Question

What causes a green plant exposed to the light on only one side, to bend toward the source of light as it grows?

• A. Light stimulates plant cells on the lighted side to grow faster.
• B. Auxin accumulates on the shaded side, stimulating greater cell elongation there.
• C. Green plants need light to perform photosynthesis.
• D. Green plants seek light because they are phototropic.

Answer 1

Answer: (B)

Auxin accumulates on the shaded side, stimulating greater cell elongation there.

Phototropism is the growth of organisms in response to a stimulus. It is most often observed in plants, but can also occur in other organisms such as fungi. The cells on the plant that are farthest from the light have a chemical called auxin that reacts when phototropism occurs. This causes the plant to have elongated cells on the farthest side from the light. Phototropism is one of the many plant tropisms or movements which respond to external stimuli. Growth towards a light source is called positive phototropism, while growth away from light is called negative phototropism.