Plant Growth and Development (NCERT Practice Paper)
Q1. Growth is defined as a/an:
Correct Answer: (b)
Growth is characterised by an irreversible increase in the size, volume, or mass of an organ or organism. Unlike reversible changes such as swelling due to water uptake, growth involves synthesis of new protoplasm and cell wall materials. It is a fundamental attribute of living systems and is accompanied by metabolic processes.
Q2. Assertion: The lag phase is the period of initial slow growth in a sigmoid curve.
Reason: It is followed by an exponential increase in growth rate.
Correct Answer: (b)
The lag phase is indeed slow initial growth, and it is followed by the exponential (log) phase. However, the reason does not explain why the lag phase is slow; it only describes the subsequent event. Both are correct but not causally linked.
Q3. Identify true statements for 'Tracheary elements': (i) Formed via differentiation. (ii) Cells lose protoplasm. (iii) Develop lignocellulosic secondary walls.
Correct Answer: (a)
Tracheary elements (xylem vessels and tracheids) differentiate from meristematic cells, undergo programmed cell death (lose protoplasm), and deposit thick lignocellulosic walls. All three statements are correct.
Q4. Which conditions are essential for growth according to the text? (i) Water and Oxygen. (ii) Nutrients. (iii) Optimum temperature.
Correct Answer: (a)
Water, oxygen, nutrients, and optimum temperature are all required for growth. Water provides turgor and medium for metabolism, oxygen for respiration, nutrients for biosynthesis, and temperature affects enzyme activity. All are essential.
Q5. Correct statements about 'Absolute vs Relative Growth Rate': (i) Fig 13.7 shows two leaves A and B. (ii) Both increase area by 5 cm2. (iii) Relative growth rate of leaf A is higher because initial size was smaller.
Correct Answer: (a)
In the figure, both leaves gain 5 cm²; leaf A (initial 5 cm²) has a higher relative growth rate than leaf B (initial 50 cm²) because the same absolute increase represents a larger percentage gain. All statements are correct.
Q6. The only gaseous plant growth regulator is:
Correct Answer: (c)
Ethylene is a simple gaseous hydrocarbon (C2H4) that acts as a PGR. It diffuses readily through plant tissues and influences a wide range of processes, including fruit ripening, senescence, abscission, and stress responses. Its gaseous nature allows rapid intercellular communication and long‑distance signalling.
Q7. Match the specific Auxin use:
Column-I
Column-II
A. Pineapple
(I) Promote flowering
B. Tomato
(II) Induce parthenocarpy
C. Tea plantation
(III) Apical dominance application
Correct Answer: (a)
Auxins are used to promote flowering in pineapple, induce parthenocarpy (seedless fruits) in tomato, and are applied in tea plantations to promote lateral shoot growth by manipulating auxin levels (often by decapitation, not direct auxin application). The mapping reflects the standard agricultural uses.
Q8. Identify correct statements for Ethylene: (i) Enhances respiration during ripening. (ii) Promotes horizontal growth of seedlings. (iii) Initiates germination in peanut seeds. (iv) Accelerates abscission in cotton.
Correct Answer: (a)
Ethylene is known to enhance respiration (climacteric), promote horizontal growth (triple response), break dormancy in peanut seeds, and accelerate abscission. All listed effects are genuine ethylene responses.
Q9. Plant growth regulators (PGRs) are also known as:
Correct Answer: (b)
Plant growth regulators are organic compounds that influence physiological processes at very low concentrations. They are often called phytohormones because they act as chemical messengers, coordinating growth, development, and responses to environmental stimuli. Unlike vitamins or minerals, they are synthesised endogenously.
Q10. Which of the following is true for 'Senescence'? (i) It is the terminal phase of life. (ii) Delayed by cytokinins. (iii) Promoted by ethylene (in organs).
Correct Answer: (a)
Senescence is the final developmental stage leading to death. Cytokinins retard senescence, whereas ethylene promotes it in various organs (e.g., leaves, flowers). All statements are correct.
Q11. Mathematically, arithmetic growth is expressed as:
Correct Answer: (b)
Arithmetic growth occurs when one daughter cell remains meristematic while the other differentiates, leading to linear increase. The equation Lt = L0 + rt describes this pattern, where r is the constant rate of growth per unit time. It results in a straight‑line graph, characteristic of organs with determinate growth.
Q12. The process of 'bolting' (internode elongation just prior to flowering) is promoted by:
Correct Answer: (b)
Bolting, the rapid elongation of the flowering stalk, is stimulated by gibberellins, especially in rosette‑forming plants like cabbage and beet. This effect is used commercially to induce early flowering in seed crops. Gibberellins overcome genetic and environmental constraints that normally delay internode expansion.
