Absorption by Roots - Complete Question Paper

Section A: Multiple Choice Questions (MCQ) - 100 Questions (1 mark each)

1. The phenomenon of absorption of water by solid particles without forming a solution is called: a) Diffusion b) Osmosis c) Imbibition d) Transpiration

2. When seeds swell after soaking in water, this process is an example of: a) Osmosis b) Imbibition c) Diffusion d) Active transport

3. The net movement of molecules from higher concentration to lower concentration is: a) Osmosis b) Imbibition c) Diffusion d) Plasmolysis

4. Osmosis is the movement of: a) Solute molecules b) Solvent molecules c) Both solute and solvent d) None of these

5. A selectively permeable membrane allows: a) All molecules to pass b) Only solvent molecules c) Only solute molecules d) No molecules

6. The minimum pressure needed to prevent osmosis is called: a) Root pressure b) Osmotic pressure c) Turgor pressure d) Atmospheric pressure

7. Root pressure is responsible for: a) Water absorption b) Sap rising in stem c) Transpiration d) Photosynthesis

8. Turgidity in plant cells is caused by: a) Water loss b) Water absorption c) Solute accumulation d) Cell division

9. When plant cells lose water in hypertonic solution, the process is called: a) Turgidity b) Plasmolysis c) Flaccidity d) Imbibition

10. The condition where plasma membrane is not pressed against cell wall is: a) Turgidity b) Plasmolysis c) Flaccidity d) Osmosis

11. Active transport requires: a) Energy b) Concentration gradient c) Passive movement d) All of these

12. Passive transport occurs: a) Against concentration gradient b) Along concentration gradient c) With energy input d) Through active sites

13. The upward movement of water from roots to aerial parts is called: a) Root pressure b) Osmotic pressure c) Ascent of sap d) Transpiration

14. Cohesion refers to: a) Attraction between unlike molecules b) Attraction between like molecules c) Repulsion between molecules d) None of these

15. Adhesion is the tendency of: a) Like molecules to stick together b) Unlike molecules to stick together c) Molecules to repel d) Water to evaporate

16. Transpiration pull is responsible for: a) Water absorption b) Water transport upward c) Photosynthesis d) Respiration

17. Which process does not require a membrane? a) Osmosis b) Active transport c) Diffusion d) None of these

18. Root hairs increase: a) Root length b) Root strength c) Surface area d) Root pressure

19. The driving force for osmosis is: a) Temperature difference b) Pressure difference c) Concentration difference d) pH difference

20. In a hypotonic solution, plant cells become: a) Flaccid b) Plasmolyzed c) Turgid d) Shrunken

21. Water potential is highest in: a) Pure water b) Concentrated solution c) Hypertonic solution d) Isotonic solution

22. The term isotonic means: a) Same concentration b) Different concentration c) Higher concentration d) Lower concentration

23. Endosmosis occurs when: a) Water moves out of cell b) Water moves into cell c) Solutes move out d) No movement occurs

24. Exosmosis results in: a) Cell swelling b) Cell shrinking c) No change d) Cell bursting

25. The cell wall of plant cells is: a) Fully permeable b) Semi-permeable c) Impermeable d) Selectively permeable

26. Turgor pressure helps in: a) Cell support b) Growth c) Opening of stomata d) All of these

27. The loss of turgor pressure leads to: a) Wilting b) Growth c) Photosynthesis d) Respiration

28. Water moves from soil to root through: a) Active transport only b) Passive transport only c) Both active and passive d) Neither

29. The concentration of solutes is highest in: a) Soil water b) Root cells c) Xylem d) Varies with plant

30. Symplastic pathway involves movement through: a) Cell walls b) Intercellular spaces c) Cytoplasm d) Xylem vessels

31. Apoplastic pathway involves movement through: a) Cytoplasm b) Cell walls c) Vacuoles d) Nucleus

32. The Casparian strip is found in: a) Epidermis b) Cortex c) Endodermis d) Pericycle

33. Water absorption is maximum during: a) Day time b) Night time c) Evening d) Constant throughout

34. The main driving force for water absorption is: a) Root pressure b) Transpiration pull c) Osmotic pressure d) All contribute

35. Guttation occurs due to: a) Transpiration b) Root pressure c) Osmosis d) Diffusion

36. Hydathodes are involved in: a) Transpiration b) Guttation c) Absorption d) Photosynthesis

37. The rate of transpiration is affected by: a) Temperature b) Humidity c) Wind speed d) All of these

38. Stomata are mainly present on: a) Upper surface b) Lower surface c) Both surfaces d) Stem only

39. Guard cells control: a) Photosynthesis b) Respiration c) Transpiration d) Absorption

40. The opening and closing of stomata depends on: a) Light b) CO2 concentration c) Water availability d) All of these

41. C4 plants have: a) Higher water use efficiency b) Lower water use efficiency c) Same as C3 plants d) No transpiration

42. Xerophytes are adapted to: a) High water availability b) Low water availability c) Moderate water d) Aquatic conditions

43. Hydrophytes are adapted to: a) Dry conditions b) Aquatic conditions c) Desert conditions d) Mountain conditions

44. Mesophytes grow in: a) Very dry conditions b) Very wet conditions c) Moderate conditions d) Extreme conditions

45. CAM plants open stomata during: a) Day time b) Night time c) Morning d) Evening

46. The waxy coating on leaves is called: a) Cuticle b) Epidermis c) Mesophyll d) Stomata

47. Succulent plants store water in: a) Roots b) Stems c) Leaves d) All of these

48. Wilting occurs when: a) Water absorption > Water loss b) Water absorption < Water loss c) Water absorption = Water loss d) No water absorption

49. Temporary wilting is due to: a) Soil water shortage b) High transpiration rate c) Disease d) Old age

50. Permanent wilting occurs when: a) Soil has no water b) Plant is diseased c) Transpiration is high d) Roots are damaged

51. The water potential of pure water is: a) Zero b) Positive c) Negative d) Infinite

52. Solute potential is always: a) Positive b) Negative c) Zero d) Variable

53. Pressure potential in turgid cells is: a) Positive b) Negative c) Zero d) Infinite

54. Water always moves from: a) Lower to higher water potential b) Higher to lower water potential c) Equal water potentials d) No specific direction

55. The unit of water potential is: a) Pascal b) Atmosphere c) Bar d) All of these

56. Plasmolysis can be reversed by placing cells in: a) Hypertonic solution b) Hypotonic solution c) Isotonic solution d) Pure water

57. Incipient plasmolysis occurs when: a) Cell membrane just separates from cell wall b) Cell is fully plasmolyzed c) Cell is turgid d) Cell is flaccid

58. The point at which plasmolysis just begins is: a) Incipient plasmolysis b) Complete plasmolysis c) Partial plasmolysis d) No plasmolysis

59. Deplasmolysis occurs when: a) Plasmolyzed cells regain water b) Turgid cells lose water c) Cells divide d) Cells die

60. Cytorrhysis is: a) Reversible plasmolysis b) Irreversible plasmolysis c) Deplasmolysis d) Turgidity

61. The term 'semipermeable membrane' was coined by: a) Traube b) Pfeffer c) De Vries d) Dutrochet

62. The first demonstration of osmosis was by: a) Traube b) Pfeffer c) Dutrochet d) De Vries

63. Osmotic pressure was first measured by: a) Traube b) Pfeffer c) Dutrochet d) De Vries

64. The study of plasmolysis was pioneered by: a) Traube b) Pfeffer c) De Vries d) Dutrochet

65. Imbibition was first studied in detail by: a) Sachs b) Reinke c) Rodewald d) All of these

66. The swelling pressure developed during imbibition can be: a) Very low b) Moderate c) Very high d) Zero

67. Imbibition is affected by: a) Temperature b) pH c) Nature of imbibant d) All of these

68. Dry seeds can imbibe water up to: a) 10-20% of their weight b) 50-100% of their weight c) 200-300% of their weight d) 1000% of their weight

69. The rate of imbibition is highest in: a) Beginning b) Middle phase c) End phase d) Constant throughout

70. Imbibition causes: a) Increase in volume b) Decrease in volume c) No change in volume d) Variable changes

71. The force responsible for ascent of sap is: a) Root pressure only b) Transpiration pull only c) Both root pressure and transpiration pull d) Osmotic pressure only

72. Cohesion-tension theory was proposed by: a) Dixon and Joly b) Godlewski c) Priestley d) Bose

73. The diameter of xylem vessels affects: a) Cohesion b) Adhesion c) Transpiration pull d) All of these

74. Cavitation in xylem occurs due to: a) High tension b) Low tension c) No tension d) Moderate tension

75. Air bubbles in xylem are called: a) Cavitation b) Embolism c) Emboli d) All of these

76. The maximum height water can rise due to capillarity alone is: a) 1-2 meters b) 10-20 meters c) 50-100 meters d) 200-300 meters

77. Root pressure can raise water up to: a) Few centimeters b) Few meters c) 10-20 meters d) 100 meters

78. Bleeding in plants is due to: a) Transpiration b) Root pressure c) Osmosis d) Diffusion

79. The tallest trees rely mainly on: a) Root pressure b) Transpiration pull c) Capillarity d) Osmotic pressure

80. Water movement in xylem is: a) Unidirectional upward b) Bidirectional c) Downward only d) Random

81. The conducting elements of xylem are: a) Vessels and tracheids b) Sieve tubes c) Companion cells d) Parenchyma

82. Tracheids are found in: a) Angiosperms only b) Gymnosperms only c) Both angiosperms and gymnosperms d) Neither

83. Vessels are characteristic of: a) Angiosperms b) Gymnosperms c) Pteridophytes d) Bryophytes

84. The end walls of vessels have: a) Simple pits b) Bordered pits c) Perforation plates d) No openings

85. Bordered pits are mainly found in: a) Vessels b) Tracheids c) Sieve tubes d) Parenchyma

86. The secondary wall thickenings in tracheids are: a) Spiral b) Annular c) Reticulate d) All of these

87. Lignification makes xylem elements: a) Living b) Dead c) Semi-living d) Variable

88. Water conduction in xylem is through: a) Living cells b) Dead cells c) Both d) Neither

89. The most efficient water conducting elements are: a) Tracheids b) Vessels c) Sieve tubes d) Parenchyma

90. Tyloses formation occurs in: a) Young xylem b) Old xylem c) Phloem d) Cambium

91. Heartwood is: a) Functional b) Non-functional c) Partially functional d) Variable

92. Sapwood is the: a) Outer functional wood b) Inner non-functional wood c) Cambium d) Phloem

93. Annual rings in wood represent: a) Age of tree b) Seasonal variations c) Environmental conditions d) All of these

94. Early wood has: a) Large vessels b) Small vessels c) No vessels d) Thick walls

95. Late wood is characterized by: a) Large vessels b) Small vessels c) Thin walls d) More parenchyma

96. Ring-porous wood has: a) Vessels uniformly distributed b) Large vessels in early wood c) Small vessels throughout d) No vessels

97. Diffuse-porous wood has: a) Vessels uniformly distributed b) Large vessels in early wood c) No vessels d) Vessels only in late wood

98. Reaction wood is formed in response to: a) Gravity b) Light c) Water d) Nutrients

99. Compression wood is found in: a) Angiosperms b) Gymnosperms c) Both d) Neither

100. Tension wood is characteristic of: a) Angiosperms b) Gymnosperms c) Both d) Neither

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Section B: Short Answer Questions (1 mark each) - 100 Questions

