1-<span>auxins in the lower sides of stems cause cell elongation that bends the stem upright
2-</span><span>thigmotropism.
3-</span><span>phototropic and gravitropic
4-</span><span>the production of anthocyanin and the breakdown of chlorophyll.
5-</span><span>exposing the plant to a brief period of light in the middle of the night</span>
Viscosity refers to the speed at which a substance can flow (i.e. the thickness of the substance/its ability to flow). I think that's the closest the English language gets.