Top 100+ Plant Growth and Development - Biology Questions and Answers For NEET 2024 Exam Preparation

Q1. An enzyme that can stimulate germination of barley seeds is

1. α-amylase
2. invertase
3. lipase
4. protease

Answer: (a)

The process by which the dormant embryo of seed resumes active growth and forms a seedling is known as germination.

The initial step in germination process is the uptake of water and rehydration of the seed tissues by the process of imbibition. The first visible sign of germination is the emergence of the radicle from the seed.

But this event is preceded by a series of biochemical reactions. Imbibition of water causes the embryo within seed to produce α- and β-amylases.

These enzymes hydrolyze the starch stored in endosperm into glucose which is necessary for use both as a respiratory substrate and as a source of carbon skeletons of the molecules needed for growth.

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Q2. Prunning of plants promotes branching, because the axillary buds get sensitized to –

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

Answer: (c)

Prunning of plants promotes branching, because the axillary buds get sensitized to cytokinin.

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Q3. Substance which originate at the tip of stem and control growth are –

1. Enzymes
2. Vitamins
3. Food materials
4. Auxins

Answer: (d)

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Q4. Skoog and miller termed cytokinin as

1. Kinetin
2. Cytokinesis
3. Both (a) and (b)
4. None of these

Answer: (a)

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Q5. What are the influences of ethylene on plants?

1. Swelling of the axis
2. Horizontal growth of seedlings
3. Apical hook formation in dicot seedling
4. All of these

Answer: (b)

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Q6. Which one among the following chemicals is used for causing defoliation of forest trees?

1. Phosphon-D
2. Amo-1618
3. Malic hydrazide
4. 2, 4-D

Answer: (d)

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Q7. When flowering is either quantitatively or qualitatively dependent or exposure to low temperature it is called ____ phenomenon.

1. Thermoperiodism
2. Photoperiodism
3. Vernalization
4. Dormancy

Answer: (b)

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Q8. Statement 1 : Phytochrome exists in two forms Pr and Pfr.

Statement 2 : Pr form stimulates and Pfr form inhibit flowering.

1. Statement -1 is True, Statement -2 is True ; Statement-2 is NOT a correct explanation for Statement - 1
2. Statement- 1 is True, Statement-2 is True, Statement-2 is a correct explanation for Statement -1
3. Statement - 1 is True, Statement- 2 is False
4. Both the statements are false

Answer: (c)

Light energy become effective when it is absorbed by a pigment. These pigments are called phytochromes. It occurs in two forms namely $P_{r}$ and $P_{fr}$. The two forms are interconvertible.

The $P_{r}$ form absorbs red light of 660 nm and is changed to $P_{fr}$.

The $P_{fr}$ form absorbs far redlight of 730 nm and changed to $P_{r}$.

The $P_{r}$ form stimulates whereas $P_{fr}$ form inhibit flowering.

The $P_{r}$ form stimulates whereas $P_{fr}$ form inhibit flowering.

$P_{fr}$ form of phytochrome is the active form.

The $P_{r}$ form is not considered to be active.

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Q9. What causes a green plant exposed to the light on only one side, to bend toward the source of light as it grows?

1. Green plants seek light because they are phototropic.
2. Green plants need the right light to perform photosynthesis.
3. Light stimulates plant cells on the lighted side to grow faster.
4. Auxin accumulates on the shaded side, stimulating greater cell elongation there.

Answer: (d)

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Q10. Abscisic acid is a

1. stress hormone
2. gaseous hormone
3. volatile hormone
4. liquid-gas mixture

Answer: (a)

Abscisic acid is also called stress hormone as it increases tolerance of plants to various kinds of stresses and causes partial closure of stomata under drought and thus acts as anti-transpirant.

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Q11. Pineapple can be made to flower in off season by :

1. Zeatin
2. Ethylene
3. Napthalene Acetic Acid (NAA)
4. Temperature

Answer: (c)

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Q12. Which of the following hormones can replace vernalization?

1. Gibberellins
2. Ethylene
3. Cytokinins
4. Auxins

Answer: (a)

Gibberellin overcomes vernalization requirement (low temperature) for flowering.

