Module 8

1. Reactive Oxygen Species (ROS) cause oxidative stress under abiotic stress.
2. Antioxidant enzymes include SOD, CAT, and peroxidase.
3. Heat shock proteins (HSPs) protect cells from heat stress damage.
4. Chilling injury occurs due to membrane phase transition at low temperature.
5. Freezing injury results from ice crystal formation in cells.
6. Thermoperiodism refers to effect of day-night temperature difference.
7. Photosynthetic efficiency in crops rarely exceeds 5%.
8. Light compensation point: photosynthesis = respiration.
9. Light saturation point: photosynthesis no longer increases with light.
10. Photooxidation causes bleaching of chlorophyll at high light intensity.
11. Quantum requirement = number of photons needed to release one O₂ molecule (≈ 8).
12. Hill reaction demonstrates photolysis of water in light reaction.
13. Emerson effect proves existence of two photosystems (PSI & PSII).
14. Photosystem I absorbs light at 700 nm; Photosystem II at 680 nm.
15. Z-scheme represents electron flow in photosynthesis.
16. Cyclic photophosphorylation produces only ATP.
17. Non-cyclic photophosphorylation produces ATP + NADPH + O₂.
18. Carbon fixation in Calvin cycle involves carboxylation of RuBP.
19. Rubisco fixes CO₂ in first step of Calvin cycle.
20. Photorespiration site: chloroplast → peroxisome → mitochondria.
21. Kranz anatomy features concentric arrangement of bundle sheath and mesophyll cells.
22. C4 plants: maize, sorghum, sugarcane, pearl millet.
23. CAM plants: pineapple, agave, opuntia.
24. C3 plants: wheat, rice, barley, soybean.
25. PEP carboxylase has higher CO₂ affinity than Rubisco.
26. Sucrose is main translocatory carbohydrate in most crops.
27. Starch is temporary storage form of carbohydrates in chloroplasts.
28. Source–sink balance affects grain filling and final yield.
29. Remobilization of stored carbohydrates occurs during grain filling.
30. Sink limitation often restricts yield in cereals.
31. Stay-green trait improves photosynthetic duration and yield stability.
32. Leaf Area Duration (LAD) = (LA₁ + LA₂)/2 × (t₂ – t₁).
33. Growth analysis helps understand physiological basis of yield.
34. Yield is the final manifestation of physiological efficiency × duration.
35. Biological yield = total dry matter produced.
36. Economic yield = usable part of biological yield.
37. Harvest Index (HI) indicates conversion efficiency of total biomass to economic yield.
38. HI improvement through partitioning of assimilates to reproductive organs.
39. Seed dormancy ensures germination only under favorable conditions.
40. Primary dormancy is innate; secondary dormancy is induced by environment.
41. Breaking dormancy by scarification, stratification, or chemicals.
42. After-ripening removes dormancy in cereals.
43. Photoblastic seeds require light for germination (e.g., lettuce).
44. Phytochrome mediates light-induced germination.
45. Germination involves imbibition → enzyme activation → radicle emergence.
46. Seedling establishment depends on reserve mobilization.
47. Enzyme α-amylase mobilizes starch in germinating seeds.
48. GA₃ promotes α-amylase synthesis in cereal endosperm.
49. ABA inhibits seed germination and promotes dormancy.
50. Senescence types: whole plant, organ, and induced.
51. Programmed cell death (PCD) occurs during senescence.
52. Leaf abscission is triggered by ethylene and ABA.
53. Hydrotropism – root growth response to water gradient.
54. Thigmotropism – growth response to touch (e.g., tendrils).
55. Nastic movements – non-directional movements (e.g., leaf folding in Mimosa).
56. Nyctinasty – sleep movement of leaves at night.
57. Turgor movement – driven by osmotic changes in motor cells.
58. Circadian rhythm – 24-hour physiological cycles regulated by internal clocks.
59. Plant hormones act synergistically or antagonistically to regulate growth.
60. Yield potential is maximum yield under ideal growth conditions.
61. Respiration rate increases with temperature up to an optimum limit.
62. Anaerobic respiration produces ethanol and CO₂ in plants.
63. Pasteur effect is inhibition of glycolysis by oxygen.
64. ATP yield per glucose molecule = 36 ATP (aerobic).
65. Glycolysis converts glucose into pyruvate producing 2 ATP.
66. Link reaction converts pyruvate to acetyl-CoA.
67. Krebs cycle yields 2 ATP, 6 NADH, and 2 FADH₂ per glucose.
68. ETC produces maximum ATP through oxidative phosphorylation.
69. Cytochromes act as electron carriers in ETC.
70. Mitochondria are called the powerhouses of the cell.
71. Pentose phosphate pathway provides NADPH and pentose sugars.
72. Respiratory quotient helps identify substrate being respired.
73. Nitrate reduction requires enzyme nitrate reductase.
74. Nitrite reduction occurs in chloroplasts via nitrite reductase.
75. Biological nitrogen fixation is carried out by Rhizobium, Azotobacter, etc.
76. Nitrogenase enzyme catalyzes N₂ → NH₃ reduction.
77. Leghaemoglobin regulates O₂ in root nodules for nitrogenase activity.
78. Phytochelatins detoxify heavy metals in plants.