Plant Hormones

Topic: Growth Regulators and Differentiation; Subtopic: Hormonal Control of Growth

Keyword Definitions:
• Parthenocarpy: Development of fruit without fertilization, often induced by auxins.
• Plant Growth Regulators (PGRs): Chemical substances that control plant growth, including auxins, cytokinins, gibberellins, ethylene, and abscisic acid.
• Dedifferentiation: Process by which differentiated cells regain the ability to divide.
• Redifferentiation: Conversion of dedifferentiated cells into specialized tissues again.
• Apical Dominance: Suppression of lateral bud growth by the apical bud due to auxins.

Lead Question - 2025
Read the following statements on plant growth and development.
A. Parthenocarpy can be induced by auxins.
B. Plant growth regulators can be involved in promotion as well as inhibition of growth.
C. Dedifferentiation is a pre-requisite for redifferentiation.
D. Abscisic acid is a plant growth promoter.
E. Apical dominance promotes the growth of lateral buds.
Choose the option with all correct statements.
(1) A, B, C only
(2) A, C, E only
(3) A, D, E only
(4) B, D, E only

Explanation:
Auxins can induce parthenocarpy and are involved in apical dominance. Dedifferentiation is necessary for redifferentiation, enabling specialized tissues to form. Plant growth regulators act both as promoters (auxins, gibberellins, cytokinins) and inhibitors (abscisic acid, ethylene). Abscisic acid inhibits growth and induces dormancy. Hence, the correct answer is (1) A, B, C only.

1. Which plant hormone is responsible for cell elongation in plants?
(1) Cytokinin
(2) Auxin
(3) Abscisic acid
(4) Ethylene

Explanation: Auxins promote elongation of cells in shoots and roots by increasing cell wall plasticity and activating proton pumps. They also influence apical dominance and parthenocarpy. Cytokinins promote cell division, while abscisic acid and ethylene are growth inhibitors. Hence, the correct answer is (2).

2. Gibberellins are primarily involved in:
(1) Root initiation
(2) Fruit ripening
(3) Internode elongation
(4) Leaf abscission

Explanation: Gibberellins stimulate stem elongation and seed germination by breaking dormancy. They also promote bolting in rosette plants. Gibberellic acid (GA₃) is the most well-known. Therefore, the correct answer is (3).

3. Which of the following hormones is known as the “stress hormone” in plants?
(1) Auxin
(2) Cytokinin
(3) Abscisic acid
(4) Gibberellin

Explanation: Abscisic acid (ABA) is called the stress hormone because it induces stomatal closure during water stress, inhibits seed germination, and promotes dormancy. It counters the effects of growth-promoting hormones. Thus, the correct answer is (3).

4. Ethylene is unique among plant hormones because it:
(1) Is gaseous in nature
(2) Promotes seed germination
(3) Induces apical dominance
(4) Inhibits fruit ripening

Explanation: Ethylene is the only gaseous plant hormone that promotes fruit ripening, leaf abscission, and senescence. It also breaks dormancy and stimulates flowering in some species. Hence, the correct answer is (1).

5. Apical dominance is caused due to the presence of:
(1) Cytokinins in lateral buds
(2) Auxins in apical buds
(3) Gibberellins in root tips
(4) Ethylene in stem

Explanation: Apical dominance occurs when the apical bud suppresses the growth of lateral buds through auxin produced at the shoot tip. When the apical bud is removed, lateral buds grow due to reduced auxin concentration. Hence, the correct answer is (2).

6. Which of the following plant hormones promotes seed germination by breaking dormancy?
(1) Abscisic acid
(2) Cytokinin
(3) Gibberellin
(4) Ethylene

Explanation: Gibberellins promote seed germination by stimulating hydrolytic enzymes like α-amylase, which mobilize stored food for embryo growth. Abscisic acid, in contrast, induces dormancy. Hence, the correct answer is (3).

Assertion–Reason Type:
7. Assertion (A): Cytokinins promote cell division in plants.
Reason (R): They are synthesized in the roots and transported to other parts.
(1) Both A and R are true and R is the correct explanation of A
(2) Both A and R are true but R is not the correct explanation of A
(3) A is true but R is false
(4) A is false but R is true

Explanation: Cytokinins are synthesized in root apices and transported via xylem to stimulate cell division and delay senescence. Since their root synthesis supports their function, both statements are true, and R explains A. Correct answer: (1).

Matching Type:
8. Match the following plant hormones with their primary function:
List I
A. Auxin
B. Gibberellin
C. Cytokinin
D. Abscisic acid
List II
1. Promotes fruit ripening
2. Induces dormancy
3. Promotes stem elongation
4. Promotes cell division
(1) A-4, B-3, C-2, D-1
(2) A-3, B-4, C-1, D-2
(3) A-4, B-3, C-4, D-2
(4) A-3, B-4, C-2, D-1

Explanation: Auxin promotes elongation, gibberellin promotes stem elongation, cytokinin promotes cell division, and abscisic acid induces dormancy. Therefore, the correct match is A-3, B-3, C-4, D-2. Correct answer: (3).

Fill in the Blanks:
9. The hormone that promotes the ripening of fruits is __________.
(1) Ethylene
(2) Cytokinin
(3) Gibberellin
(4) Abscisic acid

Explanation: Ethylene, a gaseous hormone, accelerates fruit ripening by increasing respiration rate (respiratory climacteric). It also induces senescence and leaf abscission. Thus, the correct answer is (1).

Choose the Correct Statements:
10. Statement I: Auxins promote elongation of plant cells.
Statement II: Abscisic acid promotes germination of seeds.
(1) Both statements are true
(2) Both statements are false
(3) Statement I is true, Statement II is false
(4) Statement I is false, Statement II is true

Explanation: Auxins promote elongation and apical dominance, essential for plant growth. Abscisic acid, however, inhibits germination and induces dormancy. Hence, Statement I is true, and Statement II is false. Correct answer: (3).

Subtopic: Cytokinin and Leaf Senescence

Keyword Definitions:

• Phytohormones: Naturally occurring organic substances that regulate plant growth and development.

• Cytokinin: A plant hormone that promotes cell division, nutrient mobilization, and delays leaf senescence.

• Senescence: The process of aging in plants leading to death of tissues or organs.

• Nutrient Mobilization: Redistribution of nutrients from older to younger tissues for sustained growth.

Lead Question - 2025

Which one of the following phytohormones promotes nutrient mobilization which helps in the delay of leaf senescence in plants?

(1) Ethylene

(2) Abscisic acid

(3) Gibberellin

(4) Cytokinin

Explanation:

Cytokinin promotes cell division and nutrient mobilization, delaying the process of senescence in leaves. It redirects nutrients from older tissues to growing regions, maintaining chlorophyll and photosynthetic activity. Ethylene and abscisic acid accelerate aging, while gibberellins promote elongation. Hence, cytokinin is responsible for delaying leaf senescence through nutrient redistribution. Correct answer is (4) Cytokinin.

Guessed Questions:

1. Which plant hormone is known as the anti-aging hormone in plants?

(1) Auxin

(2) Cytokinin

(3) Ethylene

(4) Abscisic acid

Explanation:

Cytokinin is called the anti-aging hormone because it prevents chlorophyll degradation and delays leaf yellowing. It maintains photosynthetic activity by mobilizing nutrients to young tissues. This hormone plays a key role in tissue culture and cell division. Thus, the correct answer is (2) Cytokinin.