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Q13. Study the four statements (A-D) given below and select the two correct ones out of them.

1. Definition of biological species was given by Ernst Mayr.
2. . Photoperiod does not affect reproduction in plants.
3. Binomial nomenclature system was given by R.H. Whittaker.
4. In unicellular organisms, reproduction is synonymous with growth.

The two correct statements are

1. C and D
2. B and C
3. A and D
4. A and B

Answer: (c)

Photoperiod affects flowering and reproduction in plants. Binomial nomenclature system was given by Carolus Linnaeus.

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Q14. Meristems are found in

1. Shoot apex
2. Root apex
3. Both (a) and (b)
4. None of these

Answer: (c)

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Q15. Abscisic acid controls

1. leaf fall and dormancy
2. cell division
3. shoot elongation
4. cell elongation and wall formation

Answer: (a)

Before a leaf fall, a special zone of cells is formed at the base of the pedicel or petiole. This zone is called abscission zone. It is delimited by a protection layer on the stem side and a separation layer on the organ side.

The leaf is ultimately separated and phenomenon is called abscission. ABA is also a growth inhibitor. It regulates the dormancy of seeds and buds perhaps by inhibiting the growth process. The ABA level decreases in the whole seed as their dormancy is broken.

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Q16. Which of the following hormones causes fruits like apple to elongate and improve its shape?

1. ABA
2. GA
3. NAA
4. 2, 4D

Answer: (b)

Gibberellins (GAs) causes fruits like apple to elongate and improve in shapes.

GA are plant hormones that regulate growth and influence various developmental processes, including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction, and leaf and fruit senescence.

GA is also responsible for bolting (internode elongation just prior to flowering).

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Q17. Plants with no such correlation between exposure to light duration and induction of flower response are called

1. Day-neutral plants
2. Long day plant
3. Short day plant
4. None of these

Answer: (b)

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Q18. Continued growth due to activity of meristem is which type of growth?

1. Open growth
2. Closed growth
3. Both (a) and (b)
4. None of these

Answer: (d)

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Q19. How many of the following auxins are obtained from plants?

IAA, IBA, NAA, 2, 4–D

1. 2
2. 1
3. 3
4. 4

Answer: (a)

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Q20. Assertion: Cytokinin delays the leaf senescence.

Reason: Cytokinin promotes nutrient mobilization.

1. If both the assertion and reason are true but the reason is not a correct explanation of the assertion.
2. If both the assertion and the reason are true and the reason is a correct explanation of the assertion.
3. If the assertion is true but the reason is false.
4. If both the assertion and reason are false.

Answer: (b)

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Q21. Assertion: ABA is known as stress hormone.

Reason: ABA increases the tolerance of plants to several kinds of stresses.

1. If both the assertion and reason are true but the reason is not a correct explanation of the assertion.
2. If both the assertion and the reason are true and the reason is a correct explanation of the assertion.
3. If the assertion is true but the reason is false.
4. If both the assertion and reason are false.

Answer: (b)

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Q22. In the expression of exponential growth 'e' stands for

1. Base of natural log
2. Exponential growth rate
3. Relative growth rate
4. Change in size

Answer: (a)

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Q23. Which is employed for artificial ripening of banana fruits?

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

Answer: (c)

Ethylene is a hormone which is used for ripening of fruit. In case of unripe banana, it can be made to ripe before proper time if they are kept in ethylene atmosphere.

Uncontrolled application of this gas may spoil the fruits. Ethylene is produced in mature but unripe fruits and then it initiates a chain of reactions that finally lead to ripening.

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Q24. Mowing grass lawn facilitates better maintenance because

1. removal of apical dominance and stimulation of intercalary meristem
2. wounding stimulates regeneration
3. removal of apical dominance
4. removal of apical dominance and promotion of lateral meristem

Answer: (a)

Mowing grass lawn facilitates better maintenance because of removal of apical dominance and stimulation of intercalary meristem.

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Q25. The growth rate shows an increase that can be

1. Arithmetic
2. Mathematical
3. Geometrical
4. Both (a) and (c)

Answer: (d)

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Q26. NAA stands for ________.

