System Physiology – Plant

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ANIL CHOUDHARY

System Physiology – Plant

1 / 61

A CAM plant is subjected to a water-deficit experiment. Nighttime stomatal opening for CO₂ uptake is normal initially, but after prolonged drought, malate accumulation decreases, leaf acidification is reduced, and daytime photosynthesis drops. Which multi-step physiological reasoning explains these observations?

A) Water deficit triggers ABA accumulation → partial stomatal closure at night → reduced CO₂ fixation → lower malate accumulation → decreased daytime CO₂ availability → reduced photosynthesis
B) Root pressure increases → daytime CO₂ rises → stomata close
C) ABA stimulates daytime stomatal opening → photosynthesis rises
D) Phloem unloading is impaired → malate accumulation decreases

A) A

B) B

C) C

D) D

2 / 61

A plant with defective aquaporins is exposed to a rapid increase in evaporative demand. Observations show leaf wilting, reduced water uptake, and decreased root pressure. Which physiological principle explains the limited water movement in this scenario?

A) Aquaporins facilitate rapid water transport; their absence reduces hydraulic conductivity, preventing adequate water supply under high demand
B) Root pressure alone compensates for water loss
C) Stomata remain fully open, increasing water uptake
D) Phloem loading drives water transport in absence of aquaporins

A) A

B) B

C) C

D) D

3 / 61

In a comparative study of phloem transport, two plants are exposed to different temperatures. High temperature initially accelerates sugar movement due to increased metabolic activity in companion cells, but prolonged exposure reduces transport efficiency. Which integrated mechanism best explains this?

A) Initial turgor-driven mass flow is enhanced; prolonged heat damages companion cell metabolism, reducing loading
B) Sugar solubility decreases at high temperature
C) Phloem transport is independent of temperature
D) ABA accumulates, increasing phloem flow

A) A

B) B

C) C

D) D

4 / 61

In a water transport study, an experimental leaf shows cavitation under high evaporative demand. Injection of a surfactant partially restores water flow. Which physiological principle is being exploited?

A) Surfactant reduces surface tension, allowing xylem refilling
B) Surfactant increases root pressure
C) Surfactant opens stomata
D) Surfactant increases transpiration

A) A

B) B

C) C

D) D

5 / 61

A researcher measures turgor pressure in guard cells under different osmotic conditions. Guard cells are plasmolyzed in hypertonic solution and swell in hypotonic solution. Which principle explains these observations?

A) Water moves along the osmotic gradient into or out of guard cells, changing turgor pressure
B) ABA directly controls water movement independent of osmosis
C) K⁺ influx is irrelevant to guard cell turgor
D) Phloem sap pressure controls guard cell volume

A) A

B) B

C) C

D) D

6 / 61

A plant is grown under low nitrogen and low water. Leaves show reduced stomatal density, smaller cell size, and reduced transpiration, but roots elongate extensively. Which set of physiological adaptations explains these traits?

A) Reduced leaf expansion decreases transpiration; ABA-mediated signaling promotes root elongation for resource acquisition
B) Reduced ABA levels increase transpiration
C) Phloem loading increases under stress
D) Leaf turgor is maintained via root pressure alone

A) A

B) B

C) C

D) D

7 / 61

During a drought experiment, leaf water potential decreases, stomata close, phloem translocation slows, and root growth continues. Which combination of mechanisms best explains these observations?

A) ABA-induced stomatal closure reduces transpiration; osmotic adjustment allows root growth to continue toward water
B) Phloem sap pressure increases under drought, accelerating sugar transport
C) High leaf turgor triggers stomatal opening despite low soil moisture
D) Root growth ceases due to lack of water

A) A

B) B

C) C

D) D

8 / 61

In a phloem transport study, a plant is exposed to a partial girdling of a stem. Radiolabelled sugars accumulate above the girdle but fail to reach the roots. Which physiological explanation is most accurate?