1. Define imbibition.
2. What is diffusion?
3. Define osmosis.
4. What is osmotic pressure?
5. Define root pressure.
6. What is turgidity?
7. Define plasmolysis.
8. What is flaccidity?
9. Define active transport.
10. What is passive transport?
11. Define ascent of sap.
12. What is cohesion?
13. Define adhesion.
14. What is transpiration pull?
15. Name the process by which seeds swell in water.
16. What type of transport requires energy?
17. In which direction does diffusion occur?
18. What is a selectively permeable membrane?
19. Name the pressure that prevents osmosis.
20. What causes sap to rise in plant stems?
21. What happens to cells in hypertonic solution?
22. What is the condition when plasma membrane detaches from cell wall?
23. Which transport process works against concentration gradient?
24. What is the upward movement of water in plants called?
25. Define water potential.
26. What is solute potential?
27. Define pressure potential.
28. What is turgor pressure?
29. Name the pathway through cell walls.
30. What is symplastic pathway?
31. Where is the Casparian strip located?
32. What is guttation?
33. Define hydathodes.
34. What controls stomatal opening?
35. Name plants adapted to dry conditions.
36. What are hydrophytes?
37. Define mesophytes.
38. When do CAM plants open stomata?
39. What is the waxy layer on leaves called?
40. Define wilting.
41. What is temporary wilting?
42. Define permanent wilting point.
43. What is incipient plasmolysis?
44. Define deplasmolysis.
45. What is cytorrhysis?
46. Name the theory explaining ascent of sap.
47. What is cavitation?
48. Define embolism in plants.
49. What is bleeding in plants?
50. Name the conducting elements of xylem.
51. What are tracheids?
52. Define vessels.
53. What are perforation plates?
54. What are bordered pits?
55. What is lignification?
56. Define tyloses.
57. What is heartwood?
58. Define sapwood.
59. What are annual rings?
60. Define early wood.
61. What is late wood?
62. Define ring-porous wood.
63. What is diffuse-porous wood?
64. Define reaction wood.
65. What is compression wood?
66. Define tension wood.
67. What is endosmosis?
68. Define exosmosis.
69. What is isotonic solution?
70. Define hypertonic solution.
71. What is hypotonic solution?
72. Define water use efficiency.
73. What are succulents?
74. Define xeromorphic adaptations.
75. What is the cuticle?
76. Define stomatal frequency.
77. What is transpiration ratio?
78. Define water deficit.
79. What is water stress?
80. Define drought resistance.
81. What is osmotic adjustment?
82. Define compatible solutes.
83. What is hydraulic conductivity?
84. Define xylem pressure potential.
85. What is the apoplast?
86. Define symplast.
87. What is the transmembrane pathway?
88. Define bulk flow.
89. What is mass flow?
90. Define hydraulic redistribution.
91. What is root hydraulic conductance?
92. Define aquaporins.
93. What is the endodermis?
94. Define the pericycle.
95. What is the cortex in roots?
96. Define root cap.
97. What are root hairs?
98. Define the zone of elongation.
99. What is the meristematic zone?
100. Define the zone of maturation.

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Section C: Short Answer Questions (2 marks each) - 100 Questions

1. Explain the process of imbibition with an example.
2. Distinguish between diffusion and osmosis.
3. Describe the factors affecting osmotic pressure.
4. Explain how root pressure is generated.
5. Compare turgid and flaccid conditions in plant cells.
6. Describe the process of plasmolysis.
7. Differentiate between active and passive transport.
8. Explain the mechanism of ascent of sap.
9. Describe the role of cohesion and adhesion in water transport.
10. Explain the transpiration pull theory.
11. Describe the structure and function of root hairs.
12. Explain the significance of water potential in plants.
13. Describe the apoplastic and symplastic pathways.
14. Explain the role of Casparian strip in water absorption.
15. Describe the process of guttation.
16. Compare stomatal and cuticular transpiration.
17. Explain the adaptations of xerophytes.
18. Describe the characteristics of hydrophytes.
19. Explain CAM photosynthesis in relation to water conservation.
20. Describe the factors causing wilting in plants.
21. Explain temporary and permanent wilting.
22. Describe the demonstration of osmosis using a thistle funnel.
23. Explain the relationship between water potential and its components.
24. Describe the mechanism of stomatal movement.
25. Explain the role of guard cells in transpiration.
26. Describe the factors affecting rate of transpiration.
27. Explain the importance of transpiration in plants.
28. Describe the structure of xylem tissue.
29. Compare vessels and tracheids.
30. Explain the formation of annual rings.
31. Describe the difference between early wood and late wood.
32. Explain the concept of cavitation in xylem.
33. Describe the role of root pressure in guttation.
34. Explain the cohesion-tension theory.
35. Describe the limitations of root pressure theory.
36. Explain the experimental evidence for transpiration pull.
37. Describe the measurement of osmotic pressure.
38. Explain the significance of turgor pressure.
39. Describe the process of plasmolysis and deplasmolysis.
40. Explain the factors affecting imbibition.
41. Describe the role of temperature in water absorption.
42. Explain the effect of soil conditions on water uptake.
43. Describe the relationship between transpiration and photosynthesis.
44. Explain the water economy of plants.
45. Describe the mechanism of water movement in soil.
46. Explain the concept of water use efficiency.
47. Describe the adaptations of desert plants.
48. Explain the water relations in halophytes.
49. Describe the role of mycorrhizae in water absorption.
50. Explain the significance of root-shoot ratio.
51. Describe the measurement of water potential.
52. Explain the concept of osmotic adjustment.
53. Describe the role of ABA in water stress.
54. Explain the mechanism of aquaporin function.
55. Describe the types of aquaporins in plants.
56. Explain the regulation of aquaporin activity.
57. Describe the path of water from soil to atmosphere.
58. Explain the soil-plant-atmosphere continuum.
59. Describe the measurement of transpiration rate.
60. Explain the diurnal variation in water absorption.
61. Describe the seasonal changes in water relations.
62. Explain the effect of environmental factors on water uptake.
63. Describe the role of calcium in water transport.
64. Explain the mechanism of ion uptake by roots.
65. Describe the coupling of water and solute transport.
66. Explain the concept of hydraulic lift.
67. Describe the embolism repair mechanisms.
68. Explain the vulnerability of xylem to cavitation.
69. Describe the safety-efficiency tradeoff in xylem.
70. Explain the role of pit membranes in water transport.
71. Describe the bordered pit structure and function.
72. Explain the difference between hardwood and softwood.
73. Describe the formation of reaction wood.
74. Explain the ecological significance of wood anatomy.
75. Describe the methods of measuring xylem pressure.
76. Explain the pressure probe technique.
77. Describe the psychrometer method for water potential.
78. Explain the thermocouple psychrometer.
79. Describe the pressure chamber technique.
80. Explain the measurement of hydraulic conductivity.
81. Describe the dye movement experiments.
82. Explain the isotope tracer studies in water transport.
83. Describe the use of MRI in studying water movement.
84. Explain the cryo-SEM studies of xylem.
85. Describe the mathematical models of water transport.
86. Explain the finite element modeling of xylem.
87. Describe the network models of xylem transport.
88. Explain the vulnerability curves of xylem.
89. Describe the acoustic detection of cavitation.
90. Explain the optical detection of emboli.
91. Describe the refilling of embolized vessels.
92. Explain the root pressure refilling mechanism.
93. Describe the seasonal patterns of embolism.
94. Explain the evolutionary aspects of xylem structure.
95. Describe the phylogenetic trends in vessel evolution.
96. Explain the developmental regulation of xylem.
97. Describe the hormonal control of xylem differentiation.
98. Explain the genetic basis of xylem formation.
99. Describe the biotechnological applications of water transport.
100. Explain the climate change impacts on plant water relations.

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Section D: Long Answer Questions (3 marks each) - 50 Questions

1. Describe the process of water absorption by roots, including the pathways involved and the driving forces.

2. Explain the cohesion-tension theory of ascent of sap. Include experimental evidence and limitations of this theory.

3. Describe the structure and function of xylem tissue. How does its anatomy relate to its function in water transport?

4. Explain the process of transpiration, its significance, and the factors that regulate it in plants.

5. Describe the various adaptations shown by xerophytic plants to conserve water. Give specific examples.

6. Explain the concept of water potential and its components. How does water potential gradient drive water movement in plants?

7. Describe the mechanism of stomatal movement. How do environmental factors influence stomatal behavior?

8. Explain the phenomenon of plasmolysis and its significance in understanding plant cell water relations.

9. Describe the different types of water transport pathways in plants from root to leaf. Compare their efficiency and regulation.

10. Explain the role of root pressure in water transport. How does it differ from transpiration pull?

11. Describe the experimental methods used to study water transport in plants. Include both classical and modern techniques.

12. Explain the relationship between plant water status and various physiological processes like photosynthesis and growth.

