Final Question Paper: Sexual Reproduction in Flowering Plants

Section A: Multiple Choice Questions (1 Mark Each)

1. Which of the following is the outermost whorl of a flower? a) Corolla b) Calyx c) Androecium d) Gynoecium

2. The male reproductive whorl of a flower is called: a) Calyx b) Corolla c) Androecium d) Gynoecium

3. How many microsporangia are typically present per anther lobe? a) 2 b) 3 c) 4 d) 5

4. The innermost nutritive layer of microsporangium is: a) Epidermis b) Endothecium c) Middle layers d) Tapetum

5. Sporopollenin is found in: a) Intine b) Exine c) Cytoplasm d) Nucleus

6. In most angiosperms, pollen grains are shed at which stage? a) 1-celled b) 2-celled c) 3-celled d) 4-celled

7. The most common type of ovule is: a) Orthotropous b) Anatropous c) Campylotropous d) Amphitropous

8. The small opening at the apex of integuments is called: a) Hilum b) Micropyle c) Chalaza d) Raphe

9. In Polygonum type of embryo sac development, how many megaspores degenerate? a) 1 b) 2 c) 3 d) 4

10. The typical mature embryo sac is: a) 6-celled, 7-nucleate b) 7-celled, 8-nucleate c) 8-celled, 7-nucleate d) 7-celled, 7-nucleate

11. The filiform apparatus is found in: a) Egg cell b) Synergids c) Antipodals d) Central cell

12. Self-pollination within the same flower is called: a) Geitonogamy b) Xenogamy c) Autogamy d) Allogamy

13. Cleistogamous flowers are characterized by: a) Large size b) Bright colors c) Never opening d) Strong fragrance

14. Wind pollination is called: a) Entomophily b) Anemophily c) Hydrophily d) Zoophily

15. In protandry, which part matures first? a) Stigma b) Anthers c) Petals d) Sepals

16. Self-incompatibility is a: a) Physical barrier b) Genetic mechanism c) Ecological factor d) Morphological feature

17. The process of removing anthers is called: a) Bagging b) Emasculation c) Rebagging d) Hybridization

18. In double fertilization, the male gamete fuses with polar nuclei to form: a) Zygote b) Embryo c) Primary endosperm nucleus d) Secondary nucleus

19. The nutritive tissue formed after triple fusion is: a) Embryo b) Endosperm c) Seed coat d) Cotyledon

20. Nuclear endosperm is characterized by: a) Immediate cell wall formation b) Free nuclear divisions c) No nuclear division d) Single nucleus

21. The embryonal axis of dicot embryo consists of: a) Only plumule b) Only radicle c) Plumule and radicle d) Only cotyledons

