Question

What is phototropism ?

Hint:

Break down the word to understand its meaning: Photo- means "light" and -tropism means "directional growth". So, phototropism is simply growth in response to light.

Answer 1

Phototropism is the directional growth of a plant, or part of a plant, in response to a light stimulus.
\[\begin{array}{rl} \bullet & \text{It is a type of tropic movement, where the direction of the stimulus determines the direction of the response.} \\ \bullet & \text{Positive Phototropism: The growth of a plant part towards the light source. This is exhibited by the shoots and stems of plants, as it helps them maximize light absorption for photosynthesis.} \\ \bullet & \text{Negative Phototropism: The growth of a plant part away from the light source. This is exhibited by the roots of most plants.} \\ \bullet & \text{Mechanism: This response is mediated by the plant hormone auxin. Auxin accumulates on the shaded side of the stem, promoting cell elongation there. This differential growth causes the stem to bend towards the light.} \\ \end{array}\]