13. Describe the anatomical and physiological adaptations of hydrophytes. How do these plants manage excess water?

14. Explain the concept of embolism in xylem and the mechanisms plants use to repair embolized vessels.

15. Describe the seasonal variations in plant water relations and how plants cope with changing water availability.

16. Explain the soil-plant-atmosphere continuum and the factors that influence water movement along this pathway.

17. Describe the role of aquaporins in plant water transport. How is their activity regulated?

18. Explain the measurement techniques for determining plant water status and their applications in research.

19. Describe the evolutionary aspects of water transport systems in plants. How has xylem anatomy evolved?

20. Explain the impact of environmental stress on plant water relations and the adaptive responses.

21. Describe the mathematical modeling approaches used to understand water transport in plants.

22. Explain the relationship between xylem structure and vulnerability to drought stress.

23. Describe the mechanism of ion transport in relation to water uptake by roots.

24. Explain the diurnal and seasonal patterns of water movement in plants and their ecological significance.

25. Describe the biotechnological applications of understanding plant water relations in crop improvement.

26. Explain the comparative water relations between C3, C4, and CAM plants.

27. Describe the hydraulic architecture of plants and its optimization for water transport efficiency.

28. Explain the molecular mechanisms underlying drought tolerance in plants.

29. Describe the interaction between water transport and plant hormones, particularly ABA.

30. Explain the climate change impacts on plant water relations and potential adaptations.

31. Describe the cavitation resistance mechanisms in different plant species.

32. Explain the trade-offs between water transport efficiency and safety in xylem design.

33. Describe the role of mycorrhizal associations in plant water uptake and drought tolerance.

34. Explain the water relations in epiphytic plants and their specialized adaptations.

35. Describe the phenomenon of hydraulic redistribution and its ecological implications.

36. Explain the osmoregulation mechanisms in halophytic plants.

37. Describe the developmental regulation of xylem differentiation and its hormonal control.

38. Explain the genetic basis of drought tolerance and water use efficiency in crops.

39. Describe the physiological basis of irrigation scheduling in agriculture.

40. Explain the water relations in succulent plants and their water storage strategies.

41. Describe the comparative anatomy of wood in relation to climate and habitat.

42. Explain the acoustic and optical methods for detecting xylem dysfunction.

43. Describe the cellular mechanisms of osmotic adjustment in drought-stressed plants.

44. Explain the water relations in parasitic plants and their host interactions.

45. Describe the hydrodynamics of water flow in plant vascular systems.

46. Explain the coordination between water transport and carbon assimilation in plants.

47. Describe the water relations in carnivorous plants and their specialized adaptations.

48. Explain the biomechanics of water transport and its relationship to plant structure.

49. Describe the ecological water relations and plant community dynamics.

50. Explain the future prospects and challenges in plant water relations research.

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Answer Key

Section A: Multiple Choice Questions

1. The phenomenon of absorption of water by solid particles without forming a solution is called:
   • Answer: c) Imbibition
2. When seeds swell after soaking in water, this process is an example of:
   • Answer: b) Imbibition
3. The net movement of molecules from higher concentration to lower concentration is:
   • Answer: c) Diffusion
4. Osmosis is the movement of:
   • Answer: b) Solvent molecules
5. A selectively permeable membrane allows:
   • Answer: b) Only solvent molecules
6. The minimum pressure needed to prevent osmosis is called:
   • Answer: b) Osmotic pressure
7. Root pressure is responsible for:
   • Answer: b) Sap rising in stem
8. Turgidity in plant cells is caused by:
   • Answer: b) Water absorption
9. When plant cells lose water in hypertonic solution, the process is called:
   • Answer: b) Plasmolysis
10. The condition where plasma membrane is not pressed against cell wall is:
    • Answer: c) Flaccidity
11. Active transport requires:
    • Answer: a) Energy
12. Passive transport occurs:
    • Answer: b) Along concentration gradient
13. The upward movement of water from roots to aerial parts is called:
    • Answer: c) Ascent of sap
14. Cohesion refers to:
    • Answer: b) Attraction between like molecules
15. Adhesion is the tendency of:
    • Answer: b) Unlike molecules to stick together
16. Transpiration pull is responsible for:
    • Answer: b) Water transport upward
17. Which process does not require a membrane?
    • Answer: c) Diffusion
18. Root hairs increase:
    • Answer: c) Surface area
19. The driving force for osmosis is:
    • Answer: c) Concentration difference
20. In a hypotonic solution, plant cells become:
    • Answer: c) Turgid
21. Water potential is highest in:
    • Answer: a) Pure water
22. The term isotonic means:
    • Answer: a) Same concentration
23. Endosmosis occurs when:
    • Answer: b) Water moves into cell
24. Exosmosis results in:
    • Answer: b) Cell shrinking
25. The cell wall of plant cells is:
    • Answer: d) Selectively permeable
26. Turgor pressure helps in:
    • Answer: d) All of these (Cell support, Growth, Opening of stomata)
27. The loss of turgor pressure leads to:
    • Answer: a) Wilting
28. Water moves from soil to root through:
    • Answer: c) Both active and passive
29. The concentration of solutes is highest in:
    • Answer: d) Varies with plant
30. Symplastic pathway involves movement through:
    • Answer: c) Cytoplasm
31. Apoplastic pathway involves movement through:
    • Answer: b) Cell walls
32. The Casparian strip is found in:
    • Answer: c) Endodermis
33. Water absorption is maximum during:
    • Answer: a) Day time
34. The main driving force for water absorption is:
    • Answer: d) All contribute
35. Guttation occurs due to:
    • Answer: b) Root pressure
36. Hydathodes are involved in:
    • Answer: b) Guttation
37. The rate of transpiration is affected by:
    • Answer: d) All of these (Temperature, Humidity, Wind speed)
38. Stomata are mainly present on:
    • Answer: b) Lower surface
39. Guard cells control:
    • Answer: c) Transpiration
40. The opening and closing of stomata depends on:
    • Answer: d) All of these (Light, CO2 concentration, Water availability)
41. C4 plants have:
    • Answer: a) Higher water use efficiency
42. Xerophytes are adapted to:
    • Answer: b) Low water availability
43. Hydrophytes are adapted to:
    • Answer: b) Aquatic conditions
44. Mesophytes grow in:
    • Answer: c) Moderate conditions
45. CAM plants open stomata during:
    • Answer: b) Night time
46. The waxy coating on leaves is called:
    • Answer: a) Cuticle
47. Succulent plants store water in:
    • Answer: d) All of these (Roots, Stems, Leaves)
48. Wilting occurs when:
    • Answer: b) Water absorption < Water loss
49. Temporary wilting is due to:
    • Answer: b) High transpiration rate
50. Permanent wilting occurs when:
    • Answer: a) Soil has no water
51. The water potential of pure water is:
    • Answer: a) Zero
52. Solute potential is always:
    • Answer: b) Negative
53. Pressure potential in turgid cells is:
    • Answer: a) Positive
54. Water always moves from:
    • Answer: b) Higher to lower water potential
55. The unit of water potential is:
    • Answer: d) All of these (Pascal, Atmosphere, Bar)
56. Plasmolysis can be reversed by placing cells in:
    • Answer: b) Hypotonic solution
57. Incipient plasmolysis occurs when:
    • Answer: a) Cell membrane just separates from cell wall
58. The point at which plasmolysis just begins is:
    • Answer: a) Incipient plasmolysis
59. Deplasmolysis occurs when:
    • Answer: a) Plasmolyzed cells regain water
60. Cytorrhysis is:
    • Answer: b) Irreversible plasmolysis
61. The term 'semipermeable membrane' was coined by:
    • Answer: a) Traube
62. The first demonstration of osmosis was by:
    • Answer: c) Dutrochet
63. Osmotic pressure was first measured by:
    • Answer: b) Pfeffer
64. The study of plasmolysis was pioneered by:
    • Answer: c) De Vries
65. Imbibition was first studied in detail by:
    • Answer: d) All of these (Sachs, Reinke, Rodewald)
66. The swelling pressure developed during imbibition can be:
    • Answer: c) Very high
67. Imbibition is affected by:
    • Answer: d) All of these (Temperature, pH, Nature of imbibant)
68. Dry seeds can imbibe water up to:
    • Answer: c) 200-300% of their weight
69. The rate of imbibition is highest in:
    • Answer: a) Beginning
70. Imbibition causes:
    • Answer: a) Increase in volume
71. The force responsible for ascent of sap is:
    • Answer: c) Both root pressure and transpiration pull
72. Cohesion-tension theory was proposed by:
    • Answer: a) Dixon and Joly
73. The diameter of xylem vessels affects:
    • Answer: d) All of these (Cohesion, Adhesion, Transpiration pull)
74. Cavitation in xylem occurs due to:
    • Answer: a) High tension
75. Air bubbles in xylem are called:
    • Answer: d) All of these (Cavitation, Embolism, Emboli)
76. The maximum height water can rise due to capillarity alone is:
    • Answer: a) 1-2 meters
77. Root pressure can raise water up to:
    • Answer: b) Few meters
78. Bleeding in plants is due to:
    • Answer: b) Root pressure
79. The tallest trees rely mainly on:
    • Answer: b) Transpiration pull
80. Water movement in xylem is:
    • Answer: a) Unidirectional upward
81. The conducting elements of xylem are:
    • Answer: a) Vessels and tracheids
82. Tracheids are found in:
    • Answer: c) Both angiosperms and gymnosperms
83. Vessels are characteristic of:
    • Answer: a) Angiosperms
84. The end walls of vessels have:
    • Answer: c) Perforation plates
85. Bordered pits are mainly found in:
    • Answer: b) Tracheids
86. The secondary wall thickenings in tracheids are:
    • Answer: d) All of these (Spiral, Annular, Reticulate)
87. Lignification makes xylem elements:
    • Answer: b) Dead
88. Water conduction in xylem is through:
    • Answer: b) Dead cells
89. The most efficient water conducting elements are:
    • Answer: b) Vessels
90. Tyloses formation occurs in:
    • Answer: b) Old xylem
91. Heartwood is:
    • Answer: b) Non-functional
92. Sapwood is the:
    • Answer: a) Outer functional wood
93. Annual rings in wood represent:
    • Answer: d) All of these (Age of tree, Seasonal variations, Environmental conditions)
94. Early wood has:
    • Answer: a) Large vessels
95. Late wood is characterized by:
    • Answer: b) Small vessels
96. Ring-porous wood has:
    • Answer: b) Large vessels in early wood
97. Diffuse-porous wood has:
    • Answer: a) Vessels uniformly distributed
98. Reaction wood is formed in response to:
    • Answer: a) Gravity
99. Compression wood is found in:
    • Answer: b) Gymnosperms
100. Tension wood is characteristic of:

• Answer: a) Angiosperms

Section B: Short Answer Questions

1. Define imbibition.
   • Answer: The phenomenon of absorption of water by the solid particles of a substance without forming a solution.
2. What is diffusion?
   • Answer: The net movement of molecules or atoms from a region of higher concentration to a region of lower concentration.
3. Define osmosis.
   • Answer: The spontaneous net movement of solvent molecules through a selectively permeable membrane into a region of higher solute concentration.
4. What is osmotic pressure?
   • Answer: The minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane.
5. Define root pressure.
   • Answer: The transverse osmotic pressure within the cells of a root system that causes sap to rise through a plant stem to the leaves.
6. What is turgidity?
   • Answer: The state of a plant cell in which the cell wall is rigid and stretched by an increase in the volume of vacuoles due to the absorption of water.
7. Define plasmolysis.
   • Answer: The process in which cells lose water in a hypertonic solution.
8. What is flaccidity?
   • Answer: The condition of a plant cell in which the plasma membrane is not pressed against the cell wall.
9. Define active transport.
   • Answer: The movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy.
10. What is passive transport?
    • Answer: The movement of ions and other atomic or molecular substances across cell membranes without need of energy input.
11. Define ascent of sap.
    • Answer: The upward movement of water from the roots to the aerial parts of the plant.
12. What is cohesion?
    • Answer: The sticking together of alike molecules, such as water molecule being attracted to another water molecule.
13. Define adhesion.
    • Answer: The tendency of dissimilar particles or surfaces to cling to one another.
14. What is transpiration pull?
    • Answer: The force that pulls water up from the roots through the xylem to the leaves.
15. Name the process by which seeds swell in water.
    • Answer: Imbibition.
16. What type of transport requires energy?
    • Answer: Active transport.
17. In which direction does diffusion occur?
    • Answer: From a region of higher concentration to a region of lower concentration.
18. What is a selectively permeable membrane?
    • Answer: A membrane that allows spontaneous net movement of solvent molecules but restricts solute movement.
19. Name the pressure that prevents osmosis.
    • Answer: Osmotic pressure.
20. What causes sap to rise in plant stems?
    • Answer: Root pressure and Transpiration pull.
21. What happens to cells in hypertonic solution?
    • Answer: They lose water, leading to plasmolysis.
22. What is the condition when plasma membrane detaches from cell wall?
    • Answer: Plasmolysis.
23. Which transport process works against concentration gradient?
    • Answer: Active transport.
24. What is the upward movement of water in plants called?
    • Answer: Ascent of sap.
25. Define water potential.
    • Answer: The potential energy of water per unit volume relative to pure water in reference conditions. It quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure, or matrix effects such as surface tension.
26. What is solute potential?
    • Answer: The component of water potential that is due to the presence of solute molecules. It is always negative or zero.
27. Define pressure potential.
    • Answer: The component of water potential that is due to the mechanical pressure. It is positive in turgid cells and zero in flaccid cells.
28. What is turgor pressure?
    • Answer: The pressure exerted by the cell contents against the cell wall due to water absorption, making the cell rigid.
29. Name the pathway through cell walls.
    • Answer: Apoplastic pathway.
30. What is symplastic pathway?
    • Answer: The pathway of water movement through the cytoplasm of cells, connected by plasmodesmata.
31. Where is the Casparian strip located?
    • Answer: In the endodermis of the root.
32. What is guttation?
    • Answer: The exudation of drops of xylem sap from the tips or edges of leaves of some vascular plants, especially when transpiration is suppressed and root pressure is high.
33. Define hydathodes.
    • Answer: Specialized pores, typically on the margins or tips of leaves, through which guttation occurs.
34. What controls stomatal opening?
    • Answer: Turgor pressure of guard cells, influenced by light, CO2 concentration, and water availability.
35. Name plants adapted to dry conditions.
    • Answer: Xerophytes.
36. What are hydrophytes?
    • Answer: Plants adapted to grow in water or very wet conditions.
37. Define mesophytes.
    • Answer: Plants that grow in moderate conditions, with adequate water supply.
38. When do CAM plants open stomata?
    • Answer: At night, to minimize water loss through transpiration during the hot day.
39. What is the waxy layer on leaves called?
    • Answer: Cuticle.
40. Define wilting.
    • Answer: The loss of rigidity of non-woody parts of plants, caused by insufficient water in the plant cells.
41. What is temporary wilting?
    • Answer: Wilting that occurs when the rate of transpiration exceeds the rate of water absorption, but the plant recovers when water is supplied.
42. Define permanent wilting point.
    • Answer: The point at which a plant can no longer recover from wilting, even when water is supplied to the soil.
43. What is incipient plasmolysis?
    • Answer: The stage of plasmolysis where the cell membrane just begins to pull away from the cell wall.
44. Define deplasmolysis.
    • Answer: The process by which a plasmolyzed cell regains water and its protoplast returns to its original position against the cell wall.
45. What is cytorrhysis?
    • Answer: The irreversible collapse of the cell wall and plasma membrane in a plant cell due to severe water loss, beyond the point of plasmolysis.
46. Name the theory explaining ascent of sap.
    • Answer: Cohesion-tension theory (or Transpiration pull theory).
47. What is cavitation?
    • Answer: The formation of air bubbles within the xylem vessels, breaking the continuous water column.
48. Define embolism in plants.
    • Answer: The blockage of xylem vessels by air bubbles (cavitation), which can impede water transport.
49. What is bleeding in plants?
    • Answer: The exudation of sap from a cut or wounded plant stem, often due to root pressure.
50. Name the conducting elements of xylem.
    • Answer: Tracheids and vessels.
51. What are tracheids?
    • Answer: Elongated, dead, and lignified cells with tapering ends and bordered pits, found in xylem, primarily responsible for water conduction in gymnosperms and some angiosperms.
52. Define vessels.
    • Answer: Wider, shorter, and dead xylem elements with perforated end walls (perforation plates), forming continuous tubes for efficient water transport, characteristic of angiosperms.
53. What are perforation plates?
    • Answer: The end walls of vessel elements that are perforated, allowing for continuous water flow.
54. What are bordered pits?
    • Answer: Pits in the cell walls of tracheids and vessels that have a thickened rim (border) around the pit aperture, regulating water flow.
55. What is lignification?
    • Answer: The process of deposition of lignin in the cell walls of xylem elements, providing mechanical strength and making them impermeable to water.
56. Define tyloses.
    • Answer: Outgrowths from adjacent parenchyma cells that protrude into the lumen of xylem vessels, often blocking them, especially in older xylem.
57. What is heartwood?
    • Answer: The older, darker, and non-functional central wood of a tree stem, primarily involved in support and storage of waste products.
58. Define sapwood.
    • Answer: The younger, lighter, and functionally active outer wood of a tree stem, responsible for water and mineral transport.
59. What are annual rings?
    • Answer: Concentric rings visible in the cross-section of a tree stem, representing one year's growth of xylem, formed due to seasonal variations in cambial activity.
60. Define early wood.
    • Answer: Also known as springwood, it is the wood formed during the early growing season, characterized by larger vessels and thinner walls, allowing for rapid water transport.
61. What is late wood?
    • Answer: Also known as autumnwood, it is the wood formed during the late growing season, characterized by smaller vessels and thicker walls, providing more mechanical support.
62. Define ring-porous wood.
    • Answer: Wood in which the vessels formed in the early wood are significantly larger than those formed in the late wood, resulting in a distinct ring pattern.
63. What is diffuse-porous wood?
    • Answer: Wood in which the vessels are more or less uniformly distributed throughout the growth ring, with little difference in size between early wood and late wood.
64. Define reaction wood.
    • Answer: Wood formed in response to gravitational stress or mechanical stress, helping to reorient the stem or branch.
65. What is compression wood?
    • Answer: A type of reaction wood formed on the lower side of leaning stems and branches in conifers (gymnosperms), characterized by increased lignin and thicker cell walls.
66. Define tension wood.
    • Answer: A type of reaction wood formed on the upper side of leaning stems and branches in angiosperms, characterized by a gelatinous layer in the cell walls and reduced lignification.
67. What is endosmosis?
    • Answer: The inward movement of water into a cell when it is placed in a hypotonic solution.
68. Define exosmosis.
    • Answer: The outward movement of water from a cell when it is placed in a hypertonic solution.
69. What is isotonic solution?
    • Answer: A solution that has the same solute concentration as the cell's cytoplasm, resulting in no net movement of water.
70. Define hypertonic solution.
    • Answer: A solution that has a higher solute concentration than the cell's cytoplasm, causing water to move out of the cell.
71. What is hypotonic solution?
    • Answer: A solution that has a lower solute concentration than the cell's cytoplasm, causing water to move into the cell.
72. Define water use efficiency.
    • Answer: The ratio of carbon assimilated (e.g., through photosynthesis) to the amount of water transpired by the plant.
73. What are succulents?
    • Answer: Plants that have adapted to arid climates by storing water in their specialized leaves, stems, or roots.
74. Define xeromorphic adaptations.
    • Answer: Structural modifications in plants that enable them to survive in dry environments, such as thick cuticles, sunken stomata, or reduced leaf surface area.
75. What is the cuticle?
    • Answer: A waxy, protective layer on the outer surface of plant epidermal cells, which reduces water loss through transpiration.
76. Define stomatal frequency.
    • Answer: The number of stomata per unit area of leaf surface.
77. What is transpiration ratio?
    • Answer: The ratio of the mass of water transpired to the mass of dry matter produced by a plant.
78. Define water deficit.
    • Answer: The condition in a plant when the water content falls below the optimal level for normal physiological functioning.
79. What is water stress?
    • Answer: The adverse effects on plant growth and development caused by a lack of available water in the environment.
80. Define drought resistance.
    • Answer: The ability of a plant to survive and grow under conditions of water scarcity.
81. What is osmotic adjustment?
    • Answer: The accumulation of solutes in plant cells in response to water stress, which lowers the osmotic potential and helps maintain turgor.
82. Define compatible solutes.
    • Answer: Organic molecules (e.g., sugars, amino acids) that accumulate in the cytoplasm of cells under stress conditions without interfering with normal metabolic processes, helping in osmotic adjustment.
83. What is hydraulic conductivity?
    • Answer: A measure of the ease with which water can move through a material, such as soil or plant tissue.
84. Define xylem pressure potential.
    • Answer: The pressure component of water potential within the xylem, typically negative (tension) during transpiration.
85. What is the apoplast?
    • Answer: The continuous system of cell walls and intercellular spaces in plant tissues, through which water and solutes can move without crossing cell membranes.
86. Define symplast.
    • Answer: The continuous network of cytoplasm connected by plasmodesmata, through which water and solutes can move from cell to cell.
87. What is the transmembrane pathway?
    • Answer: The pathway of water movement across cell membranes, involving repeated entry and exit from cells.
88. Define bulk flow.
    • Answer: The movement of a fluid driven by a pressure gradient, such as water movement in xylem.
89. What is mass flow?
    • Answer: Another term for bulk flow, referring to the movement of a substance in a mass or bulk, driven by a pressure gradient.
90. Define hydraulic redistribution.
    • Answer: The passive movement of water by plant roots from wetter to drier soil layers, or from deeper to shallower layers, through the plant's root system.
91. What is root hydraulic conductance?
    • Answer: A measure of the ease with which water flows through the root system.
92. Define aquaporins.
    • Answer: Integral membrane proteins that facilitate the rapid movement of water across biological membranes.
93. What is the endodermis?
    • Answer: A layer of cells in the root cortex that surrounds the vascular cylinder, characterized by the Casparian strip, which regulates water and solute movement into the xylem.
94. Define the pericycle.
    • Answer: A layer of cells just inside the endodermis in the root, from which lateral roots originate.
95. What is the cortex in roots?
    • Answer: The tissue region between the epidermis and the vascular cylinder in roots, primarily involved in storage.
96. Define root cap.
    • Answer: A protective layer of cells covering the tip of a root, protecting the meristem as the root grows through the soil.
97. What are root hairs?
    • Answer: Tiny, hair-like extensions of epidermal cells of roots, which greatly increase the surface area for water and mineral absorption.
98. Define the zone of elongation.
    • Answer: The region of the root behind the meristematic zone where cells increase significantly in length, pushing the root tip through the soil.
99. What is the meristematic zone?
    • Answer: The region at the tip of the root (and shoot) where active cell division occurs, producing new cells for growth.
100. Define the zone of maturation.

• Answer: The region of the root behind the zone of elongation where cells differentiate into specialized tissues, including root hairs.

