Plant Hormones

Topic: Plant Growth Regulators

Subtopic: Apical Dominance

• Apical dominance: The phenomenon where the main central stem of the plant grows more strongly than side stems due to auxin production at the apex.

• Decapitation: Removal of the apical bud to influence plant growth patterns.

• Intercalary meristem: Meristem present at the base of leaves or internodes, responsible for elongation in monocots.

• Hedge making: Formation of dense plant barriers by stimulating lateral branching.

• Auxins: Plant hormones controlling growth and apical dominance.

• Senescence: Process of aging in plants.

• Lateral branches: Side shoots emerging from nodes due to reduced apical dominance.

• Weed-free lawns: Managed turf with suppressed unwanted plant growth.

• Plant pruning: Removal of plant parts to manipulate growth and shape.

• Monocots: Group of flowering plants with single cotyledon, often showing intercalary meristem growth.

• Decapitation effect: Stimulates lateral buds, increasing bushiness and density in plants.

Lead Question - 2022 (Abroad)

Removal of apical dominance by decapitation is utilised for:

1. Suppressing the activity of intercalary meristem

2. Early senescence

3. Hedge making

4. Preparing weed-free lawns

Explanation: Decapitation removes the apical bud, reducing auxin levels and releasing lateral buds from dormancy. This stimulates branching and is commonly used in hedge making to create dense, bushy plants. It does not suppress intercalary meristem, induce senescence, or directly prepare weed-free lawns. Answer: Hedge making. Answer: 3

Q1: Which plant hormone primarily maintains apical dominance?

1. Auxin

2. Cytokinin

3. Gibberellin

4. Abscisic acid

Explanation: Auxins, produced in the apical bud, inhibit lateral bud growth and maintain apical dominance. Cytokinins promote lateral growth, gibberellins elongate stems, and abscisic acid induces dormancy. Hence, auxin is the primary hormone controlling apical dominance. Answer: Auxin. Answer: 1

Q2: Removal of apical bud results in:

1. Reduced lateral branching

2. Increased lateral branching

3. No effect on plant growth

4. Plant death

Explanation: Decapitation reduces auxin levels at the apex, releasing lateral buds from dormancy. This promotes increased lateral branching, making plants bushier. It does not reduce branching or cause plant death. Answer: Increased lateral branching. Answer: 2

Q3: Intercalary meristems are mainly found in:

1. Dicots

2. Monocots

3. Gymnosperms

4. Algae

Explanation: Intercalary meristems occur at the base of leaves or internodes, primarily in monocots such as grasses. They allow rapid elongation. Dicots and gymnosperms mainly rely on apical and lateral meristems, while algae do not have intercalary meristems. Answer: Monocots. Answer: 2

Q4: Hedge making is achieved by:

1. Promoting apical dominance

2. Removal of apical buds

3. Applying gibberellins

4. Increasing abscisic acid

Explanation: Removal of apical buds reduces auxin levels, releasing lateral buds, and produces dense bushy growth. This method is widely used in hedge making. Promoting apical dominance or gibberellin application elongates stems instead, while abscisic acid induces dormancy. Answer: Removal of apical buds. Answer: 2

Q5: Which effect is NOT caused by decapitation?

1. Stimulated lateral bud growth

2. Reduced apical dominance

3. Early flowering

4. Dense bushy growth

Explanation: Decapitation stimulates lateral buds and reduces apical dominance, leading to dense growth. It does not directly induce early flowering; flowering depends on other factors like photoperiod and hormones. Answer: Early flowering. Answer: 3

Q6: Pruning of plants is similar to decapitation in that it:

1. Removes lateral buds

2. Removes apical dominance

3. Induces leaf senescence

4. Reduces photosynthesis

Explanation: Pruning removes apical or terminal buds, reducing apical dominance and promoting lateral bud growth. It does not remove all lateral buds, induce senescence directly, or reduce photosynthesis significantly. Answer: Removes apical dominance. Answer: 2

Q7: Assertion (A): Decapitation is used to make plants bushy.
Reason (R): Removal of apical bud decreases auxin, activating lateral buds.

1. (A) is correct but R is not correct

2. (A) is not correct but R is correct

3. Both A and R are correct and R explains A

4. Both A and R are correct but R does not explain A

Explanation: Decapitation removes the apical bud, reducing auxin, which releases lateral buds from dormancy and results in bushy growth. Both assertion and reason are correct, and the reason explains the assertion. Answer: Both A and R are correct and R explains A. Answer: 3

Q8: Match the plant part with its response to decapitation:

A. Apical bud    1. Removed
B. Lateral buds    2. Activated
C. Auxin level    3. Decreased
D. Stem elongation    4. Slightly reduced

1. A-1, B-2, C-3, D-4

2. A-2, B-1, C-4, D-3

3. A-1, B-3, C-2, D-4

4. A-2, B-3, C-1, D-4

Explanation: Apical bud is removed (A-1), lateral buds are activated (B-2), auxin level decreases (C-3), and stem elongation may slightly reduce (D-4). This correctly explains plant response to decapitation. Answer: A-1, B-2, C-3, D-4. Answer: 1

Q9: Removal of the apical bud promotes ______ in plants.

1. Lateral branching

2. Senescence

3. Apical dominance

4. Leaf abscission

Explanation: Removing the apical bud reduces auxin and releases lateral buds, promoting lateral branching. Apical dominance decreases, but senescence, leaf abscission, or enhanced apical dominance are not the direct effects. Answer: Lateral branching. Answer: 1

Q10: Which of the following statements about apical dominance are correct?

1. Maintained by auxin from apical bud

2. Suppresses lateral bud growth

3. Decapitation reduces dominance

4. Promotes intercalary meristem elongation

Explanation: Apical dominance is maintained by auxin and suppresses lateral buds. Decapitation reduces dominance and activates lateral growth. It does not directly promote intercalary meristem elongation. Correct statements are 1, 2, 3. Answer: 1, 2, 3

Subtopic: Abscisic Acid and Stomatal Regulation

• Stomata: Small pores on leaf surfaces that regulate gas exchange and transpiration.

• Stomatal closure: Process by which guard cells reduce pore size to prevent water loss.

• Abscisic Acid (ABA): Plant hormone responsible for stress responses including stomatal closure.

• Cytokinin: Plant hormone promoting cell division and shoot formation.

• Gibberellin: Plant hormone involved in stem elongation, seed germination, and flowering.

• Auxin: Plant hormone regulating cell elongation, apical dominance, and tropic responses.

• Guard cells: Specialized cells flanking stomatal pores controlling opening and closing.

• Transpiration: Loss of water vapor from plant surfaces through stomata.

• Water stress: Condition where plants experience low water availability, triggering ABA responses.

• Hormonal signaling: Chemical communication within plants regulating physiological processes.

• Immediate response: Rapid physiological change in response to environmental or hormonal signals.

Lead Question - 2022 (Abroad)

Which hormone is used to induce immediate stomatal closure in leaves?

1. Cytokinin

2. Gibberellin

3. Abscisic Acid

4. Auxin

Explanation: Abscisic Acid (ABA) is a stress hormone that rapidly signals guard cells to lose turgor, causing stomatal closure and reducing water loss during drought or high light intensity. Other hormones like cytokinin, gibberellin, and auxin regulate growth and development, not immediate stomatal response. Answer: Abscisic Acid. Answer: 3

Q1: Which cells directly mediate stomatal opening and closure?