Q13. The 'efficiency index' in geometric growth is represented by:
Correct Answer: (c)
In the equation W1 = W0 ert, the parameter r is the relative growth rate or efficiency index. It measures the ability of a plant to generate new biomass relative to existing biomass per unit time. A higher r indicates more efficient growth and is used to compare growth performance among genotypes.
Q14. Which is true for growth in roots? (i) Occurs in meristematic zone. (ii) Parallel line technique detects zones of elongation. (iii) Zones A, B, C, D immediately behind apex elongate most.
Correct Answer: (a)
Root growth occurs primarily in the meristematic zone. The parallel line (ink dot) method can identify the elongation zone by measuring the separation of dots; the region just behind the apex shows maximum elongation. All statements are correct.
Q15. Select correct statements for Gibberellins: (i) They are all acidic. (ii) GA3 remains the most intensively studied form. (iii) They cause elongation of apple shape. (iv) Delay senescence.
Correct Answer: (b)
Gibberellins are acidic and GA3 is most studied. However, they promote stem elongation and fruit growth, but 'elongation of apple shape' is not a typical description; they are not known to delay senescence (cytokinins do). Thus, only (i) and (ii) are correct.
Q16. The first product of CO2 fixation in C4 plants is:
Correct Answer: (b)
In C4 plants, CO2 is fixed by PEP carboxylase into oxaloacetic acid (OAA), a four‑carbon compound, in mesophyll cells. OAA is then converted into malate or aspartate and transported to bundle sheath cells where CO2 is released for the Calvin cycle. This mechanism concentrates CO2 and reduces photorespiration.
Q17. Match the synthetic Auxin with its name:
Column-I
Column-II
A. NAA
(I) Naphthalene acetic acid
B. 2, 4-D
(II) 2, 4-dichlorophenoxyacetic
Correct Answer: (a)
NAA is naphthalene acetic acid; 2,4‑D is 2,4‑dichlorophenoxyacetic acid. Both are synthetic auxins used in agriculture, with 2,4‑D being a common herbicide.
Q18. Match the following for absolute vs relative growth:
Term
Description
A. Absolute rate
(I) Comparison of total growth
B. Relative rate
(II) Growth per unit initial parameter
Correct Answer: (a)
Absolute growth rate measures total increase in size per unit time, while relative growth rate is expressed per unit of initial size, allowing comparison between organisms of different sizes. This distinction is fundamental in growth analysis.
Q19. Spray of which PGR can increase the yield of sugarcane by as much as 20 tonnes per acre?
Correct Answer: (c)
Gibberellins are applied to sugarcane to promote internode elongation, significantly increasing cane length and, consequently, sugar yield. The treatment leads to a remarkable boost in biomass, with reported increases of up to 20 tonnes per acre. This agricultural application demonstrates the commercial importance of gibberellins.
Q20. Identify correct statements for 'Dedifferentiation': (i) Cells regain division capacity. (ii) Occurs under certain conditions. (iii) Example: formation of cork cambium.
Correct Answer: (a)
Dedifferentiation allows mature cells to revert to meristematic state; it is induced by specific conditions (e.g., wounding); and cork cambium formation is a classic example. All statements are correct.
Q21. Formation of cork cambium from fully differentiated parenchyma cells is an example of:
Correct Answer: (b)
Dedifferentiation is the reversion of mature, specialised cells to a meristematic state, regaining the ability to divide. The formation of cork cambium (phellogen) from cortical parenchyma is a classic example. This phenomenon allows plants to produce new tissues, such as periderm, in response to wounding or secondary growth.
Q22. Match the growth curve components:
Column-I
Column-II
A. Lag phase
(I) Slow initial growth
B. Log phase
(II) Rapid exponential growth
C. Stationary phase
(III) Limited nutrient supply
Correct Answer: (a)
In a sigmoid growth curve, the lag phase is slow initial growth; the log (exponential) phase is rapid expansion; and the stationary phase occurs when resources become limiting. These phases are universally observed.
Q23. Which of the following is correct regarding growth? (i) It is irreversible. (ii) It is a permanent increase in size. (iii) It is accompanied by metabolic processes.
Correct Answer: (b)
Growth is defined as an irreversible, permanent increase in size, and it involves metabolic synthesis of new protoplasm and cell walls. Therefore, all three statements are correct and collectively describe the essential nature of growth.
Q24. Which statements about Auxins are true? (i) isolated first from human urine. (ii) IAA and IBA are natural auxins. (iii) Promote flowering in pineapples. (iv) widely used to kill monocot weeds.
Correct Answer: (a)
Auxins were first isolated from human urine; IAA and IBA are natural auxins; they promote flowering in pineapple. However, they are used to kill dicot weeds, not monocots. So (i), (ii), (iii) are true.
Q25. The cells proximal to the meristematic zone represent the phase of:
Correct Answer: (b)
Just behind the meristematic region, cells cease division and enter the elongation phase where they increase in length due to water uptake and wall loosening. This zone is characterised by rapid vacuolation and stretching, preparing cells for their final size and shape before differentiation.