Section C: Short Answer Questions

1. Explain the process of imbibition with an example.
   • Answer: Imbibition is the phenomenon of absorption of water by the solid particles of a substance without forming a solution. An example is the swelling of seeds when soaked in water.
2. Distinguish between diffusion and osmosis.
   • Answer: Diffusion is the net movement of molecules from a region of higher concentration to lower concentration. Osmosis is the spontaneous net movement of solvent molecules through a selectively permeable membrane into a region of higher solute concentration.
3. Describe the factors affecting osmotic pressure.
   • Answer: Osmotic pressure is affected by the concentration of solute particles, temperature, and the degree of dissociation of the solute.
4. Explain how root pressure is generated.
   • Answer: Root pressure is generated by the active absorption of water and minerals by root cells, leading to an accumulation of solutes in the xylem sap. This creates a water potential gradient, causing water to move into the xylem by osmosis, building up pressure.
5. Compare turgid and flaccid conditions in plant cells.
   • Answer: A turgid cell has its cell wall rigid and stretched due to increased vacuole volume from water absorption, indicating sufficient water. A flaccid cell has its plasma membrane not pressed against the cell wall, indicating water loss and a lack of turgor.
6. Describe the process of plasmolysis.
   • Answer: Plasmolysis is the process where a plant cell loses water when placed in a hypertonic solution. Water moves out of the cell by osmosis, causing the protoplast (cell membrane and its contents) to shrink and pull away from the rigid cell wall.
7. Differentiate between active and passive transport.
   • Answer: Active transport moves substances across a cell membrane against their concentration gradient, requiring energy (ATP) and specific carrier proteins. Passive transport moves substances along their concentration gradient, without requiring metabolic energy, and includes diffusion, osmosis, and facilitated diffusion.
8. Explain the mechanism of ascent of sap.
   • Answer: Ascent of sap is primarily explained by the cohesion-tension theory. Transpiration from leaves creates a negative pressure (tension) in the xylem. Due to cohesion (attraction between water molecules) and adhesion (attraction between water and xylem walls), a continuous column of water is pulled upwards from the roots to the leaves.
9. Describe the role of cohesion and adhesion in water transport.
   • Answer: Cohesion refers to the strong attractive forces between water molecules, allowing them to form a continuous, unbroken column in the xylem. Adhesion refers to the attraction between water molecules and the hydrophilic walls of the xylem vessels, which helps prevent the water column from breaking and supports it against gravity.
10. Explain the transpiration pull theory.
    • Answer: The transpiration pull theory states that the primary force driving the ascent of sap in tall plants is the negative pressure (tension) generated by the evaporation of water from the leaf surface (transpiration). This tension pulls the continuous column of water upwards through the xylem from the roots.
11. Describe the structure and function of root hairs.
    • Answer: Root hairs are slender, elongated extensions of epidermal cells of young roots. Their primary function is to greatly increase the surface area of the root, maximizing the absorption of water and mineral nutrients from the soil.
12. Explain the significance of water potential in plants.
    • Answer: Water potential is crucial because it determines the direction of water movement. Water always moves from a region of higher water potential to a region of lower water potential, driving processes like water absorption by roots, ascent of sap, and transpiration.
13. Describe the apoplastic and symplastic pathways.
    • Answer: The apoplastic pathway is the movement of water and solutes through the non-living parts of the plant, such as cell walls and intercellular spaces, without crossing cell membranes. The symplastic pathway is the movement through the living cytoplasm of cells, connected by plasmodesmata.
14. Explain the role of Casparian strip in water absorption.
    • Answer: The Casparian strip, a waxy, impermeable band in the endodermis, forces water and solutes moving through the apoplast to enter the symplast. This ensures that all absorbed substances pass through a cell membrane, allowing the plant to regulate what enters the vascular tissue.
15. Describe the process of guttation.
    • Answer: Guttation is the exudation of xylem sap from specialized pores called hydathodes, typically at the leaf margins or tips. It occurs when transpiration rates are low (e.g., at night) but root pressure is high, forcing water out of the plant.
16. Compare stomatal and cuticular transpiration.
    • Answer: Stomatal transpiration is the loss of water vapor through the stomata, which are regulated pores on the leaf surface, accounting for most water loss. Cuticular transpiration is the loss of water vapor directly through the cuticle, the waxy layer covering the epidermis, and is generally much lower.
17. Explain the adaptations of xerophytes.
    • Answer: Xerophytes are plants adapted to dry environments. Adaptations include thick cuticles, sunken stomata, reduced leaf surface area (e.g., spines), succulent stems/leaves for water storage, deep root systems, and CAM photosynthesis to conserve water.
18. Describe the characteristics of hydrophytes.
    • Answer: Hydrophytes are plants adapted to aquatic environments. Characteristics include poorly developed root systems, thin or absent cuticles, large air spaces (aerenchyma) for buoyancy and gas exchange, and stomata often on the upper leaf surface (for floating leaves) or absent (for submerged leaves).
19. Explain CAM photosynthesis in relation to water conservation.
    • Answer: CAM (Crassulacean Acid Metabolism) plants open their stomata at night to take in CO2, minimizing water loss through transpiration during the hot, dry day. The CO2 is stored as malic acid and then used for photosynthesis during the day when stomata are closed, thus conserving water.
20. Describe the factors causing wilting in plants.
    • Answer: Wilting is caused by a loss of turgor pressure in plant cells, primarily due to insufficient water absorption to compensate for water loss through transpiration. Factors include drought, high temperatures, low humidity, high wind, and root damage.
21. Explain temporary and permanent wilting.
    • Answer: Temporary wilting occurs when water loss exceeds absorption, but the plant can recover turgor if water is supplied. Permanent wilting occurs when the soil water content is so low that the plant cannot regain turgor, even if water is added, leading to irreversible damage and death.
22. Describe the demonstration of osmosis using a thistle funnel.
    • Answer: A thistle funnel with its mouth covered by a semipermeable membrane is filled with a sugar solution and inverted into a beaker of pure water. Due to osmosis, water moves from the beaker (higher water potential) into the funnel (lower water potential), causing the level of the solution in the funnel stem to rise.
23. Explain the relationship between water potential and its components.
    • Answer: Water potential (Ψ) is the sum of solute potential (Ψs) and pressure potential (Ψp). Ψ = Ψs + Ψp. Solute potential is always negative (or zero) and decreases with increasing solute concentration. Pressure potential is positive in turgid cells and zero or negative in flaccid or plasmolyzed cells. Water moves down a water potential gradient.
24. Describe the mechanism of stomatal movement.
    • Answer: Stomatal opening and closing are regulated by changes in the turgor pressure of guard cells. When guard cells absorb water, they become turgid and bow outwards, opening the stomatal pore. When they lose water, they become flaccid and close the pore. This is influenced by light, CO2 concentration, and water availability.
25. Explain the role of guard cells in transpiration.
    • Answer: Guard cells surround the stomatal pores on the leaf epidermis. By changing their turgor, they control the opening and closing of stomata, thereby regulating the rate of transpiration (water vapor loss) and gas exchange (CO2 uptake) in plants.
26. Describe the factors affecting rate of transpiration.
    • Answer: Factors affecting transpiration rate include: environmental factors (temperature, humidity, wind speed, light intensity) and plant factors (number and distribution of stomata, cuticle thickness, leaf area, presence of hairs).
27. Explain the importance of transpiration in plants.
    • Answer: Transpiration is important for: 1) creating the transpiration pull, which drives water and mineral transport from roots to leaves; 2) cooling the plant surface through evaporative cooling; and 3) distributing minerals throughout the plant.
28. Describe the structure of xylem tissue.
    • Answer: Xylem tissue is a complex vascular tissue responsible for water and mineral transport. It consists primarily of dead, lignified cells: tracheids and vessel elements (which form vessels), along with living xylem parenchyma cells and xylem fibers for support.
29. Compare vessels and tracheids.
    • Answer: Both are water-conducting elements of xylem. Vessels are wider, shorter, and form continuous tubes due to perforated end walls (perforation plates), making them more efficient for water transport, typical of angiosperms. Tracheids are narrower, longer, have tapering ends, and lack perforation plates, relying on bordered pits for water flow, typical of gymnosperms.
30. Explain the formation of annual rings.
    • Answer: Annual rings (growth rings) are formed in the stems of woody plants due to seasonal variations in the activity of the vascular cambium. In spring, large-celled early wood is formed, while in summer, smaller-celled late wood is produced. The distinct boundary between late wood of one year and early wood of the next forms an annual ring.
31. Describe the difference between early wood and late wood.
    • Answer: Early wood (springwood) is formed during favorable growing conditions (spring), characterized by larger, wider vessels/tracheids and thinner walls, facilitating rapid water transport. Late wood (autumnwood) is formed during less favorable conditions (late summer/autumn), with smaller, narrower vessels/tracheids and thicker walls, providing more mechanical support.
32. Explain the concept of cavitation in xylem.
    • Answer: Cavitation is the formation of air bubbles (emboli) within the water-conducting xylem vessels or tracheids. This occurs when the tension in the water column becomes too great, causing the water to vaporize and break the continuous column, impeding water transport.
33. Describe the role of root pressure in guttation.
    • Answer: Root pressure is the positive pressure generated in the xylem of roots. When transpiration rates are low (e.g., at night), this pressure can become high enough to force water out of the leaves through hydathodes, resulting in guttation.
34. Explain the cohesion-tension theory.
    • Answer: The cohesion-tension theory posits that water is pulled up the xylem by a negative pressure (tension) generated by transpiration from the leaves. The cohesive forces between water molecules and adhesive forces between water and xylem walls maintain a continuous water column, allowing this pull to be transmitted from leaves to roots.
35. Describe the limitations of root pressure theory.
    • Answer: Limitations include: 1) Root pressure is often too low to account for water ascent in tall trees; 2) It is not universally present in all plants or at all times; 3) It is absent in rapidly transpiring plants; and 4) It cannot explain water movement during high transpiration rates.
36. Explain the experimental evidence for transpiration pull.
    • Answer: Evidence includes: 1) The rapid decrease in xylem pressure during transpiration; 2) The narrowing of tree trunks during the day due to tension; 3) The ability of a transpiring shoot to pull water from a sealed container; and 4) The cohesive strength of water demonstrated in experiments.
37. Describe the measurement of osmotic pressure.
    • Answer: Osmotic pressure can be measured using an osmometer. A semipermeable membrane separates a solution from pure water. The pressure required to prevent the net movement of water into the solution across the membrane is the osmotic pressure. Alternatively, it can be calculated using the van't Hoff equation.
38. Explain the significance of turgor pressure.
    • Answer: Turgor pressure is vital for plants. It provides rigidity and support to non-woody plant parts, maintains cell shape, drives cell expansion during growth, and is essential for processes like stomatal opening, leaf movements, and the opening of flower petals.
39. Describe the process of plasmolysis and deplasmolysis.
    • Answer: Plasmolysis is the shrinking of the protoplast away from the cell wall when a plant cell is placed in a hypertonic solution due to water loss by osmosis. Deplasmolysis is the reversal of this process; when a plasmolyzed cell is placed in a hypotonic solution, it absorbs water, and the protoplast expands back against the cell wall.
40. Explain the factors affecting imbibition.
    • Answer: Factors affecting imbibition include: 1) Nature of the imbibant (hydrophilic colloids imbibe more); 2) Surface area of the imbibant; 3) Temperature (increases with temperature); 4) Concentration of solutes in the medium (decreases with increasing solute concentration); and 5) pH.
41. Describe the role of temperature in water absorption.
    • Answer: Temperature affects water absorption by influencing both water viscosity (lower viscosity at higher temperatures, facilitating movement) and metabolic activity of root cells (active transport is temperature-dependent). Extreme temperatures can inhibit absorption.
42. Explain the effect of soil conditions on water uptake.
    • Answer: Soil conditions like water content, aeration, temperature, and solute concentration significantly affect water uptake. Optimal soil moisture, good aeration, moderate temperature, and low soil salinity promote efficient water absorption by roots.
43. Describe the relationship between transpiration and photosynthesis.
    • Answer: Transpiration and photosynthesis are interconnected. Stomata must open for CO2 uptake (photosynthesis), but this also leads to water loss (transpiration). Plants balance these processes; high transpiration can lead to stomatal closure, reducing photosynthesis, while efficient photosynthesis requires adequate water supply for transpiration.
44. Explain the water economy of plants.
    • Answer: Water economy refers to how plants manage their water resources, balancing water uptake from the soil with water loss through transpiration. It involves adaptations to minimize water loss (e.g., cuticle, stomatal regulation) and efficient water transport mechanisms to maintain hydration and support physiological processes.
45. Describe the mechanism of water movement in soil.
    • Answer: Water moves in soil primarily by bulk flow, driven by differences in water potential. It moves from areas of higher water potential (wetter soil) to lower water potential (drier soil or root surface) through interconnected soil pores, influenced by matric potential and gravity.
46. Explain the concept of water use efficiency.
    • Answer: Water use efficiency (WUE) is a measure of how effectively a plant uses water. It is typically defined as the ratio of carbon assimilated (e.g., biomass produced or CO2 fixed) to the amount of water transpired. Higher WUE means more carbon gain per unit of water lost.
47. Describe the adaptations of desert plants.
    • Answer: Desert plants (xerophytes) have adaptations to survive water scarcity, including: deep or widespread root systems, succulent tissues for water storage, reduced or modified leaves (spines), thick cuticles, sunken stomata, and CAM photosynthesis.
48. Explain the water relations in halophytes.
    • Answer: Halophytes are plants adapted to grow in saline environments. They manage high salt concentrations by: 1) accumulating salts in vacuoles; 2) excreting salts through salt glands; 3) diluting salts by water uptake; or 4) shedding salt-laden leaves. They maintain a lower water potential than the soil to absorb water.
49. Describe the role of mycorrhizae in water absorption.
    • Answer: Mycorrhizal fungi form symbiotic associations with plant roots. They extend the root system's effective surface area through their hyphae, enhancing the plant's ability to absorb water and nutrients, especially in nutrient-poor or dry soils.
50. Explain the significance of root-shoot ratio.
    • Answer: The root-shoot ratio (ratio of root biomass to shoot biomass) reflects a plant's allocation of resources. A higher root-shoot ratio indicates a greater investment in water and nutrient acquisition, which is advantageous in dry or nutrient-poor environments, while a lower ratio favors light capture and photosynthesis.
51. Describe the measurement of water potential.
    • Answer: Water potential can be measured using a pressure chamber (for xylem water potential), psychrometers (for leaf or soil water potential), or osmometers (for osmotic potential). The pressure chamber method involves applying pressure to a leaf until xylem sap exudes, indicating the tension in the xylem.
52. Explain the concept of osmotic adjustment.