1. Mesophyll cells

2. Guard cells

3. Epidermal cells

4. Phloem cells

Explanation: Guard cells flank the stomatal pore and change turgor in response to ABA, light, or CO2, regulating stomatal aperture. Mesophyll or epidermal cells do not control stomata directly. Proper guard cell function ensures efficient transpiration and photosynthesis. Answer: Guard cells. Answer: 2

Q2: ABA-induced stomatal closure helps plants primarily by:

1. Increasing photosynthesis

2. Reducing water loss

3. Promoting cell division

4. Elongating stems

Explanation: ABA triggers stomatal closure to minimize transpiration under water stress, conserving water. It does not directly affect photosynthesis, cell division, or stem elongation. Guard cells respond rapidly to ABA to prevent dehydration. Answer: Reducing water loss. Answer: 2

Q3: Which environmental stress primarily triggers ABA accumulation?

1. Excess water

2. Drought

3. Optimal temperature

4. High soil nutrients

Explanation: ABA accumulates in response to drought, signaling guard cells to close stomata and conserve water. Excess water or nutrients do not induce ABA-mediated stomatal closure. ABA functions as a stress hormone. Answer: Drought. Answer: 2

Q4: Which ion movement is associated with ABA-induced stomatal closure?

1. Potassium efflux from guard cells

2. Potassium influx into guard cells

3. Calcium efflux from mesophyll

4. Sodium influx into xylem

Explanation: ABA triggers potassium efflux from guard cells, reducing turgor and closing stomata. Calcium acts as a secondary messenger in guard cells, but K+ movement is the direct cause. Answer: Potassium efflux from guard cells. Answer: 1

Q5: Which of the following hormones promotes stomatal opening?

1. Abscisic Acid

2. Auxin

3. Gibberellin

4. Cytokinin

Explanation: Cytokinin can promote stomatal opening under favorable conditions by enhancing guard cell turgor. ABA closes stomata, while auxin and gibberellin regulate growth rather than immediate stomatal aperture. Answer: Cytokinin. Answer: 4

Q6: ABA is synthesized mainly in:

1. Roots and leaves

2. Flowers

3. Seeds only

4. Stems only

Explanation: ABA is synthesized in roots and leaves under water stress. It travels via xylem or phloem to guard cells to trigger closure. Flowers or stems are not primary sites. ABA functions as a mobile stress signal. Answer: Roots and leaves. Answer: 1

Q7: Assertion (A): ABA causes stomatal closure during drought.
Reason (R): ABA reduces guard cell turgor by ion efflux.

1. (A) is correct but R is not correct

2. (A) is not correct but R is correct

3. Both A and R are correct and R explains A

4. Both A and R are correct but R does not explain A

Explanation: ABA signals guard cells to lose potassium and chloride ions, reducing osmotic potential and turgor, resulting in stomatal closure during drought. Both assertion and reason are correct, and the reason explains the physiological mechanism. Answer: Both A and R are correct and R explains A. Answer: 3

Q8: Match the hormone with its primary function:

A. Abscisic Acid    1. Cell division
B. Cytokinin    2. Stress response/stomatal closure
C. Gibberellin    3. Stem elongation
D. Auxin    4. Tropic growth

1. A-2, B-1, C-3, D-4

2. A-1, B-2, C-3, D-4

3. A-2, B-3, C-1, D-4

4. A-4, B-1, C-2, D-3

Explanation: ABA mediates stress responses including stomatal closure. Cytokinin promotes cell division, gibberellin causes stem elongation, and auxin regulates tropic growth. Correct matching links hormones to their primary functions. Answer: A-2, B-1, C-3, D-4. Answer: 1

Q9: The plant hormone responsible for immediate stomatal closure is ______.

1. Auxin

2. Abscisic Acid

3. Gibberellin

4. Cytokinin

Explanation: Abscisic Acid (ABA) rapidly signals guard cells to reduce turgor, causing stomatal closure under water stress or high light intensity. Auxin, gibberellin, and cytokinin regulate growth processes, not rapid stomatal response. Answer: Abscisic Acid. Answer: 2

Q10: Which of the following statements about ABA are correct?

1. Induces stomatal closure

2. Produced under drought stress

3. Promotes guard cell turgor

4. Enhances water conservation

Explanation: ABA induces stomatal closure, is synthesized under drought stress, and reduces water loss. It does not increase guard cell turgor; instead, it decreases it to close stomata. Correct statements are 1, 2, and 4. Answer: 1, 2, 4

Subtopic: Phytohormones and Their Effects

Keyword Definitions:

• Phytohormones: Chemical messengers produced in plants that regulate growth and development.

• Gibberellin: A plant hormone that promotes stem elongation, seed germination, and flowering.

• Ethylene: A gaseous plant hormone responsible for fruit ripening and promotion of female flowers in certain plants.

• Cytokinin: Hormone that promotes cell division, shoot formation, and delays senescence.

• ABA (Abscisic Acid): Plant hormone that induces dormancy and stress responses.

• Female Flowers: Flowers containing pistils, responsible for fruit formation.

• Cucumber Yield: The production quantity of cucumber fruits per plant or per hectare.

Lead Question (2022)
Production of Cucumber has increased manifold in recent years. Application of which of the following phytohormones has resulted in this increased yield as the hormone is known to produce female flowers in the plants :
(1) Gibberellin
(2) Ethylene
(3) Cytokinin
(4) ABA

Explanation:
Ethylene is a gaseous phytohormone that promotes the development of female flowers in cucumber plants, increasing fruit set and yield. Its application in agricultural practices has resulted in higher cucumber production. Gibberellins, cytokinins, and ABA do not specifically enhance female flower formation. Correct answer is (2).

1. Single Correct Answer MCQ:
Which phytohormone is primarily responsible for stem elongation in plants?
(1) Ethylene
(2) ABA
(3) Gibberellin
(4) Cytokinin

Explanation:
Gibberellins stimulate stem elongation by promoting cell division and elongation in internodes. Other hormones like ABA inhibit growth, cytokinins promote cell division in shoots, and ethylene generally inhibits stem elongation. Correct answer is (3).

2. Single Correct Answer MCQ:
Which hormone is involved in breaking seed dormancy?
(1) Gibberellin
(2) ABA
(3) Ethylene
(4) Auxin

Explanation:
Gibberellins help break seed dormancy and promote germination, counteracting the inhibitory effects of ABA. Ethylene mainly regulates ripening, and auxins primarily control cell elongation and apical dominance. Correct answer is (1).

3. Single Correct Answer MCQ:
Which hormone promotes lateral bud growth and delays senescence?
(1) Gibberellin
(2) Cytokinin
(3) Ethylene
(4) ABA

Explanation:
Cytokinins promote cell division, stimulate lateral bud growth, and delay aging (senescence) in leaves. Gibberellins mainly elongate stems, ethylene controls ripening and flower sex, while ABA induces dormancy. Correct answer is (2).

4. Single Correct Answer MCQ:
Which hormone triggers fruit ripening in climacteric fruits?
(1) Gibberellin
(2) Ethylene
(3) Cytokinin
(4) ABA

Explanation:
Ethylene is the key hormone responsible for ripening climacteric fruits like banana and tomato. It regulates enzyme activity that softens tissue and converts starch to sugar. Other hormones do not directly induce ripening. Correct answer is (2).

5. Single Correct Answer MCQ:
Which hormone helps plants respond to drought and stress?
(1) ABA
(2) Gibberellin
(3) Cytokinin
(4) Ethylene

Explanation:
Abscisic acid (ABA) accumulates during water stress and helps plants close stomata, reducing transpiration. It also induces dormancy under adverse conditions. Gibberellins, cytokinins, and ethylene have other primary roles. Correct answer is (1).

