Gas exchange Systems

Gas exchange Systems

1. Animals

   • Fishes have gills through which they exchange gasses.
     • Counter-current occurs where water and blood flow in the opposite directions, via the lamellae and Gill filaments. Oxygen diffuses into the blood
       • Both these features have a large surface area making the gas exchange more efficient and faster.
       • This happens continuously so that a concentration gradient is maintained. This means diffusion can occur continuously.
   • Humans have lungs where gas exchange occurs, between the alveoli and the capillaries.
     • When we inhale, our diaphragm and external intercostal muscles contracts, increasing the volume of the thorax, so Oxygen diffuses in.
     • When we exhale, our internal intercostal muscles contracts, and the others relax, decreasing the volume but increases pressure, forcing Carbon Dioxide out.
       • The Oxygen travels down our trachea, through the bronchi, through little bronchioles, into the alveoli.
         • Alveoli have a one cell thick, and permeable membrane, allowing efficient gas exchange and fast. There are many of them which increases their surface area.
         • Due to a continuous blood circulation, a concentration gradient  is maintained so that Oxygen can always diffuse into the blood.
         • The Oxygen travels from the alveoli, through the alveolar epithelium, and through the capillary endothelium into the blood.

2. Insects

   • They have spiracles through which their gasses exchange, and there are many of them, which increases their surface area.
     • The spiracles open when gas exchange is requires and close when too much water is being lost, so that the insect does not get dehydrated.
     • The Oxygen diffuses through into the tracheoles where it diffuses into the cells, ready for respiration

3. Plants

   • Gas exchange occurs at the stomata (bottom of a leaf), which opens and closes, and is controlled by the guard cells. Stomata are gaps between mesophyll cells, at the lower epidermis.
     • Usually, the stomata closes when too much water is being lost, and the guard cells become flaccid, however, if water enters the plant, it becomes turgid opening the stomata.
   • Xerophytes (plants in heat)
     • These have specific features that allow them to adapt to warm conditions, by reducing water.
       • A waxy cuticle on surface to reduce evaporation.
       • Sunken stomata which traps water vapour.
       • A layer of hair on the epidermis to reduce water vapor around the stomata.
       • Leaves reduced to spines to reduce the amount of water lost by evaporation via leaves.

4. Single-celled organisms

   • Oxygen diffuses directly into these cells, as they are so tiny and have such a large surface area, the diffusion pathway is very small, and this makes the process faster.