Explanation
$$\textbf{Correct option: }$$ B
$$\textbf{ Solution: }$$
$$\textbf{ Option (a): }$$
$$\bullet$$ Auxins are present at the tip region of the plant stem and promote the growth of the plant.
$$\bullet$$ The tip of the plant stem is made up of meristematic tissue which is responsible for secretion and storage of auxin hormone.
$$\bullet$$ IAA stands for Indole-3-acetic acid which belongs to auxin class.
$$\textbf{ Option (B): }$$
$$\bullet$$ Abscisic acid (ABA) mainly acts as a plant inhibitor hormone. It promotes the dormancy of seeds and buds. It also inhibits the seed germination.
$$\bullet$$ This plant hormone is also responsible for the witting and falling of leaves.
$$\textbf{ Option (C): }$$
$$\bullet$$NAA stands for Naphthaleneacetic acid that is a synthetic plant hormone in the auxin family.
$$\bullet$$it is used in vegetative propagation of plants from stem and leaf cuttings.
$$\bullet$$It also plays a functional role in plant tissue culture.
$$\textbf{ Option (D): }$$
$$\bullet$$ GA stands for Gibberellic acid.
$$\bullet$$ Gibberellin is one of the plant hormones which promotes the growth and differentiation of the plant.
$$\bullet$$ It also promotes cell differentiation and cell enlargement in the presence of auxin.
$$\bullet$$ Gibberellin are involved in seed germination in certain plants.
Solution:
• Correct answer is option D
Synthetic plant hormones are synthetic growth inhibitors which have a pronounced effect on the growth and development of plants. 2 morphactins, flurenol and chloroflurenolmethyl are well known. Morphactins in combination with 2, 4- D have been found to be effective weedicides. Synthetic auxins are extensively used as herbicides, the most widely known being 2, 4-D and the notorious 2, 4, 5-T, which were used in a 1:1 combination as agent orange during the Vietnam war and sprayed over the Vietnam forests as a defoliant. Thus, the correct answer is option C.
Auxin promotes cell growth and elongation of the plant. In the elongation process, auxin alters the plant wall plasticity, making it easier for the plant to grow upwards. Auxin also influences rooting formations. By applying NAA or IBA to a plant cutting from a parental plant, rooting takes less time for the new plant greatly increasing its chance of survival. Auxin is responsible for apical dominance and phototropism. Apical dominance means that a plant has the tendency to grow quickly up the central shaft without properly filling in the plant with smaller limbs and leaves. Phototropism is a process by which auxin on the exterior of a plant is degraded to cause a slope of the plant towards the light.
Therefore, the correct answer is option D.
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