In Which of the Following Actions is Auxin Involved

Question

In which of the following actions is auxin involved?
A)hydrotropism
B)gravitropism
C)thigmotropism
D)cytotropism
E)pigmotropism

Accepted Answer

The positive gravitropism of roots and the negative gravitropism of stems occurs because the two types of tissues respond differently to auxin,which appears on the lower side of both stems and roots after gravity has been perceived.Auxin inhibits the growth of root cells;therefore,only the cells of the upper surface elongate so that the root curves downward.Auxin stimulates the growth of stem cells;therefore,the cells of the lower surface elongate,and the stem curves upward.