Structure and functions of living organisms Gas exchange Contents 1. The nature and variety of living organisms a. Characteristics of living organisms b. Variety of living organisms 2. Structure and functions of living organisms a. Level of organisation b. Cell structure c. Biological molecules d. Movement of substances into and out of cells e. Nutrition f. Respiration g. Gas exchange h. Transport i. Excretion j. Co-ordination and response k. Diseases and immunity 3. Reproduction and inheritance a. Reproduction b. Inheritance 4. Ecology and the environment a. The organism in the environment b. Feeding relationships c. Cycles within ecosystems d. Human influences on the environment 5. Use of biological resources a. Food production b. Selective breeding c. Genetic modification (genetic engineering) d. Cloning 1 Structure and functions of living organisms Gas exchange Gas exchange system The gas exchange system allows humans to exchange oxygen and carbon dioxide for continuous aerobic respiration. - Oxygen is a substrate of aerobic respiration, whereas carbon dioxide is a waste product. - The gas exchange system is also called the respiratory system. - It is composed of respiratory tracts and gas exchange surfaces. Respiratory tracts 2 Structure and functions of living organisms Gas exchange Trachea - The trachea connects the nasal cavity to the lungs. - It is surrounded by a row of C-shaped cartilage rings. - The cartilage rings keep the trachea open and prevent it from collapsing due to constantly changing air pressure. - The air is full of dust and microbes. - Goblet cells secrete a thin layer of mucus to trap dust particles and microbes to prevent them from entering the lungs. - Ciliated epithelial cells have cilia that beat together to move the mucus upwards and pass it into the oesophagus. 3 Structure and functions of living organisms Gas exchange Gaseous exchange - In animals, gaseous exchange happens by diffusion through a surface. - A gaseous exchange surface must: o be thin – a short distance for gases to diffuse; o have a large surface area – for gases to diffuse over; o be moist – for gases to dissolve into for diffusion; o have good air ventilation – to create and maintain concentration gradients; o have a good blood supply – to transport oxygen to respiring tissues and take away carbon dioxide from those tissues. Alveoli Alveoli are tiny air sacs that provide the majority of the gas exchange surface in the lungs. - Both the alveolar and capillary walls are only one cell thick. - They have grapelike structures. - The alveolar surface is moist with surfactants. - Stale air in alveoli is constantly replaced with new air. - They are surrounded by extensive capillary networks. 4 Structure and functions of living organisms Gas exchange 5 Structure and functions of living organisms Gas exchange Composition of air Effect of physical activity on breathing - Physical activity ultimately increases the rate of aerobic respiration and in turn the rate of gas exchange. - The ventilation rate has to increase to allow more gas exchange per unit time. - Tidal volume is the volume of air inhaled or exhaled in a relaxed state. - Vital capacity is the maximum possible amount of air a person can inhale or exhale. 6 Structure and functions of living organisms Gas exchange - Each breath has to be deeper, approaching the vital capacity, to inhale more oxygen and exhale more carbon dioxide. 7 Structure and functions of living organisms Gas exchange Ventilation - Ventilation is the combination of inhalation and exhalation. - Lungs are flexible but are not muscular, so they cannot contract by themselves. - Expansion of lungs relies on contraction of associated muscles. - These muscles are the diaphragm and intercostal muscles. - Contraction and relaxation of these muscles change the volume and the pressure of the thoracic cavity, thereby causing change in the lung volume. 8
