Question

The solar tracking (moving in the sun's direction) of the sunflower is called _________.
1. Thigmotropism
2. Phototropism
3. Heliotropism
4. Hydrotropism

Answer 1

Correct Answer - Option 3 : Heliotropism

The correct answer is Heliotropism.

• Heliotropic plants slowly track the motion of the sun across the sky during the day and then drift back during the nighttime.
• Sunflowers display heliotropic movement even on cloudy days.
• Floral heliotropism is controlled by motor cells located just below the flower head.

Thigmotropism	It is the directional response of a plant organ to touch or physical contact with a solid object. This response is caused by the induction of some pattern of differential growth. This phenomenon is clearly illustrated by the climbing tendrils of some plants, such as the sweet pea.
Phototropism	It is a directional response that allows plants to grow towards, or in some cases away from, a source of light. Photoperiodism is the regulation of physiology or development in response to day length.
Hydrotropism	It is a directed growth in response to water or moisture gradients and begins in the root cap with the sensing of the moisture gradient.