22. In monocot embryo, the single cotyledon is called: a) Plumule b) Radicle c) Scutellum d) Coleoptile

23. The protective sheath enclosing the plumule is: a) Coleoptile b) Coleorhiza c) Scutellum d) Testa

24. Seeds that retain endosperm are called: a) Non-albuminous b) Albuminous c) Ex-albuminous d) Endospermic

25. False fruits develop from: a) Ovary only b) Ovary and other floral parts c) Receptacle only d) Petals only

26. Apomixis is a form of: a) Sexual reproduction b) Asexual reproduction c) Vegetative reproduction d) Fragmentation

27. Parthenocarpic fruits are: a) Seeded b) Seedless c) Multiple seeded d) Hard

28. Polyembryony means: a) Multiple flowers b) Multiple fruits c) Multiple embryos in one seed d) Multiple seeds

29. Anemochory refers to dispersal by: a) Water b) Wind c) Animals d) Explosion

30. Endozoochory involves: a) External attachment b) Consumption and defecation c) Wind dispersal d) Water dispersal

31. The stalk of the flower is called: a) Pedicel b) Peduncle c) Petiole d) Rachis

32. The swollen tip of pedicel is: a) Receptacle b) Thalamus c) Both a and b d) Neither a nor b

33. Petals are collectively called: a) Calyx b) Corolla c) Perianth d) Androecium

34. Each stamen consists of: a) Anther only b) Filament only c) Anther and filament d) Anther, filament, and style

35. The pollen-producing part of stamen is: a) Filament b) Anther c) Style d) Stigma

36. The female reproductive part of flower is: a) Androecium b) Gynoecium c) Corolla d) Calyx

37. The receptive tip for pollen grains is: a) Ovary b) Style c) Stigma d) Ovule

38. The elongated tube connecting ovary to stigma is: a) Style b) Filament c) Pedicel d) Funicle

39. Microsporogenesis occurs in: a) Ovary b) Anther c) Style d) Stigma

40. Microspore mother cells are: a) Haploid b) Diploid c) Triploid d) Tetraploid

41. Each microspore mother cell produces: a) 2 microspores b) 3 microspores c) 4 microspores d) 5 microspores

42. The vegetative cell in pollen grain is responsible for: a) Forming male gametes b) Forming pollen tube c) Fertilization d) Forming embryo

43. The generative cell divides to form: a) Vegetative cells b) Pollen tubes c) Male gametes d) Female gametes

44. Germ pores are present in: a) Intine b) Exine c) Cytoplasm d) Nucleus

45. The funicle attaches ovule to: a) Style b) Stigma c) Placenta d) Ovary wall

46. The point of attachment of funicle to ovule is: a) Micropyle b) Hilum c) Chalaza d) Raphe

47. The ridge formed by fusion of funicle with ovule body is: a) Hilum b) Micropyle c) Raphe d) Chalaza

48. The basal part of ovule opposite to micropyle is: a) Hilum b) Chalaza c) Raphe d) Funicle

49. Megasporogenesis occurs in: a) Anther b) Ovule c) Style d) Stigma

50. In most flowering plants, how many megaspores remain functional? a) 1 b) 2 c) 3 d) 4

51. The functional megaspore is usually: a) Micropylar b) Chalazal c) Middle d) Any one

52. The embryo sac undergoes how many free nuclear divisions? a) 2 b) 3 c) 4 d) 5

53. The egg apparatus consists of: a) Egg cell only b) Synergids only c) Egg cell and synergids d) Egg cell and antipodals

54. Antipodal cells are located at: a) Micropylar end b) Chalazal end c) Center d) Sides

55. The central cell contains: a) One nucleus b) Two nuclei c) Three nuclei d) Four nuclei

56. Cross-pollination between different plants is: a) Autogamy b) Geitonogamy c) Xenogamy d) Cleistogamy

57. Flowers that always remain closed are: a) Chasmogamous b) Cleistogamous c) Dichogamous d) Homogamous

58. Hydrophily is found in about how many genera? a) 20 b) 30 c) 40 d) 50

59. Sticky pollen is an adaptation for: a) Wind pollination b) Water pollination c) Insect pollination d) Self-pollination

60. Bird pollination is called: a) Entomophily b) Ornithophily c) Chiropterophily d) Anemophily

61. Bat pollination is called: a) Entomophily b) Ornithophily c) Chiropterophily d) Zoophily

62. When stigma matures before anthers, it is: a) Protandry b) Protogyny c) Homogamy d) Dichogamy

63. Different lengths of styles and stamens is called: a) Dichogamy b) Herkogamy c) Heterostyly d) Self-incompatibility

64. Plants with male and female flowers on same plant are: a) Monoecious b) Dioecious c) Hermaphrodite d) Unisexual

65. Plants with male and female flowers on different plants are: a) Monoecious b) Dioecious c) Hermaphrodite d) Bisexual

66. Pollen tube usually enters ovule through: a) Chalaza b) Integuments c) Micropyle d) Hilum

67. Entry of pollen tube through chalaza is: a) Porogamy b) Chalazogamy c) Mesogamy d) Acrogamy

68. The pollen tube typically enters which synergid? a) Left synergid b) Right synergid c) Either synergid d) Both synergids

69. In artificial hybridization, bagging is done to: a) Prevent self-pollination b) Prevent contamination c) Collect pollen d) Induce pollination

