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1. Which plant hormone is primarily responsible for apical dominance?
A. Auxin
B. Gibberellin
C. Cytokinin
D. Abscisic Acid
Answer: A. Auxin
Explanation: Auxin produced at the shoot apex inhibits the growth of lateral (axillary) buds, a phenomenon known as apical dominance.
2. Who isolated auxin from the tips of coleoptiles of oat seedlings?
A. F.W. Went
B. E. Kurosawa
C. Skoog and Miller
D. Cousins
Answer: A. F.W. Went
Explanation: F.W. Went isolated auxin from coleoptile tips of oat (Avena sativa) seedlings using agar blocks.
3. 'Foolish Seedling' (Bakanae) disease of rice seedlings is caused by which pathogen?
A. Gibberella fujikuroi
B. Fusarium oxysporum
C. Puccinia graminis
D. Rhizopus stolonifer
Answer: A. Gibberella fujikuroi
Explanation: Bakanae disease is caused by the fungal pathogen Gibberella fujikuroi, which leads to excessive elongation of stems due to gibberellins.
4. Which plant hormone is gaseous in nature?
A. Ethylene
B. Abscisic acid
C. Indole-3-acetic acid
D. Zeatin
Answer: A. Ethylene
Explanation: Ethylene (C2H4) is a simple gaseous plant growth regulator that plays a key role in fruit ripening and senescence.
5. Which hormone is known as the 'stress hormone' in plants?
A. Abscisic Acid (ABA)
B. Auxin
C. Cytokinin
D. Gibberellic Acid
Answer: A. Abscisic Acid (ABA)
Explanation: ABA stimulates the closure of stomata under water stress and increases plant tolerance to various kinds of stresses.
6. Cytokinins were first discovered as kinetin by Skoog and Miller from:
A. Autoclaved herring sperm DNA
B. Coconut milk
C. Corn kernels
D. Fungus culture
Answer: A. Autoclaved herring sperm DNA
Explanation: Miller et al. discovered kinetin (a modified form of adenine) from autoclaved herring sperm DNA.
7. The mathematical expression for geometric growth is given by:
A. W1 = W0 * e^(rt)
B. Lt = L0 + rt
C. W1 = W0 + rt
D. Lt = L0 * e^(rt)
Answer: A. W1 = W0 * e^(rt)
Explanation: In geometric growth, W1 is final size, W0 is initial size, r is growth rate, t is time, and e is base of natural logarithms.
8. Sigmoid growth curve is a characteristic feature of:
A. Living organisms growing in a natural environment
B. Root elongation under constant conditions
C. Single cell dividing by amitosis only
D. Non-living matter accumulation
Answer: A. Living organisms growing in a natural environment
Explanation: A S-shaped (sigmoid) curve is typical of most living organisms growing under natural resource-limited environments.
9. Bolt action (bolting) before flowering in cabbage and beet is promoted by:
A. Gibberellins
B. Auxins
C. Cytokinins
D. Ethylene
Answer: A. Gibberellins
Explanation: Bolting is internode elongation prior to flowering, which is induced by gibberellins in rosette plants.
10. Natural cytokinin isolated from corn kernels and coconut milk is:
A. Zeatin
B. Kinetin
C. IAA
D. IBA
Answer: A. Zeatin
Explanation: Zeatin was the first naturally occurring cytokinin isolated from corn kernels (Zea mays).
11. The phenomenon where plants follow different pathways in response to environment or phases of life to form different structures is called:
A. Plasticity
B. Differentiation
C. Redifferentiation
D. Vernalisation
Answer: A. Plasticity
Explanation: Plasticity is the ability of plants to alter their development (e.g., heterophylly in cotton, coriander, and larkspur) in response to environment.
12. Which hormone promotes respiratory climacteric in ripening fruits?
A. Ethylene
B. Auxin
C. Abscisic acid
D. Cytokinin
Answer: A. Ethylene
Explanation: Ethylene enhances the respiration rate during fruit ripening, called respiratory climacteric.
13. Which synthetic auxin is widely used as a selective herbicide to kill dicotyledonous weeds?
A. 2,4-D
B. IAA
C. IBA
D. NAA
Answer: A. 2,4-D
Explanation: 2,4-Dichlorophenoxyacetic acid (2,4-D) is widely used to eradicate broad-leaved dicot weeds in cereal lawns.
14. Formative phase of plant growth is also known as:
A. Meristematic phase
B. Elongation phase
C. Maturation phase
D. Senescence phase
Answer: A. Meristematic phase
Explanation: The phase of growth involving active cell division at root tip and shoot tip is called the meristematic or formative phase.
15. The site of perception of light/dark duration for photoperiodism in plants is:
A. Leaves
B. Shoot apex
C. Root apex
D. Floral buds
Answer: A. Leaves
Explanation: Leaves are the sites of perception of light/dark duration required for photoperiodic flowering response.