1. Nitro aceto acetate
2. Nitroacetic acid
3. Naphthaleneacetic acid
4. Naphthaloaceto acetic acid

Answer: (c)

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Q27. The growth of the given system per unit time which is expressed on a common basis or per unit initial parameter is known as

1. Relative growth rate
2. Absolute growth rate
3. Both (a) and (b)
4. None of these

Answer: (a)

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Q28. Etiolation in plants is caused when

1. they are grown in dark.
2. they have a mineral deficiency.
3. they are grown in intense light.
4. they are grown in blue light.

Answer: (a)

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Q29. What kind of plants require the exposure to light for a period less than critical duration?

1. Day-neutral plants
2. Short day plants
3. Long day plants
4. None of these

Answer: (c)

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Q30. Extrinsic factor for plant development includes ________

1. Temperature
2. Light
3. Water
4. All of these

Answer: (d)

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Q31. Day neutral plants relate to

1. flowering in all possible photoperiods.
2. loss of activity during day time.
3. overactive during the time.
4. no flowering in any photoperiods.

Answer: (b)

Day neutral plants are those plants where day length does not influence flowering. These plants flower in both shorter and longer photoperiod. For example, maize, cotton, tomato etc.

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Q32. What causes a green plant exposed to the light on only one side, to bend toward the source of light as it grows?

1. Light stimulates plant cells on the lighted side to grow faster
2. Green plants seek light because they are phototropic
3. Auxin accumulates on the shaded side, stimulating greater cell elongation there.
4. Green plants need light to perform photosynthesis

Answer: (c)

Auxin stimulates cell elongation. It accumulates on shaded side which results in more elongation of cells toward shaded side of the plant. This causes bending of the plant towards source of light.

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Q33. Highest concentration of cytokinin is found in

1. meristematic region only.
2. area of continuous growth and meristematic region.
3. mature leaves.
4. ripened fruit.

Answer: (b)

Cytokinins (CK) are a class of plant growth substances that promote cell division, or cytokinesis, in plant roots and shoots. Cytokinins are found in abundance in young roots, leaves and young fruits where rapid cell division occurs and are synthesized in the meristematic regions of the plants.

Cytokinins have been implicated in many plant activities; usually along with some other plant hormone such as auxins or ethylene. Among these are: mitosis, chloroplast development, differentiation of the shoot meristem, stimulating the development of lateral buds and therefore branching, differentiation of the tissues of the root, leaf formation and leaf senescence.

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Q34. Which one of the following is not a biofertilizer?

1. Rhizobium
2. Agrobacterium
3. Nostoc
4. Mycorrhiza

Answer: (b)

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Q35. Nutrition is included in which phase of plant development?

1. Latter
2. Former
3. Both (a) and (b)
4. None of these

Answer: (a)

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Q36. Phytochrome is involved in

1. photorespiration
2. phototropism
3. photoperiodism
4. geotropism

Answer: (c)

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Q37. Pruning of plants promotes branching, because the axillary buds get sensitized to –

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

Answer: (c)

Prunning of plants promotes branching, because the axillary buds get sensitized to cytokinin.

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Q38. Oxygen is exchanged in which phase of plant development?

1. Latter
2. Former
3. Both (a) and (b)
4. None of these

Answer: (b)

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Q39. Which of the following instruments can be used to record plant growth in seconds?

1. Arc indicator
2. Arc auxanometer
3. Space marker disc
4. Cresco graph

Answer: (d)

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Q40. Assertion: Vernalization refers specially to the promotion of flowering by a period of low temprature.

Reason: Vernalization also seen in biennial plants.

1. If both the assertion and reason are true but the reason is not a correct explanation of the assertion.
2. If both the assertion and the reason are true and the reason is a correct explanation of the assertion.
3. If the assertion is true but the reason is false.
4. If both the assertion and reason are false.

Answer: (c)

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Q41. Maximal size in terms of wall thickening and protoplasmic modification are achieved by

1. cells of maturation phase.
2. cells of divisional phase.
3. cells of elongation phase.
4. cells of meristematic tissue.

Answer: (a)

The period of growth is generally divided into three phases: meristematic (cells of apical meristem divide), elongation (proteins, protoplasm, cell wall material is synthesized) and maturation (secondary walls are laid down).

