Hint: The plant growth regulators play a vital role in growth and development of the plants. Auxin is mainly present on the tip of the plants. The plant movements towards light and gravity can be regulated by the plant growth regulators.
The phototropic movement refers to the movement of the plants towards light. The response of the plants towards light is due to presence of auxin hormone on its tips. The auxin hormone is also called the growth regulator. It causes growth of seedling and shoots of mature plants to grow towards the light.
The geotropic movement refers to the movement of the plant towards gravity. It is directional growth of the plant organs.
The auxin hormones are redistributed to the lower side of horizontally growing root cells and inhibits the growth of the lower side of roots. The upper side of the plants grows normally which in turn curves the roots downwards. Enzymes catalysis is biological reactions. They are not responsible for the growth and movement of the plants.
The plants prepare their food in the form of starch by the process of photosynthesis.
Gibberellins play an important role in the plant growth including stem elongation and germination.
From the above information we have found that Phototropic and geotropic movements in plants have been traced to be linked with auxin.
Hence, the correct answer is option (D).
Note: The plants have five types of growth regulators: Auxin, gibberellins, cytokines, abscisic acid, ethylene. All these growth regulators play a very important role in the growth and development of the plant. The gibberellins and cytokines initiate cell differentiation and cell elongation. The abscisic acid works as an inhibitor hormone. Ethylene helps in the ripening of the fruits.