Soil plant atmosphere continuum Soil plant atmosphere continuum The soil-plant-atmosphere continuum (SPAC) is the pathway for water moving from soil through plants to the atmosphere. Continuum in the description highlights the continuous nature of water connection through the pathway. The low water potential of the atmosphere, and relatively higher (i.e. less negative) water potential inside leaves, leads to a diffusion gradient across the stomatal pores of leaves, drawing water out of the leaves as vapour. As water vapour transpires out of the leaf, further water molecules evaporate off the surface of mesophyll cells to replace the lost molecules since water in the air inside
Mastoid cells is not pneumatized, but becomes aerated over the first year of life. Poor pneumatization is associated with eustachian tube dysfunction. Infections in the middle ear can easily spread into the mastoid area via the aditus ad antrum and mastoid antrum. Mastoid cells A section of the mastoid process of the temporal bone of the cranium shows it to be hollowed out into a number of spaces, the mastoid cells, which exhibit great variety in their size and number. At the upper and front part of the process they are large and irregular and contain air (a form of skeletal pneumaticity),