6. Single Correct Answer MCQ:
Which hormone promotes seed germination in cereals?
(1) Gibberellin
(2) ABA
(3) Cytokinin
(4) Ethylene

Explanation:
Gibberellins stimulate the synthesis of enzymes like amylase in cereal seeds, breaking down stored starch into sugars to support germination. ABA inhibits germination, cytokinins promote cell division, and ethylene mainly controls fruit and flower processes. Correct answer is (1).

7. Assertion-Reason MCQ:
Assertion (A): Ethylene promotes female flower formation in cucumbers.
Reason (R): Gibberellins are responsible for inducing female flowers.
Options:
(1) Both A and R are correct and R explains A
(2) A correct, R incorrect
(3) A incorrect, R correct
(4) Both A and R incorrect

Explanation:
Ethylene induces the formation of female flowers in cucumbers, increasing fruit yield. Gibberellins, although growth-promoting, do not specifically induce female flowers. Therefore, Assertion is correct and Reason is incorrect. Correct answer is (2).

8. Matching Type MCQ:
Match hormone with its primary effect:
A. Gibberellin — 1. Stem elongation
B. Ethylene — 2. Fruit ripening and female flowers
C. ABA — 3. Stress response
D. Cytokinin — 4. Cell division
Options:
(1) A–1, B–2, C–3, D–4
(2) A–2, B–1, C–3, D–4
(3) A–1, B–3, C–2, D–4
(4) A–1, B–2, C–4, D–3

Explanation:
Gibberellins elongate stems, ethylene ripens fruits and induces female flowers, ABA mediates stress responses, and cytokinins promote cell division. Correct matching is A–1, B–2, C–3, D–4. Correct answer is (1).

9. Fill in the Blanks:
_________ is a gaseous hormone that induces female flower formation in cucumbers.
(1) ABA
(2) Ethylene
(3) Gibberellin
(4) Cytokinin

Explanation:
Ethylene is a gaseous plant hormone that promotes the development of female flowers in cucumber plants, enhancing fruit production. Gibberellins, cytokinins, and ABA do not specifically cause female flower formation. Correct answer is (2).

10. Choose the Correct Statements:
(a) Ethylene promotes female flower formation in cucumbers
(b) Gibberellin promotes stem elongation
(c) ABA induces stress responses
(d) Cytokinin inhibits cell division
Options:
(1) a, b, c
(2) a and d only
(3) b and d only
(4) all of the above

Explanation:
Ethylene induces female flowers (a), gibberellins promote stem elongation (b), and ABA triggers stress responses (c). Cytokinins actually promote cell division, so (d) is false. Correct statements are a, b, c. Correct answer is (1).

Topic: Plant Growth Regulators
Subtopic: Ethylene – The Gaseous Plant Hormone

Keyword Definitions:

• Ethylene: A gaseous plant hormone regulating fruit ripening, senescence, and abscission processes.

• Apical Dominance: Suppression of lateral buds by the apical bud through auxin action.

• Malting: Process of germinating and drying grains to convert starch into sugars during brewing.

• Root Hair Formation: Growth of root epidermal cells to increase surface area for water absorption.

Lead Question (2022)
The gaseous plant growth regulator is used in plants to:
(1) Promote root growth and root hair formation to increase the absorption surface
(2) Help overcome apical dominance
(3) Kill dicotyledonous weeds in the fields
(4) Speed up the malting process

Explanation:
Ethylene, a gaseous plant hormone, is used to break dormancy and accelerate the malting process by stimulating enzyme production for starch breakdown during seed germination. Hence, the correct answer is (4).

1. Which of the following is a gaseous hormone in plants?
(1) Auxin
(2) Cytokinin
(3) Ethylene
(4) Gibberellin

Explanation:
Among plant growth regulators, ethylene is the only gaseous hormone. It influences fruit ripening, senescence, and stress responses. Hence, the correct answer is (3).

2. Ethylene is produced from which precursor in plants?
(1) Methionine
(2) Tryptophan
(3) Adenine
(4) Asparagine

Explanation:
Ethylene is synthesized from the amino acid methionine through S-adenosyl methionine (SAM) and ACC intermediates. Hence, the correct answer is (1).

3. Which plant growth regulator helps in fruit ripening?
(1) Auxin
(2) Gibberellin
(3) Ethylene
(4) Cytokinin

Explanation:
Ethylene accelerates fruit ripening by converting starches to sugars and softening tissues. It also promotes color and aroma development. Hence, the correct answer is (3).

4. Which of the following effects is not caused by ethylene?
(1) Fruit ripening
(2) Flower initiation
(3) Leaf abscission
(4) Triple response in seedlings

Explanation:
Ethylene promotes leaf abscission, fruit ripening, and triple response but does not induce flower initiation. Hence, the correct answer is (2).

5. Ethylene helps in overcoming:
(1) Phototropism
(2) Apical dominance
(3) Gravitropism
(4) Leaf fall

Explanation:
Ethylene counteracts the effect of auxin and promotes lateral bud growth, thus helping in overcoming apical dominance. Hence, the correct answer is (2).

6. Commercially, ethylene effect is mimicked by:
(1) IAA
(2) NAA
(3) Ethephon
(4) Zeatin

Explanation:
Ethephon releases ethylene in aqueous solution and is used to regulate fruit ripening, leaf drop, and flowering in pineapple. Hence, the correct answer is (3).

7. Assertion-Reason Type:
Assertion (A): Ethylene promotes senescence and fruit ripening.
Reason (R): It increases the synthesis of hydrolytic enzymes that degrade cell walls.
(1) Both A and R are correct, and R explains A
(2) Both A and R are correct, but R does not explain A
(3) A is false but R is true
(4) Both A and R are false

Explanation:
Ethylene accelerates ripening by stimulating enzymes like pectinase and cellulase, softening fruit tissues. Thus, both statements are correct, and R explains A. Hence, the correct answer is (1).

8. Matching Type:
Match the following:
A. Ethylene — 1. Fruit ripening
B. Auxin — 2. Apical dominance
C. Cytokinin — 3. Cell division
D. Gibberellin — 4. Stem elongation

(1) A–1, B–2, C–3, D–4
(2) A–2, B–1, C–4, D–3
(3) A–3, B–4, C–2, D–1
(4) A–4, B–3, C–1, D–2

Explanation:
Ethylene promotes fruit ripening, auxin maintains apical dominance, cytokinin stimulates cell division, and gibberellin enhances stem elongation. Hence, the correct answer is (1).

9. Fill in the Blanks:
Ethylene is commonly known as the ________ hormone.
(1) Ripening
(2) Growth
(3) Dormancy
(4) Stress

Explanation:
Ethylene is called the ripening hormone because it accelerates fruit maturation and softening. Hence, the correct answer is (1).

10. Choose the Correct Statements:
(a) Ethylene promotes fruit ripening.
(b) Ethephon is a source of ethylene.
(c) Ethylene is a solid plant hormone.
(d) Ethylene promotes apical dominance.

(1) (a) and (b) only
(2) (a) and (d) only
(3) (b) and (c) only
(4) All of the above

Explanation:
Ethylene is a gaseous hormone released from Ethephon, promoting fruit ripening and reducing apical dominance. Hence, only (a) and (b) are correct. Correct answer is (1).

Topic: Plant Hormones
Subtopic: Auxins and Their Applications

Keyword Definitions:

• NAA (Naphthaleneacetic Acid): A synthetic auxin used to stimulate root formation in plant cuttings.