Maximal size in term of wall thickening and protoplasmic modification are achieved by cells of maturation phase.

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Q42. Which hormone is used to induce rooting from cut end of the stem?

1. Indole butyric acid
2. Kinetin
3. $GA_{3}$
4. Abscisic acid

Answer: (a)

IBA (indole butyric acid) is a natural plant hormone in the auxin family and is an ingredient in many commercial horticultural plant rooting products. It is used for stimulating plant growth and root formation.

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Q43. Skoog and Miller stimulated cell division in tobacco plant with degraded DNA. The active ingredient in stimulants, which resembles cytokinins, was modified

1. auxin
2. adenine
3. terpenes
4. carotenoids

Answer: (b)

Kinetin (cytokinin) is a modified form of adenine, a purine.

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Q44. Assertion: Auxins used for plant propagation.

Reason: They help to initiate rooting in stem cuttings.

1. If both the assertion and reason are true but the reason is not a correct explanation of the assertion.
2. If both the assertion and the reason are true and the reason is a correct explanation of the assertion.
3. If the assertion is true but the reason is false.
4. If both the assertion and reason are false.

Answer: (b)

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Q45. Who crystallized cytokinin?

1. Charles Darwin
2. Skoog and miller
3. Both (a) and (b)
4. F. W. Went

Answer: (b)

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Q46. Auxin can be bioassayed by

1. lettuce hypocotyl elongation
2. potometer
3. Avena coleoptile curvature
4. hydroponics.

Answer: (c)

Auxin bioassay is a quantitative test as it measures concentration of auxin to produce the effect and the amount of the effect. Avena Curvature is based upon experiments of Went (1928). 10° curvature is produced by auxin concentration of 150 mg/litre at 25°C and 90% relative humidity.

The test can measure auxin upto 300 mg/litre. Auxin from a shoot tip or any other plant organ is allowed to diffuse in a standard size agar block (generally 2 × 2 × 1 mm).

Auxin can also be dissolved directly in agar. 15– 30 mm long oat coleoptile grown in dark is held vertically over water. 1 mm tip of coleoptile is removed without injuring the primary leaf. After 3 hours a second decapitation is carried out for a distance of 4 mm.

Primary leaf is now pulled loose and agar block supported against it at the tip of decapitated coleoptile. After 90–110 minutes, the coleoptile is found to have bent. The curvature is measured. It can also be photographed and the curvature known from shadow graph.

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Q47. Proteinaceous pigment which control activities concerned with light

1. chlorophyll
2. phytochrome
3. anthocyanin
4. carotenoids

Answer: (b)

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Q48. Bananas can be prevented from over-ripening by

1. refrigeration
2. maintaining them at room temperature
3. dipping in ascorbic acid solution
4. storing in a freezer

Answer: (c)

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Q49. Living organism growing in a natural environment can be found graphically by the presence of

1. Linear curve
2. Sigmoid curve
3. Straight line
4. All of these

Answer: (b)

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Q50. Abscisic acid causes

1. stem elongation
2. stomatal closure
3. leaf expansion
4. root elongation

Answer: (b)

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Q51. Assertion: Growth in plant is measurable.

Reason: We can measure growth of pollen tube in terms of its length.

1. If both the assertion and reason are true but the reason is not a correct explanation of the assertion.
2. If both the assertion and the reason are true and the reason is a correct explanation of the assertion.
3. If the assertion is true but the reason is false.
4. If both the assertion and reason are false.

Answer: (b)

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Q52. Phytochrome is involved in

1. photorespiration
2. phototropism
3. photoperiodism
4. geotropism.

Answer: (c)

Phytochrome is a photoreceptor molecule which mediates several developmental and morphogenetic responses of plants to light. This is called photoperiodism.

Borthwick, Hendricks and Parker in 1952, discovered phytochrome, which is a pigment that received light and existed in two interconvertible forms: active form and inactive form.

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Q53. To increase the sugar production in sugarcanes, they are sprayed with

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

Answer: (c)

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Q54. Assertion: Plant retains the capacity for unlimited growth throughout their life.