A) Symplastic continuity is disrupted, preventing mass flow in sieve tubes
B) Xylem sap reverses direction to compensate
C) ABA accumulation in roots accelerates phloem transport
D) Root pressure bypasses the girdle

A) A

B) B

C) C

D) D

9 / 61

In an experiment, a C3 plant is subjected to high CO₂ and high light simultaneously. Initially, photosynthesis increases, but over several days, stomatal conductance decreases, and photosynthesis plateaus. Which integrated mechanism explains these changes?

A) High CO₂ reduces photorespiration; ABA-mediated feedback reduces stomatal opening to conserve water
B) High light damages PSII, reducing photosynthesis
C) Stomata remain fully open regardless of CO₂
D) Root pressure compensates for photosynthetic rate

A) A

B) B

C) C

D) D

10 / 61

10.

In a controlled experiment, blue light is applied to a leaf in darkness. Rapid stomatal opening occurs in the illuminated region. Which sequence of events best describes this light-induced opening?

A) Photoreceptors perceive blue light → activation of H⁺-ATPase → K⁺ influx → guard cell turgor increases → stomata open
B) Blue light induces ABA synthesis → stomatal closure
C) Ethylene accumulation triggers K⁺ efflux → stomata close
D) Xylem pressure changes drive opening

A) A

B) B

C) C

D) D

11 / 61

11.

A root is placed in a solution containing a high concentration of an impermeable solute. Observations show reduced water uptake, reduced root pressure, and partial wilting of leaves. Which principle explains these phenomena?

A) Water potential gradient is reduced due to osmotic imbalance
B) Root pressure is independent of solute concentration
C) Transpiration increases, compensating for reduced uptake
D) Phloem loading drives water uptake

A) A

B) B

C) C

D) D

12 / 61

12.

In a study on phloem transport, radiolabelled sugars are traced in a plant exposed to different temperatures. High temperature accelerates translocation initially but prolonged heat reduces flow rate. Which combination of effects explains this?

A) Temperature increases metabolism and turgor-driven flow initially; prolonged heat stresses companion cells, reducing active loading
B) High temperature reduces sugar solubility, slowing transport
C) Phloem flow is independent of temperature
D) ABA accumulation under high temperature accelerates transport

A) B

B) C

C) D

D) A

13 / 61

13.

A mutant plant has defective aquaporins in roots. Under well-watered conditions, transpiration rate is slightly lower than wild type, but under high evaporative demand, leaf water potential drops sharply. Which physiological explanation is most plausible?

A) Impaired water transport through root membranes limits water supply under high demand
B) Aquaporin mutation increases stomatal conductance
C) Photosynthetic rate declines due to CO₂ limitation only
D) Root pressure increases to compensate

A) A

B) B

C) C

D) D

14 / 61

14.

In a tall redwood tree, during a hot dry day, sap ascent is measured using pressure probes. Observations show extremely negative xylem pressures and occasional cavitation. Which combined factors explain both continuous water ascent and cavitation risk?

A) Cohesion-tension in xylem maintains water column; negative pressure increases cavitation risk
B) Root pressure alone drives water ascent
C) Phloem loading prevents xylem embolism entirely
D) High humidity mitigates negative pressure

A) A

B) B

C) C

D) D

15 / 61

15.

In an experiment, a Venus flytrap is mechanically stimulated on its sensitive hairs, causing rapid lobe closure. This involves action potentials, Ca²⁺ spikes, and rapid water movement in cells. Which combination of physiological events explains this rapid movement?

A) Electrical signals induce localized turgor change by K⁺ efflux, causing water redistribution and lobe closure
B) ABA accumulation in lobes triggers K⁺ influx, increasing turgor pressure
C) Ethylene stimulates cell wall expansion, leading to slow closure
D) Stomatal aperture changes control movement

A) b

B) a

C) c

D) d

16 / 61

16.