• 2,4-D (2,4-Dichlorophenoxyacetic Acid): A synthetic auxin commonly used as a herbicide to control broadleaf weeds.

• IBA (Indole-3-butyric Acid): A plant hormone that promotes root initiation in cuttings and tissue culture.

• IAA (Indole-3-acetic Acid): A natural auxin produced in plant apical meristems, regulating growth and development.

• Auxins: Plant hormones that regulate cell elongation, root initiation, and other growth processes.

• Herbicide: A chemical used to destroy or inhibit the growth of unwanted plants.

• Weed Control: The process of eliminating undesirable plants from fields to improve crop yield.

• Rooting Hormone: Chemicals like NAA or IBA used to enhance root formation in plant propagation.

Lead Question - 2021

The plant hormone used to destroy weeds in a field is:
(1) NAA
(2) 2,4–D
(3) IBA
(4) IAA

Explanation: The correct answer is (2) 2,4–D. This synthetic auxin acts as a selective herbicide, causing uncontrolled growth in broadleaf weeds, leading to their death, while leaving monocot crops largely unaffected. Its use improves crop yield by eliminating competing unwanted plants in agricultural fields.

Guessed Questions:

1) Which auxin is commonly used to induce rooting in cuttings?
(1) 2,4-D
(2) NAA
(3) IAA
(4) GA3

Explanation: The correct answer is (2) NAA. Naphthaleneacetic acid promotes root formation in plant cuttings by stimulating cell division and elongation in root primordia. It is widely used in horticulture and plant propagation to improve success rates of vegetative reproduction.

2) Assertion (A): IBA is used to stimulate root growth in plant cuttings.
Reason (R): It is a synthetic auxin similar to IAA.
(1) Both A and R true, R explains A
(2) Both A and R true, R does not explain A
(3) A true, R false
(4) A false, R true

Explanation: The correct answer is (1). Indole-3-butyric acid (IBA) is a synthetic auxin used to promote root initiation in cuttings. It mimics natural auxins like IAA, stimulating cell division and elongation in root primordia, making plant propagation more efficient.

3) Which plant hormone regulates cell elongation and apical dominance?
(1) Auxins
(2) Gibberellins
(3) Cytokinins
(4) Ethylene

Explanation: The correct answer is (1) Auxins. Auxins like IAA control cell elongation, apical dominance, and differentiation. They are produced in apical meristems and influence growth direction, organ formation, and responses to light and gravity in plants.

4) Fill in the blank: The synthetic auxin _______ is widely used as a selective herbicide.
(1) NAA
(2) 2,4-D
(3) IBA
(4) IAA

Explanation: The correct answer is (2) 2,4-D. 2,4-Dichlorophenoxyacetic acid mimics natural auxin but at higher concentrations disrupts cell growth in broadleaf weeds. This leads to uncontrolled elongation and eventual death, making it an effective selective herbicide in crop fields.

5) Which auxin is naturally synthesized in shoot tips?
(1) NAA
(2) 2,4-D
(3) IBA
(4) IAA

Explanation: The correct answer is (4) IAA. Indole-3-acetic acid is a natural plant hormone synthesized in apical meristems, young leaves, and developing seeds. It regulates cell elongation, apical dominance, and differentiation, playing a central role in plant growth and development.

6) Which synthetic auxin is used in tissue culture to promote adventitious root formation?
(1) 2,4-D
(2) IAA
(3) NAA
(4) GA3

Explanation: The correct answer is (3) NAA. Naphthaleneacetic acid enhances adventitious root development in tissue culture by stimulating cell division and elongation in root primordia. It is widely used for clonal propagation and micropropagation techniques in horticultural and forestry applications.

7) Choose the correct statements:
a. 2,4-D is used as a herbicide.
b. NAA stimulates rooting in cuttings.
c. IAA is synthetic auxin used in tissue culture.
d. IBA promotes root initiation.
(1) a, b, d
(2) a, c, d
(3) b, c
(4) a, b, c, d

Explanation: The correct answer is (1) a, b, d. 2,4-D kills broadleaf weeds, NAA stimulates rooting in cuttings, and IBA promotes root initiation. IAA is a natural auxin, not synthetic, making statement c incorrect.

8) Assertion (A): 2,4-D selectively kills broadleaf weeds.
Reason (R): It is a synthetic auxin that causes uncontrolled cell elongation in susceptible plants.
(1) Both A and R true, R explains A
(2) Both A and R true, R does not explain A
(3) A true, R false
(4) A false, R true

Explanation: The correct answer is (1). 2,4-D disrupts normal auxin-controlled growth in broadleaf weeds, causing abnormal elongation and eventual death. Monocots are largely unaffected, making it a selective herbicide widely used in agriculture for weed control.

9) Matching Type: Match auxin with its common use.
List-I    List-II
(a) NAA  (i) Herbicide
(b) 2,4-D  (ii) Rooting of cuttings
(c) IBA  (iii) Root initiation in tissue culture
(d) IAA  (iv) Natural growth regulation
Select correct answer:
(a) (b) (c) (d)
(1) ii, i, iii, iv
(2) i, ii, iii, iv
(3) iii, i, ii, iv
(4) ii, iii, i, iv

Explanation: The correct answer is (1) ii, i, iii, iv. NAA promotes rooting of cuttings (ii), 2,4-D is used as herbicide (i), IBA initiates roots in tissue culture (iii), and IAA regulates natural growth and development (iv). This classification reflects practical applications of auxins in agriculture and horticulture.

10) Fill in the blank: The selective herbicide used in crop fields to remove unwanted broadleaf plants is _______.
(1) IBA
(2) NAA
(3) 2,4-D
(4) IAA

Explanation: The correct answer is (3) 2,4-D. This synthetic auxin kills broadleaf weeds by inducing abnormal cell elongation and uncontrolled growth, without significantly affecting monocot crops, making it an essential tool in modern agriculture for effective weed management.

Subtopic: Phytohormones and Their Functions

Keyword Definitions:

• Phytohormone: Natural plant chemicals regulating growth, development, and responses to stress.

• Fruit ripener: Substance or hormone that accelerates fruit maturation and softening.

• Bolting agent: Hormone inducing rapid stem elongation before flowering, commonly gibberellins.

• Herbicide: Chemical that inhibits or kills unwanted plants, e.g., 2,4-D.

• Stress hormone: Plant hormone that helps resist abiotic stress; commonly abscisic acid.

• GA3: Gibberellic acid, promotes stem elongation, seed germination, and bolting.

• Abscisic acid (ABA): Regulates stomatal closure, dormancy, and stress responses.

• Ethephon: Releases ethylene and accelerates fruit ripening.

• 2,4-D: Synthetic auxin used as a selective herbicide.

• Plant growth regulators: Compounds controlling various physiological processes.

• Ethylene: Gas hormone involved in fruit ripening and leaf abscission.

Lead Question - 2020 (COVID Reexam)

Match the following concerning the activity/function and the phytohormone involved:

(a) Fruit ripener (i) Abscisic acid
(b) Herbicide (ii) GA3
(c) Bolting agent (iii) 2,4-D
(d) Stress hormone (iv) Ethephon

Select the correct option:
1. (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)
2. (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)
3. (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)
4. (a)-(iv), (b)-(ii), (c)-(i), (d)-(iii)

Explanation: Fruit ripening is promoted by ethephon which releases ethylene. Bolting is induced by GA3, 2,4-D is used as a herbicide, and stress responses are mediated by abscisic acid. Correct answer is option 3: (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i). These map hormones to their respective physiological roles. (50 words)

Guessed Question 1. Single Correct Answer MCQ: Which phytohormone promotes stem elongation and bolting?