Reason: This ability of the plants is due to the presence of meristem at certain location of body.

1. If both the assertion and reason are true but the reason is not a correct explanation of the assertion.
2. If both the assertion and the reason are true and the reason is a correct explanation of the assertion.
3. If the assertion is true but the reason is false.
4. If both the assertion and reason are false.

Answer: (c)

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Q55. Abscisic acid causes

1. stem elongation
2. stomatal closure
3. leaf expansion
4. root elongation.

Answer: (b)

Absisic acid is a hormone produced during adverse environmental condition. It also causes the closure of stomata under conditions of water stress as also under high concentration of $CO_2$ in the guard cells.

Abscisic acid inhibits the $K^{+}$ uptake by guard cells and promotes the leakage of malic acid. It results in reduction of osmotically active solutes so that the guard cells become flaccid and stomata get closed.

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Q56. The term synergistic action of hormones refers to

1. When two hormones act together and contribute to the same function.
2. When two hormones act together but bring about opposite effects.
3. When one hormone affects more than one function.
4. When many hormones bring about any one function.

Answer: (a)

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Q57. Which process is not directly affected by auxin?

1. Parthenocarpy.
2. Apical dominance and root initiation.
3. Synthesis of ?-amylase by barley seeds.
4. Leaf abscission.

Answer: (c)

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Q58. The hormone produced during adverse environmental conditions is

1. bichlorophenoxy acetic acid
2. benzyl aminopurine
3. ethylene
4. abscisic acid.

Answer: (d)

Abscisic acid is a hormone which is produced during adverse environmental condition. It also causes the closure of stomata under conditions of water stress as also under high concentration of $CO_2$ in the guard cells.

ABA plays an important role in plants during water stress and drought conditions. The concentration of ABA increases in the leaves of plants facing such stresses, hence it is called as a stress hormone.

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Q59. Ethephon hastens fruit ripening in

1. Tomato
2. Mango
3. Apple
4. Both (a) and (c)

Answer: (d)

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Q60. Match the plant hormones listed in column-I with their major role listed in column-II. Select the correct option from the codes given below.

Codes:

1. A – II; B – IV; C – III; D – 1
2. A – IV; B – V; C – III; D – I
3. A – II; B – V; C – III; D – I
4. A – III; IV B – V; C – II; D – I

Answer: (c)

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Q61. What helps in releasing the metabolic energy essential for growth activities?

1. Water
2. Oxygen
3. Nutrients
4. None of these

Answer: (b)

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Q62. Dwarfness can be controlled by treating the plant with

1. gibberellic acid
2. cytokinin
3. auxin
4. antigibberellin

Answer: (a)

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Q63. Assertion: Floral initiation is done by hormonal substance.

Reason: Hormonal substance is translocated from flowers to leaves.

1. If both the assertion and reason are true but the reason is not a correct explanation of the assertion.
2. If both the assertion and the reason are true and the reason is a correct explanation of the assertion.
3. If the assertion is true but the reason is false.
4. If both the assertion and reason are false.

Answer: (c)

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Q64. The unique ability to retain the capacity of growth in plants is due to the presence of

1. Activator hormones
2. Lifetime differentiation
3. Chlorophyll to utilize energy lifetime
4. Meristems at certain locations

Answer: (d)

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Q65. The Avena curvature is used for bioassay of :

1. $GA_{3}$
2. ABA
3. IAA
4. Ethylene

Answer: (c)

Auxin has been clearly demonstrated in the leaf sheath or coleoptile of oat plant (Avena sativa). This plant coleoptile has been used for the test of hormone Auxin(IAA) participating in the growth of the plant.

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Q66. Which one of the following pairs is not correctly matched?

1. Gibberellic acid — Leaf fall
2. Abscisic acid — Stomatal closure
3. Cytokinin — Cell division
4. IAA — Cell wall elongation

Answer: (a)

Gibberellin helps in cell growth of stem, leaves and other aerial parts.

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Q67. Coconut water contains

1. auxin
2. ABA
3. cytokinin
4. gibberellins

Answer: (c)

The fruit of cocount is a drupe. It has an edible endospermic layer. Coconut milk is the liquid endosperm in unripened fruit and is rich in plant hormone cytokinin.

