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.
Forest degradation and loss from the spontaneous expansion of people's activities into forest lands is notoriously difficult to quantify. Shifting agriculture is the primary cause of deforestation, accounting for about 45 per cent of the 7.5 million ha losses in tropical forests in 1976-1980. In 1980 it accounted for 35 per cent of deforestation in Latin America, 70 per cent in Africa, and 49 per cent in South-East Asia (notably Sri Lanka, Thailand, north-east India, Laos, Malaysia, and the Philippines) (Tolba et al., 1992).