Question

Name the external stimuli that of the plant move upwards and down wards

Answer 1

plant is +vely phototrophic and _vely geotrophic.so the external stimulus may be light and gravity.in first case plant grow in direction of light and in second case root of plant grow downward due to gravity.
i think this is the answer.

Answer 2

movement of plant parts is due to various stimuli like gravity, water, light, chemical, touch, etc. So, the function of control and coordination in plants is performed by the chemical substances called plant hormones or phytohormones.