Q26. Assertion: ABA is called the stress hormone.
Reason: It stimulates the closure of stomata and increases plant tolerance to various kinds of stresses.
Correct Answer: (a)
ABA is widely known as the stress hormone because it accumulates under drought, salinity, cold, and osmotic stress. Its primary role is to induce stomatal closure, reducing water loss, and to upregulate stress‑responsive genes. The reason correctly explains the basis for its stress‑related epithet.
Q27. Identify the correct phylum/group being described? (i) Small molecules of diverse chemical composition. (ii) Also called phytohormones. (iii) Five major groups: Auxins, Gibberellins, Cytokinins, ABA, Ethylene.
Correct Answer: (a)
Plant Growth Regulators (PGRs) are small molecules, often called phytohormones, and include five major classes. They act at very low concentrations to regulate growth and development. This description matches PGRs exactly.
Q28. 2, 4-D is widely used as a/an:
Correct Answer: (b)
2,4‑D (2,4‑dichlorophenoxyacetic acid) is a synthetic auxin that acts as a selective herbicide, killing broadleaf weeds while leaving grasses largely unaffected. It disrupts normal auxin physiology, causing abnormal growth and eventual plant death. It is one of the most widely used agricultural herbicides.
Q29. A fruit that shows a rise in respiration rate during ripening is called:
Correct Answer: (b)
Climacteric fruits, such as tomato, banana, and apple, exhibit a sharp increase in respiration (climacteric peak) during ripening, associated with ethylene production. This surge triggers changes in colour, texture, flavour, and aroma, marking the fruit's readiness for consumption. Non‑climacteric fruits show a steady decline in respiration.
Q30. Assertion: Dedifferentiation allows differentiated cells to regain the capacity to divide.
Reason: Interfascicular cambium is formed from fully differentiated parenchyma cells.
Correct Answer: (a)
Dedifferentiation is precisely the reversion of mature cells to a meristematic state, enabling them to divide. The formation of interfascicular cambium from parenchyma cells between vascular bundles is a direct example. This process is essential for secondary growth and wound healing.
Q31. Who isolated Auxin from tips of coleoptiles of oat seedlings?
Correct Answer: (b)
F.W. Went isolated auxin by placing agar blocks on oat coleoptile tips and testing their curvature‑inducing activity. He demonstrated that the growth‑promoting substance diffused from the tip and could be collected. This classic experiment provided the first evidence for a chemical messenger controlling phototropism.
Q32. Correct statements about 'Auxin' migration: (i) Produced by growing apices. (ii) They migrate to the regions of their action. (iii) Isolated first from urine.
Correct Answer: (a)
Auxins are synthesised in shoot and root tips and translocate to target tissues; they were first isolated from human urine. All three statements are correct facts about auxin biology and history.
Q33. Assertion: High temperature destroys enzymatic activity.
Reason: Heat causes the denaturation of proteins.
Correct Answer: (a)
Enzymes are proteins, and high temperatures disrupt their three‑dimensional structure, leading to denaturation and loss of catalytic activity. This loss of function directly explains why high temperature destroys enzymatic activity. The reason is the correct mechanistic explanation.
Q34. Which are correct regarding the discovery of PGRs? (i) Most were accidental discoveries. (ii) started with Charles Darwin. (iii) Darwin used canary grass coleoptiles.
Correct Answer: (a)
Many PGR discoveries were serendipitous; Darwin's work on phototropism using canary grass coleoptiles initiated the field. He observed that the tip perceived light and transmitted a signal. Thus all statements are correct.
Q35. Growth is measurable at the cellular level by an increase in the amount of:
Correct Answer: (b)
Cellular growth fundamentally involves an increase in protoplasmic content, including proteins, nucleic acids, and organelles. Although cell wall and vacuole also expand, the primary synthetic activity is in the protoplasm. Measuring dry weight or protein content can quantify this growth at the cellular level.
Q36. Match the PGR with its chemical nature:
Column-I (PGR)
Column-II (Chemical Nature)
A. Auxins
(I) Terpenes
B. Gibberellins
(II) Indole compounds
C. Cytokinins
(III) Carotenoid derivatives
D. ABA
(IV) Adenine derivatives
Correct Answer: (a)
Auxins are indole compounds (e.g., IAA); gibberellins are terpenoids (diterpenes); cytokinins are adenine derivatives; and ABA is a carotenoid‑derived sesquiterpenoid. These chemical groups reflect their biosynthetic origins and are important for understanding their structures and functions.
Q37. Which are correct for Abscisic Acid (ABA)? (i) Inhibits seed germination. (ii) Antagonist to GAs. (iii) Closes stomata. (iv) Discovered for its role in regulating dormancy.
Correct Answer: (a)
ABA inhibits germination, counteracts gibberellins, induces stomatal closure, and was discovered for its role in dormancy and abscission. All four statements accurately describe ABA functions.