2. Which of the following is NOT a function of cytokinin?

(1) Cell division

(2) Apical dominance

(3) Delay of leaf senescence

(4) Nutrient mobilization

Explanation:

Cytokinin promotes cell division, delays senescence, and mobilizes nutrients. However, apical dominance is controlled by auxin, which suppresses lateral bud growth. Cytokinin counteracts auxin’s effect. Hence, the correct answer is (2) Apical dominance.

3. Which plant hormone promotes fruit ripening and leaf abscission?

(1) Cytokinin

(2) Ethylene

(3) Gibberellin

(4) Auxin

Explanation:

Ethylene accelerates fruit ripening, leaf abscission, and senescence. It acts as a gaseous hormone that regulates many stress responses and developmental processes. Hence, the correct answer is (2) Ethylene.

4. Which hormone promotes cell elongation in plants?

(1) Gibberellin

(2) Cytokinin

(3) Ethylene

(4) Abscisic acid

Explanation:

Gibberellins promote stem elongation, seed germination, and fruit development. They break seed dormancy and stimulate enzyme synthesis in germinating seeds. Hence, the correct answer is (1) Gibberellin.

5. Which of the following hormones induces dormancy in seeds?

(1) Gibberellin

(2) Cytokinin

(3) Abscisic acid

(4) Ethylene

Explanation:

Abscisic acid (ABA) is known as the stress hormone. It induces dormancy in seeds and buds, helping plants survive adverse conditions. It inhibits growth-promoting hormones like gibberellins. Hence, the correct answer is (3) Abscisic acid.

6. The interaction between auxin and cytokinin regulates:

(1) Flowering

(2) Fruit ripening

(3) Organ formation in tissue culture

(4) Seed germination

Explanation:

In tissue culture, the ratio of auxin to cytokinin determines organ development. High auxin favors root formation, while high cytokinin promotes shoot formation. Balanced levels induce callus formation. This hormonal interaction is crucial for plant morphogenesis. Correct answer: (3) Organ formation in tissue culture.

Assertion-Reason Question

7. Assertion (A): Cytokinin delays leaf senescence.

Reason (R): It enhances nutrient mobilization towards young tissues.

(1) Both A and R are true, and R is the correct explanation of A

(2) Both A and R are true, but R is not the correct explanation of A

(3) A is true but R is false

(4) A is false but R is true

Explanation:

Cytokinin delays leaf senescence by mobilizing nutrients towards young tissues, keeping them green and photosynthetically active. Thus, both assertion and reason are true, and the reason correctly explains the assertion. Correct answer: (1) Both A and R are true, and R is the correct explanation of A.

Matching Type Question

8. Match the following plant hormones with their major functions:

A. Cytokinin — 1. Cell division

B. Abscisic acid — 2. Dormancy induction

C. Ethylene — 3. Fruit ripening

D. Gibberellin — 4. Stem elongation

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

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

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

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

Explanation:

Cytokinin promotes cell division, abscisic acid induces dormancy, ethylene controls fruit ripening, and gibberellin causes stem elongation. Therefore, the correct match is (1) A-1, B-2, C-3, D-4. These hormones coordinate growth and development throughout a plant’s life cycle.

Fill in the Blanks Question

9. ______ delays senescence in leaves by promoting nutrient mobilization.

(1) Cytokinin

(2) Ethylene

(3) Gibberellin

(4) Abscisic acid

Explanation:

Cytokinin delays leaf senescence by mobilizing nutrients from older tissues to developing ones, maintaining chlorophyll and vitality. It acts antagonistically to ethylene and abscisic acid, which promote aging. Therefore, the correct answer is (1) Cytokinin.

Choose the Correct Statements (Statement I & II)

10. Statement I: Cytokinin helps in nutrient mobilization and delays leaf senescence.

Statement II: Ethylene promotes the delay of senescence in leaves.

(1) Both Statement I and II are correct

(2) Both Statement I and II are incorrect

(3) Statement I is correct but Statement II is incorrect

(4) Statement I is incorrect but Statement II is correct

Explanation:

Cytokinin delays senescence through nutrient mobilization, keeping leaves green. Ethylene accelerates aging and abscission. Hence, Statement I is correct, while Statement II is incorrect. Correct answer: (3) Statement I is correct but Statement II is incorrect. 

Subtopic: Growth Regulators and Their Functions

Keyword Definitions:
• Phytohormones: Chemical substances produced in plants that regulate growth and development.
• Ethylene: A gaseous plant hormone that promotes fruit ripening and senescence.
• Cytokinins: Hormones that promote cell division and delay leaf senescence.
• Abscisic acid (ABA): A stress hormone that induces dormancy and inhibits seed germination.
• Gibberellins: Hormones responsible for stem elongation and seed germination.

Lead Question - 2024 (Jhajjhar)
Which of the following correctly matches the plant hormones with their functions?

List-I      List-II
A. Ethylene  I. Increase length of stem
B. Cytokinins  II. Promotion of senescence and abscission
C. ABA  III. Delaying leaf senescence
D. Gibberellins  IV. Inhibition of seed germination

1. A-III, B-I, C-IV, D-II
2. A-II, B-III, C-IV, D-I
3. A-IV, B-II, C-I, D-III
4. A-III, B-IV, C-I, D-II

Explanation: The correct answer is Option 2 (A-II, B-III, C-IV, D-I). Ethylene promotes senescence and abscission, Cytokinins delay senescence, Abscisic acid inhibits germination, and Gibberellins increase stem length. Each plant hormone coordinates specific physiological activities ensuring survival, growth, and reproduction. This matching confirms hormone specialization in regulating plant development and stress responses.

1. Which hormone is known as the stress hormone in plants?
1. Auxin
2. Cytokinin
3. Abscisic acid
4. Gibberellin

Explanation: The correct answer is Abscisic acid (ABA). It is synthesized in response to stress conditions like drought or cold. ABA induces stomatal closure to prevent water loss and promotes seed dormancy during unfavorable conditions. Its primary role is adaptation and survival under abiotic stress, balancing growth and protection.

2. Which of the following hormones promotes fruit ripening?
1. Auxin
2. Cytokinin
3. Ethylene
4. Gibberellin

Explanation: The correct answer is Ethylene. It is a gaseous plant hormone involved in ripening climacteric fruits like bananas, apples, and tomatoes. Ethylene also promotes leaf abscission, flower wilting, and fruit softening. It acts synergistically with other hormones to coordinate senescence and developmental transitions in plants.

3. Gibberellins were first discovered in association with which disease?
1. Bacterial blight
2. Bakanae disease in rice
3. Powdery mildew
4. Downy mildew

Explanation: The correct answer is Bakanae disease in rice. The disease caused by the fungus Gibberella fujikuroi led to the discovery of gibberellins. Infected plants grew abnormally tall due to excessive stem elongation. This observation revealed the hormone’s crucial role in promoting internodal elongation and seed germination.

4. Fill in the blanks:
_________ delays senescence and is commonly used in tissue culture to promote cell division.

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

Explanation: The correct answer is Cytokinin. It delays senescence by maintaining chlorophyll and protein synthesis. In tissue culture, cytokinins induce cell division and shoot formation. They work antagonistically with auxins to balance root and shoot development, thereby sustaining active growth and tissue regeneration.

5. Assertion-Reason Question:
Assertion (A): Abscisic acid induces dormancy in seeds.
Reason (R): ABA enhances seed germination and breaks dormancy.

