Tropical orchids grow into tree bark in rainforests. They require the trees for support and obtain nutrients from debris on the bark, but they do not harm the trees. This demonstrates which type of interaction, and what is the effect of the interaction on the two species

On a spring day, a middle-latitude city (about 40? north latitude) has a surface (sea-level) temperature of 10 ? c. if vertical soundings reveal a nearly constant environmental lapse rate of 6.5 ? c per kilometer and a temperature at the tropopause of –55 ? c, what is the height of the tropopause?