Q38. Turgidity of cells is important for growth because it helps in:
Correct Answer: (b)
Turgor pressure, generated by water uptake into vacuoles, provides the driving force for cell enlargement by stretching the cell wall. This extension growth is essential for elongation of stems, roots, and leaves. Without adequate turgidity, cells cannot expand, and growth is arrested.
Q39. Which are correct for 'Ethephon'? (i) Aqueous solution is used. (ii) Readily absorbed by plants. (iii) Releases ethylene slowly.
Correct Answer: (a)
Ethephon is formulated as an aqueous solution, is easily absorbed, and releases ethylene gradually at physiological pH. These properties make it a practical ethylene source for agricultural applications.
Q40. Assertion: Ethylene is a gaseous PGR.
Reason: It is primarily used to break dormancy in seeds.
Correct Answer: (b)
Ethylene is indeed a gaseous hormone, but its primary agricultural uses include fruit ripening, senescence, and abscission, not seed dormancy breaking (though it can break dormancy in some species). The two statements are independently correct, but the fact that it is gaseous does not explain its role in dormancy break.
Q41. Heterophylly in cotton, coriander and larkspur is an example of:
Correct Answer: (b)
In these plants, leaves of juvenile individuals differ in shape from those of mature plants, a phenomenon called heterophylly due to age or phase change. This is a form of developmental plasticity programmed into the plant's life cycle, not a response to external environment. The transition is regulated by internal factors, including hormones.
Q42. Apical dominance is caused by:
Correct Answer: (b)
Apical dominance, where the growing shoot tip suppresses the outgrowth of lateral buds, is primarily mediated by auxins produced in the apical meristem. Auxin moves basipetally and inhibits bud growth indirectly, often through interaction with other hormones. Decapitation removes the auxin source, allowing lateral buds to sprout.
Q43. Which of the following statements about 'Plant Growth' is true? (i) It is generally indeterminate. (ii) New cells are added by meristems. (iii) It is defined as the 'closed form of growth.'
Correct Answer: (a)
Plant growth is indeterminate due to meristems, and new cells are indeed added by meristem activity. However, it is the 'open form of growth,' not closed, because growth continues throughout life. Therefore, (i) and (ii) are true, but (iii) is false.
Q44. Assertion: Auxins are used in tea plantations and hedge-making.
Reason: They promote the growth of lateral buds by removing apical dominance.
Correct Answer: (c)
Auxins are indeed used in tea plantations and hedge‑making to promote lateral shoot growth. However, this is achieved by decapitation (removing the apical bud) to reduce auxin levels, not by applying auxins. Auxins themselves cause apical dominance and inhibit lateral buds. Hence the reason is incorrect.
Q45. Ethephon is a source of ______ used in agriculture.
Correct Answer: (c)
Ethephon (2‑chloroethylphosphonic acid) is a synthetic compound that releases ethylene upon breakdown. It is widely applied as a plant growth regulator to promote fruit ripening, abscission, and senescence. Its aqueous formulation ensures easy absorption and controlled ethylene release in the field.
Q46. Match the physiological effect with the PGR:
Column-I
Column-II
A. Apical dominance
(I) Ethylene
B. Bolting
(II) Abscisic Acid
C. Fruit ripening
(III) Auxins
D. Stomatal closure
(IV) Gibberellins
Correct Answer: (a)
Apical dominance is mediated by auxins; bolting (stem elongation) is promoted by gibberellins; fruit ripening is enhanced by ethylene; and stomatal closure is induced by ABA. These are standard physiological assignments supported by extensive research.
Q47. Match the growth parameter with the example:
Column-I (Parameter)
Column-II (Example)
A. Cell number
(I) Pollen tube
B. Cell size
(II) Maize root
C. Length
(III) Dorsiventral leaf
D. Surface area
(IV) Watermelon
Correct Answer: (a)
Maize root apical meristem produces many cells (cell number); watermelon fruit grows by cell enlargement (cell size); pollen tube elongates (length); and dorsiventral leaf expands in surface area. These are classic examples from the text.
Q48. The typical growth curve for all cells, tissues, and organs of a plant in a natural environment is:
Correct Answer: (b)
Sigmoid growth curve shows an initial lag phase (slow growth), followed by a rapid exponential (log) phase, and finally a stationary phase as resources become limiting. This pattern is observed in most living organisms under natural conditions. It reflects the interplay of internal and external factors limiting growth.
Q49. Cytokinins were discovered as ______ from autoclaved herring sperm DNA.
Correct Answer: (b)
Cytokinins were first identified as kinetin, a compound derived from autoclaved herring sperm DNA that promoted cell division in tobacco callus. Later, zeatin was isolated from corn kernels as a natural cytokinin. Kinetin is not naturally occurring but paved the way for understanding cytokinin function.