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Q68. The name 'Auxin' was given to which chemical?

1. Indole-6-acetic acid
2. Indole-3-acetic acid
3. Indole-3-butyric acid
4. Indole-6-butyric acid

Answer: (b)

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Q69. Senescence as an active developmental cellular process in the growth and functioning of a flowering plant, is indicated in

1. floral parts
2. annual plants
3. vessels and tracheid differentiation
4. leaf abscission.

Answer: (c)

Senescence is the process of ageing which is caused by cellular breakdown, increased metabolic failure, increased entropy etc. It occurs in the period between reproductive maturity and death. Cell division followed by cell enlargement and differentiation, precede the actual separation.

Senescence of cell in distal region lead to lignification of cell wall. Tylose formation in tracheary element and callose deposition in sieve elements which occur in advance of abscission (i.e. senescence) finally, lead to actual separation.

Thus, vessels and tracheid (trachery elements) differentiation indicates senescence.

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Q70. Root development is promoted by

1. auxin
2. abscisic acid
3. gibberellin
4. ethylene.

Answer: (d)

Ethylene promotes root growth and root hair formation. In low concentration ethylene is used for initiation of roots and also of lateral roots.

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Q71. Which one of the following pairs, is not correctly matched?

1. Cytokinin - Cell division
2. Gibberellic acid - Leaf fall
3. IAA - Cell wall elongation
4. Abscissic acid - Stomatal closure

Answer: (b)

Gibberellic acid is a simple weakly acidic plant growth hormone which promotes cell elongation of both leaves and stems in general and internodal length of genetically dwarf plants in particular.

It is in general a growth promoting hormone and does not inhibit growth. So leaf abscission is not associated with gibberellic acid but with abscisic acid.

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Q72. Proteinaceous pigment which controls the activities concerned with light is

1. chlorophyll
2. phytochrome
3. anthocyanin
4. carotenoids

Answer: (b)

Phytochrome is a plant pigment that can detect the presence or absence of light and is involved in regulating many processes that are linked to day length (photoperiod), such as seed germination and initiation of flowering.

It consists of a light-detecting portion, called a chromophore, linked to a small protein and exists in two interconvertible forms with different physical properties, particularly in the ability to bind to membranes.

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Q73. Fanners have reported over 50% higher yields of rice by using which of the following biofertilizer?

1. Azolla pinnata
2. Mycorrhiza
3. Cyanobacteria
4. Legume-Rhizobium symbiosis

Answer: (a)

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Q74. What is the special feature of meristem?

1. Its capacity to divide
2. It is present in every tissue
3. Its capacity to self-perpetuate
4. Both (a) and (c)

Answer: (d)

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Q75. Native auxin (Endogenous) is transported in the plant

1. From the root tip in the upward direction
2. From the shoot tip in the downward direction
3. Through vascular systems in plants
4. By a special transport system in the root

Answer: (b)

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Q76. Which of the following statement is correct regarding ethylene?

1. It decreases the respiration rate during fruit ripening.
2. It delays senescence.
3. It breaks seed and bud dormancy.
4. It inhibits flowering in mango.

Answer: (c)

Ethylene promotes senescence and abscission of plant organs especially of leaves and flowers. It enhances the respiration rate during fruit ripening. Ethylene is also used to initiate flowering and for synchronising fruit sets in pineapples. It also induces flowering in mango.

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Q77. Which hormone breaks dormancy of potato tuber?

1. IAA
2. Gibberellin
3. ABA
4. Zeatin

Answer: (b)

Gibberellin is the hormone that breaks seed/ bud dormancy. The tubers of potato reproduce vegetatively to give rise to new plants. So the dormancy of these tubers can be overcome by applying gibberellins.

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Q78. The regulator which retards ageing/senescence of plant parts is

1. auxin
2. cytokinin
3. gibberellin
4. abscisic acid.

Answer: (b)

Richmond and Lang, 1967 observed that degradation of protein and chlorophyll was delayed in the detached leaves, if there was cytokinin in the medium.

The senescence in the detached leaves was controlled by cytokinin first by keeping the stomata open thus allowing more $CO_2$ to enter. This suppresses the action of ethylene which promotes senescence.

