What are the three main plant tropisms and what exactly do they do/ are cause of?

1)  phototropism—This refers to how plants tend to response to "light" as a stimulus; for instance, plants may grow in a "bending" pattern TOWARD light.

2)  gravitotropism—This refers to how plants respond to gravity.  The "stems" of plants exhibit "negative gravitotropism";  that is, the stems of plants tend to "pull up" (away from the force of gravity).  The roots of plants exhibit "positive gravitotropism";  that is, they tend to grow "downward" toward the Earth.

3)  thigmotropism—This refers to how plants responds when "exposed to touch."  For instance, when plants grow around a fence or trellis.

Interacting group of various species in a common location. for example, a forest of trees and undergrowth plants, inhabited by animals and rooted in soil containing bacteria and fungi, constitutes a biological community.