A CAM plant is studied under normal and water-limited conditions. During daytime, stomata remain closed, but malate accumulated at night is decarboxylated during the day to provide CO₂ for photosynthesis. Which physiological advantage is most critical in this context?

A) Reduced water loss due to nocturnal CO₂ uptake
B) Higher transpiration due to increased daytime stomatal opening
C) Increased root pressure driving CO₂ into leaves
D) Enhanced phloem loading for sucrose transport

A) A

B) B

C) C

D) D

17 / 61

17.

In a plant under simulated drought stress, the following is observed: leaf wilting, decreased root pressure, accumulation of osmolytes such as proline, and increased abscisic acid. Which of the following sequences of physiological events best explains these observations?

A) Water deficit → ABA accumulation → stomatal closure → osmotic adjustment in cells → partial turgor recovery
B) Osmotic adjustment → ABA synthesis → transpiration increases → leaf wilting
C) Root pressure decreases → ABA decreases → stomatal opening → leaf turgor increases
D) ABA accumulation → increased transpiration → proline synthesis → leaf curling

A) A

B) B

C) C

D) D

18 / 61

18.

A researcher measures phloem transport in a source-sink pair using radiolabelled carbon. Under normal conditions, translocation is rapid. When ABA is applied exogenously to the leaves, translocation slows down, while phloem sap sugar concentration increases. Which mechanism best explains this observation?

A) ABA induces stomatal closure, reducing transpiration-driven water flow into phloem
B) ABA inhibits sucrose loading at the source, reducing turgor pressure difference
C) ABA increases sink demand, pulling more sugars
D) ABA directly blocks sieve plate pores, slowing flow

A) A

B) B

C) C

D) D

19 / 61

19.

In a comparative study, C3 and C4 plants are exposed to drought conditions. Leaf gas exchange, stomatal conductance, and mesophyll enzyme activities are measured. It is observed that C4 plants maintain higher photosynthesis rates under mild drought. Which combination of physiological processes accounts for this observation?

A) C4 plants have higher PEP carboxylase activity and lower stomatal conductance, conserving water while fixing CO₂ efficiently
B) C4 plants exhibit higher ABA accumulation leading to rapid stomatal closure
C) C3 plants maintain higher transpiration, which increases CO₂ uptake under drought
D) C4 plants shift carbon fixation to chloroplasts in bundle sheath to avoid photorespiration entirely

A) A

B) B

C) C

D) D

20 / 61

20.

A plant is placed in a controlled environment where the potassium channels in guard cells are blocked chemically. Despite high light and normal water availability, stomatal opening is severely limited. Considering osmotic regulation and turgor changes, which is the most plausible mechanistic explanation?

A) Inability of guard cells to accumulate K⁺ prevents osmotic water influx, so turgor pressure does not rise
B) K⁺ blockage increases malate synthesis in guard cells, reducing stomatal aperture
C) Cytoplasmic ABA accumulation causes turgor decrease independent of K⁺
D) Water potential in xylem directly controls stomatal aperture

A) A

B) B

C) C

D) D

21 / 61

21.

In an experiment, a detached transpiring shoot is cut under water and connected to a manometer to measure xylem tension. The shoot is exposed to different light intensities while air humidity is varied. It is observed that under high light and low humidity, xylem tension becomes extremely negative, leading to intermittent cavitation events. Which explanation best describes the observed phenomenon?

A) Increased root pressure is unable to maintain continuous water column due to high transpiration
B) High transpiration and low humidity increase the tension in xylem sap, promoting air bubble formation
C) Phloem loading compensates for xylem tension, preventing embolism
D) Guard cells close stomata immediately, preventing cavitation

A) A

B) B

C) C

D) D

22 / 61

22.

Which combination of hormonal and ionic signals triggers rapid closure of Venus flytrap lobes?

A) Ca²⁺ spike → action potential → water flux
B) ABA accumulation → K⁺ influx → turgor increase
C) Auxin gradient → proton pump → growth
D) Ethylene → Cl⁻ efflux → opening

A) A

B) B

C) C

D) D

23 / 61

23.