Q50. Match the term to example in figure 13.1:
A. Cotyledons
Food storage
B. Hypocotyl
Part below cotyledons
C. Epicotyl
Part above cotyledons
Correct Answer: (a)
In the seedling diagram, cotyledons serve as food storage organs; hypocotyl is the region below cotyledons; epicotyl is the region above cotyledons. All three descriptions are accurate.
Q51. Match the plasticity example with the plant:
Column-I
Column-II
A. Heterophylly (Life Phase)
(I) Buttercup
B. Heterophylly (Environment)
(II) Cotton
Correct Answer: (a)
Cotton, coriander, and larkspur show heterophylly due to age (life phase); buttercup displays heterophylly due to environmental factors (air vs. water). These illustrate the two types of plasticity.
Q52. Assertion: Growth in terms of cell number is exemplified by watermelon.
Reason: Watermelon cells can increase in size by up to 3,50,000 times.
Correct Answer: (d)
Watermelon fruit growth is due to enormous cell enlargement, not an increase in cell number. The huge size increase (up to 350,000 times) is a classic example of growth by cell expansion. Therefore, the assertion is false, but the reason is true.
Q53. Which PGR promotes nutrient mobilisation to help delay leaf senescence?
Correct Answer: (b)
Cytokinins promote the movement of nutrients into treated tissues, thereby delaying senescence and maintaining greenness. They are known to enhance protein synthesis and chloroplast integrity. This effect is exploited in agriculture to extend leaf longevity and improve crop yields.
Q54. Which statement is true for seed survival? (i) Absence of favorable conditions leads to suspended growth. (ii) Seeds resume metabolic activities when conditions return. (iii) This is called development.
Correct Answer: (a)
Seeds enter a state of suspended growth (dormancy) under unfavourable conditions and resume growth when conditions improve. This process is not called development; development is the entire sequence from germination to senescence. Thus, (i) and (ii) are true.
Q55. Assertion: Seed germination is the first step of plant growth.
Reason: Seeds germinate only under favorable conditions like proper water and temperature.
Correct Answer: (b)
Seed germination is indeed the initial event in plant growth. However, the requirement for favourable conditions is a separate fact that does not explain why germination is the first step; it merely describes a prerequisite. Both are true but unrelated.
Q56. Assertion: Ethylene enhances the respiration rate during ripening of fruits.
Reason: This rise in rate of respiration is called respiratory climactic.
Correct Answer: (a)
Ethylene triggers a respiratory climacteric, a sharp increase in respiration, during fruit ripening. The reason correctly defines this phenomenon. This respiratory burst is associated with ethylene production and leads to ripening‑related changes.
Q57. Assertion: Differentiation in plants is open.
Reason: Cells arising out of the same meristem always have the same structure at maturity.
Correct Answer: (c)
Differentiation is open because cells derived from the same meristem can follow diverse developmental pathways depending on their position and signals, resulting in different cell types. The reason is false because cells from the same meristem do not always differentiate identically; they acquire specialised structures according to their fate.
Q58. Increase in surface area is the parameter used to measure growth in:
Correct Answer: (b)
A dorsiventral leaf expands primarily by increasing its surface area to maximise light capture for photosynthesis. While thickness may also increase slightly, the most significant growth dimension is the planar expansion. Therefore, surface area serves as the best indicator of leaf growth.
Q59. The primary CO2 acceptor in C3 plants is:
Correct Answer: (a)
Ribulose‑1,5‑bisphosphate (RuBP) is the five‑carbon sugar that accepts CO2 in the Calvin cycle. The enzyme RuBisCO catalyses the carboxylation reaction, producing two molecules of 3‑phosphoglycerate (PGA). RuBP is the first stable intermediate in the C3 pathway.
Q60. Regarding Plasticity, which is true? (i) Cotton shows different leaf shapes in different life stages. (ii) Buttercup shows different shapes based on air/water media. (iii) Heterophylly is a type of plasticity.
Correct Answer: (a)
Plasticity encompasses all examples of environmentally or developmentally induced morphological variation. Heterophylly in cotton (phase‑dependent) and buttercup (environment‑dependent) are classic cases, and heterophylly itself is a form of plasticity.
Q61. Match the discovery with the scientist:
Column-I
Column-II
A. Auxin isolation
(I) Cousins
B. Gaseous ethylene
(II) Went
C. Bakanae disease
(III) Darwin
D. Phototropism site
(IV) Kurosawa
Correct Answer: (a)
Went isolated auxin; Cousins demonstrated gaseous nature of ethylene; Kurosawa studied bakanae disease and discovered gibberellins; Darwin identified the tip as the site of phototropism perception. These historical milestones are well‑documented.
Q62. The ability of plants to follow different pathways in response to environment to form different kinds of structures is:
Correct Answer: (b)
Phenotypic plasticity is the ability of a genotype to produce different phenotypes in response to environmental changes. In plants, it allows adaptation to varying conditions, such as leaf shape modifications in different light or water regimes. This flexibility enhances survival and fitness.
