The chemical precursor for the biosynthesis of Auxin is usually:
- Mevalonic acid
- Acetyl CoA
- Tryptophan
- Methionine
Explanation: The amino acid Tryptophan is the primary precursor for the biosynthesis of Indole-3-acetic acid (IAA) in plants.
Which hormone is essential for maintaining the 'Seed Bank' in soil by preventing premature germination?
- Auxin
- Ethylene
- Gibberellic acid
- Abscisic acid
Explanation: By inducing and maintaining seed dormancy, Abscisic Acid (ABA) ensures that seeds do not germinate until they experience favorable environmental triggers.
Which hormone is responsible for the 'Malting' industry's high efficiency in barley processing?
- Gibberellin
- Ethylene
- Auxin
- Abscisic acid
Explanation: Gibberellins are used to accelerate the hydrolysis of starch in barley seeds during the malting process for beer production.
Which hormone allows a plant to survive during heavy flood or drought by slowing down metabolism?
- Cytokinin
- Indole acetic acid
- Abscisic acid
- Gibberellic acid
Explanation: ABA induces a state of metabolic inactivity or dormancy, helping the plant conserve resources and survive stressful environmental conditions.
The discovery of Gibberellins was associated with which specific kingdom of life?
- Fungi
- Plantae
- Monera
- Protista
Explanation: Gibberellins were first isolated from the fungus *Gibberella fujikuroi*, which caused the 'foolish seedling' disease in rice.
In tissue culture, which hormone is essential for xylem differentiation?
- Gibberellin
- Auxin
- Ethylene
- Abscisic acid
Explanation: Auxin controls xylem differentiation and also plays a significant role in helping cells divide during tissue culture.
Statement I: Abscisic acid is a derivative of carotenoids.
Statement II: Abscisic acid promotes cell division in the cambium.
- Statement I correct
- Statement II correct
- Both are correct
- Both are incorrect
Explanation: Statement I is correct; ABA is a C15 terpenoid derived from carotenoids. Statement II is incorrect; ABA inhibits growth and division.
Which hormone helps a plant survive by inducing dormancy in lateral buds during winter?
- Ethylene
- Auxin
- Abscisic acid
- Gibberellin
Explanation: Abscisic acid (ABA) acts as a general growth inhibitor and induces dormancy in buds and seeds during unfavorable environmental conditions.
Which of the following hormones is derived from terpenes?
- Auxins
- Cytokinins
- Gibberellins
- Abscisic acid
Explanation: Gibberellins are chemically classified as terpenes, while Auxins are derived from indole compounds and ABA from carotenoids.
Regarding fruit production, Gibberellins are often used to increase the size of which fruit?
- Pineapples
- Grapes
- Bananas
- Tomatoes
Explanation: Gibberellins are widely used in viticulture to increase the size of individual grapes and the length of the fruit bunches.
Which hormone is used to promote the 'malting' process in the barley industry?
Explanation: GA3 (Gibberellic acid) is used in the brewing industry to speed up the malting process in barley seeds.
Abscisic acid inhibits the synthesis of which essential cellular material during dormancy?
- Storage lipids
- Lignin
- Cellulose
- RNA and proteins
Explanation: ABA inhibits the transcription of growth-related genes and the synthesis of proteins required for cell expansion and division.
Auxins help in preventing the early fruit and leaf drop but promote the abscission of:
- Young leaves
- Lateral buds
- Apical meristems
- Older leaves
Explanation: Auxins prevent the abscission of young leaves and fruits, but they promote the abscission of older, mature leaves and fruits.
Which hormone acts as an anti-transpirant by controlling the aperture of stomata?
- Auxin
- Abscisic acid
- Gibberellin
- Cytokinin
Explanation: By inducing stomatal closure, ABA reduces water loss through transpiration, acting as an anti-transpirant.
Auxins are chemically defined as being derivatives of which compound?
- Indole
- Carotenoid
- Terpene
- Adenine
Explanation: Natural auxins like IAA (Indole-3-acetic acid) are derivatives of the indole ring system.
The synthesis of Abscisic acid is stimulated by which environmental condition?
- Water stress
- Low light
- High humidity
- Abundant nitrogen
Explanation: When a plant experiences water deficit, ABA levels rise sharply in the leaves to coordinate a defensive response (like stomatal closure).