Which of the following explains why leaves of sun and shade plants have different transpiration rates under same irradiance?

A) Sun leaves have higher cuticular conductance
B) Shade leaves have thicker cuticles
C) Sun leaves have higher stomatal density and higher mesophyll conductance
D) Shade leaves produce more ABA

A) A

B) B

C) C

D) D

24 / 61

24.

Which factor is least likely to limit phloem translocation under normal conditions?

A) Companion cell metabolism
B) Source-sink turgor gradient
C) Soil water potential
D) Xylem water potential

A) A

B) B

C) C

D) D

25 / 61

25.

Which experimental manipulation would test the effect of ABA on stomatal kinetics?

A) Apply exogenous ABA to leaves in light and measure aperture change
B) Block K⁺ channels in roots and measure transpiration
C) Radiolabel sucrose and track phloem loading
D) Sever phloem and observe xylem tension

A) A

B) B

C) C

D) D

26 / 61

26.

Which of the following best describes “tension-induced cavitation”?

A) Air bubbles form in xylem due to high negative pressure
B) Phloem sap flow slows due to low turgor
C) Stomata open due to light-induced K⁺ influx
D) Root pressure pushes water to leaves

A) A

B) B

C) C

D) D

27 / 61

27.

Which combination is most critical for root hydrotropic response?

A) ABA, auxin redistribution, cytoskeleton reorientation
B) Ethylene, gibberellin, cell wall softening
C) Cytokinin, photosynthesis, transpiration
D) Xylem pressure, K⁺ flux, sugar loading

A) A

B) B

C) C

D) D

28 / 61

28.

Which is the main physiological basis for CAM plants’ nocturnal CO₂ fixation?

A) High daytime transpiration
B) Nighttime PEP carboxylase activity and malate accumulation
C) Enhanced stomatal conductance in day
D) Root pressure-driven CO₂ influx

A) A

B) B

C) C

D) D

29 / 61

29.

How does leaf turgor recovery occur after temporary wilting in drought-prone plants?

A) ABA-induced K⁺ efflux from guard cells
B) Osmotic adjustment via accumulation of proline and sugars
C) Passive xylem embolism repair
D) Leaf shedding

A) A

B) B

C) C

D) D

30 / 61

30.

Which combination of environmental factors maximizes transpiration rate in C3 leaves?

A) High humidity, low light, low temperature
B) Low humidity, high light, high temperature
C) High CO₂, low light, high humidity
D) Low wind, low temperature, high soil moisture

A) A

B) B

C) C

D) D

31 / 61

31.

Which of the following best explains phloem unloading in growing fruits?

A) Symplastic unloading into sink cells due to turgor gradient
B) Passive diffusion through cuticle
C) Evaporation-driven sucrose movement
D) Active pumping via xylem parenchyma

A) A

B) B

C) C

D) D

32 / 61

32.

Which experiment provides strongest evidence for cohesion-tension theory?

A) Cutting a transpiring shoot and observing xylem sap exudation
B) Measuring root respiration under hypoxia
C) Applying ABA and observing stomatal closure
D) Tracking sucrose transport using radiolabelled carbon

A) A

B) B

C) C

D) D

33 / 61

33.

The Münch hypothesis predicts phloem sap flow depends on

A) Turgor difference between source and sink
B) Active loading of water at sink
C) ABA concentration in sieve tubes
D) Xylem pressure alone

A) A

B) B

C) C

D) D

34 / 61

34.

Which combination of ions and osmolytes primarily drives stomatal opening under blue light?

A) K⁺, Cl⁻, malate²⁻
B) Na⁺, NO₃⁻, sucrose
C) Ca²⁺, HCO₃⁻, glutamate
D) Mg²⁺, PO₄³⁻, ABA

A) A

B) B

C) C

D) D

35 / 61

35.