Q63. The 'bakanae' disease of rice seedlings was caused by the fungal pathogen:
Correct Answer: (b)
Bakanae (foolish seedling) disease is caused by the fungus Gibberella fujikuroi. Infection leads to excessive elongation of rice seedlings, a symptom that later led to the discovery of gibberellins. This pathogen produces gibberellic acid as a secondary metabolite, which disrupts normal growth regulation.
Q64. Which statements regarding Cytokinins are correct? (i) They were discovered as kinetin. (ii) Zeatin was isolated from corn-kernels. (iii) They help overcome apical dominance. (iv) Found in regions of rapid cell division.
Correct Answer: (a)
Cytokinins were discovered as kinetin; zeatin from corn kernels; they promote lateral bud growth, thus overcoming apical dominance; and they are abundant in regions of active cell division. All statements are correct.
Q65. The act leading to maturation to perform specific functions is termed as:
Correct Answer: (b)
Differentiation is the process by which cells develop specialised structures and functions, such as forming xylem vessels, phloem sieve tubes, or mesophyll cells. It involves changes in cell wall composition, organelle distribution, and metabolic activities, enabling the cell to fulfil a particular role in the plant body.
Q66. Assertion: Growth is measurable.
Reason: It is easy to measure the increase in protoplasm directly.
Correct Answer: (c)
While growth is measurable using parameters like length, area, volume, or dry weight, direct measurement of protoplasmic increase is difficult and rarely done. Growth is typically assessed by indirect methods because protoplasm is not easily isolated and weighed. Thus, the reason provided is false.
Q67. Cells of the ______ zone attain their maximal size in terms of wall thickening and protoplasmic modifications.
Correct Answer: (c)
In the maturation zone, cells complete their differentiation, achieving maximum size and specialised structural features. They undergo secondary wall thickening and often lose protoplasm (e.g., tracheary elements). This phase is the final stage of cellular development before functioning in the tissue.
Q68. Regarding 'Geometric Growth', which are correct? (i) Both progeny cells retain division capacity. (ii) Initial growth is fast (lag phase). (iii) Final size depends on the initial size.
Correct Answer: (a)
In geometric growth, both daughter cells divide, leading to exponential increase; the initial phase is slow (lag), not fast; and final size depends on initial size because growth is proportional. Hence, (i) and (iii) are correct.
Q69. Development in plants is the sum of two processes:
Correct Answer: (b)
Development encompasses all changes from seed germination to senescence. It is explicitly defined as the combined outcome of growth (increase in size) and differentiation (attainment of specialised structure and function). These two processes together orchestrate the entire life cycle of a plant, from embryo to mature organism.
Q70. Match the enzyme with its reaction from unit intro:
Column-I
Column-II
A. RuBisCO
(I) C3/C4 pathway enzyme
B. Carbonic anhydrase
(II) 600,000 molecules/sec
Correct Answer: (a)
RuBisCO catalyses the carboxylation of RuBP in both C3 and C4 plants; carbonic anhydrase is a very fast enzyme, converting CO2 to bicarbonate at a rate of ~600,000 molecules per second. These enzymatic properties are well established.
Q71. Thinning of cotton, cherry, and walnut is accelerated by:
Correct Answer: (c)
Ethephon, an ethylene releasing agent, promotes abscission, which is used to thin fruit loads in agriculture. By accelerating the shedding of excess fruits, it helps improve the size and quality of the remaining ones. Ethylene triggers the formation of abscission zones and activates cell wall‑degrading enzymes.
Q72. Which PGR is used to induce immediate stomatal closure in leaves under water stress?
Correct Answer: (c)
ABA plays a critical role in drought response by triggering stomatal closure within minutes. It activates ion channels in guard cells, causing loss of potassium and water, leading to stomatal closure and reduced transpiration. This rapid response helps plants conserve water during dry periods.
Q73. The form of growth where new cells are always being added to the plant body by the activity of meristems is called:
Correct Answer: (b)
Open form of growth refers to the continuous production of new cells by meristems, which are perpetually dividing. This contrasts with closed form where growth ceases after a fixed number of divisions. The presence of apical, lateral, and intercalary meristems allows plants to grow in length and girth throughout their life span.
Q74. Match the growth stage with its characteristic:
Column-I
Column-II
A. Meristematic
(I) Maximum wall thickening
B. Elongation
(II) Dense protoplasm, large nuclei
C. Maturation
(III) Increased vacuolation
Correct Answer: (a)
Meristematic cells are characterised by dense cytoplasm, prominent nuclei, and thin walls; elongation zone cells have large vacuoles; maturation zone cells undergo secondary wall thickening and loss of protoplasm in some cases. Each stage has distinct cytological features.