    • Answer: Osmotic adjustment is a physiological response to water stress where plant cells accumulate solutes (e.g., sugars, amino acids, ions) in their cytoplasm and vacuoles. This lowers the cell's osmotic potential, allowing it to maintain turgor and absorb water even when external water potential is low.
53. Describe the role of ABA in water stress.
    • Answer: Abscisic acid (ABA) is a plant hormone that plays a crucial role in mediating responses to water stress. Under drought, ABA levels increase, leading to stomatal closure (reducing water loss), promoting root growth, and inducing the expression of stress-responsive genes, thus enhancing drought tolerance.
54. Explain the mechanism of aquaporin function.
    • Answer: Aquaporins are channel proteins embedded in cell membranes that facilitate the rapid, passive movement of water across the membrane. They form hydrophilic pores that allow water molecules to pass through while blocking the passage of ions and other solutes, thus increasing membrane permeability to water.
55. Describe the types of aquaporins in plants.
    • Answer: Plant aquaporins are diverse and include several subfamilies, such as Plasma Membrane Intrinsic Proteins (PIPs), Tonoplast Intrinsic Proteins (TIPs), and Nodulin-26-like Intrinsic Proteins (NIPs). They are found in various membranes (plasma membrane, tonoplast, peribacteroid membrane) and have different specificities and regulatory mechanisms.
56. Explain the regulation of aquaporin activity.
    • Answer: Aquaporin activity is regulated at multiple levels: 1) Transcriptional control (changes in gene expression); 2) Post-translational modifications (e.g., phosphorylation, which can open or close the channels); 3) Gating (physical opening/closing of the pore in response to pH, Ca2+, or turgor changes); and 4) Protein trafficking to the membrane.
57. Describe the path of water from soil to atmosphere.
    • Answer: Water moves from the soil, through the root epidermis, cortex, endodermis, and pericycle, into the xylem vessels of the root. It then ascends through the xylem of the stem and leaves, moves into the leaf cells, evaporates into the intercellular spaces, and finally diffuses out through the stomata into the atmosphere.
58. Explain the soil-plant-atmosphere continuum.
    • Answer: The soil-plant-atmosphere continuum (SPAC) describes the continuous pathway for water movement from the soil, through the plant, and into the atmosphere. Water moves along a decreasing water potential gradient from the relatively high potential in the soil to the very low potential in the atmosphere, driven primarily by transpiration.
59. Describe the measurement of transpiration rate.
    • Answer: Transpiration rate can be measured using various methods: 1) Potometer (measures water uptake by a shoot); 2) Weighing method (measures weight loss of a potted plant over time); 3) Gas exchange systems (measures water vapor flux from leaves); and 4) Sap flow sensors (measures water movement in stems).
60. Explain the diurnal variation in water absorption.
    • Answer: Water absorption typically shows a diurnal pattern. It is generally lower during the day when transpiration rates are high (due to sunlight and heat), leading to a temporary water deficit in the plant. Absorption increases at night when transpiration is low and soil water potential is relatively higher.
61. Describe the seasonal changes in water relations.
    • Answer: Seasonal changes in water relations reflect environmental conditions. In temperate regions, plants may experience water stress in summer (high temperatures, low rainfall) or winter (frozen soil). Deciduous trees shed leaves to avoid winter water stress. Evergreen plants have adaptations to cope with year-round water availability fluctuations.
62. Explain the effect of environmental factors on water uptake.
    • Answer: Environmental factors like soil water content, soil temperature, aeration, and solute concentration directly affect water uptake. Low soil water, cold soil, poor aeration, and high soil salinity can all reduce water absorption by roots.
63. Describe the role of calcium in water transport.
    • Answer: Calcium plays a role in maintaining the integrity of cell membranes and cell walls, which are crucial for water transport. It also influences the regulation of aquaporin activity and stomatal movements, indirectly affecting water flow.
64. Explain the mechanism of ion uptake by roots.
    • Answer: Ion uptake by roots occurs through both passive and active transport. Passive uptake involves diffusion through ion channels. Active uptake requires energy and specific carrier proteins to move ions against their concentration gradient, often coupled with proton pumps.
65. Describe the coupling of water and solute transport.
    • Answer: Water and solute transport are coupled in plants. Water movement (e.g., in xylem) carries dissolved solutes (mass flow). Conversely, solute accumulation (e.g., in root cells for osmotic adjustment) creates water potential gradients that drive water movement. Active ion transport in roots is essential for water absorption.
66. Explain the concept of hydraulic lift.
    • Answer: Hydraulic lift is the process where deep-rooted plants absorb water from moist soil layers and release it into drier, shallower soil layers through their roots, typically at night. This water can then be used by the same plant or neighboring plants.
67. Describe the embolism repair mechanisms.
    • Answer: Plants have mechanisms to repair embolized xylem vessels, though not all species can do so effectively. These include: 1) Root pressure refilling (positive pressure pushes air out); 2) Refilling from adjacent living cells; and 3) Formation of new xylem vessels.
68. Explain the vulnerability of xylem to cavitation.
    • Answer: Xylem is vulnerable to cavitation (air bubble formation) when the tension in the water column becomes too high, typically under severe drought stress. Wider vessels are generally more vulnerable than narrower tracheids, as larger pores in pit membranes are more likely to aspirate air.
69. Describe the safety-efficiency tradeoff in xylem.
    • Answer: There is a fundamental tradeoff in xylem design between hydraulic efficiency (ability to transport large volumes of water rapidly) and safety (resistance to cavitation). Wider vessels are more efficient but less safe, while narrower tracheids are safer but less efficient. Plants adapt their xylem structure based on their environment.
70. Explain the role of pit membranes in water transport.
    • Answer: Pit membranes are porous structures between adjacent xylem conduits (tracheids or vessels) that allow water to pass while preventing the spread of air bubbles (emboli). Their pore size and structure are critical for maintaining the integrity of the water column and preventing cavitation spread.
71. Describe the bordered pit structure and function.
    • Answer: Bordered pits are specialized pits found in tracheids and vessel elements. They have a thickened rim (border) around the pit aperture and a central torus (in conifers) within the pit membrane. They regulate water flow between conduits and can seal off embolized conduits to prevent air spread.
72. Explain the difference between hardwood and softwood.
    • Answer: Hardwood comes from angiosperm trees and typically contains both vessels and tracheids, often with a more complex structure. Softwood comes from gymnosperm trees and primarily consists of tracheids, lacking vessels. Hardwoods are generally denser and harder than softwoods.
73. Describe the formation of reaction wood.
    • Answer: Reaction wood is abnormal wood formed in leaning stems or branches in response to gravitational stress. In conifers, it's compression wood (on the lower side), and in angiosperms, it's tension wood (on the upper side). It helps reorient the stem/branch to an upright position.
74. Explain the ecological significance of wood anatomy.
    • Answer: Wood anatomy is ecologically significant as it reflects adaptations to different environments. For example, ring-porous wood (large earlywood vessels) is common in temperate trees needing rapid water transport in spring, while diffuse-porous wood (uniform vessels) is found in tropical trees with less seasonal variation.
75. Describe the methods of measuring xylem pressure.
    • Answer: Xylem pressure (tension) is commonly measured using a pressure chamber. A leaf or shoot is placed in a sealed chamber, and pressure is applied until sap just appears at the cut surface, indicating the tension in the xylem. Other methods include xylem psychrometers.
76. Explain the pressure probe technique.
    • Answer: The pressure probe is a microscopic device used to directly measure turgor pressure in individual plant cells. A fine glass microcapillary is inserted into the cell, and changes in pressure are detected, providing insights into cell water status and membrane properties.
77. Describe the psychrometer method for water potential.
    • Answer: The psychrometer method measures water potential by determining the water vapor pressure in equilibrium with a plant tissue sample. A small tissue sample is placed in a sealed chamber with a thermocouple. The temperature depression caused by water evaporation from the sample is related to its water potential.
78. Explain the thermocouple psychrometer.
    • Answer: A thermocouple psychrometer is a device used to measure water potential. It consists of a small chamber containing a thermocouple junction. When a plant tissue sample is placed in the chamber, water evaporates from it, cooling the thermocouple. The temperature difference is converted to water potential.
79. Describe the pressure chamber technique.
    • Answer: The pressure chamber technique (Scholander pressure bomb) is a widely used method to measure xylem water potential. A detached leaf or shoot is placed in a sealed chamber, and compressed air is gradually introduced until xylem sap is forced back to the cut surface, indicating the tension (negative pressure) in the xylem.
80. Explain the measurement of hydraulic conductivity.
    • Answer: Hydraulic conductivity (K) measures the ease of water flow through a material. In plants, it can be measured for whole plants, organs (e.g., stems, roots), or individual cells. Methods involve measuring water flow rate under a known pressure gradient, often using specialized flow meters or pressure probes.
81. Describe the dye movement experiments.
    • Answer: Dye movement experiments involve introducing a colored dye into the transpiration stream of a plant (e.g., through a cut stem). The subsequent observation of the dye's distribution within the plant (e.g., in xylem vessels) provides visual evidence of water transport pathways and rates.
82. Explain the isotope tracer studies in water transport.
    • Answer: Isotope tracer studies use stable isotopes of water (e.g., deuterium or oxygen-18) to track water movement in plants. By introducing labeled water and then measuring its concentration in different plant parts over time, researchers can determine water uptake rates, transport pathways, and residence times.
83. Describe the use of MRI in studying water movement.
    • Answer: Magnetic Resonance Imaging (MRI) can be used non-invasively to visualize and quantify water movement in living plants. It detects the signal from hydrogen nuclei in water molecules, allowing for real-time imaging of water flow pathways, rates, and distribution within plant tissues.
84. Explain the cryo-SEM studies of xylem.
    • Answer: Cryo-scanning electron microscopy (cryo-SEM) involves rapidly freezing plant samples to preserve their native water status, then examining them under a scanning electron microscope. This technique allows for direct visualization of the water column, air bubbles (emboli), and the structure of xylem conduits in situ.
85. Describe the mathematical models of water transport.
    • Answer: Mathematical models of water transport in plants use equations to describe water flow based on physical principles (e.g., Darcy's Law) and plant hydraulic properties. These models help predict water potential gradients, flow rates, and the impact of environmental changes on plant water status, from cell to whole-plant levels.
86. Explain the finite element modeling of xylem.
    • Answer: Finite element modeling (FEM) is a computational technique used to simulate complex physical phenomena, including water flow in xylem. It divides the xylem structure into small elements and solves equations for each element, allowing for detailed analysis of water potential distribution and flow patterns within the intricate xylem network.
87. Describe the network models of xylem transport.
    • Answer: Network models represent the xylem as a series of interconnected conduits (vessels and tracheids) and nodes. These models simulate water flow through the network, considering factors like conduit dimensions, pit membrane properties, and the spread of cavitation, to understand overall hydraulic conductance and vulnerability.
88. Explain the vulnerability curves of xylem.
    • Answer: Vulnerability curves plot the percentage loss of hydraulic conductivity in xylem against increasing xylem tension (negative pressure). They characterize a species' resistance to cavitation, showing the tension at which xylem conduits begin to embolize and the tension at which most conductivity is lost.
89. Describe the acoustic detection of cavitation.
    • Answer: Acoustic detection of cavitation involves using sensitive microphones to detect the ultrasonic acoustic emissions (clicks) produced when air bubbles form in xylem vessels. Each cavitation event generates a sound wave, allowing researchers to monitor the occurrence and frequency of embolism in real-time.
90. Explain the optical detection of emboli.
    • Answer: Optical detection of emboli involves using high-resolution microscopy to directly visualize air bubbles within xylem conduits. This can be done by observing transparent plant parts (e.g., petioles) or by using specialized techniques like X-ray microtomography to image embolized vessels in opaque stems.
91. Describe the refilling of embolized vessels.
    • Answer: Refilling of embolized vessels is the process by which air-filled xylem conduits are restored to functionality by being refilled with water. This can occur through positive root pressure, local water secretion from living parenchyma cells, or by drawing water from adjacent functional conduits, though it is often a slow and energy-intensive process.
92. Explain the root pressure refilling mechanism.
    • Answer: The root pressure refilling mechanism involves the generation of positive pressure in the xylem by the roots, typically at night when transpiration is low. This positive pressure pushes the air bubbles out of the embolized vessels, allowing them to refill with water and regain functionality.
93. Describe the seasonal patterns of embolism.
    • Answer: Seasonal patterns of embolism vary with climate and species. In temperate regions, embolism may accumulate during summer droughts and be repaired during periods of high root pressure (e.g., spring). In arid regions, embolism may be a constant challenge, with plants relying on rapid repair or high cavitation resistance.
94. Explain the evolutionary aspects of xylem structure.
    • Answer: The evolution of xylem structure reflects adaptations to terrestrial life and increasing plant height. Early plants had simple tracheids. The evolution of wider vessels in angiosperms allowed for more efficient water transport, but also increased vulnerability to cavitation, leading to diverse strategies for balancing efficiency and safety.
95. Describe the phylogenetic trends in vessel evolution.
    • Answer: Phylogenetic trends in vessel evolution show a progression from narrow, long tracheids to wider, shorter vessel elements with more elaborate perforation plates. This trend generally correlates with increased hydraulic efficiency, but also with increased vulnerability to cavitation, leading to diverse vessel arrangements across plant lineages.
96. Explain the developmental regulation of xylem.
    • Answer: The development of xylem (xylogenesis) is a complex process regulated by plant hormones (e.g., auxins, cytokinins, gibberellins), transcription factors, and environmental cues. These factors control the differentiation of procambial and cambial cells into various xylem elements, including vessels and tracheids.
97. Describe the hormonal control of xylem differentiation.
    • Answer: Xylem differentiation is strongly influenced by plant hormones. Auxin is a key promoter of xylem formation, while cytokinins interact with auxin to regulate vascular tissue development. Gibberellins and brassinosteroids also play roles in promoting xylem differentiation and lignification.
98. Explain the genetic basis of xylem formation.
    • Answer: Xylem formation is controlled by a complex network of genes. Transcription factors (e.g., NAC and MYB families) regulate the expression of genes involved in cell wall biosynthesis, lignification, and programmed cell death of xylem elements. Genetic studies help identify genes crucial for hydraulic efficiency and drought tolerance.
99. Describe the biotechnological applications of water transport.
    • Answer: Biotechnological applications include: 1) Developing drought-tolerant crops by engineering genes involved in water uptake, transport, or stress response (e.g., aquaporins, osmotic adjustment genes); 2) Improving water use efficiency in agriculture; and 3) Understanding plant responses to climate change for sustainable agriculture.
100. Explain the climate change impacts on plant water relations.