70. Emasculation is not required in: a) Bisexual flowers b) Male flowers c) Female flowers d) Hermaphrodite flowers

71. The fusion of male gamete with egg is called: a) Triple fusion b) Syngamy c) Double fertilization d) Plasmogamy

72. The fusion involving polar nuclei is called: a) Syngamy b) Triple fusion c) Double fertilization d) Karyogamy

73. The primary endosperm nucleus is: a) Haploid b) Diploid c) Triploid d) Tetraploid

74. Double fertilization is characteristic of: a) Gymnosperms b) Angiosperms c) Pteridophytes d) Bryophytes

75. After fertilization, ovary develops into: a) Seed b) Fruit c) Embryo d) Endosperm

76. After fertilization, ovule develops into: a) Fruit b) Seed c) Embryo d) Endosperm

77. Coconut water is an example of: a) Cellular endosperm b) Nuclear endosperm c) Helobial endosperm d) No endosperm

78. The white kernel of coconut is: a) Nuclear endosperm b) Cellular endosperm c) Embryo d) Seed coat

79. Helobial endosperm is common in: a) Dicots b) Monocots c) Gymnosperms d) Pteridophytes

80. The suspensor in dicot embryo development: a) Forms the embryo b) Provides nourishment c) Protects the embryo d) Both b and c

81. The hypophysis is the: a) First cell of suspensor b) Last cell of suspensor c) Embryonal cell d) Endosperm cell

82. The portion below cotyledons is: a) Epicotyl b) Hypocotyl c) Plumule d) Radicle

83. The portion above cotyledons is: a) Epicotyl b) Hypocotyl c) Plumule d) Radicle

84. Coleorhiza encloses: a) Plumule b) Radicle c) Scutellum d) Coleoptile

85. The seed coat develops from: a) Nucellus b) Integuments c) Endosperm d) Embryo

86. The outer seed coat is called: a) Testa b) Tegmen c) Hilum d) Micropyle

87. The inner seed coat is called: a) Testa b) Tegmen c) Hilum d) Micropyle

88. Apple is an example of: a) True fruit b) False fruit c) Aggregate fruit d) Multiple fruit

89. Wheat seeds are: a) Albuminous b) Non-albuminous c) Ex-albuminous d) Endospermic

90. Pea seeds are: a) Albuminous b) Non-albuminous c) Endospermic d) Both a and c

91. In non-albuminous seeds, food is stored in: a) Endosperm b) Cotyledons c) Embryo d) Seed coat

92. Recurrent apomixis produces: a) Haploid embryo b) Diploid embryo c) Triploid embryo d) Tetraploid embryo

93. Banana is an example of: a) Apomixis b) Parthenocarpy c) Polyembryony d) Vivipary

94. Citrus shows: a) Apomixis b) Parthenocarpy c) Polyembryony d) Both a and c

95. Seeds with wings are adapted for: a) Water dispersal b) Wind dispersal c) Animal dispersal d) Self-dispersal

96. Coconut is dispersed by: a) Wind b) Water c) Animals d) Explosion

97. Xanthium shows: a) Anemochory b) Hydrochory c) Epizoochory d) Endozoochory

98. Explosive fruits show: a) Anemochory b) Hydrochory c) Zoochory d) Autochory

99. The primary function of fruit is: a) Nutrition b) Protection c) Seed dispersal d) Attraction

100. Genetic diversity is promoted by: a) Self-pollination b) Cross-pollination c) Cleistogamy d) Autogamy

Section B: Short Answer Questions (1 mark each)