16. The cold treatment given to seeds or seedlings to promote early flowering is termed as:
A. Vernalisation
B. Photoperiodism
C. Stratification
D. Scarification
Answer: A. Vernalisation
Explanation: Vernalisation refers specifically to the promotion of flowering by a period of low temperature treatment.
17. Dedifferentiation is the process wherein:
A. Differentiated parenchyma cells regain the capacity to divide
B. Meristematic cells undergo structural maturation
C. Divided cells lose power of division permanently
D. Cells undergo programmed cell death
Answer: A. Differentiated parenchyma cells regain the capacity to divide
Explanation: Dedifferentiation is the capacity of living mature cells that have lost the capacity to divide, to regain it under specific conditions (e.g., interfascicular cambium formation).
18. Interfascicular cambium and cork cambium are examples of tissues formed by:
A. Dedifferentiation
B. Differentiation
C. Redifferentiation
D. Plasticity
Answer: A. Dedifferentiation
Explanation: Fully differentiated parenchyma cells undergo dedifferentiation to form secondary meristems like interfascicular cambium and cork cambium.
19. Which hormone delays leaf senescence (Richmond-Lang effect)?
A. Cytokinin
B. Auxin
C. Ethylene
D. Abscisic acid
Answer: A. Cytokinin
Explanation: Cytokinins delay senescence of leaves by promoting nutrient mobilization and chlorophyll preservation.
20. What is the most common commercial compound used as a source of ethylene?
A. Ethephon
B. Zeatin
C. AMO-1618
D. NAA
Answer: A. Ethephon
Explanation: Ethephon in aqueous solution is readily absorbed and transported within the plant and releases ethylene slowly.
21. Seed dormancy can be broken by applying which combination of growth regulators?
A. Gibberellins and Cytokinins
B. ABA and Auxin
C. Ethylene and ABA
D. High concentration of ABA only
Answer: A. Gibberellins and Cytokinins
Explanation: GA3 and cytokinins overcome seed dormancy by activating hydrolytic enzymes and overcoming inhibitory effects of ABA.
22. Arithmetic growth is characterized by a linear curve represented by equation:
A. Lt = L0 + rt
B. Lt = L0 * rt
C. W1 = W0 * e^(rt)
D. Lt = L0 - rt
Answer: A. Lt = L0 + rt
Explanation: In arithmetic growth, only one daughter cell continues to divide while the other differentiates, resulting in a constant linear growth rate (Lt = L0 + rt).
23. Environmental heterophylly is distinctly observed in:
A. Buttercup (Ranunculus)
B. Cotton
C. Coriander
D. Larkspur
Answer: A. Buttercup (Ranunculus)
Explanation: In Buttercup, leaves produced in air and those in water show different shapes, depicting environmental heterophylly.
24. Which plant hormone promotes female flower formation (feminisation) in cucumbers?
A. Ethylene
B. Gibberellin
C. Auxin
D. Abscisic Acid
Answer: A. Ethylene
Explanation: Ethylene promotes female flowers in cucumbers, thereby increasing yield.
25. Parthenocarpy (development of seedless fruits) in tomatoes can be induced by:
A. Auxins
B. Abscisic acid
C. Ethylene
D. High nitrogen supply
Answer: A. Auxins
Explanation: Application of low concentrations of auxins induces parthenocarpy in tomatoes.
26. Relative growth rate is defined as:
A. Growth per unit time expressed per unit initial parameter
B. Total growth per unit area
C. Final size minus initial size
D. Constant cell division rate
Answer: A. Growth per unit time expressed per unit initial parameter
Explanation: Relative growth rate measures the growth of a system per unit time expressed on a common basis, e.g., per unit initial size.
27. Which pigment absorbs light and acts as a photoreceptor in photoperiodic responses?
A. Phytochrome
B. Chlorophyll a
C. Carotenoid
D. Anthocyanin
Answer: A. Phytochrome
Explanation: Phytochrome is a chromoprotein pigment that perceives light signals for photoperiodism and flowering.
28. Which hormone acts as an antagonist to Gibberellins regarding seed germination?
A. Abscisic acid
B. Auxin
C. Cytokinin
D. Ethylene
Answer: A. Abscisic acid
Explanation: ABA inhibits seed germination and promotes dormancy, whereas GA promotes seed germination by synthesizing hydrolytic enzymes.
29. Root initiation in stem cuttings for vegetative propagation is promoted by:
A. Auxins
B. Gibberellins
C. ABA
D. Ethylene
Answer: A. Auxins
Explanation: Synthetic auxins like IBA and NAA are commonly applied to stem cuttings to promote adventitious root development.
30. Tea plantation growers periodically prune tea bushes to:
A. Overcome apical dominance and promote lateral branching
B. Induce bolting
C. Prevent leaf senescence
D. Promote root development
Answer: A. Overcome apical dominance and promote lateral branching
Explanation: Decapitation (removing shoot tips) removes the source of auxin, overcoming apical dominance and allowing lateral buds to grow into bushy shoots.
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