Q75. Match the cell process with the term:
Column-I
Column-II
A. Regaining division capacity
(I) Differentiation
B. Maturing for function
(II) Dedifferentiation
C. Maturing again after division
(III) Redifferentiation
Correct Answer: (a)
Dedifferentiation is the re‑acquisition of division capacity; differentiation is the maturation for specific function; redifferentiation is the maturation of dedifferentiated cells. These terms describe the developmental plasticity of plant cells.
Q76. The growth of a pollen tube is measured in terms of its:
Correct Answer: (c)
Pollen tube growth is a tip‑elongation process where the tube extends linearly through the style to reach the ovule. Since the tube is thread‑like, its length is the most practical parameter to quantify growth. Measuring weight or volume is difficult due to its tiny size and irregular shape.
Q77. Assertion: Sigmoid curve is typical for all cells, tissues and organs of a plant.
Reason: It is a characteristic of living organisms growing in a natural environment.
Correct Answer: (a)
The sigmoid growth pattern is universally observed in plant organs and whole plants under natural conditions. It reflects the interaction of intrinsic growth potential and environmental constraints. The reason correctly attributes this pattern to the typical response of living systems to limited resources and competition.
Q78. Assertion: Plant growth is generally indeterminate.
Reason: Plants have the capacity for unlimited growth throughout their life due to meristems.
Correct Answer: (a)
Indeterminate growth is a hallmark of plants because they retain meristematic tissues that continue to divide. These meristems produce new cells for roots, shoots, and lateral organs throughout the plant's life. The reason correctly explains why growth is not fixed or limited to a juvenile phase.
Q79. Assertion: ABA helps seeds to withstand desiccation.
Reason: ABA inhibits seed germination.
Correct Answer: (b)
ABA promotes desiccation tolerance and dormancy in seeds, helping them survive dry conditions. It also inhibits germination. However, the inhibition of germination is a separate effect and does not explain the desiccation tolerance mechanism. Both are true but not causally related.
Q80. Assertion: Auxin controls xylem differentiation.
Reason: Auxins are produced by the growing apices of stems and roots.
Correct Answer: (b)
Auxin does promote xylem differentiation, and auxins are indeed produced in apical meristems. However, the site of production does not explain the mechanism of xylem differentiation; the causal link is through auxin gradients and gene expression, not the origin alone. Both statements are true but the reason is not the correct explanation.
Q81. Assertion: Oxygen is essential for growth.
Reason: It helps in releasing metabolic energy essential for growth activities.
Correct Answer: (a)
Oxygen is required for aerobic respiration, which generates ATP, the energy currency for biosynthesis and cell expansion. Without sufficient oxygen, energy production diminishes, halting growth. Therefore, the reason correctly explains why oxygen is indispensable for growth.
Q82. Assertion: Growth can be defined mathematically.
Reason: Arithmetic growth follows the linear equation Lt = L0 + rt.
Correct Answer: (a)
Mathematical models like arithmetic and exponential growth equations can describe growth patterns. The arithmetic equation Lt = L0 + rt is a precise mathematical definition of a constant growth rate, providing a quantitative measure. This example supports the assertion that growth can be expressed mathematically.
Q83. A single maize root apical meristem can give rise to more than ______ new cells per hour.
Correct Answer: (b)
The high rate of cell production in maize root meristems is well documented, with figures reaching over 17,500 cells per hour. This remarkable proliferative capacity supports the rapid elongation of roots as they explore the soil for water and nutrients. Such rates underscore the efficiency of meristematic activity in plant growth.
Q84. Assertion: Cytokinins help in the delay of leaf senescence.
Reason: They promote nutrient mobilisation.
Correct Answer: (a)
Cytokinins delay senescence by attracting nutrients and metabolites to the treated area, maintaining protein synthesis and chlorophyll content. This nutrient mobilisation effect is the mechanistic basis for their anti‑senescence action. Thus, the reason correctly explains the assertion.
Q85. The first step in the process of plant growth is:
Correct Answer: (b)
Plant growth begins with the activation of the dormant embryo within the seed. Germination marks the transition from a quiescent state to active metabolism, leading to radicle and plumule emergence. All subsequent developmental events, including cell division, elongation, and differentiation, depend on successful germination.
Q86. Assertion: Heterophylly in buttercup is due to the environment.
Reason: Shapes of leaves produced in air are different from those produced in water.
Correct Answer: (a)
In buttercup, submerged leaves are finely dissected, while aerial leaves are broader, an adaptation to different environmental conditions (water vs. air). The reason correctly explains that the environment triggers these morphological differences, which is a form of plasticity.
Q87. Which of the following is correct? (i) Melvin Calvin received Nobel Prize in 1961. (ii) He mapped the carbon assimilation pathway. (iii) He used C14 isotopes.
Correct Answer: (a)
Melvin Calvin won the 1961 Nobel Prize in Chemistry for elucidating the Calvin cycle (carbon fixation pathway) using radioactive ¹⁴C isotopes. All three statements are historically accurate.