1. Define a flower.
2. What are sepals?
3. What is the function of petals?
4. Name the male reproductive whorl of a flower.
5. What is a stamen?
6. Define gynoecium.
7. What are the three parts of a carpel?
8. What is pedicel?
9. What is thalamus?
10. How many microsporangia are present in a typical anther?
11. What is tapetum?
12. Define microsporogenesis.
13. What is a pollen mother cell?
14. What is sporopollenin?
15. What are germ pores?
16. What is intine?
17. What is the function of vegetative cell in pollen grain?
18. What is generative cell?
19. Define anatropous ovule.
20. What is funicle?
21. What is hilum?
22. What is micropyle?
23. What is chalaza?
24. What is nucellus?
25. Define megasporogenesis.
26. What is megaspore mother cell?
27. How many megaspores are formed from one MMC?
28. What is embryo sac?
29. What is egg apparatus?
30. What are synergids?
31. What is filiform apparatus?
32. What are antipodal cells?
33. What is central cell?
34. Define pollination.
35. What is autogamy?
36. What are cleistogamous flowers?
37. What is geitonogamy?
38. What is xenogamy?
39. What is anemophily?
40. What is hydrophily?
41. What is entomophily?
42. What is ornithophily?
43. What is chiropterophily?
44. What is dichogamy?
45. What is protandry?
46. What is protogyny?
47. What is herkogamy?
48. What is heterostyly?
49. What is self-incompatibility?
50. What are monoecious plants?
51. What are dioecious plants?
52. What is emasculation?
53. What is bagging?
54. What is artificial hybridization?
55. Define double fertilization.
56. What is syngamy?
57. What is triple fusion?
58. What is primary endosperm nucleus?
59. What is endosperm?
60. What is nuclear endosperm?
61. What is cellular endosperm?
62. What is helobial endosperm?
63. What is embryogeny?
64. What is suspensor?
65. What is hypophysis?
66. What is plumule?
67. What is radicle?
68. What is hypocotyl?
69. What is epicotyl?
70. What is scutellum?
71. What is coleoptile?
72. What is coleorhiza?
73. What is seed coat?
74. What is testa?
75. What is tegmen?
76. What is true fruit?
77. What is false fruit?
78. What are albuminous seeds?
79. What are non-albuminous seeds?
80. What is apomixis?
81. What is parthenocarpy?
82. What is polyembryony?
83. What is anemochory?
84. What is hydrochory?
85. What is zoochory?
86. What is epizoochory?
87. What is endozoochory?
88. What is autochory?
89. What is porogamy?
90. What is chalazogamy?
91. What is mesogamy?
92. What is recurrent apomixis?
93. What is non-recurrent apomixis?
94. What is parthenogenesis?
95. Name the wall layers of microsporangium.
96. What is sporogenous tissue?
97. What is exine made of?
98. What is raphe?
99. What is integument?
100. What is the function of endosperm?

Section C: Short Answer Questions (2 marks each)

1. Describe the structure of a typical flower.
2. Explain the parts of a stamen.
3. Describe the structure of gynoecium.
4. Explain the wall layers of microsporangium.
5. Describe the process of microsporogenesis.
6. Explain the structure of a pollen grain.
7. Describe pollen grain development.
8. Explain the structure of anatropous ovule.
9. Describe the process of megasporogenesis.
10. Explain the development of embryo sac.
11. Describe the organization of mature embryo sac.
12. Explain the types of pollination.
13. Describe cleistogamous and chasmogamous flowers.
14. Explain wind pollination and its adaptations.
15. Describe water pollination and its adaptations.
16. Explain insect pollination and its adaptations.
17. Describe animal pollination and its adaptations.
18. Explain dichogamy and its types.
19. Describe herkogamy and heterostyly.
20. Explain self-incompatibility.
21. Describe unisexuality in plants.
22. Explain the process of pollen-pistil interaction.
23. Describe the steps of artificial hybridization.
24. Explain double fertilization.
25. Describe the significance of double fertilization.
26. Explain the types of endosperm development.
27. Describe dicot embryo development.
28. Explain monocot embryo development.
29. Describe the structure of dicot embryo.
30. Explain the structure of monocot embryo.
31. Describe seed formation and its parts.
32. Explain the difference between true and false fruits.
33. Describe albuminous and non-albuminous seeds.
34. Explain apomixis and its types.
35. Describe parthenocarpy and its significance.
36. Explain polyembryony and its causes.
37. Describe the significance of seed dispersal.
38. Explain the agents of seed dispersal.
39. Describe wind dispersal adaptations.
40. Explain water dispersal adaptations.
41. Describe animal dispersal and its types.
42. Explain the role of tapetum in pollen development.
43. Describe the function of filiform apparatus.
44. Explain the role of antipodal cells.
45. Describe the formation of polar nuclei.
46. Explain the difference between microspore and pollen grain.
47. Describe the role of suspensor in embryo development.
48. Explain the significance of endosperm.
49. Describe the formation of seed coat.
50. Explain the difference between testa and tegmen.
51. Describe the structure of grass embryo.
52. Explain the function of cotyledons.
53. Describe nuclear endosperm formation.
54. Explain cellular endosperm formation.
55. Describe helobial endosperm formation.
56. Explain the role of integuments in ovule.
57. Describe the formation of raphe.
58. Explain the significance of micropyle.
59. Describe the function of chalaza.
60. Explain the role of nucellus in ovule.
61. Describe the formation of male gametes.
62. Explain the entry of pollen tube into ovule.
63. Describe the release of male gametes.
64. Explain the formation of zygote.
65. Describe the formation of primary endosperm nucleus.
66. Explain post-fertilization changes in flower.
67. Describe the development of fruit from ovary.
68. Explain the development of seed from ovule.
69. Describe the advantages of cross-pollination.
70. Explain the disadvantages of self-pollination.
71. Describe the adaptations for wind pollination.
72. Explain the adaptations for insect pollination.
73. Describe the mechanism of self-incompatibility.
74. Explain the genetic basis of self-incompatibility.
75. Describe the process of emasculation.
76. Explain the technique of bagging.
77. Describe the importance of artificial hybridization.
78. Explain the commercial importance of parthenocarpy.
79. Describe the significance of polyembryony in Citrus.
80. Explain the role of apomixis in plant breeding.
81. Describe the mechanism of explosive fruit dispersal.
82. Explain the adaptations for animal dispersal.
83. Describe the structure of winged seeds.
84. Explain the floatation mechanism in coconut.
85. Describe the hook mechanism in Xanthium.
86. Explain the fleshy fruit adaptations.
87. Describe the formation of accessory fruits.
88. Explain the nutritive role of endosperm.
89. Describe the protective role of seed coat.
90. Explain the germination process in seeds.
91. Describe the role of micropyle in germination.
92. Explain the function of hilum in seeds.
93. Describe the development of plumule.
94. Explain the development of radicle.
95. Describe the role of scutellum in monocots.
96. Explain the function of coleoptile.
97. Describe the function of coleorhiza.
98. Explain the difference between epicotyl and hypocotyl.
99. Describe the formation of cotyledons.
100. Explain the significance of sexual reproduction in plants.

