How do sunflowers work?

Question

What biological/chemical or otherwise natural mechanism allows for sunflowers to face always at the sun whenever it is visible?

Answer 1

The mechanism is called a photo tropism.

Photo tropism  is directional growth in which the direction of growth is determined by the direction of the light source. In other words, it is the growth and response to a light stimuli. Phototropism is most often observed in plants, but can also occur in other organisms such as fungi. Phototropism is one of the many plant tropisms or movements which respond to external stimuli. Growth towards a light source is a positive phototropism, while growth away from light is called negative phototropism (or Skototropism). Most plant shoots exhibit positive phototropism, while roots usually exhibit negative phototropism, although gravitropism may play a larger role in root behavior and growth. Some vine shoot tips exhibit negative phototropism, which allows them to grow towards dark, solid objects and climb them.

Phototropism in plants such as Arabidopsis thaliana is regulated by blue light receptors called phototropins. Other photosensitive receptors in plants include phytochromes that sense red light and cryptochromes that sense blue light. Different organs of the plant may exhibit different phototropic reactions to different wavelengths of light. Stem tips exhibit positive phototropic reactions to blue light, while root tips exhibit negative phototropic reactions to blue light. Both root tips and most stem tips exhibit positive phototropism to red light.

Phototropism is enabled by auxins. Auxins are plant hormones that have many functions. In this respect, auxins are responsible for expelling H+ ions (creating proton pumps) which decreases pH in the cells on the dark side of the plant. This acidification of the cell wall region activates enzymes known as expansins which break bonds in the cell wall structure, making the cell walls less rigid. In addition, the acidic environment causes disruption of hydrogen bonds in the cellulose that makes up the cell wall. The decrease in cell wall strength causes cells to swell, exerting the mechanical pressure that drives phototropic movement. Phototropism relates to photosynthesis.

Answer 2

The sunflower (Helianthus annuus) is an annual plant native to the Americas in the family Asteraceae, with a large flowering head (inflorescence).

Typically, there are 34 spirals in 1 direction and 55 in the other; on a very large sunflower you may see 89 in one direction and 144 in the other.

A model for the pattern of florets in the head of a sunflower was proposed by H Vogel. This is expressed in polar coordinates

    r = c \sqrt{n},

    \theta = n \times 137.5^{\circ},

where θ is the angle, r is the radius or distance from the center, and n is the index number of the floret and c is a constant scaling factor. It is a form of Fermat's spiral. The angle 137.5° is related to the golden ratio and gives a close packing of florets. This model has been used to produce computer graphics representations of sunflowers.

hope this helps u.............