1. Abscisic acid
2. Gibberellic acid (GA3)
3. Ethephon
4. 2,4-D

Explanation: Gibberellic acid (GA3) promotes cell elongation, stem growth, and bolting in long-day plants. Correct answer is option 2: GA3. It accelerates flowering and stem elongation, playing a key role in developmental processes like seed germination and vegetative growth. (50 words)

Guessed Question 2. Single Correct Answer MCQ: Ethephon is used primarily as a:

1. Herbicide
2. Fruit ripening agent
3. Stress hormone
4. Bolting agent

Explanation: Ethephon releases ethylene upon decomposition, accelerating fruit ripening and leaf abscission. Correct answer is option 2: Fruit ripening agent. It is widely used commercially to regulate maturation of fruits like bananas and tomatoes. (50 words)

Guessed Question 3. Single Correct Answer MCQ: 2,4-D is commonly used as:

1. Growth promoter
2. Synthetic auxin herbicide
3. Ripening agent
4. Bolting agent

Explanation: 2,4-D is a synthetic auxin that disrupts plant growth, acting as a selective herbicide. Correct answer is option 2: Synthetic auxin herbicide. It is used to control broadleaf weeds without affecting grasses in agriculture. (50 words)

Guessed Question 4. Single Correct Answer MCQ: Abscisic acid mainly functions as a:

1. Fruit ripener
2. Growth promoter
3. Stress hormone
4. Bolting agent

Explanation: Abscisic acid (ABA) regulates plant stress responses, induces dormancy, and closes stomata during water deficit. Correct answer is option 3: Stress hormone. It ensures survival under adverse environmental conditions and coordinates adaptive physiological responses. (50 words)

Guessed Question 5. Assertion-Reason MCQ:

Assertion (A): Ethephon accelerates fruit ripening.
Reason (R): Ethephon releases ethylene gas in plant tissues.
1. Both A and R true, R explains A
2. Both A and R true, R not correct explanation
3. A true, R false
4. A false, R true

Explanation: Ethephon decomposes to release ethylene, which is the actual signal for fruit ripening. Both assertion and reason are correct, with R explaining A. Correct answer is option 1. Ethylene controls ripening, abscission, and some stress responses in plants. (50 words)

Guessed Question 6. Matching Type MCQ:

Column I - Phytohormone
(a) GA3 (i) Bolting agent
(b) ABA (ii) Stress hormone
(c) Ethephon (iii) Fruit ripening agent
(d) 2,4-D (iv) Herbicide
Options:
1. (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
2. (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)
3. (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)
4. (a)-(i), (b)-(iii), (c)-(iv), (d)-(ii)

Explanation: GA3 induces bolting, ABA mediates stress responses, ethephon promotes fruit ripening, and 2,4-D acts as herbicide. Correct answer is option 1: (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv). Matching identifies hormones with their physiological or commercial applications. (50 words)

Guessed Question 7. Fill in the blank:

The synthetic auxin used as herbicide is _______.

1. GA3
2. 2,4-D
3. Ethephon
4. ABA

Explanation: 2,4-D is a synthetic auxin that functions as a herbicide by disrupting cell growth and differentiation in weeds. Correct answer is option 2: 2,4-D. It selectively affects dicotyledonous plants while leaving monocot crops largely unaffected. (50 words)

Subtopic: Cytokinins

Keyword Definitions:

• Kinetin: First discovered cytokinin that promotes cell division in plants.

• Cytokinins: Plant hormones that regulate cell division, differentiation, and apical dominance.

• Skoog and Miller: Scientists who discovered kinetin in 1955 from autoclaved DNA.

• Darwin: Early researcher of plant phototropism and growth responses.

• Went: Discovered auxins, a different class of plant hormones promoting elongation.

• Kurosawa: First suggested presence of growth-promoting substances in plant tissues.

• Cell division: Process of mitosis promoted by cytokinins.

• Callus culture: Undifferentiated plant tissue used to study hormone effects.

• Hormonal balance: Ratio of auxins and cytokinins controlling differentiation.

• Meristem: Plant tissue where active division occurs under cytokinin influence.

• Plant tissue culture: In vitro technique to study hormone effects on growth.

Lead Question - 2020 (COVID Reexam)

Who coined the term 'Kinetin'?

1. Skoog and Miller
2. Darwin
3. Went
4. Kurosawa

Explanation: The term 'Kinetin' was coined by Skoog and Miller in 1955 when they discovered a compound that promoted cell division in plant tissues. It belongs to the class of cytokinins. Correct answer is option 1: Skoog and Miller. This discovery paved the way for plant tissue culture research. (50 words)

Guessed Question 1. Single Correct Answer MCQ: Kinetin primarily promotes:

1. Cell elongation
2. Cell division
3. Root hair formation
4. Leaf senescence

Explanation: Kinetin, a cytokinin, mainly stimulates cell division in meristematic tissues and callus cultures. Correct answer is option 2: Cell division. It regulates differentiation and growth patterns, especially when applied in tissue culture experiments. (50 words)

Guessed Question 2. Single Correct Answer MCQ: The first cytokinin discovered from autoclaved DNA was:

1. Auxin
2. Kinetin
3. Gibberellin
4. Ethylene

Explanation: Kinetin was the first cytokinin identified from autoclaved DNA by Skoog and Miller. Correct answer is option 2: Kinetin. It promotes mitotic division and is widely used in plant tissue culture studies. (50 words)

Guessed Question 3. Single Correct Answer MCQ: Kurosawa is known for:

1. Coining 'Kinetin'
2. Suggesting presence of growth substances
3. Discovering auxins
4. Studying phototropism

Explanation: Kurosawa first suggested that plant tissues contain growth-promoting substances, paving the way for cytokinins discovery. Correct answer is option 2: Suggesting presence of growth substances. He did not coin kinetin but contributed to the understanding of plant hormones. (50 words)

Guessed Question 4. Single Correct Answer MCQ: Cytokinins are primarily synthesized in:

1. Roots
2. Leaves
3. Flowers
4. Seeds

Explanation: Cytokinins, including kinetin, are mainly synthesized in root apical meristems and transported to shoots via xylem. Correct answer is option 1: Roots. They regulate cell division, shoot growth, and delay leaf senescence. (50 words)

Guessed Question 5. Assertion-Reason MCQ:

Assertion (A): Kinetin promotes cell division in plant tissues.
Reason (R): It is a type of cytokinin that influences meristematic activity.
1. Both A and R true, R explains A
2. Both A and R true, R not correct explanation
3. A true, R false
4. A false, R true

Explanation: Kinetin stimulates cell division and differentiation in meristematic tissues. Being a cytokinin, it directly influences mitotic activity. Both assertion and reason are true, with R correctly explaining A. Correct answer is option 1. This property makes kinetin vital in tissue culture experiments. (50 words)

Guessed Question 6. Matching Type MCQ:

Column I - Hormone/Scientist
(a) Kinetin (i) Skoog and Miller
(b) Auxin (ii) Went
(c) Gibberellin (iii) Kurosawa
(d) Ethylene (iv) Ripening hormone
Options:
1. (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
2. (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)
3. (a)-(i), (b)-(iii), (c)-(ii), (d)-(iv)
4. (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)

Explanation: Kinetin was discovered by Skoog and Miller, auxins by Went, gibberellins studied by Kurosawa, and ethylene is a ripening hormone. Correct answer is option 1: (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv). This helps map hormones to discoverers or function. (50 words)

Guessed Question 7. Fill in the blank:

The first cytokinin discovered from autoclaved DNA is _______.