1. Both A and R are true and R is the correct explanation of A
2. Both A and R are true but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true

Explanation: The correct answer is Option 3 (A is true but R is false). Abscisic acid promotes seed dormancy by inhibiting germination. It prevents precocious germination during unfavorable conditions. Gibberellins, not ABA, break dormancy and trigger germination. Thus, ABA helps maintain seed viability and ensures proper germination timing.

6. Choose the correct statements (Statement I & II):
Statement I: Gibberellins promote stem elongation.
Statement II: Cytokinins promote seed dormancy.

1. Both statements are correct
2. Both statements are incorrect
3. Statement I is correct and Statement II is incorrect
4. Statement I is incorrect and Statement II is correct

Explanation: The correct answer is Option 3 (Statement I is correct and Statement II is incorrect). Gibberellins stimulate cell elongation and division in stem internodes, promoting height growth. Cytokinins, on the other hand, promote cell division and delay senescence but do not induce dormancy, which is controlled by Abscisic acid.

7. Which of the following plant hormones causes abscission of leaves and fruits?
1. Ethylene
2. Cytokinin
3. Auxin
4. Gibberellin

Explanation: The correct answer is Ethylene. It accelerates abscission by promoting the breakdown of cell walls at the abscission zone. Ethylene concentration increases during aging or stress, leading to natural shedding of leaves and fruits, allowing the plant to conserve energy and redirect resources to growth and reproduction.

8. Matching Type:
Match the following plant hormones with their primary function:
A. Auxin — I. Fruit ripening
B. Cytokinin — II. Cell division
C. Ethylene — III. Root initiation
D. Gibberellin — IV. Stem elongation

1. A-III, B-II, C-I, D-IV
2. A-II, B-III, C-IV, D-I
3. A-IV, B-I, C-II, D-III
4. A-I, B-IV, C-III, D-II

Explanation: The correct answer is Option 1 (A-III, B-II, C-I, D-IV). Auxin promotes root initiation, Cytokinin stimulates cell division, Ethylene induces fruit ripening, and Gibberellin enhances stem elongation. These hormones work synergistically and antagonistically to regulate diverse developmental processes and environmental adaptations in plants.

9. Which of the following hormones promotes seed germination by breaking dormancy?
1. Auxin
2. Abscisic acid
3. Gibberellin
4. Cytokinin

Explanation: The correct answer is Gibberellin. It stimulates hydrolytic enzyme production in the aleurone layer, converting stored starch into sugars for embryo growth. Gibberellins overcome dormancy, promote flowering in long-day plants, and elongate stems, thus playing a pivotal role in developmental transitions in plants.

10. Which hormone combination promotes cell elongation and division simultaneously?
1. Auxin and Ethylene
2. Gibberellin and Cytokinin
3. Auxin and Cytokinin
4. Ethylene and ABA

Explanation: The correct answer is Auxin and Cytokinin. Auxin promotes cell elongation, while Cytokinin induces cell division. Together, they regulate tissue differentiation and organ development. Their ratio determines root or shoot formation in tissue culture. Balanced interaction between both ensures coordinated plant growth and morphogenesis.

Topic: Plant Growth Regulators; Subtopic: Role of Growth Hormones in Crop Improvement

Keyword Definitions:

• Gibberellins: Plant hormones that promote stem elongation, seed germination, and flowering by stimulating cell elongation and division.

• Auxins: Growth hormones that promote cell elongation, apical dominance, and root initiation, mainly synthesized in shoot tips.

• Cytokinins: Plant hormones that promote cell division, delay leaf senescence, and are synthesized mainly in root tips.

• Abscisic Acid (ABA): A stress hormone that induces dormancy, inhibits growth, and promotes stomatal closure during water stress.

Lead Question - 2024

Spraying sugarcane crop with which of the following plant growth regulators increases the length of stem, thus increasing the yield?
(1) Gibberellin
(2) Cytokinin
(3) Abscisic acid
(4) Auxin

Explanation: Spraying sugarcane with Gibberellins enhances stem elongation and yield. Gibberellic acid (GA3) promotes internode elongation by stimulating cell elongation and division. It increases sugar yield by extending cane length and enhancing photosynthetic efficiency. This hormone plays a major role in breaking dormancy, promoting bolting, and improving vegetative growth in crops such as sugarcane and rice.

Guessed Questions:

1. Which plant growth regulator is used to induce seedless fruit formation in grapes and tomatoes?
(1) Gibberellin
(2) Cytokinin
(3) Ethylene
(4) Abscisic acid
Explanation: Gibberellins induce parthenocarpy, resulting in seedless fruits in grapes and tomatoes. They promote cell division and elongation of the ovary wall without fertilization. By enhancing metabolic activities and reducing dormancy, GA3 ensures fruit enlargement and higher productivity, which are beneficial for commercial cultivation and fruit quality improvement.

2. Which plant hormone promotes cell division in plant tissues?
(1) Cytokinin
(2) Gibberellin
(3) Ethylene
(4) Auxin
Explanation: Cytokinins stimulate cell division, especially in shoot meristems and developing fruits. They work synergistically with auxins to regulate growth and morphogenesis. By delaying senescence and promoting nutrient mobilization, cytokinins play a key role in tissue culture, enhancing shoot formation, and maintaining vitality in growing plants and crops.

3. Which of the following hormones is known as a stress hormone?
(1) Auxin
(2) Cytokinin
(3) Abscisic acid
(4) Gibberellin
Explanation: Abscisic acid (ABA) is called the stress hormone. It induces stomatal closure during drought, prevents wilting, and promotes seed dormancy under adverse conditions. ABA helps plants survive water scarcity by conserving moisture and modulating gene expression involved in dehydration resistance and growth inhibition.

4. Which plant growth regulator promotes abscission and fruit ripening?
(1) Ethylene
(2) Cytokinin
(3) Gibberellin
(4) Auxin
Explanation: Ethylene accelerates fruit ripening, senescence, and leaf abscission. It acts as a gaseous plant hormone that regulates enzymatic activities like pectinase and cellulase, softening fruit tissues. Ethylene’s coordinated role in ripening helps in synchronized harvesting and improves marketable quality of fruits like bananas, mangoes, and tomatoes.

5. Which combination of hormones promotes apical dominance in plants?
(1) Auxin and Cytokinin
(2) Auxin and Ethylene
(3) Gibberellin and ABA
(4) Cytokinin and Gibberellin
Explanation: Auxins maintain apical dominance by suppressing lateral bud growth, while cytokinins promote it. The balance between auxin concentration at the apex and cytokinin levels in lateral buds determines branch development. This mechanism allows the plant to grow upward efficiently, optimizing light capture and improving overall photosynthetic productivity.

6. Which plant hormone delays leaf senescence?
(1) Cytokinin
(2) Ethylene
(3) Gibberellin
(4) Abscisic acid
Explanation: Cytokinins delay leaf senescence by maintaining chlorophyll and protein levels in leaves. They promote nutrient mobilization and counteract the aging effects of ethylene. This prolongs photosynthetic activity and increases productivity. Cytokinins are widely used in agriculture and tissue culture for enhancing shoot growth and rejuvenating aging plant parts.

7. Assertion-Reason Question
Assertion (A): Gibberellins are used to increase sugarcane yield.
Reason (R): Gibberellins increase internodal elongation in sugarcane, enhancing cane length.
(1) Both A and R are true, and R is the correct explanation of A.
(2) Both A and R are true, but R is not the correct explanation of A.
(3) A is true, but R is false.
(4) A is false, but R is true.
Explanation: Both assertion and reason are true, and R correctly explains A. Gibberellins enhance internodal elongation by stimulating cell division and elongation in sugarcane. This results in taller canes, higher sugar yield, and improved photosynthesis. Therefore, gibberellin application is an effective agricultural practice to boost sugarcane productivity.

