3.1 - Exchange Surfaces

• Multicellular organisms require specialised gas exchange surfaces due to their smaller surface area to volume ratio, meaning the distance that needs to be crossed is larger and substances cannot easily enter the cells as in a single-celled organism.
• Surface area to volume ratio is calculated as Ratio = Surface area Volume.
• Three features of an efficient gas exchange surface are: Large surface area, such as root hair cells; Thin/short distance, like alveoli; and Steep concentration gradient, maintained by blood supply or ventilation, like gills.
• The trachea is a wide tube supported by C-shaped cartilage to keep the air passage open during pressure changes, lined by ciliated epithelium cells which move mucus, produced by goblet cells, towards the throat to be swallowed, preventing lung infections, and carries air to the bronchi.
• The bronchi are supported by rings of cartilage and are lined by ciliated epithelium cells and goblet cells, but are narrower and there are two of them, one for each lung, allowing passage of air into the bronchioles.
• In the countercurrent exchange system, blood and water flow across the lamellae in opposite directions, maximising the amount of oxygen absorbed by the fish.
• In the process of gas exchange in insects, gases move in and out of the tracheae through the spiracles, and a diffusion gradient allows oxygen to diffuse into the body tissue while waste CO2 diffuses out.
• Breathing rate is the number of breaths we take per minute, which can be calculated from the spirometer graph by counting the number of peaks in one minute.
• The two main features of a fish’s gas transport system are gills, located within the body, supported by arches, along which are multiple projections of gill filaments, stacked up in piles, and lamellae, at right angles to the gill filaments, giving an increased surface area.
• The three main features of an insect’s gas transport system are spiracles, holes on the body’s surface which may be opened or closed by a valve for gas or water exchange, tracheae, large tubes extending through all body tissues, supported by rings to prevent collapse, and tracheoles, smaller branches dividing off the tracheae.
• Tidal volume is the volume of air we breathe in and out during each breath at rest, which can be calculated from the spirometer graph by finding the amplitude at rest.
• During expiration, external intercostal muscles relax, bringing the ribs down and in, while the diaphragm contracts and domes upwards, decreasing the volume of the thorax, causing air to move out to rebalance.
• The walls of alveoli are only one cell thick, covered with a network of capillaries, 300 million in each lung, facilitating gas diffusion.
• Vital capacity is the maximum volume of air that can be taken in or expelled from the lungs in one breath, which can be calculated from the spirometer graph by finding the maximum amplitude.
• Spirometers are used to measure lung volume.
• Alveoli are mini air sacs, lined with epithelium cells, site of gas exchange.
• During inspiration, external intercostal muscles contract, pulling the ribs up and out, while the diaphragm relaxes and flattens, increasing the volume of the thorax, causing air to move in to rebalance.
• The bronchioles are the smallest gas exchange surfaces in the mammalian gaseous exchange system, narrower than the bronchi, and allow passage of air into the alveoli.
• Multicellular organisms require specialised gas exchange surfaces due to their smaller surface area to volume ratio, meaning the distance that needs to be crossed is larger and substances cannot easily enter the cells as in a single-celled organism.
• Three features of an efficient gas exchange surface are: Large surface area, such as root hair cells; Thin/short distance, like alveoli; and Steep concentration gradient, maintained by blood supply or ventilation, like gills.
• The trachea is a wide tube supported by C-shaped cartilage to keep the air passage open during pressure changes, lined by ciliated epithelium cells which move mucus, produced by goblet cells, towards the throat to be swallowed, preventing lung infections, and carries air to the bronchi.
• The two main features of a fish’s gas transport system are gills, located within the body, supported by arches, along which are multiple projections of gill filaments, stacked up in piles, and lamellae, at right angles to the gill filaments, giving an increased surface area.
• In the countercurrent exchange system, blood and water flow across the lamellae in opposite directions, maximising the amount of oxygen absorbed by the fish.
• The three main features of an insect’s gas transport system are spiracles, holes on the body’s surface which may be opened or closed by a valve for gas or water exchange, tracheae, large tubes extending through all body tissues, supported by rings to prevent collapse, and tracheoles, smaller branches dividing off the tracheae.
• Breathing rate is the number of breaths we take per minute, which can be calculated from the spirometer graph by counting the number of peaks in one minute.
• In the process of gas exchange in insects, gases move in and out of the tracheae through the spiracles, and a diffusion gradient allows oxygen to diffuse into the body tissue while waste CO2 diffuses out.
• The bronchi are supported by rings of cartilage and are lined by ciliated epithelium cells and goblet cells, but are narrower and there are two of them, one for each lung, allowing passage of air into the bronchioles.
• Tidal volume is the volume of air we breathe in and out during each breath at rest, which can be calculated from the spirometer graph by finding the amplitude at rest.
• During expiration, external intercostal muscles relax, bringing the ribs down and in, while the diaphragm contracts and domes upwards, decreasing the volume of the thorax, causing air to move out to rebalance.
• The walls of alveoli are only one cell thick, covered with a network of capillaries, 300 million in each lung, facilitating gas diffusion.
• Vital capacity is the maximum volume of air that can be taken in or expelled from the lungs in one breath, which can be calculated from the spirometer graph by finding the maximum amplitude.
• Spirometers are used to measure lung volume.
• Alveoli are mini air sacs, lined with epithelium cells, site of gas exchange.
• During inspiration, external intercostal muscles contract, pulling the ribs up and out, while the diaphragm relaxes and flattens, increasing the volume of the thorax, causing air to move in to rebalance.
• The bronchioles are the smallest gas exchange surfaces in the mammalian gaseous exchange system, narrower than the bronchi, and allow passage of air into the alveoli.