Which statement explains why root pressure cannot account for water ascent in very tall redwoods?

A) Root pressure is negative
B) Water potential in leaves is higher than in roots
C) Generated pressure (~1–2 MPa) is insufficient to overcome gravitational potential
D) Xylem vessels are dead

A) A

B) B

C) C

D) D

36 / 61

36.

Which is the most plausible effect of ABA on phloem transport during water stress?

A) Enhances loading at source
B) Inhibits translocation to sink
C) Stimulates sieve tube sap flow
D) Reduces companion cell metabolic activity

A) A

B) B

C) C

D) D

37 / 61

37.

In a C4 plant under drought stress, which of the following physiological changes is expected first?

A) Increased stomatal conductance
B) Reduced PEP carboxylase activity
C) Enhanced mesophyll chlorophyll content
D) Increased leaf turgor pressure

A) A

B) B

C) C

D) D

38 / 61

38.

Which scenario most likely leads to embolism formation in xylem?

A) Low transpiration, high soil water potential
B) High transpiration, low soil water potential
C) Nighttime root pressure
D) High humidity, low temperature

A) A

B) B

C) C

D) D

39 / 61

39.

Which of the following correctly differentiates phloem loading in C3 vs C4 plants?

A) C3: apoplastic pathway; C4: symplastic pathway
B) C3: sucrose actively transported; C4: sucrose diffuses passively
C) C3: mesophyll to bundle sheath; C4: mesophyll to companion cells
D) C3: source-sink pressure difference; C4: root pressure dependent

A) A

B) B

C) C

D) D

40 / 61

40.

During stomatal opening, turgor pressure in guard cells increases. Which combination of events is most critical?

A) K⁺ influx → osmotic water uptake → swelling
B) Cl⁻ efflux → water loss → shrinkage
C) ABA accumulation → K⁺ efflux → water influx
D) Na⁺ influx → turgor decrease → opening

A) A

B) B

C) C

D) D

41 / 61

41.

Which of the following mechanisms best explains the ascent of xylem sap in very tall trees under high transpiration rates?

A) Root pressure alone
B) Capillarity alone
C) Cohesion-tension theory with cavitation prevention
D) Diffusion gradient of ions

A) A

B) B

C) C

D) D

42 / 61

42.

The term “source” in phloem transport refers to

A) Area of sugar utilization
B) Area of sugar production
C) Area of water absorption
D) Area of auxin synthesis

A) A

B) B

C) C

D) D

43 / 61

43.

Guard cells are unique because they

A) Lack chloroplasts
B) Are dead at maturity
C) Have asymmetric cell wall thickening
D) Are part of xylem

A) A

B) B

C) C

D) D

44 / 61

44.

Which of the following hormones promotes bolting in plants?

A) Auxin
B) Cytokinin
C) Gibberellin
D) Ethylene

A) A

B) B

C) C

D) D

45 / 61

45.

Which of the following is a hydrotropic response?

A) Root growth towards water
B) Leaf movement towards light
C) Stem growth away from gravity
D) Seed germination in dark

A) A

B) B

C) C

D) D

46 / 61

46.

Root pressure is maximum during

A) Nighttime
B) Early morning
C) Midday
D) Afternoon

A) A

B) B

C) C

D) D

47 / 61

47.

In C4 plants, the initial CO₂ fixation occurs in

A) Bundle sheath cells
B) Mesophyll cells
C) Guard cells
D) Xylem

A) A

B) B

C) C

D) D

48 / 61

48.

The pressure-flow hypothesis was proposed by

A) Dixon & Joly
B) Münch
C) Went
D) Darwin

A) A

B) B

C) C

D) D

49 / 61

49.

Which pigment is responsible for blue light perception in plants?

A) Phytochrome
B) Cryptochrome
C) Chlorophyll
D) Carotenoid

A) A

B) B

C) C

D) D

50 / 61

50.

Which type of transport in plants requires metabolic energy?