8. Matching Type Question
Match the hormone with its physiological effect:
A. Auxin – I. Root initiation
B. Gibberellin – II. Stem elongation
C. Cytokinin – III. Cell division
D. Abscisic acid – IV. Stomatal closure
(1) A–I, B–II, C–III, D–IV
(2) A–II, B–I, C–IV, D–III
(3) A–IV, B–III, C–II, D–I
(4) A–III, B–II, C–I, D–IV
Explanation: Auxins promote root initiation (A–I), Gibberellins stimulate stem elongation (B–II), Cytokinins promote cell division (C–III), and Abscisic acid causes stomatal closure during drought (D–IV). These growth regulators function synergistically or antagonistically to control developmental processes, ensuring optimal adaptation and productivity in varying environmental conditions.

9. Fill in the Blanks
_________ is used to break seed dormancy and promote germination in barley and rice.
(1) Cytokinin
(2) Abscisic acid
(3) Gibberellin
(4) Auxin
Explanation: Gibberellins break seed dormancy in barley and rice by stimulating the synthesis of hydrolytic enzymes like α-amylase, which converts stored starch into sugars. These sugars provide energy for embryo growth during germination, making GA3 essential in malting and agriculture for uniform seedling emergence and high-yield crop establishment.

10. Choose the Correct Statements
Statement I: Gibberellins promote stem elongation and leaf expansion.
Statement II: Abscisic acid promotes cell division in meristematic tissues.
(1) Both statements are true.
(2) Both statements are false.
(3) Statement I is true, Statement II is false.
(4) Statement I is false, Statement II is true.
Explanation: Gibberellins promote stem elongation and leaf expansion, enhancing vegetative growth, while abscisic acid inhibits cell division and promotes dormancy. Therefore, Statement I is true and Statement II is false. Gibberellins act as growth promoters, whereas ABA acts as a growth inhibitor under stress conditions, maintaining physiological balance in plants.

Subtopic: Auxins

Keyword Definitions:

• Auxin: A class of plant hormones that regulate growth, cell elongation, apical dominance, and rooting.

• Abscission: The natural shedding of leaves, flowers, or fruits from a plant.

• Mature monocotyledonous plants: Plants with one cotyledon, e.g., grasses; often resistant to certain herbicides.

• Cell division: Process by which cells replicate to increase tissue growth.

• Apical dominance: Phenomenon where the main central stem grows more strongly than lateral shoots due to auxin.

• Herbicide: Chemical substance used to destroy unwanted plants or weeds.

• Weed-free lawns: Lawns maintained without damaging grasses, often using selective herbicides.

Lead Question – 2024

Auxin is used by gardeners to prepare weed-free lawns. But no damage is caused to grass. Auxin:

(1) promotes abscission of immature leaves only
(2) does not affect mature monocotyledonous plants
(3) can help in cell division in grasses, to produce growth
(4) promotes apical dominance

Explanation: Auxins are plant hormones that regulate growth, cell elongation, and apical dominance. When applied to lawns, selective auxin-based herbicides target broad-leaved dicots (weeds) but have little or no effect on mature monocotyledonous grasses. This property allows gardeners to control weeds without harming the grass. Auxin does not promote leaf abscission in mature plants, though it can influence apical dominance and growth processes in younger tissues. Understanding auxin's selective activity is essential in agriculture and horticulture to manage weeds safely. (Answer: 2)

1. Single Correct Answer:
Which of the following plant hormones primarily promotes cell elongation?
(1) Cytokinin
(2) Auxin
(3) Gibberellin
(4) Ethylene

Explanation: Auxin stimulates elongation of plant cells by loosening cell walls and promoting water uptake. Cytokinins stimulate cell division, gibberellins promote stem elongation and seed germination, and ethylene regulates fruit ripening and abscission. Auxin’s elongation effect is crucial in tropic responses and growth regulation. (Answer: 2)

2. Single Correct Answer:
Which hormone is responsible for maintaining apical dominance in plants?
(1) Gibberellin
(2) Auxin
(3) Cytokinin
(4) Abscisic acid

Explanation: Auxin produced in the shoot apex suppresses lateral bud growth, maintaining apical dominance. Cytokinins promote lateral bud growth, gibberellins stimulate elongation, and abscisic acid inhibits growth under stress. Auxin’s role ensures the main stem grows dominantly over side branches. (Answer: 2)

3. Single Correct Answer:
Selective auxin-based herbicides target which type of plants?
(1) Monocot grasses
(2) Broad-leaved dicots
(3) Gymnosperms
(4) Mosses

Explanation: Synthetic auxins selectively affect broad-leaved dicots by disrupting growth processes, while monocot grasses remain largely unaffected. This property allows weed control in lawns without damaging desired grass species. Gymnosperms and mosses are not primary targets. Understanding selective herbicidal action is crucial for horticulture and agriculture. (Answer: 2)

4. Single Correct Answer:
Which hormone can promote rooting in plant cuttings?
(1) Auxin
(2) Cytokinin
(3) Gibberellin
(4) Ethylene

Explanation: Auxin induces root initiation in cuttings by stimulating cell division and elongation at the site of application. Cytokinins promote shoot formation, gibberellins enhance stem elongation, and ethylene regulates ripening. Auxin’s rooting effect is widely applied in micropropagation and vegetative propagation techniques. (Answer: 1)

5. Single Correct Answer:
Which hormone’s excess can cause epinasty (downward curling) of leaves?
(1) Gibberellin
(2) Auxin
(3) Cytokinin
(4) Abscisic acid

Explanation: Excess auxin can cause epinasty by uneven cell elongation in leaf tissues, leading to downward curling. Gibberellins mainly elongate stems, cytokinins stimulate cell division, and abscisic acid induces dormancy or stress responses. Recognizing auxin’s effects is critical for understanding plant morphology and herbicide action. (Answer: 2)

6. Single Correct Answer:
Auxin applied to which plant part promotes elongation predominantly?
(1) Roots
(2) Shoot apices
(3) Leaves
(4) Lateral buds

Explanation: Auxin is produced mainly at shoot apices, promoting cell elongation in stems and young leaves. Application at shoot tips influences apical growth, while roots respond differently and lateral buds may be inhibited due to apical dominance. Auxin distribution determines plant morphology and tropic responses. (Answer: 2)

7. Assertion-Reason:
Assertion (A): Auxin can selectively kill broad-leaved weeds without affecting grasses.
Reason (R): Grasses are monocots and mature monocotyledonous plants are resistant to auxin-based herbicides.
(1) Both A and R are true, R explains A
(2) Both A and R are true, R does not explain A
(3) A true, R false
(4) A false, R true

Explanation: Auxin-based herbicides selectively target broad-leaved dicots, sparing monocot grasses due to their natural resistance. Both assertion and reason are true, and the resistance of monocots explains the selectivity of the herbicide. (Answer: 1)

8. Matching Type:
Match List I (Auxin Action) with List II (Effect):
A. Promotes root initiation – (i) Apical dominance
B. Inhibits lateral buds – (ii) Rooting in cuttings
C. Promotes cell elongation – (iii) Stem elongation
Options:
(1) A-ii, B-i, C-iii
(2) A-i, B-ii, C-iii
(3) A-iii, B-i, C-ii
(4) A-ii, B-iii, C-i