Section D: Long Answer Questions (3 marks each)

1. Describe the complete structure of a flower with labeled diagram.
2. Explain the structure and function of microsporangium.
3. Describe the process of microsporogenesis with diagram.
4. Explain the development of male gametophyte from microspore.
5. Describe the structure of anatropous ovule with labeled diagram.
6. Explain the process of megasporogenesis in detail.
7. Describe the development of female gametophyte (embryo sac).
8. Explain the organization and functions of mature embryo sac.
9. Describe the different types of pollination with examples.
10. Explain the various agents of pollination and their adaptations.
11. Describe the outbreeding devices in flowering plants.
12. Explain the mechanism of self-incompatibility in plants.
13. Describe the process of artificial hybridization in detail.
14. Explain the complete process of double fertilization.
15. Describe the significance and advantages of double fertilization.
16. Explain the different types of endosperm development.
17. Describe the process of embryo development in dicots.
18. Explain the process of embryo development in monocots.
19. Describe the structure of mature dicot and monocot embryos.
20. Explain the post-fertilization changes in flowering plants.
21. Describe the formation of seed and its structure.
22. Explain the difference between true and false fruits with examples.
23. Describe the difference between albuminous and non-albuminous seeds.
24. Explain apomixis, its types, and significance.
25. Describe parthenocarpy and its commercial importance.
26. Explain polyembryony, its causes, and significance.
27. Describe the importance of seed and fruit dispersal.
28. Explain the various methods of seed dispersal with examples.
29. Describe the adaptations for wind dispersal in plants.
30. Explain the adaptations for water dispersal in plants.
31. Describe the adaptations for animal dispersal in plants.
32. Explain the role of insects in pollination with adaptations.
33. Describe the adaptations of flowers for bird pollination.
34. Explain the adaptations of flowers for bat pollination.
35. Describe the mechanism of pollen-pistil interaction.
36. Explain the process of pollen germination and tube growth.
37. Describe the entry of pollen tube into ovule and embryo sac.
38. Explain the release of male gametes and fertilization.
39. Describe the formation and significance of suspensor.
40. Explain the role of endosperm in seed development.
41. Describe the formation of seed coat and its layers.
42. Explain the structure and function of cotyledons.
43. Describe the specialized structures in monocot embryo.
44. Explain the protective structures in grass embryo.
45. Describe the nutritive tissues in seeds.
46. Explain the mechanism of seed germination.
47. Describe the factors affecting pollination efficiency.
48. Explain the evolutionary significance of flower structure.
49. Describe the relationship between flower structure and pollination.
50. Explain the genetic control of flower development.
51. Describe the hormonal regulation of fruit development.
52. Explain the environmental factors affecting reproduction.
53. Describe the ecological importance of flowering plants.
54. Explain the economic importance of sexual reproduction.
55. Describe the role of sexual reproduction in evolution.
56. Explain the advantages of sexual reproduction over asexual reproduction.
57. Describe the molecular mechanisms of fertilization.
58. Explain the biochemical changes during pollen tube growth.
59. Describe the cellular changes during embryo development.
60. Explain the metabolic changes during seed development.
61. Describe the physiological changes during fruit ripening.
62. Explain the molecular basis of self-incompatibility.
63. Describe the genetic mechanisms of apomixis.
64. Explain the hormonal control of parthenocarpy.
