Doug plants a few peas. after two days, he sees the shoot and the root forming. he observes that the shoot grows upward, toward the light. the root grows downward, into the soil. why do these embryonic organs grow in a specific direction?
a. the shoot is positively phototropic and positively gravitropic; the root is positively phototropic and positively gravitropic.
b. the shoot is positively phototropic and negatively gravitropic; the root is positively gravitropic and negatively phototropic.
c. the shoot is positively gravitropic and negatively phototropic; the root is positively phototropic and negatively gravitropic.

The answer is B. The shoot is positively phototropic and negatively gravitropic; the root is positively gravitropic and negatively phototropic.

Phototropism is reaction of a plant to a light stimulus. Growth of the plant or its part grow towards the light stimulus is called positive phototropism. Growth of the plant or its part away from the light stimulus is called negative phototropism.
Gravitropism is reaction of a plant to gravity. Growth of the plant or its part in the same direction as gravity is called positive gravitropism. Growth of the plant or its part grow in the opposite direction of gravity is called negative gravitropism.

The shoot is positively phototropic (grows toward the light) and negatively gravitropic (grows upward, in opposite direction of gravity).
The root is negatively phototropic (grows into the soil, away from the light) and positively gravitropic (grows downward, in the same direction as gravity).