Explanation: Auxin promotes root initiation in cuttings (A-ii), maintains apical dominance inhibiting lateral buds (B-i), and promotes cell elongation in stems (C-iii). Matching highlights auxin’s multifaceted roles in growth and development. (Answer: 1)

9. Fill in the Blanks:
Auxin promotes __________ in stems and __________ in lateral buds.
(1) Cell elongation, inhibition
(2) Cell division, activation
(3) Abscission, dormancy
(4) Ripening, elongation

Explanation: Auxin stimulates cell elongation in stems and inhibits lateral bud growth due to apical dominance. It does not induce dormancy, abscission, or fruit ripening directly. Understanding these effects is essential for horticultural practices like pruning and weed management. (Answer: 1)

10. Choose Correct Statements:
Statement I: Auxin regulates cell elongation and apical dominance.
Statement II: Auxin selectively affects broad-leaved dicots while sparing grasses.
Options:
(1) Both statements are true
(2) Statement I true, Statement II false
(3) Statement I false, Statement II

Topic: Plant Growth Regulators; Subtopic: Functions of Phytohormones

• Auxin: A plant hormone that promotes cell elongation, apical dominance, and differentiation of vascular tissue.

• Gibberellin: A plant growth regulator responsible for stem elongation, seed germination, and breaking dormancy.

• Cytokinin: A plant hormone that stimulates cell division and delays senescence; involved in shoot formation.

• Ethylene: A gaseous plant hormone regulating fruit ripening, flower senescence, and stress responses.

• Apical dominance: Suppression of lateral bud growth by the apical meristem, influenced by auxin.

• Promoter of flowering: Hormonal regulation that induces flowering in specific plant species.

• Female flower formation: Development of pistillate flowers, influenced by hormonal balance in plants like cucumber.

• Stem elongation: Increase in internode length due to gibberellins.

• Plant growth regulators (PGRs): Chemicals that influence plant physiological processes at low concentrations.

• Phytohormone: Naturally occurring hormone in plants regulating growth and development.

• Overcoming apical dominance: Process by which cytokinins or pruning stimulate lateral bud growth.

Lead Question - 2023 (Manipur)

Match List-I with List-II:
List-I List-II
(A) Auxin (I) Promotes female flower formation in cucumber
(B) Gibberellin (II) Overcoming apical dominance
(C) Cytokinin (III) Increase in the length of grape stalks
(D) Ethylene (IV) Promotes flowering in pineapple

Choose the correct answer from the options given below:

• 1. II I IV III

• 2. IV III II I

• 3. I III IV II

• 4. III II I IV

Explanation: Auxin promotes female flower formation in cucumber and is involved in apical dominance. Gibberellin increases stem elongation, as in grape stalks. Cytokinin helps overcome apical dominance and stimulates lateral bud growth. Ethylene promotes flowering in pineapple and regulates senescence. Correct matching: (A-I), (B-III), (C-II), (D-IV). This demonstrates the specific physiological effects of major plant growth regulators on development and flowering processes, facilitating manipulation of plant growth in horticulture and agriculture. Correct answer: 3.

1. Which hormone primarily breaks seed dormancy and promotes germination?

• a) Gibberellin

• b) Auxin

• c) Cytokinin

• d) Ethylene

Explanation: Gibberellins promote seed germination by stimulating production of hydrolytic enzymes that mobilize food reserves in endosperm. Auxin influences cell elongation, cytokinins stimulate division, and ethylene regulates ripening. Hence, gibberellin is essential for breaking dormancy and initiating growth. Correct answer: a.

2. Auxin primarily promotes:

• a) Cell elongation

• b) Leaf senescence

• c) Flower abscission

• d) Seed dormancy

Explanation: Auxin stimulates cell elongation by loosening cell walls, thus promoting stem growth and tropic responses. It does not directly induce senescence, abscission, or dormancy. Correct answer: a.

3. Cytokinin application can:

• a) Promote lateral bud growth

• b) Suppress shoot formation

• c) Inhibit cell division

• d) Promote apical dominance

Explanation: Cytokinins stimulate cell division and promote lateral bud growth, effectively overcoming apical dominance caused by auxin. They do not suppress shoots or inhibit division. Correct answer: a.

4. Ethylene regulates:

• a) Fruit ripening

• b) Seed germination

• c) Stem elongation

• d) Leaf expansion

Explanation: Ethylene is a gaseous hormone that promotes fruit ripening, flower senescence, and abscission. It does not primarily induce germination, stem elongation, or leaf expansion. Correct answer: a.

5. Auxin’s role in apical dominance is to:

• a) Suppress lateral bud growth

• b) Stimulate lateral buds

• c) Promote flowering

• d) Induce fruit ripening

Explanation: Auxin produced in the apical meristem inhibits the growth of lateral buds, maintaining apical dominance. Cytokinin counteracts this effect. Auxin does not directly promote flowering or fruit ripening. Correct answer: a.

6. Gibberellin-induced elongation of grape stalks demonstrates its effect on:

• a) Internode elongation

• b) Flower initiation

• c) Leaf senescence

• d) Fruit abscission

Explanation: Gibberellins increase internode length, resulting in taller stems or elongated grape stalks. They do not primarily trigger flowering, senescence, or fruit abscission. Correct answer: a.

7. Assertion (A): Cytokinins can overcome apical dominance.
Reason (R): Cytokinins promote cell division and lateral bud growth.

• a) Both A and R are true, R explains A

• b) Both A and R are true, R does not explain A

• c) A is true, R is false

• d) A is false, R is true

Explanation: Cytokinins stimulate cell division and promote lateral bud development, counteracting auxin-induced apical dominance. Both assertion and reason are correct, and the reason explains the assertion. Correct answer: a.

8. Match List-I with List-II:

(A) Auxin (I) Promotes female flower formation in cucumber
(B) Gibberellin (II) Overcoming apical dominance
(C) Cytokinin (III) Increase in the length of grape stalks
(D) Ethylene (IV) Promotes flowering in pineapple

• a) A-I, B-III, C

Topic: Plant Growth Regulators; Subtopic: Auxins and Tropic Responses

• Auxin: Plant hormone that regulates growth and responses to stimuli.

• Phototropism: Growth of plant organs towards or away from light.

• Gravitropism: Growth response of plant organs to gravity.

• Apical Dominance: Suppression of lateral bud growth by the shoot apex.

• Root Initiation: Formation of adventitious roots, often promoted by auxin.

• Plant Hormone: Chemical messengers controlling plant growth and development.

• Tropic Response: Directional growth of plant parts in response to environmental stimuli.

• IAA (Indole-3-acetic acid): The most common natural auxin in plants.

• Lateral Bud: Buds located on the side of stems that can develop into branches.

• Cell Elongation: Increase in cell size, a major mechanism for plant organ growth.

• Photoreceptor: Pigments that detect light and mediate phototropic responses.

Lead Question - 2023 (Manipur)

The phenomenon which is influenced by auxin and also played a major role in its discovery is:

• 1. Phototropism

• 2. Root initiation

• 3. Gravitropism

• 4. Apical Dominance

Explanation: Phototropism, the growth of plant parts towards light, was central to the discovery of auxins. Charles Darwin and Francis Darwin observed differential growth in coleoptiles responding to light, leading to the identification of auxin as the chemical mediator. Auxin promotes cell elongation on the shaded side, causing bending towards light. Root initiation, gravitropism, and apical dominance are also influenced by auxin but were not the primary phenomena that led to its discovery. Correct answer: 1. Phototropism. This highlights auxin's pivotal role in directional growth and early plant hormone research.

