Question Video: Understanding What Tropism Causes Plants to Tilt Towards the Sun Biology

During growth, π»π‘’π‘™π‘–π‘Žπ‘›π‘‘β„Žπ‘’π‘ , or sunflowers, are well known for tilting during the day to face the Sun. What tropism is taking place here?

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Video Transcript

During growth, Helianthus, or sunflowers, are well known for tilting during the day to face the Sun. What tropism is taking place here? (A) Hydrotropism, (B) chemotropism, (C) phototropism or heliotropism, (D) thigmotropism or haptotropism, or (E) geotropism.

A tropism is a directional growth or movement response of an organism, in this case a plant, either toward or away from a stimulus. In this example, the stimulus is sunlight and the response is for the sunflower to grow toward the light.

Whenever we are referring to light, we use the prefix photo-. So this type of response is known as phototropism. And because the sunflower grows toward the light, it is exhibiting positive phototropism. If it were to grow away from the light, it would be negative phototropism.

In this example, the sunflower is specifically receiving light from the Sun. So its response can also be termed heliotropism, because helio- means Sun. It’s not a coincidence that this same prefix can be found in the Latin name for sunflowers, Helianthus. They were named for their tendency to respond in this way.

We have therefore determined that the correct answer is (C). The tropism that is taking place when sunflowers tilt during the day to face the Sun is phototropism or heliotropism.

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