1. Gibberellin
2. Kinetin
3. Auxin
4. Ethylene

Explanation: Kinetin was the first cytokinin identified from autoclaved DNA. Correct answer is option 2: Kinetin. It promotes cell division in plant tissues and is widely used in tissue culture experiments to induce mitotic activity. (50 words)

Guessed Question 8. Single Correct Answer MCQ: Cytokinins delay:

1. Seed germination
2. Leaf senescence
3. Flowering
4. Root elongation

Explanation: Cytokinins like kinetin delay leaf senescence by maintaining chlorophyll content and metabolic activity. Correct

Topic: Plant Growth Regulators

Subtopic: Hormonal Effects on Crop Yield

Keyword Definitions:

• Gibberellin – Plant hormone promoting stem elongation, seed germination, and fruit development.

• Cytokinin – Hormone that stimulates cell division and shoot formation.

• Ethylene – Gaseous hormone regulating fruit ripening and leaf abscission.

• Abscisic acid – Hormone involved in stress response, seed dormancy, and stomatal closure.

• Stem elongation – Increase in plant height due to cell division and elongation.

• Plant growth regulator – Chemical substances affecting plant physiological processes even in small amounts.

Lead Question - 2020

Name the plant growth regulator which upon spraying on sugarcane crop, increases the length of stem, thus increasing the yield of sugarcane crop.

(1) Ethylene
(2) Abscisic acid
(3) Cytokinin
(4) Gibberellin

Explanation: Gibberellins promote stem elongation by stimulating cell division and elongation. In sugarcane, exogenous spraying of gibberellin increases internode length, thereby enhancing sugarcane yield. Correct answer is (4) Gibberellin.

1. Single Correct Answer: Which hormone promotes seed germination and stem elongation?
(1) Ethylene
(2) Gibberellin
(3) Abscisic acid
(4) Cytokinin

Explanation: Gibberellin breaks seed dormancy and promotes stem elongation by activating enzymes that mobilize stored food. Correct answer is (2) Gibberellin.

2. Single Correct Answer: Cytokinin primarily affects:
(1) Root growth
(2) Cell division in shoots
(3) Fruit ripening
(4) Leaf abscission

Explanation: Cytokinins stimulate cell division and differentiation mainly in shoots and young tissues, influencing organ formation. Correct answer is (2) Cell division in shoots.

3. Single Correct Answer: Ethylene in plants is responsible for:
(1) Stem elongation
(2) Seed germination
(3) Fruit ripening and leaf abscission
(4) Cell division

Explanation: Ethylene regulates fruit ripening, leaf senescence, and abscission, acting as a gaseous hormone. It does not promote stem elongation. Correct answer is (3) Fruit ripening and leaf abscission.

4. Assertion (A): Gibberellin application increases sugarcane yield.
Reason (R): Gibberellin enhances stem elongation and internode length.
(1) Both A and R true, R explains A
(2) Both A and R true, R does not explain A
(3) A true, R false
(4) A false, R true

Explanation: Exogenous gibberellin promotes stem elongation by stimulating cell division, increasing internode length, and enhancing sugarcane yield. Both Assertion and Reason are correct, and R explains A. Correct answer is (1).

5. Single Correct Answer: Abscisic acid primarily functions in:
(1) Promoting stem elongation
(2) Stress response and stomatal closure
(3) Cell division in shoots
(4) Fruit ripening

Explanation: Abscisic acid regulates plant responses to stress, maintains seed dormancy, and controls stomatal closure. It does not promote growth. Correct answer is (2) Stress response and stomatal closure.

6. Single Correct Answer: Which hormone stimulates internode elongation in plants?
(1) Ethylene
(2) Gibberellin
(3) Abscisic acid
(4) Cytokinin

Explanation: Gibberellins stimulate internode elongation by promoting cell division and elongation, increasing plant height and productivity. Correct answer is (2) Gibberellin.

7. Match the hormones with their effects:
a. Gibberellin – i. Stem elongation
b. Cytokinin – ii. Cell division
c. Ethylene – iii. Fruit ripening
d. Abscisic acid – iv. Stress response
(1) a-i, b-ii, c-iii, d-iv
(2) a-ii, b-i, c-iv, d-iii
(3) a-iii, b-iv, c-i, d-ii
(4) a-i, b-iii, c-ii, d-iv

Explanation: Gibberellin promotes stem elongation (a-i), Cytokinin stimulates cell division (b-ii), Ethylene regulates fruit ripening (c-iii), and Abscisic acid mediates stress response (d-iv). Correct answer is (1).

8. Fill in the blank: The hormone that increases internode length and sugarcane yield is ______.
(1) Cytokinin
(2) Gibberellin
(3) Ethylene
(4) Abscisic acid

Explanation: Gibberellin promotes internode elongation and enhances sugarcane yield through increased cell division and elongation. Correct answer is (2) Gibberellin.

9. Single Correct Answer: Application of gibberellin in crops mainly affects:
(1) Root hair formation
(2) Stem and internode elongation
(3) Leaf abscission
(4) Seed dormancy

Explanation: Gibberellin application enhances stem and internode elongation, increasing plant height and crop yield. Correct answer is (2) Stem and internode elongation.

10. Choose the correct statements:
(a) Gibberellin promotes stem elongation
(b) Cytokinin stimulates cell division
(c) Ethylene enhances sugarcane yield
(d) Abscisic acid induces stress tolerance
(1) a, b, d only
(2) a, c, d only
(3) b, c, d only
(4) a, b, c, d

Explanation: Gibberellin promotes stem elongation (a), Cytokinin stimulates cell division (b), Abscisic acid mediates stress tolerance (d). Ethylene does not increase sugarcane yield (c). Correct answer is (1) a, b, d only.

Subtopic: Flowering Regulation

Keyword Definitions:

• Pineapple: A tropical fruit plant known for long juvenile period before flowering.

• Auxin: Plant hormone involved in cell elongation, apical dominance, and rooting.

• Ethylene: Gaseous plant hormone that promotes fruit ripening and can induce flowering in some species.

• Gibberellin: Plant hormone that promotes stem elongation, flowering, and seed germination.

• Cytokinin: Plant hormone that promotes cell division and can influence shoot formation and flowering.

• Abscisic acid: Plant hormone involved in dormancy, stress responses, and inhibition of growth.

• Flowering induction: Artificial or natural triggering of flower formation in plants.

Lead Question (2019):

It takes very long time for pineapple plants to produce flowers. Which combination of hormones can be applied to artificially induce flowering in pineapple plants throughout the year to increase yield:
(1) Auxin and Ethylene
(2) Gibberellin and Cytokinin
(3) Gibberellin and Abscisic acid
(4) Cytokinin and Abscisic acid

Explanation: Correct answer is (1). Ethylene stimulates flowering in pineapple by inducing floral initiation, and auxin enhances its effect. Applying this combination artificially can synchronize and induce flowering throughout the year, increasing fruit production and yield efficiently.

1) Single Correct Answer MCQ:
Which hormone primarily induces flowering in pineapple plants?
(1) Gibberellin
(2) Ethylene
(3) Cytokinin
(4) Abscisic acid

Explanation: Correct answer is (2). Ethylene is the primary hormone used to induce flowering in pineapple. It triggers floral initiation and, when combined with auxin, ensures uniform flowering across plants for increased yield.