1. Which auxin is most commonly found in plants?

• a) Indole-3-acetic acid (IAA)

• b) Gibberellic acid

• c) Cytokinin

• d) Abscisic acid

Explanation: Indole-3-acetic acid (IAA) is the principal natural auxin present in most plants, regulating cell elongation, root initiation, and phototropism. Other hormones like gibberellins, cytokinins, and abscisic acid play roles in growth, differentiation, and stress response but are not primary auxins. Correct answer: a.

2. Apical dominance is primarily maintained by:

• a) Cytokinin from roots

• b) Auxin from shoot apex

• c) Gibberellin from leaves

• d) Abscisic acid from seeds

Explanation: Apical dominance occurs due to auxin produced at the shoot apex, which suppresses lateral bud growth, ensuring upward growth of the main stem. Cytokinin promotes lateral bud growth, gibberellins influence stem elongation, and abscisic acid regulates dormancy. Correct answer: b.

3. Gravitropism in roots is influenced by:

• a) Auxin distribution

• b) Light perception

• c) Cytokinin

• d) Ethylene only

Explanation: Gravitropism, growth response to gravity, is mediated by asymmetric auxin distribution. Higher auxin concentration on lower side inhibits root elongation, causing downward bending. Light perception affects phototropism, cytokinins regulate cell division, and ethylene influences stress responses. Correct answer: a.

4. Which plant part shows positive phototropism?

• a) Roots

• b) Stems

• c) Lateral roots

• d) Rhizomes

Explanation: Stems exhibit positive phototropism, growing towards light, guided by auxin-mediated differential cell elongation. Roots typically show negative phototropism (away from light). Lateral roots and rhizomes are influenced by gravitropism or internal growth patterns. Correct answer: b.

5. Auxin promotes cell elongation by:

• a) Acidifying cell wall and loosening cellulose

• b) Increasing chlorophyll synthesis

• c) Stimulating DNA replication

• d) Inhibiting mitosis

Explanation: Auxin acidifies the cell wall, activating expansins that loosen cellulose microfibrils, allowing water uptake and cell elongation. Chlorophyll synthesis, DNA replication, or inhibition of mitosis are not primary mechanisms for auxin-induced elongation. Correct answer: a.

6. Root initiation in cuttings is induced by:

• a) Cytokinin

• b) Auxin

• c) Gibberellin

• d) Ethylene

Explanation: Auxins, especially IAA or synthetic analogues, promote adventitious root formation in stem cuttings by stimulating cell division and elongation. Cytokinins stimulate shoot growth, gibberellins promote stem elongation, and ethylene is involved in stress and senescence responses. Correct answer: b.

7. Assertion (A): Phototropism is essential for maximum light capture.
Reason (R): Auxin redistribution causes bending towards light.

• a) Both A and R are true, and R is the correct explanation of A

• b) Both A and R are true, but R is not the correct explanation of A

• c) A is true, R is false

• d) A is false, R is true

Explanation: Phototropism allows plant stems and leaves to bend towards light, optimizing photosynthesis. This bending occurs due to auxin redistribution, promoting elongation on the shaded side. Both assertion and reason are correct, with reason explaining the assertion. Correct answer: a.

8. Match the following:

• Column I: 1. Phototropism 2. Gravitropism 3. Root initiation 4. Apical dominance

• Column II: a. Auxin-mediated suppression of lateral buds b. Growth towards light c. Auxin-induced downward growth of roots d. Adventitious root formation

Choices:
a) 1-b, 2-c, 3-d, 4-a
b) 1-c, 2-b, 3-a, 4-d
c) 1-d, 2-a, 3-b, 4-c
d) 1-a, 2-d, 3-c, 4-b

Explanation: Phototropism: growth towards light (1-b), Gravitropism: root downward growth (2-c), Root initiation: adventitious roots (3-d), Apical dominance: suppression of lateral buds (4-a). Auxin mediates all these responses. Correct matching: 1-b, 2-c, 3-d, 4-a. Correct answer: a.

9. Fill in the blank: Auxin promotes ____________ on the shaded side of stem to cause phototropic bending.

• a) Cell elongation

• b) Cell division

• c) Root initiation

• d) Lateral bud suppression

Explanation: Auxin accumulates on the shaded side of stems, promoting cell elongation, which causes the shoot to bend toward light during phototropism. Cell division, root initiation, or lateral bud suppression are different auxin-mediated processes but not responsible for bending. Correct answer: a.

10. Choose the correct statements:

Statement I: Auxin influences phototropism, gravitropism, root initiation, and apical dominance.
Statement II: Auxin exclusively promotes lateral bud growth.

• a) Both Statement I and Statement II are correct

• b) Statement I is correct, Statement II is incorrect

• c) Statement I is incorrect, Statement II is correct

• d) Both Statement I and Statement II are incorrect

Explanation: Auxin regulates multiple processes: phototropism, gravitropism, root initiation, and apical dominance, but it suppresses lateral bud growth rather than promoting it. Statement I is correct, Statement II is incorrect. This illustrates auxin's diverse roles in plant growth regulation. Correct answer: b.

Topic: Plant Hormones; Subtopic: Phytohormones in Reproduction

Keyword Definitions:

• Phytohormones: Naturally occurring plant hormones that regulate growth, development, and responses to stimuli.

• Zeatin: A type of cytokinin that promotes cell division and shoot initiation.

• Abscisic Acid: Plant hormone involved in stress responses, seed dormancy, and stomatal closure.

• Indole-3-butyric Acid (IBA): An auxin that promotes root formation and growth.

• Gibberellic Acid (GA3): A gibberellin that stimulates stem elongation, flowering, and seed germination.

• Juvenile Conifers: Young coniferous trees that have not yet reached reproductive maturity.

• Maturity Period: Stage at which plants are capable of producing viable seeds.

• Seed Production: Formation of seeds as a result of reproductive maturity.

• Cytokinins: Class of phytohormones that promote cell division and shoot differentiation.

• Auxins: Phytohormones regulating elongation, apical dominance, and rooting.

• Gibberellins: Plant hormones controlling growth, flowering, and fruit development.

Lead Question - 2023:

Spraying of which of the following phytohormone on juvenile conifers helps in hastening the maturity period, that leads to early seed production?
(1) Zeatin
(2) Abscisic Acid
(3) Indole-3-butyric acid
(4) Gibberellic acid

Answer & Explanation: (4) Gibberellic acid. Gibberellic acid (GA3) is widely used to promote early flowering and hasten reproductive maturity in juvenile conifers. Application of GA3 stimulates the development of reproductive structures and accelerates seed production by breaking juvenile phase limitations. Unlike auxins or cytokinins, GA3 specifically induces elongation of shoots and reproductive tissues. Abscisic acid generally inhibits growth and promotes dormancy. Proper timing and concentration of GA3 application ensures effective seed yield, making it a crucial hormone in forestry and horticulture practices for early propagation and productivity enhancement in conifers and other perennial plants.

1. Which hormone is mainly responsible for cell division in shoots?
(1) Auxin
(2) Cytokinin
(3) Gibberellin
(4) Abscisic Acid
Explanation: Cytokinins, such as Zeatin, promote cell division and shoot initiation. Correct answer is (2).