The 'triple response' in seedlings is often used to study ethylene, but its initial elongation is controlled by:
- Abscisic acid
- Gibberellin
- Auxin
- Cytokinin
Explanation: Auxin is the primary hormone responsible for the initial elongation of cells in the seedling's coleoptile or hypocotyl.
The ratio between which two hormones determines whether a tissue culture will produce roots or shoots?
- Auxin and Cytokinin
- Gibberellin and ABA
- Ethylene and Auxin
- Auxin and ABA
Explanation: A higher Auxin-to-Cytokinin ratio promotes root formation, while a higher Cytokinin-to-Auxin ratio promotes shoot formation.
During seed germination, which specific enzyme's synthesis is stimulated by Gibberellins?
- Alpha-amylase
- Lipase
- Catalase
- Protease
Explanation: Gibberellins trigger the aleurone layer to produce alpha-amylase, which breaks down stored starch into glucose to provide energy for the growing embryo.
The elongation of genetic dwarf plants can be achieved by applying:
- Auxins
- Abscisic acid
- Cytokinins
- Gibberellins
Explanation: Gibberellins are effective in increasing the internode length of genetically dwarf plants like peas and maize.
Which hormone is used to produce seedless (parthenocarpic) watermelons and cucumbers?
- Auxin
- Abscisic acid
- Cytokinin
- Gibberellin
Explanation: Application of Auxins to unpollinated flowers can trigger fruit development without fertilization, resulting in seedless fruits.
The 'Bolting' phenomenon induced by Gibberellins is typically followed by which process?
- Rooting
- Dormancy
- Flowering
- Abscission
Explanation: Bolting is the rapid elongation of the stem internodes, which acts as a precursor to the reproductive (flowering) phase in rosette plants.
Statement I: Auxin application actively promotes the growth of lateral buds.
Statement II: The removal of shoot tips is a common practice in tea plantations.
- Only Statement II is correct
- Only Statement I is correct
- Both statements are correct
- Both statements are incorrect
Explanation: Statement I is incorrect; apical dominance driven by auxin inhibits, rather than promotes, lateral bud growth. Statement II is correct; decapitation removes this apical auxin, promoting lateral growth (bushiness) in tea plantations.
Auxin is synthesized primarily in which plant part?
- Growing apices
- Senescent tissues
- Mature leaves
- Xylem vessels
Explanation: Auxins are produced by the growing apices of stems and roots, from where they migrate to the regions of their action.
Which plant hormone is famously recognized as the 'stress hormone' due to its critical role in stimulating the closure of stomata under severe environmental stress?
- Zeatin cytokinin
- Gibberellic acid
- Abscisic acid
- Indole acetic acid
Explanation: Abscisic acid (ABA) acts as a general plant stress hormone. During water stress or drought conditions, it signals the guard cells to close the stomata, preventing further water loss, and increases the tolerance of plants to various kinds of stresses.
Which of the following is a primary physiological effect of Abscisic acid on the plant epidermis?
- Lignin deposition
- Stomatal closure
- Cell division
- Cuticle thinning
Explanation: ABA is known as the 'stress hormone' because it triggers the rapid closure of stomata to prevent excessive water loss during drought conditions.
Which hormone is synonymous with 'Inhibitor-B' and 'Dormin' in early research?
- Cytokinin
- Gibberellin
- Auxin
- Abscisic acid
Explanation: In the mid-1960s, three independent researchers discovered Inhibitor-B, Abscission II, and Dormin, which were later found to be chemically identical and named Abscisic Acid.
Abscisic acid is synthesized primarily in which part of the plant?
- Shoot apical meristems
- Chloroplasts
- Root tips
- Phloem cells
Explanation: ABA is synthesized primarily in chloroplasts and other plastids via the carotenoid pathway.
Auxins are known to initiate which of the following processes in stem cuttings?
- Seed dormancy
- Leaf abscission
- Internode shortening
- Rooting
Explanation: Auxins like IBA and NAA are extensively used in agricultural practices to initiate rooting in stem cuttings for plant propagation.
Which hormone is often used to spray sugarcane crops to increase the sugar yield?
- Cytokinin
- Gibberellin
- Abscisic acid
- Auxin
Explanation: Spraying sugarcane with gibberellins increases the length of the stem, thus increasing the yield by as much as 20 tonnes per acre.
Which hormone is functionally characterized as a general 'Plant Growth Inhibitor'?
