. Oxygen combines with haemoglobin in the red blood cells to form oxyhaemoglobin. This reaction is reversible, depending on amount of oxygen in surroundings. When blood passes through oxygen-poor tissues, the reaction will shift to the left (see figure below) to release oxygen to the tissues. 5.5 Transport of Carbon Dioxide Carbon dioxide is constantly produced by our cells in respiration. It can be transported o i) in the form of hydrogen carbonate ions in the blood plasma (majority of how carbon dioxide is transported) o ii) by dissolving directly in the blood plasma for transport o iii) by binding to haemoglobin in red blood cells (to form carbaminohaemoglobin) 10  Carbonic Anhydrase is an enzyme found only in the red blood cells. It catalyses a reversible reaction between water and carbon dioxide to form carbonic acid. The direction of the reversible reaction depends on the relative concentration of carbon dioxide and water with respect to carbonic acid. At the tissues, concentration of water and carbon dioxide is high. Carbonic anhydrase catalyses the formation of carbonic acid from water and carbon dioxide. The carbonic acid dissociates to form hydrogencarbonate ions and hydrogen ions. This dissociation does not require carbonic anhydrase. The hydrogencarbonate ions diffuse out of the red blood cells and is carried in the blood plasma. In the lungs, hydrogencarbonate ions diffuse back into the red blood cells where they are converted into carbonic acid. Carbonic anhydrase catalyses the conversion of carbonic acid into water and carbon dioxide. The carbon dioxide then diffuses out of the blood capillaries into the alveoli and is expelled during exhalation. FYI: You do not need to know what happens to the hydrogen ions or the involvement of chloride ions. 11 6. RESPIRATORY DISEASES CAUSED BY SMOKING Chronic Bronchitis Causes Signs & Symptoms Smoking; ▪ Paralysed cilia Continual exposure and inhalation of polluted air ▪ Inflammation of the membrane of the trachea and the bronchi ▪ Excessive production of mucus ▪ Chronic cough ▪ Difficulty in breathing as airways are narrowed. ▪ Lungs become susceptible to infection. ▪ May eventually result in emphysema and lung failure. Emphysema Causes Signs & Symptoms Smoking; ▪ Chronic coughing from chronic bronchitis breakdown of the Continual exposure and partition walls of the alveoli. inhalation of polluted air; Developed from chronic ▪ Alveoli enlarged and surface area is reduced. bronchitis ▪ Lungs expand and lose elasticity. ▪ Great difficulty in breathing leading to a strain on the heart. ▪ Lung tissue is damaged beyond repair. Fig. 6.1: Comparing the alveolus of a healthy person with one suffering from emphysema 12  Lung Cancer Causes Signs & Symptoms Smoking; ▪ Uncontrolled growth of cells in a small area of lungs may Continual exposure and spread throughout lungs and block bronchioles inhalation of smoke; Polluted air and vehicle ▪ The cancerous growth may eventually spread throughout the exhaust fumes body ▪ Difficulty in breathing ▪ Blood in sputum Fig. 6.2: Various respiratory diseases and their effects 13