2. Abscisic acid primarily functions in:
(1) Flowering
(2) Seed dormancy and stress response
(3) Shoot elongation
(4) Root initiation
Explanation: ABA regulates seed dormancy and closes stomata under stress. Correct answer is (2).

3. Indole-3-butyric acid is mainly used to:
(1) Promote flowering
(2) Induce root formation
(3) Stimulate fruiting
(4) Enhance photosynthesis
Explanation: IBA is an auxin that promotes root initiation. Correct answer is (2).

4. Gibberellic acid application results in:
(1) Dormancy
(2) Shoot elongation and early flowering
(3) Leaf abscission
(4) Root inhibition
Explanation: GA3 stimulates stem elongation and early reproductive development. Correct answer is (2).

5. Which hormone breaks seed dormancy?
(1) Gibberellin
(2) Auxin
(3) Cytokinin
(4) Ethylene
Explanation: Gibberellins break dormancy and initiate germination. Correct answer is (1).

6. Which hormone promotes shoot elongation in rice internodes?
(1) Gibberellin
(2) Cytokinin
(3) Auxin
(4) Abscisic Acid
Explanation: GA3 promotes internode elongation, especially in deep water rice. Correct answer is (1).

Assertion-Reason Type Question
7. Assertion (A): GA3 application hastens reproductive maturity in conifers.
Reason (R): GA3 stimulates elongation of shoots and reproductive organs.
(1) Both A and R are true and R explains A
(2) Both A and R are true but R does not explain A
(3) A true, R false
(4) A false, R true
Explanation: GA3 accelerates maturation by promoting shoot and reproductive tissue growth. Both statements are correct and R explains A. Correct answer is (1).

Matching Type Question
8. Match hormone with primary function:
A. Gibberellin – (i) Cell division
B. Cytokinin – (ii) Root formation
C. IBA – (iii) Shoot elongation
D. Abscisic Acid – (iv) Dormancy induction
(1) A-(iii), B-(i), C-(ii), D-(iv)
(2) A-(i), B-(ii), C-(iii), D-(iv)
(3) A-(iv), B-(iii), C-(i), D-(ii)
(4) A-(ii), B-(iv), C-(iii), D-(i)
Explanation: GA3 stimulates shoot elongation; Cytokinins promote cell division; IBA induces roots; ABA induces dormancy. Correct answer is (1).

Fill in the Blanks Question
9. Hormone used to accelerate seed production in juvenile conifers is ______.
(1) Zeatin
(2) Abscisic Acid
(3) Indole-3-butyric acid
(4) Gibberellic acid
Explanation: Gibberellic acid accelerates reproductive maturity and seed production in juvenile conifers. Correct answer is (4).

Choose the Correct Statements Question
10. Statement I: GA3 promotes early flowering.
Statement II: Abscisic acid promotes early seed production.
(1) I true, II false
(2) I false, II true
(3) Both true
(4) Both false
Explanation: GA3 promotes early flowering and maturity, whereas ABA induces dormancy. Correct answer is (1).

Topic: Plant Growth Regulators; Subtopic: Hormonal Regulation of Elongation in Deep Water Rice

Keyword Definitions:

• Ethylene: A gaseous plant hormone involved in fruit ripening, leaf abscission, and stress responses, including flooding tolerance.

• 2,4-D: Synthetic auxin used as a herbicide and growth regulator, promoting cell elongation in some contexts.

• GA3 (Gibberellic acid): A plant hormone that promotes stem elongation, seed germination, and flowering.

• Kinetin: A cytokinin that promotes cell division, shoot initiation, and delay of senescence.

• Internode: The segment of a plant stem between two nodes where leaves attach.

• Petiole: The stalk that attaches a leaf blade to the stem.

• Deep water rice: Rice variety adapted to grow in water up to several meters, responding to flooding with rapid elongation of internodes and petioles.

Lead Question - 2023:

Which hormone promotes internode/petiole elongation in deep water rice?
(1) Ethylene
(2) 2,4–D
(3) GA3
(4) Kinetin

Answer & Explanation: (1) Ethylene. In deep water rice, flooding triggers ethylene accumulation, which induces rapid elongation of internodes and petioles, allowing leaves to remain above water. Ethylene interacts with gibberellins to enhance elongation, but it is the primary signal for flood-induced growth. GA3 also promotes elongation but is not the primary flooding-induced hormone. Kinetin mainly promotes cell division, and 2,4-D is a synthetic auxin with limited role in deep water elongation. This ethylene-mediated adaptation allows survival in flood-prone habitats by preventing submergence and ensuring photosynthesis continues effectively.

1. Which hormone mainly triggers flooding responses in rice?
(1) Gibberellins
(2) Ethylene
(3) Auxins
(4) Cytokinins
Explanation: Ethylene accumulates under submerged conditions, triggering elongation of internodes and petioles in deep water rice. Gibberellins act downstream, aiding elongation, but ethylene is the main flood response hormone. Hence, the correct answer is (2) Ethylene.

2. GA3 primarily promotes:
(1) Internode elongation in deep water rice
(2) Fruit ripening
(3) Leaf abscission
(4) Flowering inhibition
Explanation: GA3 promotes stem elongation and leaf growth. In deep water rice, it supports ethylene-mediated elongation but is not the main flooding-induced signal. GA3 also promotes seed germination and flowering. Hence, the correct answer is (1) Internode elongation in deep water rice.

3. Kinetin function is mainly:
(1) Promote internode elongation
(2) Promote cell division
(3) Trigger flood responses
(4) Induce fruit ripening
Explanation: Kinetin is a cytokinin that promotes cell division and shoot initiation, delaying senescence. It does not directly induce internode elongation in deep water rice, which is ethylene-mediated. Hence, the correct answer is (2) Promote cell division.

4. 2,4-D is:
(1) Natural auxin
(2) Synthetic auxin
(3) Cytokinin
(4) Gibberellin
Explanation: 2,4-D is a synthetic auxin used as a herbicide or growth regulator. It can promote cell elongation but does not mediate flood-induced internode elongation. Hence, the correct answer is (2) Synthetic auxin.

5. Deep water rice adapts to flooding by:
(1) Leaf abscission
(2) Internode elongation
(3) Dormancy
(4) Flower inhibition
Explanation: Deep water rice survives submergence by rapidly elongating internodes and petioles to keep leaves above water. Ethylene accumulation triggers this response, ensuring photosynthesis continues. Other options like dormancy or leaf abscission are less relevant. Hence, the correct answer is (2) Internode elongation.

6. Ethylene interacts with which hormone to enhance elongation?
(1) Kinetin
(2) GA3
(3) 2,4-D
(4) ABA
Explanation: Ethylene promotes elongation in deep water rice and acts synergistically with gibberellins (GA3) to maximize internode and petiole growth. Kinetin and ABA do not play a major role in this process. Hence, the correct answer is (2) GA3.

Assertion-Reason Type Question
7. Assertion (A): Flooding induces ethylene accumulation in rice.
Reason (R): Ethylene triggers internode and petiole elongation to prevent submergence.
(1) Both A and R are true, and R is the correct explanation of A.
(2) Both A and R are true, but R is not the correct explanation of A.
(3) A is true but R is false.
(4) A is false but R is true.
Explanation: Flooding triggers ethylene accumulation in deep water rice, which induces rapid elongation of internodes and petioles, allowing the plant to rise above water and maintain photosynthesis. Both statements are true and R explains A. Correct answer is (1).