65. Describe the cytological basis of polyembryony.
66. Explain the adaptive significance of different fruit types.
67. Describe the coevolution of flowers and pollinators.
68. Explain the role of sexual reproduction in plant breeding.
69. Describe the biotechnological applications of reproduction.
70. Explain the conservation aspects of plant reproduction.
71. Describe the tissue culture techniques in plant reproduction.
72. Explain the molecular markers in plant breeding.
73. Describe the genetic engineering approaches in reproduction.
74. Explain the cryopreservation of pollen and seeds.
75. Describe the in vitro fertilization techniques in plants.
76. Explain the somatic hybridization techniques.
77. Describe the protoplast fusion in plant breeding.
78. Explain the chromosome engineering in plants.
79. Describe the polyploidy induction techniques.
80. Explain the mutation breeding in plants.
81. Describe the hybrid vigor and its utilization.
82. Explain the heterosis and its commercial exploitation.
83. Describe the incompatibility systems in crop plants.
84. Explain the male sterility and its applications.
85. Describe the seed production technology.
86. Explain the quality control in seed production.
87. Describe the seed testing and certification.
88. Explain the seed storage and viability.
89. Describe the seed dormancy and its breaking.
90. Explain the germination requirements of seeds.
91. Describe the seedling establishment and growth.
92. Explain the transplantation techniques.
93. Describe the nursery management practices.
94. Explain the propagation techniques in horticulture.
95. Describe the grafting and budding techniques.
96. Explain the layering and cutting techniques.
97. Describe the micropropagation techniques.
98. Explain the organogenesis and embryogenesis.
99. Describe the somaclonal variation and its uses.
100. Explain the future prospects of plant reproduction research.

Answer Key

Section A: Multiple Choice Questions

1. b) Calyx
2. c) Androecium
3. c) 4
4. d) Tapetum
5. b) Exine
6. b) 2-celled
7. b) Anatropous
8. b) Micropyle
9. c) 3
10. b) 7-celled, 8-nucleate
11. b) Synergids
12. c) Autogamy
13. c) Never opening
14. b) Anemophily
15. b) Anthers
16. b) Genetic mechanism
17. b) Emasculation
18. c) Primary endosperm nucleus
19. b) Endosperm
20. b) Free nuclear divisions
21. c) Plumule and radicle
22. c) Scutellum
23. a) Coleoptile
24. b) Albuminous
25. b) Ovary and other floral parts
26. b) Asexual reproduction
27. b) Seedless
28. c) Multiple embryos in one seed
29. b) Wind
30. b) Consumption and defecation
31. a) Pedicel
32. c) Both a and b
33. b) Corolla
34. c) Anther and filament
35. b) Anther
36. b) Gynoecium
37. c) Stigma
38. a) Style
39. b) Anther
40. b) Diploid
41. c) 4 microspores
42. b) Forming pollen tube
43. c) Male gametes
44. b) Exine
45. c) Placenta
46. b) Hilum
47. c) Raphe
48. b) Chalaza
49. b) Ovule
50. a) 1
51. b) Chalazal
52. b) 3
53. c) Egg cell and synergids
54. b) Chalazal end
55. b) Two nuclei
56. c) Xenogamy
57. b) Cleistogamous
58. b) 30
59. c) Insect pollination
60. b) Ornithophily
61. c) Chiropterophily
62. b) Protogyny
63. c) Heterostyly
64. a) Monoecious
65. b) Dioecious
66. c) Micropyle
67. b) Chalazogamy
68. c) Either synergid
69. b) Prevent contamination
70. c) Female flowers
71. b) Syngamy
72. b) Triple fusion
73. c) Triploid
74. b) Angiosperms
75. b) Fruit
76. b) Seed
77. b) Nuclear endosperm
78. b) Cellular endosperm
79. b) Monocots
80. b) Provides nourishment
81. b) Last cell of suspensor
82. b) Hypocotyl
83. a) Epicotyl
84. b) Radicle
85. b) Integuments
86. a) Testa
87. b) Tegmen
88. b) False fruit
89. a) Albuminous
90. b) Non-albuminous
91. b) Cotyledons
92. b) Diploid embryo
93. b) Parthenocarpy
94. d) Both a and c
95. b) Wind dispersal
96. b) Water
97. c) Epizoochory
98. d) Autochory
99. c) Seed dispersal
100. b) Cross-pollination