- Gibberellin
- Abscisic acid
- Cytokinin
- Auxin
Explanation: While Auxins and Gibberellins are growth promoters, ABA is a growth inhibitor that regulates senescence and dormancy.
Gibberellic acid (GA3) is used to speed up the maturity period in which group of plants?
- Aquatic herbs
- Juvenile conifers
- Cereal crops
- Mature dicots
Explanation: Spraying juvenile conifers with Gibberellins hastens the maturity period, leading to earlier seed production.
Which of the following is a natural auxin?
Explanation: Indole-3-acetic acid (IAA) and Indole butyric acid (IBA) have been isolated from plants and are considered natural auxins.
Statement I: Auxins are used to promote the growth of weeds.
Statement II: High concentrations of Auxin are toxic to many dicot plants.
- Statement I correct
- Statement II correct
- Both are correct
- Both are incorrect
Explanation: Statement I is incorrect; auxins are used to kill weeds. Statement II is correct; synthetic auxins in high doses over-stimulate growth until the plant dies. (A/R answer avoided).
Which hormone acts as an inhibitor of the effects of both Auxins and Gibberellins?
- Abscisic acid
- Ethylene
- Nitric oxide
- Zeatin
Explanation: ABA is generally antagonistic to the growth-promoting effects of Auxins and Gibberellins, maintaining a balance in plant development.
The 'Avena curvature test' is a classic bioassay used to identify which hormone?
- Auxin
- Zeatin
- Abscisic acid
- Gibberellin
Explanation: The Avena (oat) coleoptile curvature test was developed by F.W. Went to measure the concentration and effect of Auxins.
Which hormone can be applied to increase the shelf-life of fruits by delaying senescence?
- Gibberellin
- Abscisic acid
- 2,4-D
- Auxin
Explanation: By delaying the aging process (senescence), Gibberellins allow fruits to stay on the plant longer or survive transport better.
The 'Bakanae' (foolish seedling) disease in rice led to the discovery of which hormone?
- Auxin
- Abscisic acid
- Cytokinin
- Gibberellin
Explanation: The disease was caused by the fungus Gibberella fujikuroi. E. Kurosawa identified that the symptoms were due to a chemical substance later named Gibberellin.
Auxins are primarily responsible for which of the following 'tropisms' in roots?
- Negative geotropism
- Negative hydrotropism
- Positive geotropism
- Positive phototropism
Explanation: In roots, high concentrations of Auxin inhibit growth, causing the root to bend downward toward gravity (positive geotropism).
Gibberellins are known to delay which of the following processes in fruits?
- Senescence
- Growth
- Transpiration
- Respiration
Explanation: Gibberellins delay senescence, allowing fruits to be left on the tree for longer periods to extend the market period.
The 'Bolting' effect in rosette plants like cabbage is induced by which hormone?
- Auxin
- Abscisic acid
- Ethylene
- Gibberellin
Explanation: Bolting is the sudden elongation of the internode just prior to flowering, which can be artificially induced by treating plants with Gibberellins.
Which hormone is used to bypass the requirement of 'Vernalization' (cold treatment) in some plants?
- Abscisic acid
- Gibberellin
- Zeatin
- Auxin
Explanation: In some biennials, Gibberellin treatment can replace the requirement for low temperatures to induce flowering.
Which hormone is functionally antagonistic to Gibberellins regarding seed germination?
- Ethylene
- Abscisic acid
- Auxin
- Cytokinin
Explanation: Gibberellins promote seed germination by breaking dormancy, while Abscisic acid (ABA) induces seed dormancy and inhibits germination.
Gibberellins are used in the brewing industry primarily to speed up which process?
- Stomatal opening
- Malting process
- Lateral branching
- Fruit ripening
Explanation: Gibberellins (GA3) are used to increase the yield and speed up the malting process in the brewing industry by stimulating alpha-amylase production.
Which hormone prevents the 'cluttering' of seeds by maintaining their dormancy?
- Gibberellin
- Auxin
- Abscisic acid
- Zeatin
Explanation: ABA maintains seed dormancy, ensuring that seeds do not germinate until environmental conditions are suitable.
In the absence of shoot-tip decapitation, the growth of lateral buds is suppressed by:
- Lateral auxin
- Stem gibberellin
- Root cytokinin
- Apical auxin
Explanation: Auxin produced at the apical meristem travels downward and prevents the development of axillary (lateral) buds.