Matching Type Question
8. Match the hormone with its effect:
A. Ethylene – (i) Cell division
B. GA3 – (ii) Stem elongation
C. Kinetin – (iii) Flood response
D. 2,4-D – (iv) Synthetic auxin effect
(1) A-(iii), B-(ii), C-(i), D-(iv)
(2) A-(ii), B-(i), C-(iii), D-(iv)
(3) A-(iv), B-(iii), C-(ii), D-(i)
(4) A-(iii), B-(i), C-(iv), D-(ii)
Explanation: Ethylene mediates flood response, GA3 promotes stem elongation, Kinetin promotes cell division, and 2,4-D acts as a synthetic auxin. Hence, correct matching is A-(iii), B-(ii), C-(i), D-(iv). Answer is (1).

Fill in the Blanks Question
9. The hormone responsible for internode elongation in deep water rice is ______.
(1) GA3
(2) Ethylene
(3) Kinetin
(4) 2,4-D
Explanation: Internode and petiole elongation in deep water rice during flooding is primarily triggered by ethylene accumulation, which interacts with GA3 but ethylene is the key hormonal signal. Hence, the correct answer is (2) Ethylene.

Choose the Correct Statements Question
10. Statement I: Ethylene promotes internode elongation in flooded rice.
Statement II: Kinetin is the main hormone responsible for flood-induced elongation.
(1) Both statements are true.
(2) Statement I is true, Statement II is false.
(3) Statement I is false, Statement II is true.
(4) Both statements are false.
Explanation: Ethylene triggers internode and petiole elongation in flooded rice. Kinetin promotes cell division but is not responsible for flood-induced elongation. Hence, Statement I is correct, Statement II is false. Correct answer is (2).

Chapter: Plant Growth and Development; Topic: Plant Hormones; Subtopic: Cytokinins and their Functions

Keyword Definitions:

• Cytokinin: Plant hormone that promotes cell division and is derived from adenine.

• Auxin: Hormone that promotes cell elongation, root initiation, and apical dominance.

• Abscisic Acid (ABA): Growth-inhibiting hormone responsible for dormancy and stress resistance.

• Ethylene: A gaseous hormone responsible for fruit ripening and senescence.

• Adenine: A nitrogenous base found in DNA, RNA, and some plant growth regulators like cytokinins.

Lead Question - 2022 (Ganganagar)
Which of the following growth regulators is an adenine derivative?
1. Auxin
2. Cytokinin
3. Ethylene
4. Abscisic acid

Explanation:
Cytokinins are plant growth regulators that promote cell division and are derived from the purine base adenine. They help in delaying leaf senescence, promoting nutrient mobilization, and inducing shoot growth. The first discovered cytokinin was kinetin, followed by zeatin from maize kernels. Hence, the correct answer is cytokinin.

1. Which plant hormone delays senescence in leaves?
1. Gibberellin
2. Cytokinin
3. Auxin
4. Ethylene
Explanation:
Cytokinin delays senescence by maintaining chlorophyll and nutrient balance in leaves. It enhances the transport of nutrients and stimulates protein synthesis. Cytokinin is synthesized mainly in root apices and moves upward through the xylem to other plant parts, ensuring prolonged leaf activity and delayed aging. Hence, the answer is cytokinin.

2. Which of the following hormones promotes cell elongation?
1. Cytokinin
2. Ethylene
3. Auxin
4. ABA
Explanation:
Auxin promotes cell elongation by increasing cell wall plasticity, leading to expansion. It is primarily produced in shoot apices and young leaves. Indole-3-acetic acid (IAA) is the most common natural auxin. Auxin also influences phototropism and gravitropism, directing plant growth toward light or gravity. Hence, the answer is auxin.

3. Which of the following is known as the stress hormone in plants?
1. ABA
2. Cytokinin
3. Ethylene
4. Auxin
Explanation:
Abscisic acid (ABA) is called the stress hormone because it helps plants tolerate drought and cold by closing stomata and inducing dormancy. It prevents water loss and slows growth under stress conditions. ABA also counteracts gibberellins and cytokinins in promoting growth. Hence, the correct answer is abscisic acid.

4. The natural cytokinin found in maize kernels is:
1. Zeatin
2. Kinetin
3. ABA
4. IAA
Explanation:
Zeatin is a naturally occurring cytokinin isolated from maize kernels. It promotes cell division, chloroplast development, and shoot differentiation. Kinetin, although the first discovered cytokinin, is synthetic. Zeatin is structurally related to adenine and acts as a major regulator in tissue culture. Hence, the answer is zeatin.

5. Which plant hormone is responsible for fruit ripening?
1. Auxin
2. Cytokinin
3. Ethylene
4. Gibberellin
Explanation:
Ethylene is a gaseous hormone that accelerates fruit ripening, leaf abscission, and flower wilting. It promotes the conversion of starches to sugars, softens cell walls, and changes fruit color. Ethylene is synthesized from methionine and functions in a feedback loop with other hormones. Hence, the correct answer is ethylene.

6. Which hormone promotes root initiation on stem cuttings?
1. Gibberellin
2. Auxin
3. Cytokinin
4. ABA
Explanation:
Auxin promotes root initiation by stimulating the formation of adventitious roots in stem cuttings. It influences gene expression related to root meristem formation. The application of synthetic auxins like NAA or IBA enhances root formation in vegetative propagation. Hence, the correct answer is auxin.

7. Assertion-Reason Type:
Assertion (A): Cytokinins are mainly synthesized in roots.
Reason (R): Cytokinins promote chlorophyll degradation in leaves.
1. Both (A) and (R) are correct, and (R) is the correct explanation of (A)
2. Both (A) and (R) are correct, but (R) is not the correct explanation of (A)
3. (A) is correct but (R) is incorrect
4. (A) is incorrect but (R) is correct
Explanation:
Cytokinins are synthesized in root apices and transported upward to promote cell division and chlorophyll retention. The reason is incorrect because cytokinins prevent, not promote, chlorophyll degradation. Thus, (A) is correct but (R) is incorrect. Hence, the correct answer is option 3.

8. Matching Type:
Match the following:
(a) Auxin – (i) Cell elongation
(b) Cytokinin – (ii) Cell division
(c) ABA – (iii) Dormancy induction
(d) Ethylene – (iv) Fruit ripening
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-iv), (b-iii), (c-ii), (d-i)
Explanation:
Auxin promotes cell elongation, Cytokinin induces cell division, ABA causes dormancy, and Ethylene helps in fruit ripening. These hormones work together to regulate plant growth and responses to the environment. Hence, the correct matching is (a-i), (b-ii), (c-iii), (d-iv), option 1.

9. Fill in the Blanks Type:
Cytokinins promote __________ in plant cells.
1. Cell elongation
2. Cell division
3. Dormancy
4. Abscission
Explanation:
Cytokinins promote cell division (cytokinesis) in plant tissues. They act synergistically with auxins in tissue culture to balance shoot and root formation. High cytokinin-to-auxin ratio favors shoot development, while low ratio induces roots. Hence, the correct answer is cell division.

10. Choose the Correct Statements:
Statement I: Cytokinins promote cell division and delay senescence.
Statement II: Abscisic acid promotes seed dormancy and stress tolerance.
1. Both statements are correct
2. Both statements are incorrect
3. Only Statement I is correct
4. Only Statement II is correct
Explanation:
Both statements are correct because cytokinins delay aging by maintaining chlorophyll and promoting cell division, while ABA induces dormancy and helps plants survive water stress. These hormones play opposite but complementary roles in plant growth regulation. Hence, option 1 is correct.

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.