Section B: 1 Mark Short Answer Questions

1. A flower is a modified, condensed shoot of a plant, specialized for sexual reproduction.
2. Sepals are the green, leaf-like structures that form the outermost whorl (calyx) and protect the flower in its bud stage.
3. Petals are often brightly colored to attract pollinators.
4. The male reproductive whorl is the Androecium.
5. A stamen is the male reproductive organ of a flower, consisting of an anther and a filament.
6. Gynoecium is the female reproductive part of a flower, consisting of one or more carpels.
7. A carpel consists of the stigma, style, and ovary.
8. The pedicel is the stalk that supports a single flower.
9. The thalamus (or receptacle) is the swollen tip of the pedicel where the floral whorls are attached.
10. A typical anther is bilobed, with each lobe containing two microsporangia (pollen sacs), for a total of four.
11. The tapetum is the innermost nutritive layer of the microsporangium wall.
12. Microsporogenesis is the process of formation of haploid microspores from a diploid microspore mother cell through meiosis.
13. A pollen mother cell (PMC) or microspore mother cell is the diploid cell in the microsporangium that undergoes meiosis to form four haploid microspores.
14. Sporopollenin is a highly resistant organic polymer that forms the exine (outer wall) of a pollen grain.
15. Germ pores are thin areas or apertures in the exine of a pollen grain where the intine can emerge to form a pollen tube.
16. The intine is the thin, inner wall of a pollen grain, made of cellulose and pectin.
17. The vegetative cell (or tube cell) provides nourishment and forms the pollen tube upon germination.
18. The generative cell is the smaller cell within the pollen grain that divides mitotically to form two male gametes.
19. An anatropous ovule is one that is inverted, with the micropyle facing the placenta. It is the most common type of ovule.
20. The funicle is the stalk that attaches the ovule to the placenta in the ovary.
21. The hilum is the point on the ovule where the funicle attaches.
22. The micropyle is a small opening in the integuments of the ovule through which the pollen tube typically enters.
23. The chalaza is the basal part of the ovule, opposite the micropyle, where the integuments and nucellus originate.
24. The nucellus is the mass of parenchymatous tissue within the ovule that encloses the embryo sac.
25. Megasporogenesis is the process of formation of haploid megaspores from a diploid megaspore mother cell through meiosis.
26. The megaspore mother cell (MMC) is the diploid cell in the nucellus that undergoes meiosis to form four haploid megaspores.
27. Four haploid megaspores are formed from one MMC.
28. The embryo sac is the female gametophyte of a flowering plant, which contains the egg cell.
29. The egg apparatus, located at the micropylar end of the embryo sac, consists of one egg cell and two synergids.
30. Synergids are two cells that flank the egg cell and help guide the pollen tube.
31. The filiform apparatus is a finger-like projection in the synergids that guides the pollen tube's entry.
32. Antipodal cells are three cells located at the chalazal end of the embryo sac, with a nutritive function.
33. The central cell is the large, central cell of the embryo sac containing two polar nuclei.
34. Pollination is the transfer of pollen grains from the anther to the stigma of a flower.
35. Autogamy is self-pollination within the same flower.
36. