Gas Exchange
- Small organisms can diffuse oxygen and nutrients into the body from outside
- Diffusion distances from the outside to the inside is very small
- Large surface area to volume ratio
- Metabolic demands are low
- Large organisms have a large distance from the outside to the inside with smaller SA:Vol ratio and larger demands
- Have specialised systems to exchange the gases they need
- Factors affecting the rate of diffusion
- Surface area
- Concentration gradient of particles diffusing
- Distance over which diffusion is taking place
- Mammalian gas exchange system
- Alveoli
- Large surface area; alveoli are globular with many folds
- Short diffusion distance; alveoli are one cell thick and the capillaries run close to the lining
- Steep concentration gradient; blood is continuously taking away the oxygen and bringing CO2 maintaining large differences
- Breathing
- Inhalation is an active process
- Muscles contract, flattening diaphragm
- Volume increases
- Intercostal muscles contract and rib cage goes up and out
- Exhalation is a passive process
- Muscle relaxes, doming the diaphragm
- Volume decreases
- Intercostal muscles relax and rib cage falls
- Inhalation is an active process
- Protection for the lungs
- The air may contain pathogens
- Respiratory system produces lots of mucus that lines your airways which traps tiny particles and organisms
- Mucus swept into the stomach where it is digested
- Gas exchange in fish
- There is far less oxygen in water compared to air so typical lungs would not be efficient enough
- Bony fish are very active but cannot diffuse oxygen in due to impermeable skin
- While swimming water passes over the gills in one direction transferring oxygen
- Bony fish have an operculum which maintains a flow of water even when the fish is stationary
- Cartilaginous fish do not have an opercula so need to swim all the time
- Structure of the gills
- Gill filaments occur in a large stack needing water to stop them sticking together
- Rich blood supply and large surface area
- Blood moves in opposite way to the water allowing for more effective gas exchange
- If a fishes gill filaments stick together the exposed surface area is not big enough
- Ventilating the gills
- Cartilaginous fish do not have an operculum
- They therefore have to maintain a steady stream of water over the filaments to make sure they do not stick
- Maximising gas exchange
- Countercurrent exchange system
- Overlapping gill filaments
- Diffusion in water is slow however overlapping gill filaments causes resistance to water flow slowing down the stream. This allows more opportunity for diffusion
- Gas exchange in insects
- The whole process relies on diffusion alone
- Activeness of insect correlates to number of sphincters open
- Water will be at the end of tracheoles to help diffusion but also to maintain osmotic levels in the cell when lactic acid is produced
- The opening of spiracles is stimulated by the presence of carbon dioxide , lactic acid and lack of oxygen
- Very active insects that require more oxygen
- Mechanical ventilation, air is actively pumped into the tracheal system by muscles which draw air in and out of the trachea and tracheoles
- Collapsible trachea or air sacs, these act as air reservoirs allowing them to be accessed in periods of high activity