A) Simple diffusion
B) Facilitated diffusion
C) Active transport
D) Bulk flow

A) A

B) B

C) C

D) D

51 / 61

51.

Which plant hormone promotes cell division?

A) Auxin
B) Cytokinin
C) Gibberellin
D) Ethylene

A) A

B) B

C) C

D) D

52 / 61

52.

Which of the following is a fast plant response to touch (thigmonasty)?

A) Mimosa pudica
B) Sunflower heliotropism
C) Venus flytrap closure
D) Both A & C

A) A

B) B

C) C

D) D

53 / 61

53.

Which ion is mainly involved in opening of stomata?

A) Na⁺
B) K⁺
C) Ca²⁺
D) Mg²⁺

A) A

B) B

C) C

D) D

54 / 61

54.

The cohesion-tension theory explains

A) Phloem transport
B) Xylem water transport
C) Photosynthesis mechanism
D) Nitrogen fixation

A) A

B) B

C) C

D) D

55 / 61

55.

Which of the following is not a function of abscisic acid (ABA)?

A) Induces stomatal closure
B) Promotes seed dormancy
C) Stimulates cell elongation
D) Helps in stress response

A) A

B) B

C) C

D) D

56 / 61

56.

Which process in plants is responsible for “source-to-sink” movement of sugars?

A) Transpiration
B) Translocation
C) Photosynthesis
D) Respiration

A) A

B) B

C) C

D) D

57 / 61

57.

Stomatal opening in most plants is caused by

A) Water loss from guard cells
B) Accumulation of potassium ions in guard cells
C) Reduction of turgor pressure in guard cells
D) Ethylene accumulation

A) A

B) B

C) C

D) D

58 / 61

58.

Which of the following factors does not directly affect the rate of transpiration?

A) Temperature
B) Humidity
C) Light intensity
D) Soil pH

A) A

B) B

C) C

D) D

59 / 61

59.

Which plant tissue is mainly responsible for water conduction?

A) Phloem
B) Xylem
C) Collenchyma
D) Parenchyma

A) A

B) B

C) C

D) D

60 / 61

60.

Which of the following statements about phloem transport is correct?

A) It is unidirectional from root to shoot
B) It occurs by bulk flow under positive pressure
C) Water does not participate in phloem transport
D) Sieve tubes are dead cells

A) A

B) B

C) C

D) D

61 / 61

61.

Which plant hormone is primarily responsible for fruit ripening?

A) Auxin
B) Gibberellin
C) Ethylene
D) Cytokinin

A) A

B) B

C) C

D) D

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ByANIL CHOUDHARY

A plant with defective aquaporins is exposed to a rapid increase in evaporative demand. Observations show leaf wilting, reduced water uptake, and decreased root pressure. Which physiological principle explains the limited water movement in this scenario?

In a water transport study, an experimental leaf shows cavitation under high evaporative demand. Injection of a surfactant partially restores water flow. Which physiological principle is being exploited?

A researcher measures turgor pressure in guard cells under different osmotic conditions. Guard cells are plasmolyzed in hypertonic solution and swell in hypotonic solution. Which principle explains these observations?

A plant is grown under low nitrogen and low water. Leaves show reduced stomatal density, smaller cell size, and reduced transpiration, but roots elongate extensively. Which set of physiological adaptations explains these traits?

During a drought experiment, leaf water potential decreases, stomata close, phloem translocation slows, and root growth continues. Which combination of mechanisms best explains these observations?

In a phloem transport study, a plant is exposed to a partial girdling of a stem. Radiolabelled sugars accumulate above the girdle but fail to reach the roots. Which physiological explanation is most accurate?

In an experiment, a C3 plant is subjected to high CO₂ and high light simultaneously. Initially, photosynthesis increases, but over several days, stomatal conductance decreases, and photosynthesis plateaus. Which integrated mechanism explains these changes?

In a controlled experiment, blue light is applied to a leaf in darkness. Rapid stomatal opening occurs in the illuminated region. Which sequence of events best describes this light-induced opening?

A root is placed in a solution containing a high concentration of an impermeable solute. Observations show reduced water uptake, reduced root pressure, and partial wilting of leaves. Which principle explains these phenomena?

In a study on phloem transport, radiolabelled sugars are traced in a plant exposed to different temperatures. High temperature accelerates translocation initially but prolonged heat reduces flow rate. Which combination of effects explains this?

A mutant plant has defective aquaporins in roots. Under well-watered conditions, transpiration rate is slightly lower than wild type, but under high evaporative demand, leaf water potential drops sharply. Which physiological explanation is most plausible?

In a tall redwood tree, during a hot dry day, sap ascent is measured using pressure probes. Observations show extremely negative xylem pressures and occasional cavitation. Which combined factors explain both continuous water ascent and cavitation risk?

In an experiment, a Venus flytrap is mechanically stimulated on its sensitive hairs, causing rapid lobe closure. This involves action potentials, Ca²⁺ spikes, and rapid water movement in cells. Which combination of physiological events explains this rapid movement?

A CAM plant is studied under normal and water-limited conditions. During daytime, stomata remain closed, but malate accumulated at night is decarboxylated during the day to provide CO₂ for photosynthesis. Which physiological advantage is most critical in this context?

In a plant under simulated drought stress, the following is observed: leaf wilting, decreased root pressure, accumulation of osmolytes such as proline, and increased abscisic acid. Which of the following sequences of physiological events best explains these observations?

Which combination of hormonal and ionic signals triggers rapid closure of Venus flytrap lobes?

Which of the following explains why leaves of sun and shade plants have different transpiration rates under same irradiance?

Which factor is least likely to limit phloem translocation under normal conditions?

Which experimental manipulation would test the effect of ABA on stomatal kinetics?

Which of the following best describes “tension-induced cavitation”?

Which combination is most critical for root hydrotropic response?

Which is the main physiological basis for CAM plants’ nocturnal CO₂ fixation?

How does leaf turgor recovery occur after temporary wilting in drought-prone plants?

Which combination of environmental factors maximizes transpiration rate in C3 leaves?

Which of the following best explains phloem unloading in growing fruits?

Which experiment provides strongest evidence for cohesion-tension theory?

The Münch hypothesis predicts phloem sap flow depends on

Which combination of ions and osmolytes primarily drives stomatal opening under blue light?

Which statement explains why root pressure cannot account for water ascent in very tall redwoods?

Which is the most plausible effect of ABA on phloem transport during water stress?

In a C4 plant under drought stress, which of the following physiological changes is expected first?

Which scenario most likely leads to embolism formation in xylem?

Which of the following correctly differentiates phloem loading in C3 vs C4 plants?

During stomatal opening, turgor pressure in guard cells increases. Which combination of events is most critical?

Which of the following mechanisms best explains the ascent of xylem sap in very tall trees under high transpiration rates?

The term “source” in phloem transport refers to

Guard cells are unique because they

Which of the following hormones promotes bolting in plants?

Which of the following is a hydrotropic response?

Root pressure is maximum during

In C4 plants, the initial CO₂ fixation occurs in

The pressure-flow hypothesis was proposed by

Which pigment is responsible for blue light perception in plants?

Which type of transport in plants requires metabolic energy?

Which plant hormone promotes cell division?

Which of the following is a fast plant response to touch (thigmonasty)?

Which ion is mainly involved in opening of stomata?

The cohesion-tension theory explains

Which of the following is not a function of abscisic acid (ABA)?

Which process in plants is responsible for “source-to-sink” movement of sugars?

Stomatal opening in most plants is caused by

Which of the following factors does not directly affect the rate of transpiration?

Which plant tissue is mainly responsible for water conduction?

Which of the following statements about phloem transport is correct?

Which plant hormone is primarily responsible for fruit ripening?

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