Q88. In a sigmoid curve, the initial slow growth phase is called:
Correct Answer: (b)
The lag phase is the initial period of slow growth where cells are adapting to the environment, synthesising enzymes, and preparing for rapid division. It is followed by the log (exponential) phase where growth accelerates, and finally the stationary phase when growth plateaus due to resource depletion.
Q89. Development includes all changes from ______ to ______.
Correct Answer: (c)
Development is a comprehensive term covering the entire life cycle, starting from germination (or embryogenesis) and ending with senescence and death. It includes growth, differentiation, maturation, and reproductive changes. This continuous process integrates genetic programs and environmental signals throughout the plant's life.
Q90. Identify the correct statements for 'Arithmetic Growth': (i) Only one daughter cell continues to divide. (ii) It produces a sigmoid curve. (iii) It is expressed as Lt = L0 + rt.
Correct Answer: (a)
In arithmetic growth, one daughter cell remains meristematic, while the other differentiates, leading to linear increase (Lt = L0 + rt). It produces a linear curve, not sigmoid. Thus, (i) and (iii) are correct.
Q91. Which of the following is a stress hormone?
Correct Answer: (d)
Abscisic acid (ABA) is widely known as the stress hormone because it accumulates under drought, salinity, and cold stress. It induces stomatal closure to reduce water loss, promotes root growth, and enhances tolerance to adverse conditions. Its levels increase significantly when plants encounter environmental stress.
Q92. Regarding PGR interaction: (i) PGRs can act synergistically. (ii) PGRs can act antagonistically. (iii) ABA acts as an antagonist to GAs.
Correct Answer: (a)
PGRs often interact synergistically or antagonistically to fine‑tune responses. For example, auxin and cytokinin interact synergistically in callus differentiation, while ABA and gibberellins have antagonistic effects on seed germination. All statements are true.
Q93. Match the PGR groups:
Column-I
Column-II
A. Growth Promoters
(I) Auxin, Gibberellin, Cytokinin
B. Growth Inhibitors
(II) ABA, Ethylene (largely)
Correct Answer: (a)
Auxins, gibberellins, and cytokinins are generally growth promoters; ABA and ethylene are often growth inhibitors, though ethylene can have stimulatory effects. This grouping reflects their predominant physiological roles.
Q94. In dicotyledonous plants, increase in the girth of organs is due to:
Correct Answer: (c)
Lateral meristems, specifically vascular cambium and cork cambium, are responsible for secondary growth in dicots. They divide periclinally, adding secondary xylem (wood) and phloem, and cork layers, which increase the diameter of stems and roots. Apical meristems only contribute to elongation, not girth.
Q95. Identify correct features of 'Aleurone layer' (unit intro): (i) It is a proteinous layer. (ii) Part of monocot seed.
Correct Answer: (a)
The aleurone layer is a protein‑rich outer layer of the endosperm in monocot seeds, such as cereals. It secretes hydrolytic enzymes during germination, aiding in starch and protein breakdown. Both statements are correct.
Q96. Plant growth is unique because plants retain the capacity for:
Correct Answer: (b)
Plants possess meristematic tissues that remain embryonic and divide throughout the plant's life. This allows continuous addition of new cells to the body, enabling indeterminate growth. In contrast, animals generally have determinate growth, ceasing after a certain age or size.
Q97. Which are correct for 'Kranz Anatomy' (unit intro)? (i) Bundle sheath cells form several layers. (ii) Large number of chloroplasts. (iii) Impervious to gaseous exchange.
Correct Answer: (a)
Kranz anatomy features bundle sheath cells with dense chloroplasts and thick walls that restrict gas exchange. These characteristics are essential for the C4 pathway to concentrate CO2 around RuBisCO. All statements are true.
Q98. Match the natural source of Cytokinin:
Column-I
Column-II
A. Kinetin
(I) herring sperm DNA
B. Zeatin
(II) corn-kernels / coconut milk
Correct Answer: (a)
Kinetin was first obtained from autoclaved herring sperm DNA; zeatin was isolated from corn kernels and is also found in coconut milk. These sources are classic examples of cytokinin discovery.
Q99. Assertion: Gibberellins are used in the brewing industry.
Reason: GA3 is used to speed up the malting process.
Correct Answer: (a)
GA3 promotes the production of amylases in barley seeds, accelerating starch breakdown during malting. This makes gibberellins valuable in brewing to shorten processing time and improve yield. The reason directly explains the industrial application.
Q100. In the equation W1 = W0 ert, 'r' represents:
Correct Answer: (c)
In the exponential growth equation, r is the relative growth rate, also called the efficiency index. It quantifies the ability of the plant to produce new material per unit of existing mass per unit time. A higher r value indicates more efficient growth and is often used to compare different genotypes or treatments.