• Answer: Climate change impacts plant water relations through increased temperatures (leading to higher transpiration), altered precipitation patterns (more droughts or floods), and increased CO2 levels (which can reduce stomatal aperture). These changes can lead to increased water stress, reduced growth, and shifts in plant distribution.

Section D: Long Answer Questions

1. Describe the process of water absorption by roots, including the pathways involved and the driving forces.
   • Answer: Water absorption by roots involves processes like imbibition (absorption by solid particles), diffusion (movement from high to low concentration), and osmosis (solvent movement across a semipermeable membrane). Water moves through the apoplast (cell walls and intercellular spaces) and symplast (cytoplasm via plasmodesmata). Driving forces are root pressure (positive pressure from active solute uptake) and transpiration pull (negative pressure from water evaporation from leaves).
2. Explain the cohesion-tension theory of ascent of sap. Include experimental evidence and limitations of this theory.
   • Answer: The cohesion-tension theory states that water is pulled up the xylem by a negative pressure (tension) generated by transpiration from leaves. Cohesion (attraction between water molecules) maintains a continuous water column, and adhesion (attraction to xylem walls) prevents it from breaking. Evidence includes: rapid decrease in xylem pressure during transpiration, narrowing of tree trunks during the day, and the cohesive strength of water. Limitations include: it doesn't fully explain refilling of embolized vessels and the role of root pressure in some cases.
3. Describe the structure and function of xylem tissue. How does its anatomy relate to its function in water transport?
   • Answer: Xylem is a complex vascular tissue primarily for water and mineral transport. It consists of dead, lignified tracheids and vessel elements (forming vessels), along with living parenchyma and fibers. Tracheids are narrow, elongated cells with pitted walls, while vessels are wider, shorter tubes with perforated end walls. Their hollow, continuous, and lignified structure provides efficient, strong conduits for unidirectional water flow against gravity.
4. Explain the process of transpiration, its significance, and the factors that regulate it in plants.
   • Answer: Transpiration is the loss of water vapor from plants, mainly through stomata. Its significance includes creating the transpiration pull (driving water ascent), cooling the plant, and distributing minerals. It is regulated by environmental factors (light, temperature, humidity, wind) and plant factors (stomatal density, cuticle thickness, leaf area, water availability).
5. Describe the various adaptations shown by xerophytic plants to conserve water. Give specific examples.
   • Answer: Xerophytes adapt to dry conditions by: 1) Reducing water loss: thick cuticle (e.g., cacti), sunken stomata (e.g., Nerium), reduced/modified leaves (e.g., spines in cacti), hairy leaves. 2) Storing water: succulent stems/leaves (e.g., cacti, aloes). 3) Efficient water uptake: deep or widespread root systems. 4) Specialized metabolism: CAM photosynthesis (e.g., succulents).
6. Explain the concept of water potential and its components. How does water potential gradient drive water movement in plants?
   • Answer: Water potential (Ψ) is the potential energy of water, determining its movement. It is the sum of solute potential (Ψs, negative, due to dissolved solutes) and pressure potential (Ψp, positive in turgid cells, negative in xylem under tension). Water always moves passively from a region of higher water potential to a region of lower water potential, driving absorption, ascent, and transpiration.
7. Describe the mechanism of stomatal movement. How do environmental factors influence stomatal behavior?
   • Answer: Stomatal movement is controlled by changes in guard cell turgor. When guard cells absorb water, they become turgid and bow outwards, opening the stomata. When they lose water, they become flaccid and close. Environmental factors like light (promotes opening), CO2 concentration (low CO2 promotes opening), and water availability (drought causes closure) influence this turgor.
8. Explain the phenomenon of plasmolysis and its significance in understanding plant cell water relations.
   • Answer: Plasmolysis is the shrinking of the protoplast away from the cell wall when a plant cell is placed in a hypertonic solution, due to water loss by osmosis. Its significance lies in demonstrating the semipermeable nature of the cell membrane, the importance of turgor for cell rigidity, and the effects of external solute concentrations on plant cell viability and water status.
9. Describe the different types of water transport pathways in plants from root to leaf. Compare their efficiency and regulation.
   • Answer: Water moves from root to leaf primarily through the xylem (long-distance transport). Within tissues, water moves via: 1) Apoplast: through cell walls and intercellular spaces (fast, unregulated). 2) Symplast: through cytoplasm connected by plasmodesmata (slower, regulated). 3) Transmembrane: across cell membranes (regulated by aquaporins). Xylem transport is highly efficient due to wide, continuous vessels, while symplastic and transmembrane pathways allow for cellular regulation.
10. Explain the role of root pressure in water transport. How does it differ from transpiration pull?
    • Answer: Root pressure is a positive pressure generated in the xylem of roots due to active solute accumulation and subsequent osmotic water uptake. It can push water up the stem over short distances, especially when transpiration is low (e.g., guttation). Transpiration pull, conversely, is a negative pressure (tension) generated by water evaporation from leaves, pulling water up. Transpiration pull is the primary force for water ascent in tall plants, while root pressure is a weaker, secondary force.
11. Describe the experimental methods used to study water transport in plants. Include both classical and modern techniques.
    • Answer: Classical methods include: 1) Potometer: measures water uptake by a shoot. 2) Dye movement experiments: tracks water pathways using colored dyes. 3) Pressure chamber (Scholander bomb): measures xylem water potential. Modern techniques include: 1) Isotope tracer studies: uses labeled water (e.g., D2O, H218O) to track water movement. 2) MRI: non-invasively visualizes water flow in living plants. 3) Cryo-SEM: visualizes xylem conduits and emboli in situ. 4) Acoustic detection: detects cavitation events.
12. Explain the relationship between plant water status and various physiological processes like photosynthesis and growth.
    • Answer: Plant water status profoundly affects physiological processes. Water deficit leads to stomatal closure, reducing CO2 uptake and thus photosynthesis. Severe water stress inhibits enzyme activity, impairs nutrient transport, and reduces cell expansion, thereby limiting growth and overall plant productivity. Maintaining optimal water status is critical for plant survival and performance.
13. Describe the anatomical and physiological adaptations of hydrophytes. How do these plants manage excess water?
    • Answer: Hydrophytes (aquatic plants) adapt to abundant water. Anatomical adaptations include: 1) Reduced root systems (water absorbed directly by leaves/stems). 2) Thin or absent cuticles. 3) Large air spaces (aerenchyma) for buoyancy and gas exchange. 4) Stomata on upper leaf surface (floating leaves) or absent (submerged leaves). Physiologically, they have efficient gas exchange in water and can tolerate low oxygen conditions in submerged parts.
14. Explain the concept of embolism in xylem and the mechanisms plants use to repair embolized vessels.
    • Answer: Embolism is the formation of air bubbles (cavitation) in xylem conduits, breaking the continuous water column and impeding transport. Plants repair emboli through: 1) Root pressure refilling: positive root pressure pushes air out, typically at night. 2) Refilling from adjacent living parenchyma cells: water is secreted into embolized conduits. 3) Formation of new xylem: new conduits are produced to replace non-functional ones. Repair is often slow and energy-intensive.
15. Describe the seasonal variations in plant water relations and how plants cope with changing water availability.
    • Answer: Plant water relations vary seasonally with climate. In temperate zones, plants face winter drought (frozen soil) and summer drought. Deciduous trees shed leaves to avoid winter water stress. Many plants increase root growth during dry periods. In spring, rapid growth requires high water uptake. Plants adjust stomatal behavior and osmotic potential to cope with fluctuating water availability throughout the year.
16. Explain the soil-plant-atmosphere continuum and the factors that influence water movement along this pathway.
    • Answer: The soil-plant-atmosphere continuum (SPAC) describes the continuous pathway of water movement from the soil, through the plant, and into the atmosphere. Water moves along a decreasing water potential gradient. Factors influencing movement include: soil water potential, root hydraulic conductivity, xylem hydraulic conductivity, stomatal conductance, and atmospheric humidity and temperature (driving transpiration).
17. Describe the role of aquaporins in plant water transport. How is their activity regulated?
    • Answer: Aquaporins are membrane channel proteins that facilitate rapid, passive water movement across cell membranes. They increase membrane permeability to water, enhancing water uptake by roots and cell-to-cell transport. Their activity is regulated by: 1) Gene expression (transcriptional control). 2) Phosphorylation (post-translational modification, opening/closing channels). 3) Gating (physical opening/closing in response to pH, Ca2+, turgor). 4) Trafficking to/from the membrane.
18. Explain the measurement techniques for determining plant water status and their applications in research.
    • Answer: Plant water status is determined by measuring water potential and its components. Techniques include: 1) Pressure chamber: measures xylem water potential (tension). 2) Psychrometers: measures water potential of tissues by vapor pressure. 3) Osmometers: measures osmotic potential of cell sap. These are applied in research to study drought stress, irrigation needs, plant hydraulic architecture, and responses to environmental changes.
19. Describe the evolutionary aspects of water transport systems in plants. How has xylem anatomy evolved?
    • Answer: The evolution of water transport systems reflects the transition from aquatic to terrestrial life and increasing plant size. Early land plants had simple conducting cells. Xylem evolved from tracheids (found in ferns, gymnosperms) to more efficient vessels (dominant in angiosperms). This progression allowed for greater hydraulic efficiency, supporting taller growth, but also introduced challenges like cavitation, leading to diverse anatomical adaptations for balancing efficiency and safety.
20. Explain the impact of environmental stress on plant water relations and the adaptive responses.
    • Answer: Environmental stresses like drought, salinity, and extreme temperatures significantly impact plant water relations. Drought causes water deficit, leading to stomatal closure, reduced photosynthesis, and wilting. Salinity lowers external water potential, making water uptake difficult. Plants adapt by: 1) Osmotic adjustment (accumulating solutes). 2) Stomatal regulation. 3) Altering root architecture. 4) Producing stress-protective compounds. 5) Modifying xylem structure for cavitation resistance.
21. Describe the mathematical modeling approaches used to understand water transport in plants.
    • Answer: Mathematical models use equations to describe water flow based on physical principles (e.g., Darcy's Law) and plant hydraulic properties. Approaches include: 1) Whole-plant models: simulate water potential and flow from soil to atmosphere. 2) Network models: represent xylem as interconnected conduits to study flow and cavitation spread. 3) Finite element models: analyze detailed flow patterns within complex xylem structures. These models help predict plant responses to environmental changes and optimize water use.
22. Explain the relationship between xylem structure and vulnerability to drought stress.
    • Answer: Xylem structure significantly influences drought vulnerability. Wider vessels are more efficient for water transport but are more prone to cavitation (air bubble formation) under tension. Narrower tracheids are safer but less efficient. Plants in arid environments often have narrower conduits or specialized pit membranes to increase cavitation resistance, even at the cost of reduced hydraulic efficiency.
23. Describe the mechanism of ion transport in relation to water uptake by roots.
    • Answer: Ion transport is closely linked to water uptake. Roots actively absorb mineral ions from the soil, often against a concentration gradient, using energy. This active uptake of solutes lowers the water potential inside root cells, creating an osmotic gradient that drives water movement into the roots by osmosis. Thus, active ion transport indirectly facilitates passive water absorption.
24. Explain the diurnal and seasonal patterns of water movement in plants and their ecological significance.