2) Single Correct Answer MCQ:
Auxin in pineapple flowering helps in:
(1) Dormancy induction
(2) Enhancing ethylene effect
(3) Inhibiting flowering
(4) Seed germination

Explanation: Correct answer is (2). Auxin synergistically enhances ethylene’s effect in flowering induction in pineapple. It promotes cell elongation and improves response to ethylene, resulting in uniform and timely flowering.

3) Single Correct Answer MCQ:
Which hormone combination delays flowering in plants?
(1) Auxin and Ethylene
(2) Gibberellin and Cytokinin
(3) Gibberellin and Abscisic acid
(4) Cytokinin and Ethylene

Explanation: Correct answer is (3). Abscisic acid inhibits growth and delays flowering. Gibberellin alone may promote elongation but when combined with ABA, it cannot efficiently induce flowering.

4) Single Correct Answer MCQ:
Cytokinin is mainly involved in:
(1) Dormancy induction
(2) Cell division and shoot formation
(3) Flower initiation in pineapple
(4) Fruit ripening

Explanation: Correct answer is (2). Cytokinin promotes cell division and shoot formation. While it supports growth, it does not directly induce flowering in pineapple, unlike ethylene.

5) Single Correct Answer MCQ:
Gibberellins in plants generally:
(1) Inhibit stem elongation
(2) Promote stem elongation and flowering
(3) Induce dormancy
(4) Inhibit ethylene production

Explanation: Correct answer is (2). Gibberellins stimulate stem elongation, seed germination, and flowering in many plants. However, pineapple flowering is specifically ethylene-dependent, with gibberellin having minimal effect.

6) Single Correct Answer MCQ:
Which hormone inhibits flowering under stress conditions?
(1) Gibberellin
(2) Auxin
(3) Abscisic acid
(4) Ethylene

Explanation: Correct answer is (3). Abscisic acid promotes dormancy and stress tolerance and can inhibit flowering. It counteracts growth-promoting hormones and is not used for artificial induction in pineapple.

7) Assertion-Reason MCQ:
Assertion (A): Ethylene induces flowering in pineapple plants.
Reason (R): Auxin enhances ethylene-induced floral initiation.
Options:
(1) A true, R true, R correct explanation
(2) A true, R true, R not correct explanation
(3) A true, R false
(4) A false, R true

Explanation: Correct answer is (1). Ethylene triggers flowering, and auxin enhances its effect by promoting cellular responsiveness, making the reason correctly explain the assertion.

8) Matching Type MCQ:
Match the hormone with its function:
(a) Ethylene - (i) Dormancy
(b) Auxin - (ii) Cell elongation and ethylene enhancement
(c) Abscisic acid - (iii) Flowering inhibition
(d) Cytokinin - (iv) Cell division and shoot formation
Options:
(1) a-iii, b-ii, c-i, d-iv
(2) a-iv, b-ii, c-iii, d-i
(3) a-ii, b-i, c-iv, d-iii
(4) a-iii, b-iv, c-i, d-ii

Explanation: Correct answer is (1). Ethylene induces flowering, auxin enhances ethylene effects, abscisic acid inhibits flowering, and cytokinin promotes cell division and shoot growth.

9) Fill in the Blanks MCQ:
_______ is used to artificially induce flowering in pineapple along with auxin.
(1) Gibberellin
(2) Ethylene
(3) Cytokinin
(4) Abscisic acid

Explanation: Correct answer is (2). Ethylene is applied with auxin to trigger flowering artificially in pineapple plants, ensuring synchronized and timely floral initiation.

10) Choose the correct statements MCQ:
(1) Ethylene induces flowering in pineapple
(2) Auxin enhances ethylene effect
(3) Abscisic acid promotes flowering
(4) Cytokinin directly induces flowering in pineapple

Topic: Plant Growth Regulators
Subtopic: Role in Fruit and Leaf Abscission

• Gibberellic acid: Plant hormone promoting stem elongation, seed germination, and fruit growth.

• Cytokinins: Hormones that promote cell division, delay leaf senescence, and influence nutrient mobilization.

• Ethylene: Gaseous plant hormone that promotes fruit ripening, leaf and flower abscission.

• Auxins: Hormones regulating cell elongation, apical dominance, and inhibiting leaf and fruit drop.

• Abscission: The natural detachment of leaves, flowers, or fruits from plants.

• Fruit Drop: Premature shedding of immature fruits due to hormonal imbalance or stress.

• Leaf Drop: Premature leaf shedding affecting photosynthesis and plant productivity.

• Plant Growth Regulators (PGRs): Chemical substances influencing plant growth and development at low concentrations.

• Clinical Relevance: Knowledge of PGRs is applied in agriculture, horticulture, and crop yield management.

• Stress Management: Application of hormones prevents premature organ abscission under environmental stress.

Lead Question - 2017: Fruit and leaf drop at early stages can be prevented by the application of :

1. Gibberellic acid

2. Cytokinins

3. Ethylene

4. Auxins

Explanation: Correct answer is (4). Auxins inhibit the formation of the abscission layer, preventing premature fruit and leaf drop. Clinically and agriculturally, auxin sprays are applied to improve fruit retention and reduce losses, enhancing yield and maintaining plant health under stress conditions.

Chapter: Plant Physiology
Topic: Plant Growth Regulators
Subtopic: Role in Fruit and Leaf Abscission

• Gibberellic acid: Promotes stem elongation, seed germination, and fruit growth.

• Cytokinins: Promote cell division, delay leaf senescence.

• Ethylene: Promotes fruit ripening and organ abscission.

• Auxins: Regulate cell elongation and prevent organ drop.

• Abscission: Natural detachment of plant organs.

• Fruit Drop: Premature shedding of immature fruits.

• Leaf Drop: Premature leaf shedding affecting productivity.

• Plant Growth Regulators (PGRs): Chemicals affecting plant growth at low doses.

• Clinical Relevance: PGRs are used to improve crop yield and plant health.

• Stress Management: Hormonal application reduces organ abscission under stress.

1. Which hormone promotes fruit ripening?

1. Auxins

2. Ethylene

3. Gibberellic acid

4. Cytokinins

Explanation: Correct answer is (2). Ethylene promotes fruit ripening and senescence. Its application is used to control timing of harvest and improve post-harvest handling in agriculture, showing clinical relevance in crop management.

2. Delayed leaf senescence is mainly due to:

1. Gibberellic acid

2. Ethylene

3. Cytokinins

4. Auxins

Explanation: Correct answer is (3). Cytokinins delay leaf senescence by promoting nutrient mobilization and cell division. Agriculturally, cytokinins are applied to enhance photosynthetic duration and increase crop yield.

3. Which hormone promotes stem elongation?

1. Auxins

2. Gibberellic acid

3. Ethylene

4. Cytokinins

Explanation: Correct answer is (2). Gibberellic acid promotes stem elongation, seed germination, and fruit growth. Its application helps in agriculture for improving plant height and yield.

4. Leaf and flower abscission is promoted by:

1. Auxins

2. Ethylene

3. Cytokinins

4. Gibberellic acid

Explanation: Correct answer is (2). Ethylene promotes abscission by activating enzymes that break down cell walls in the abscission zone. Clinically, understanding ethylene’s role aids in controlling premature leaf and flower drop in crops.

5. Application of auxins prevents:

1. Fruit drop

2. Seed dormancy

3. Flower initiation

4. Stem elongation

Explanation: Correct answer is (1). Auxins inhibit abscission layer formation, preventing fruit and leaf drop. Agriculturally, exogenous auxin sprays improve yield by retaining immature fruits and maintaining plant health.