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Q79. A plant hormone used for inducing morphogenesis in plant tissue culture is

1. cytokinins
2. gibberellins
3. ethylene
4. abscisic acid

Answer: (a)

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Q80. Statement 1 : Ethylene cause climacteric ripening of fruits.

Statement 2 : Climacteric fruits show a rise in respiration at the time of ripening.

1. Statement -1 is True, Statement -2 is True ; Statement-2 is NOT a correct explanation for Statement - 1
2. Statement- 1 is True, Statement-2 is True, Statement-2 is a correct explanation for Statement -1
3. Statement - 1 is True, Statement- 2 is False
4. Both the statements are false

Answer: (a)

In most fruits the rate of respiration will undergo a sharp rise and then fall near the end of ripening. Kidd and Westtermed this phenomenon "climacteric rise".

The climacteric acts as a trigger that sets in progress those changes that rapidly transform the fruit from an unripe to a ripe condition. Finally, application of ethylene to unripe fruit will bring on a premature climactic and accelerate ripening.

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Q81. One of the commonly used plant growth hormone in tea plantations is

1. abscisic acid
2. ethylene
3. zeatin
4. indole-3-acetic acid

Answer: (d)

Indole-3-acetic acid (auxin) is a phytohormone which is generally produced by the growing apices of the stems and roots, from where they migrate to the regions of their action.

It is observed that the growing apical bud inhibits the growth of the lateral (axillary) bud (apical dominance). Since apical meristem is the site of auxin synthesis, it is the physiological effect of the auxin which results in the phenomenon of apical dominance.

When shoot tip is removed it usually results in the growth of lateral buds. This phenomenon is widely applied in tea plantations and hedge-making because as in tea plantation and industries, the apical bud is plucked for tea processing which results in more lateral buds thus enhancing plantation and further industrial purposes.

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Q82. Which one is the first Gibberellins to be discovered and remains the most intensively studied form?

1. $GA_{2}$
2. $GA_{1}$
3. $GA_{3}$
4. $GA_{0}$

Answer: (c)

$GA_{3}$ was one of the first gibberellins to be discovered and remains the most extensively studied form.

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Q83. A pigment which absorbs red and far-red light is

1. xanthophyll
2. cytochrome
3. phytochrome
4. carotene

Answer: (c)

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Q84. Differentiation of shoot is controlled by

1. high cytokinin : auxin ratio
2. high auxin : cytokinin ratio
3. high gibberellin : auxin ration
4. high gibberellin : cytokinin ratio

Answer: (a)

The major physiological function of cytokinin is to enhance cell division. In tissue culture the undifferentiated mass of cells formed in the culture tubes is called callus. The callus may remain in the undifferentiated condition or differentiation may take place in this.

If it is differentiated, then root and shoot may be formed. Skoog and Miller had reported that cytokinins induce shoot formation and auxins induce root formation.

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Q85. Dr. F. Went noted that if coleoptile tips were removed and placed on agar for one hour, the agar would produce a bend-ing when placed on one side of freshly-cut coleoptile stumps. Of what significance is this experiment?

1. It is the basis for the quantitative determination of small amounts of growth-promoting substances.
2. It made possible the isolation and exact identification of auxin.
3. It supports the hypothesis that IAA is auxin.
4. It demonstrated the polar movement of auxins.

Answer: (a)

Charles Darwin and his son Francis Darwin observedthat the coleoptiles of Oat (Avena sativa)and canary grass (Phalariscanariensis) responded to unilateral illumination by growing towards the light source (phototropic curvature or phototropism).

After a series of experiments, it was concluded that the tip of the coleoptile was the site of production of a substance, that caused the bending of coleoptile.

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Q86. Which one among the following chemicals is used for causing defoliation of forest trees?

1. 2, 4-D
2. Malic hydrazide
3. Amo-1618
4. Phosphon D

Answer: (a)

2,4-D is a famous herbicide or weedicide which especially kills broad-leaved weeds. It kills weeds perhaps by overstimulated root growth.

Other auxins like 2, 4, 5 -T have also been used as defoliants during early sixties.