    • Answer: Diurnal patterns: Transpiration is highest during the day (light, heat), leading to lower plant water potential and increased water uptake. At night, transpiration is low, and root pressure can cause guttation. Seasonal patterns: Water availability varies seasonally, influencing growth and water use strategies. In dry seasons, plants may reduce leaf area or enter dormancy. Ecologically, these patterns influence plant distribution, competition, and ecosystem water cycling.
25. Describe the biotechnological applications of understanding plant water relations in crop improvement.
    • Answer: Biotechnological applications aim to improve crop water use efficiency and drought tolerance. This includes: 1) Genetic engineering: introducing or enhancing genes for aquaporins, osmotic adjustment, or stress-responsive pathways. 2) Marker-assisted selection: identifying genes linked to drought resistance. 3) Developing crops with optimized root systems or stomatal control. These efforts contribute to sustainable agriculture in water-limited environments.
26. Explain the comparative water relations between C3, C4, and CAM plants.
    • Answer: C3 plants (most common) have moderate water use efficiency (WUE), with stomata open during the day. C4 plants (e.g., corn, sugarcane) have higher WUE due to spatial separation of CO2 fixation, allowing them to fix CO2 more efficiently at lower stomatal conductances. CAM plants (e.g., succulents) have the highest WUE, opening stomata only at night to minimize water loss, storing CO2, and photosynthesizing during the day with closed stomata.
27. Describe the hydraulic architecture of plants and its optimization for water transport efficiency.
    • Answer: Hydraulic architecture refers to the arrangement and properties of the water-conducting system (xylem) within a plant. It is optimized for efficient water transport while minimizing the risk of cavitation. This involves tradeoffs between conduit size (wider = more efficient, but more vulnerable) and density, and the structure of pit membranes. Different species have evolved diverse architectures suited to their habitats.
28. Explain the molecular mechanisms underlying drought tolerance in plants.
    • Answer: Molecular mechanisms include: 1) Gene expression changes: up-regulation of genes for stress proteins (e.g., chaperones), enzymes for osmotic adjustment (e.g., proline synthesis), and aquaporins. 2) Hormone signaling: ABA plays a central role in coordinating drought responses. 3) Antioxidant defense: production of enzymes to scavenge reactive oxygen species. 4) Membrane stabilization: synthesis of compatible solutes to protect cellular structures.
29. Describe the interaction between water transport and plant hormones, particularly ABA.
    • Answer: Plant hormones regulate water transport. Abscisic acid (ABA) is a key drought hormone. Under water stress, ABA levels increase, leading to stomatal closure (reducing transpiration) and promoting root growth (enhancing water uptake). ABA also influences aquaporin activity and hydraulic conductivity. Other hormones like auxins and cytokinins also play roles in root development and xylem differentiation, indirectly affecting water transport.
30. Explain the climate change impacts on plant water relations and potential adaptations.
    • Answer: Climate change impacts include increased temperatures (higher evaporative demand), altered precipitation (more frequent/intense droughts or floods), and elevated CO2. These can lead to increased water stress, reduced growth, and shifts in species distribution. Potential adaptations include: 1) Phenological shifts (earlier flowering). 2) Increased water use efficiency. 3) Deeper root systems. 4) Enhanced cavitation resistance. 5) Migration to more favorable habitats.
31. Describe the cavitation resistance mechanisms in different plant species.
    • Answer: Cavitation resistance varies among species and involves: 1) Narrower xylem conduits (tracheids or vessels) which are less prone to air seeding. 2) Specialized pit membranes with smaller pores that prevent air bubble spread. 3) Thicker cell walls providing structural support. 4) Efficient embolism repair mechanisms (e.g., root pressure refilling). 5) Shedding of embolized branches or leaves.
32. Explain the trade-offs between water transport efficiency and safety in xylem design.
    • Answer: Xylem design involves a fundamental trade-off: wider conduits (vessels) offer higher hydraulic efficiency (faster water flow) but are more vulnerable to cavitation under tension. Narrower conduits (tracheids) are safer (more resistant to cavitation) but less efficient. Plants adapt their xylem structure to balance these competing demands based on their habitat and water availability.
33. Describe the role of mycorrhizal associations in plant water uptake and drought tolerance.
    • Answer: Mycorrhizal fungi form symbiotic relationships with plant roots, extending the root system's effective surface area through their hyphae. This greatly enhances the plant's ability to absorb water and nutrients, especially in dry or nutrient-poor soils. Mycorrhizae can improve drought tolerance by increasing water uptake and potentially altering root hydraulic properties.
34. Explain the water relations in epiphytic plants and their specialized adaptations.
    • Answer: Epiphytic plants (e.g., orchids, bromeliads) grow on other plants, not in soil, and thus face unique water challenges. Adaptations include: 1) Specialized aerial roots (velamen) for rapid water absorption from rain/dew. 2) Water-storing tissues (succulence). 3) CAM photosynthesis. 4) Trichomes (hair-like structures) to capture atmospheric moisture. 5) Crassulacean acid metabolism (CAM) to minimize water loss.
35. Describe the phenomenon of hydraulic redistribution and its ecological implications.
    • Answer: Hydraulic redistribution (or hydraulic lift/descent) is the passive movement of water by plant roots from wetter to drier soil layers, or from deeper to shallower layers, through the plant's root system. This process can redistribute water within the soil profile, benefiting the same plant or neighboring plants, and influencing ecosystem water dynamics and nutrient cycling.
36. Explain the osmoregulation mechanisms in halophytic plants.
    • Answer: Halophytes (salt-tolerant plants) employ various osmoregulation mechanisms to cope with high salinity: 1) Salt exclusion: preventing salt uptake at the roots. 2) Salt excretion: secreting excess salt through salt glands on leaves. 3) Salt accumulation: compartmentalizing salts in vacuoles to avoid cytoplasmic toxicity. 4) Osmotic adjustment: synthesizing compatible solutes to maintain turgor. 5) Succulence: diluting salts by storing water.
37. Describe the developmental regulation of xylem differentiation and its hormonal control.
    • Answer: Xylem differentiation (xylogenesis) is a complex developmental process where undifferentiated cells become mature xylem elements. It is tightly regulated by plant hormones, particularly auxin (promotes xylem formation) and cytokinins (interact with auxin to regulate vascular patterning). Gibberellins and brassinosteroids also play roles in promoting cell elongation and lignification during xylem development.
38. Explain the genetic basis of drought tolerance and water use efficiency in crops.
    • Answer: Drought tolerance and water use efficiency (WUE) are complex traits with a genetic basis. Genes involved include those for: 1) Osmotic adjustment (e.g., proline synthesis). 2) Stress-protective proteins (e.g., chaperones). 3) Root development (e.g., deeper roots). 4) Stomatal regulation (e.g., ABA signaling). 5) Aquaporins. Biotechnological approaches aim to identify and manipulate these genes to develop more resilient crops.
39. Describe the physiological basis of irrigation scheduling in agriculture.
    • Answer: Irrigation scheduling is based on understanding plant water needs and soil water availability. Physiological indicators include: 1) Plant water potential (measured by pressure chamber). 2) Stomatal conductance. 3) Canopy temperature (indicating water stress). Soil moisture sensors and evapotranspiration models are also used to determine when and how much to irrigate, optimizing water use and crop yield.
40. Explain the water relations in succulent plants and their water storage strategies.
    • Answer: Succulent plants are adapted to arid environments by storing large amounts of water in specialized tissues (stems, leaves, or roots). Their water relations are characterized by: 1) High water storage capacity. 2) Thick cuticles and reduced stomata to minimize water loss. 3) CAM photosynthesis (opening stomata at night). These strategies allow them to survive prolonged dry periods by utilizing stored water.
41. Describe the comparative anatomy of wood in relation to climate and habitat.
    • Answer: Wood anatomy varies significantly with climate and habitat, reflecting adaptations for water transport and mechanical support. For example, ring-porous wood (large earlywood vessels) is common in temperate deciduous trees, allowing rapid water transport in spring. Diffuse-porous wood (uniformly distributed vessels) is found in tropical trees. Conifers (softwoods) with tracheids are well-suited to cold or dry environments due to their cavitation resistance.
42. Explain the acoustic and optical methods for detecting xylem dysfunction.
    • Answer: Xylem dysfunction (embolism) can be detected by: 1) Acoustic methods: using sensitive microphones to detect ultrasonic acoustic emissions (clicks) produced when air bubbles form during cavitation. 2) Optical methods: direct visualization of air bubbles in transparent xylem conduits using high-resolution microscopy or X-ray microtomography. These methods provide insights into the dynamics of embolism formation and repair.
43. Describe the cellular mechanisms of osmotic adjustment in drought-stressed plants.
    • Answer: Osmotic adjustment involves the active accumulation of solutes (e.g., proline, sugars, ions like K+) within the cytoplasm and vacuoles of plant cells in response to drought. This lowers the cell's osmotic potential, allowing it to maintain turgor and water uptake even when external water potential is low, thus improving drought tolerance.
44. Explain the water relations in parasitic plants and their host interactions.
    • Answer: Parasitic plants obtain water and nutrients from a host plant via specialized structures called haustoria. Their water relations are often dependent on the host; they may have reduced root systems and high transpiration rates, relying on the host's water supply. Some can induce changes in host water transport to their benefit.
45. Describe the hydrodynamics of water flow in plant vascular systems.
    • Answer: The hydrodynamics of water flow in plants is governed by Poiseuille's Law, which describes flow through narrow tubes. Water moves through the xylem (tracheids and vessels) driven by a pressure gradient (tension). Factors like conduit diameter (larger = faster flow), conduit length, and the resistance of pit membranes influence the overall hydraulic conductance of the vascular system.
46. Explain the coordination between water transport and carbon assimilation in plants.
    • Answer: Water transport and carbon assimilation (photosynthesis) are tightly coordinated. Stomata regulate both CO2 uptake and water loss. Under water stress, stomata close to conserve water, but this also reduces CO2 uptake, limiting photosynthesis. Plants balance these processes to optimize carbon gain while maintaining water status, often through complex signaling pathways involving hormones like ABA.
47. Describe the water relations in carnivorous plants and their specialized adaptations.
    • Answer: Carnivorous plants often grow in nutrient-poor, waterlogged soils. Their water relations are adapted to these conditions. They typically have shallow root systems and rely on their carnivorous traps to obtain nutrients. Some may have adaptations to tolerate anoxic conditions in their roots, while others (e.g., pitcher plants) collect rainwater in their traps.
48. Explain the biomechanics of water transport and its relationship to plant structure.
    • Answer: The biomechanics of water transport relates the physical properties of water (cohesion, adhesion) and xylem structure to the mechanical forces involved in water ascent. The lignified xylem walls provide structural integrity to withstand the high tensions generated during transpiration. The arrangement of xylem conduits and supporting tissues influences the plant's overall mechanical strength and resistance to collapse under water stress.
49. Describe the ecological water relations and plant community dynamics.
    • Answer: Ecological water relations influence plant community dynamics by determining species distribution, competition, and ecosystem productivity. Water availability is a key limiting factor. Different species have varying water use strategies (e.g., drought avoidance, drought tolerance), leading to niche partitioning and shaping community structure in response to water gradients and disturbances.
50. Explain the future prospects and challenges in plant water relations research.
    • Answer: Future prospects include: 1) Developing more drought-resilient crops using genetic engineering and breeding. 2) Understanding complex interactions between water, nutrients, and other stresses. 3) Utilizing advanced imaging and modeling techniques for real-time water transport studies. Challenges include: 1) Predicting plant responses to climate change. 2) Bridging knowledge gaps from cellular to ecosystem scales. 3) Translating research findings into practical agricultural solutions for water scarcity.