6. Cytokinins mainly affect:

1. Cell division and leaf senescence

2. Fruit ripening

3. Abscission

4. Stem elongation

Explanation: Correct answer is (1). Cytokinins promote cell division and delay leaf senescence. Clinically, cytokinins help maintain photosynthetic activity and improve crop productivity.

7. Assertion (A): Ethylene promotes fruit ripening.
Reason (R): It stimulates enzymatic breakdown of cell walls and chlorophyll degradation.

1. A is true, R is true, R explains A

2. A is true, R is true, R does not explain A

3. A is true, R is false

4. A is false, R is true

Explanation: Correct answer is (1). Ethylene promotes fruit ripening by activating enzymes that degrade cell walls and chlorophyll, causing color change, softening, and aroma development. Agriculturally, ethylene is used to control ripening and market timing.

8. Match the hormone with its main effect:

1. Auxins

2. Ethylene

3. Cytokinins

4. Gibberellic acid

A. Prevents organ drop
B. Promotes abscission and ripening
C. Delays leaf senescence
D. Promotes stem elongation

Explanation: Correct matching: 1-A, 2-B, 3-C, 4-D. Each PGR has a specific physiological role. Understanding their functions is crucial for crop management, yield improvement, and stress mitigation.

9. Fill in the blank: Premature fruit drop can be prevented by applying ______.

1. Ethylene

2. Auxins

3. Gibberellic acid

4. Cytokinins

Explanation: Correct answer is (2). Auxins inhibit abscission layer formation and prevent premature fruit drop. This is widely applied in horticulture to increase fruit retention and overall crop yield.

10. Choose the correct statements about plant growth regulators:

1. Auxins prevent premature organ drop

2. Ethylene promotes fruit ripening and abscission

3. Cytokinins delay leaf senescence

4. All of the above

Explanation: Correct answer is (4). Auxins prevent organ drop, ethylene promotes ripening and abscission, cytokinins delay senescence. Clinically and agriculturally, these hormones are critical for improving yield, quality, and stress management in crops.

Keywords:

• Avena curvature: A bioassay method using oat coleoptile curvature to study plant hormones.

• ABA (Abscisic Acid): Plant hormone regulating stress responses and seed dormancy.

• GA3 (Gibberellic Acid): Plant hormone promoting stem elongation, seed germination, and flowering.

• IAA (Indole-3-acetic acid): Principal auxin in plants, regulating cell elongation and tropic responses.

• Ethylene: Gaseous plant hormone controlling fruit ripening and senescence.

• Bioassay: Experimental setup to measure the biological activity of a substance.

• Coleoptile: Protective sheath covering emerging shoot in monocots.

• Phototropism: Growth response of plant organs towards light.

• Clinically relevant: Understanding plant hormones can assist in crop improvement and stress management studies.

• Experimental setup: Controlled lab conditions to measure response of plant tissue to hormones.

• Oat seedlings: Common model used in Avena curvature assay.

Chapter: Plant Physiology

Topic: Plant Hormones

Subtopic: Auxins and Bioassays

Lead Question - 2016 (Phase 1): The Avena curvature is used for bioassay of :

(1) ABA
(2) GA3
(3) IAA
(4) Ethylene

Answer: 3

Explanation: The Avena curvature bioassay involves measuring the curvature of oat coleoptiles in response to a chemical. IAA (Indole-3-acetic acid), an auxin, induces elongation on the shaded side, causing bending towards light. ABA, GA3, or ethylene do not produce this specific response.

1. Single Correct Answer MCQ: Which hormone primarily induces cell elongation in stems?

(A) ABA
(B) GA3
(C) IAA
(D) Ethylene

Answer: C

Explanation: IAA promotes cell elongation by loosening cell walls and stimulating proton pumps, leading to water uptake and expansion, which is essential for tropic responses like phototropism in plants.

2. Single Correct Answer MCQ: The bending of oat coleoptile towards light is called:

(A) Geotropism
(B) Phototropism
(C) Thigmotropism
(D) Hydrotropism

Answer: B

Explanation: Phototropism is the directional growth of plant organs in response to light, mediated by auxins like IAA, causing differential cell elongation on shaded and illuminated sides.

3. Single Correct Answer MCQ: Which part of the oat seedling is used in Avena curvature bioassay?

(A) Root tip
(B) Leaf blade
(C) Coleoptile
(D) Shoot apex

Answer: C

Explanation: The coleoptile, a protective sheath covering the emerging shoot, is used in the Avena bioassay to detect auxin activity based on curvature induced by IAA.

4. Single Correct Answer MCQ: High concentration of IAA may cause:

(A) Stimulation of root growth
(B) Inhibition of elongation
(C) Rapid seed germination
(D) Fruit ripening

Answer: B

Explanation: Excess IAA can inhibit elongation by over-saturating auxin receptors, disrupting normal cell wall loosening, and causing abnormal growth responses.

5. Single Correct Answer MCQ: Avena curvature assay helps to determine:

(A) Auxin activity
(B) Gibberellin content
(C) Ethylene concentration
(D) ABA levels

Answer: A

Explanation: The assay quantitatively measures auxin activity by observing curvature in oat coleoptiles, reflecting the biological effect of IAA.

6. Single Correct Answer MCQ: Which factor affects the degree of curvature in the Avena bioassay?

(A) Hormone concentration
(B) Light intensity
(C) Age of coleoptile
(D) All of the above

Answer: D

Explanation: Hormone concentration, light exposure, and coleoptile age influence the sensitivity and magnitude of curvature, making these parameters critical for accurate bioassay results.

7. Assertion-Reason MCQ:
Assertion (A): IAA causes bending of plant stems towards light.
Reason (R): Auxins accumulate on the shaded side, stimulating differential growth.

(A) Both A and R are true, R is correct explanation of A
(B) Both A and R are true, R is NOT correct explanation of A
(C) A is true, R is false
(D) A is false, R is true

Answer: A

Explanation: Differential distribution of IAA on the shaded side promotes cell elongation, causing stems to bend towards light, demonstrating phototropic response.

8. Matching Type MCQ: Match hormones with their primary function:

1. IAA   A. Stress response
2. GA3   B. Cell elongation
3. ABA   C. Seed dormancy
4. Ethylene   D. Fruit ripening

(A) 1-B, 2-A, 3-C, 4-D
(B) 1-B, 2-C, 3-A, 4-D
(C) 1-A, 2-B, 3-C, 4-D
(D) 1-B, 2-D, 3-A, 4-C

Answer: A

Explanation: IAA promotes elongation, GA3 aids germination and growth, ABA regulates dormancy and stress, while ethylene controls fruit ripening and senescence.

9. Fill in the Blanks: In the Avena curvature assay, _______ is used to detect the activity of _______.

(A) Oat coleoptile; IAA
(B) Root tip; GA3
(C) Leaf blade; ABA
(D) Shoot apex; Ethylene

Answer: A

Explanation: Oat coleoptile curvature serves as a sensitive indicator of IAA activity, allowing quantification of auxin potency in experimental setups.

10. Passage-based MCQ:
Passage: A researcher places a strip of agar containing a plant hormone on the shaded side of oat coleoptile. The coleoptile bends towards the light. The magnitude of bending is measured to quantify hormone effect.
Question: Which hormone is most likely tested in this experiment?

(A) ABA
(B) GA3
(C) IAA
(D) Ethylene

Answer: C

Explanation: The experiment describes classic Avena curvature bioassay, where IAA applied to coleoptile causes differential growth, bending the shoot towards light, indicating auxin activity.