NEET Practice Questions (MCQs) with Answers & Solutions

Synthetic auxins, such as 2,4-D, are used as herbicides (weedicides). When applied in higher concentrations, they promote uncontrolled growth leading to the death of the plant, which is why they are effective as weed killers.

2,4-D (2,4-Dichlorophenoxyacetic acid) is a synthetic auxin, which is a type of plant growth regulator. It is widely used as a herbicide. The other options like IAA (Indole-3-acetic acid), GA (Gibberellic acid), and IBA (Indole-3-butyric acid) are naturally occurring plant hormones.

ABA (Abscisic acid) is a plant hormone that inhibits seed germination and promotes dormancy. It is known to play a major role in inhibiting the sprouting of potato tubers during storage by maintaining dormancy.

The decrease in auxin concentration in a developing plant can lead to increased activity in lateral buds. Auxin is known to inhibit the growth of lateral buds through a process called apical dominance. When the level of auxin decreases, the inhibition is lifted, leading to the activation and growth of lateral buds.

Gibberellins were first discovered in Japan in the 1920s when a fungal pathogen, Gibberella fujikuroi, was found to cause abnormal growth in rice plants. The fungus produced a substance that caused the rice plants to grow excessively tall and spindly, which was later identified as the plant hormone gibberellin.

Gibberellins play a crucial role in promoting stem elongation, especially in dwarf plants. They stimulate cell elongation and division, leading to the longitudinal growth of dwarf plants and enabling them to reach a more typical size.

Cytokinins are a class of plant hormones that promote cell division, or cytokinesis, in plant roots and shoots. They work in conjunction with auxins to control the growth and development of plant tissues.

Cytokinins are known to delay the senescence (aging) of leaves and other plant organs by promoting cell division and growth. They help maintain the green color of leaves by preventing chlorophyll degradation. This is why treating a garland of green leaves with cytokinin can keep it green for a longer period.

Cytokinins inhibit senescence of vegetative parts and plants by promoting cell division and delaying the aging process. These hormones are crucial for maintaining the vitality and longevity of plant tissues.

Abscisic acid (ABA) is a natural growth inhibitor and senescence-inducing hormone. It plays a key role in processes such as leaf abscission, seed dormancy, and response to environmental stress, which are all associated with the aging and senescence of plant tissues.