Air is then breathed into the windpipe and lungs, while the mucus is swallowed (figure 3). Other. Other interesting structures associated with the nasal and sinus tract: Tear duct (called the nasolacrimal duct): drains tears from the inside corner of the eye into the nasal cavity (figure 1).
Human activity is the main cause of soil degradation. Agriculture plays a large part in soil degradation, especially clearing, irrigation, the spreading of chemical fertilizer â¦ s and pesticides, overgrazing and even the passage of heavy farming equipment. Tillage and the clearing and deforestation of large plots of land also lead to soil degradation.
Little reliable data is available on the extent of land degradation in Africa. However, anyone who has travelled through the continent has observed that land degradation is widespread and serious. The presence of gullies and sand dunes, of degraded forests and grazing lands are obvious, although the effects of sheet erosion and declining soil fertility are less noticeable.