Which plant hormone is primarily responsible for the phenomenon of 'Apical Dominance'?
- Cytokinins
- Auxins
- Abscisic acid
- Gibberellins
Explanation: Auxins produced at the shoot tip inhibit the growth of lateral buds. Removing the tip (decapitation) usually results in the growth of lateral buds.
Statement I: Abscisic acid promotes the abscission of leaves and fruits.
Statement II: Abscisic acid is a general plant growth stimulator.
- Statement II correct
- Statement I correct
- Both are correct
- Both are incorrect
Explanation: Statement I is correct; ABA promotes senescence and abscission. Statement II is incorrect because ABA is a plant growth inhibitor, not a stimulator.
In the process of root initiation in a laboratory, which hormone is most effective?
- Gibberellic acid
- Abscisic acid
- Naphthalene acetic acid
- Zeatin
Explanation: NAA is a synthetic auxin frequently used in plant tissue culture and horticulture to induce root formation in cuttings.
Which specific hormone helps in maintaining the apical hook in dicot seedlings?
- Auxin
- Cytokinin
- Gibberellin
- Abscisic acid
Explanation: Auxin (along with ethylene) is responsible for maintaining the sub-apical hook that protects the tender shoot tip as it pushes through the soil.
Which hormone acts as a 'Stress Hormone' by triggering stomatal closure during water scarcity?
- Gibberellic acid
- Naphthalene acetic acid
- Indole-3-acetic acid
- Abscisic acid
Explanation: Abscisic Acid (ABA) stimulates the closure of stomata in the epidermis and increases the tolerance of plants to various kinds of stresses.
Gibberellins have been shown to increase the yield of sugarcane by promoting the growth of:
- Leaves
- Lateral roots
- Sugar molecules
- Stem internodes
Explanation: Gibberellins stimulate the elongation of the stem internodes, which is where sugarcane stores its sugar-rich juice.
Which hormone is used to increase the length of the axis in grape stalks?
- Zeatin
- Auxin
- Gibberellin
- Abscisic acid
Explanation: Gibberellins cause an increase in the length of the axis, which is used to increase the length of grapes stalks and improve fruit spacing.
The chemical substance 2,4-D, used as a herbicide, belongs to which category of hormones?
- Synthetic auxin
- Stress inhibitor
- Natural gibberellin
- Growth promoter
Explanation: 2,4-D is a synthetic auxin that disrupts the growth of broad-leaved dicot weeds without affecting monocot crops like wheat or maize.
Which of the following is a synthetic auxin commonly utilized as a broad-leaf weedkiller?
Explanation: 2,4-dichlorophenoxyacetic acid (2,4-D) is widely used to kill dicotyledonous weeds while leaving monocotyledonous cereal plants unaffected.
Statement I: Abscisic acid helps seeds withstand desiccation.
Statement II: Abscisic acid promotes the synthesis of alpha-amylase in germinating seeds.
- Statement II correct
- Statement I correct
- Both are correct
- Both are incorrect
Explanation: Statement I is correct; by inducing dormancy, ABA helps seeds survive unfavorable conditions. Statement II is incorrect as alpha-amylase synthesis is a function of Gibberellins.
Which hormone can induce parthenocarpy (seedless fruit production) in tomatoes?
- Abscisic acid
- Auxin
- Gibberellin
- Both Auxin/Gibberellin
Explanation: Both Auxins and Gibberellins can be used to induce parthenocarpy in various fruits, including tomatoes and grapes.
The transport of Auxin within the plant body is primarily:
- Polar
- Via xylem
- Via phloem
- Non-polar
Explanation: Auxin transport is characteristically polar (unidirectional), usually moving from the apex downward (basipetal transport).
The term 'Basipetal Transport' (movement from the apex downward to the base) is most distinctly characteristic of which plant hormone?
- Ethylene gas
- Abscisic acid
- Gibberellic acid
- Auxin hormone
Explanation: Auxin exhibits distinct polar transport. Basipetal transport refers to the downward movement of Auxin from its primary synthesis site at the shoot apex toward the roots.
Which plant hormone mediates the growth response toward a unidirectional light source (Phototropism)?
- Cytokinin
- Gibberellin
- Auxin
- Abscisic acid
Explanation: Auxin migrates to the shaded side of the shoot, stimulating greater cell elongation there, which causes the plant to bend toward the light.