Plant Hormones

1. Which one of the following is a plant hormone ?

Which one of the following is a plant hormone ?

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Oestrogen
Cytokinin
Insulin
Thyroxin
This question was previously asked in
UPSC CISF-AC-EXE – 2021
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Cytokinin is one of the major classes of plant hormones. Plant hormones (or phytohormones) are signaling molecules produced within plants that occur in extremely low concentrations. Hormones regulate various aspects of plant growth and development. Oestrogen, Insulin, and Thyroxin are animal hormones.
Cytokinins are a group of plant hormones that promote cell division (cytokinesis) in plant roots and shoots. They are involved in various processes such as cell growth, differentiation, apical dominance, and delaying senescence (aging) of leaves.
Major classes of plant hormones include auxins, gibberellins, cytokinins, abscisic acid (ABA), and ethylene. These hormones interact with each other in complex ways to regulate plant development. Oestrogen is a primary female sex hormone in animals. Insulin is a peptide hormone produced by the pancreas that regulates blood sugar levels in animals. Thyroxin is a thyroid hormone produced by the thyroid gland in animals that regulates metabolism.

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2. Which one among the following hormones inhibits the growth activity in

Which one among the following hormones inhibits the growth activity in plants ?

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Auxins
Cytokinins
Abscisic acid
Gibberellins
This question was previously asked in
UPSC CDS-2 – 2024
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Abscisic acid (ABA) is a plant hormone that acts as an inhibitor of growth and metabolism. It promotes dormancy, stomatal closure during water stress, and leaf senescence.
Plant hormones regulate various aspects of plant growth, development, and responses to environmental stimuli.
Auxins, Cytokinins, and Gibberellins are generally considered growth-promoting hormones, although their effects can vary depending on concentration and plant tissue. Ethylene is another plant hormone, often associated with fruit ripening and senescence, and can also inhibit growth in some contexts.

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3. A student was doing an experiment on increasing the cell division amon

A student was doing an experiment on increasing the cell division among plants. She asked her supervisor to suggest the specific plant hormone for the same. Had you been her supervisor, which plant hormone would you suggest ?

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Abscisic acid
Gibberellins
Cytokinin
Auxin
This question was previously asked in
UPSC CDS-1 – 2021
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The plant hormone to suggest for increasing cell division among plants would be Cytokinin.
Cytokinins are a class of plant hormones that promote cell division (cytokinesis) in plant roots and shoots. They are involved in cell growth, differentiation, and delay of senescence.
Auxins primarily promote cell elongation, although they interact with cytokinins in regulating cell division and differentiation. Gibberellins promote stem elongation and germination. Abscisic acid is primarily involved in inhibiting growth and promoting dormancy and stress responses.

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4. The plant growth regulators are small, simple molecules of diverse che

The plant growth regulators are small, simple molecules of diverse chemical composition. They are

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carbohydrates, fats and proteins
indole compounds, adenine derivatives, carotenoids and terpenes
fatty acids, glucose and vitamins
vitamin C, vitamin D and glucose
This question was previously asked in
UPSC CDS-1 – 2017
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Plant growth regulators are small, simple molecules including indole compounds, adenine derivatives, carotenoids and terpenes.
Plant growth regulators (PGRs), also known as phytohormones, are organic compounds other than nutrients which in small amounts promote, inhibit or otherwise modify any physiological process in plants. The main classes of PGRs include Auxins (indole compounds, e.g., IAA), Cytokinins (adenine derivatives, e.g., kinetin), Gibberellins (terpenes, e.g., GA3), Abscisic Acid (carotenoid derivatives/terpenes, e.g., ABA), and Ethylene (a gaseous hormone). These chemical classifications align with the options provided.
Carbohydrates, fats, and proteins are macronutrients providing energy and building blocks. Vitamins are essential micronutrients, primarily for animal metabolism (some roles in plants are indirect). Fatty acids and glucose are basic organic molecules and metabolic intermediates, not classified as plant growth regulators in the same way as phytohormones.

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