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Q87. Which one among the following chemicals is used for causing defoliation of forest trees?

1. 2, 4-D
2. Malic hydrazide
3. Amo-1618
4. Phosphon D

Answer: (a)

Defoliation is the process of leaves falling off a plant naturally or by inducing using strong chemicals. 2, 4–D (2, 4 dichloro phenoxy acetic acid) is an auxin hormone.

It over stimulates the growth activities of the root cells due to which roots get destroyed and thus plants finally destroyed. 2, 4-D is used as defoliant for broad leaves dicots.

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Q88. The process of growth is maximum during

1. lag phase
2. log phase
3. senescence
4. dormancy

Answer: (b)

In most systems, the initial growth is slow i.e., lag phase, and it increases rapidly thereafter – at an exponential rate i.e., log or exponential phase.

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Q89. Which of the following hormones are responsible for bud break in the spring in deciduous trees?

1. Cytokinins
2. Auxins
3. Gibberellins
4. Ethylene

Answer: (c)

Gibberellins are responsible for bud break in deciduous trees.

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Q90. Senescence as an active developmental cellular process in the growth and functioning of a flowering plant, is indicated in

1. floral parts
2. annual plants
3. vessels and tracheid differentiation
4. leaf abscission

Answer: (c)

Senescence is the process of ageing which is caused by cellular breakdown, increased metabolic failure, increased entropy, etc. It occurs in the period between reproductive maturity and death.

Cell division followed by cell enlargement and differentiation, precede the actual separation. Senescence of cell in distal region lead to lignification of cell wall.

Tylose formation in tracheary element and callose deposition in sieve elements which occur in advance of abscission (i.e. senescence) finally, lead to actual separation.

Thus, vessels and tracheid (trachery elements) differentiation indicates senescence.

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Q91. Auxins are mainly produced by

1. Root cambium
2. Apical root meristem
3. Apical shoot meristem
4. Phloem in shoot tip

Answer: (c)

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Q92. Assertion: Secondary xylem is example of redifferentiated cells.

Reason: Secondary xylem develops from dedifferentiated cells.

1. If both the assertion and reason are true but the reason is not a correct explanation of the assertion.
2. If both the assertion and the reason are true and the reason is a correct explanation of the assertion.
3. If the assertion is true but the reason is false.
4. If both the assertion and reason are false.

Answer: (b)

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Q93. Zeatin was isolated from what?

1. Coconut milk
2. Corn kernels
3. Both (a) and (b)
4. None of these

Answer: (c)

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Q94. When are winter varieties planted?

1. Winter
2. Spring
3. Autumn
4. All of these

Answer: (a)

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Q95. Monocarpic plants are those which

1. flower once and die
2. bear flowers with one ovary
3. bear only one flower
4. All of these

Answer: (a)

Monocarpic plants flower only once and die. The plants like Bamboo flower only once during their life cycle. Thus, these plants are called monocarpic plants.

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Q96. In short-day plants, flowering is induced by

1. photoperiod below a critical length and uninterrupted long night
2. photoperiod less than 12 hr
3. long night
4. short photoperiod and interrupted long night

Answer: (a)

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Q97. Mowing grass lawn facilitates better maintenance because

1. removal of apical dominance and stimulation of intercalary meristem
2. wounding stimulates regeneration
3. removal of apical dominance
4. removal of apical dominance and promotion of lateral meristem

Answer: (d)

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Q98. At cellular level, growth is an

1. Increase in size
2. Increase in cytoplasm
3. Increase in nuclear size
4. Increase in protoplasm

Answer: (d)

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Q99. Which of the following prevents the fall of fruits?

1. NAA
2. $GA_3$
3. Ethylene
4. Zeatin

Answer: (a)

α-Naphthalene acetic acid (NAA) is a synthetic or exogenous auxin. It prevents the formation of abscission layer, which is a layer of dead cells in the petiole and pedicel that causes fall of leaf or fruit.

NAA prevents formation of this layer and so it prevents fall of leaf or fruit.

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Q100. Which of the growth substance act as a stimulant during nodule formation in Leguminous plant ?

1. ABA
2. Ethylene
3. IAA
4. Morphactin

Answer: (c)

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