Exchange surfaces GapFill

While unicellular organisms can often exchange all the substances they need to with their environment by  simple diffusionfacilitated diffusionco-transportactive transport, larger organisms have a smaller  diffusion distanceexchange areasurface-area-to-volume ratioconcentration gradient and need specialised exchange surfaces to maintain their higher metabolic rate.

Insects have a number of pores called  alveolilamellaespiraclesstomata and a system of internal passages called  alveolibronchiarteriolestracheae to exchange respiratory gases. Meanwhile, bony fish use  gillsbronchiolesmesophylllungs containing a series of stacked filaments lined with  lamellaespiraclesmyofibrilsopercula to increase the surface area for gas exchange. They also use  mass flowosmosiscountercurrent flowtranslocation to maintain a steep concentration gradient of oxygen in their blood.

Humans have specialised organs for gas exchange called  heartslungsbronchiribs. These contain small air sacs called  tracheolesstomataalveolibronchioles, which can stretch and recoil during inhalation and exhalation due to the presence of  tendonboneelasticglobular fibres. The airways (consisting of the  vena cavaaortapulmonary veintrachea, which branches into bronchi and bronchioles) contain ciliated epithelium and are lined with  goblet cellsmyelin sheathSchwann cellscardiac muscle, which produce mucus to trap any pathogens. They are also ringed with  cartilagecardiac muscletendonssquamous epithelia to prevent them collapsing when air is drawn into them. A  spirometerpotometerdialysis machinepacemaker can be used to calculate oxygen uptake and take measurements such as  vital capacitybreathing rateresidual volumetidal volume, which is the maximum volume of air that can be moved in a single breath.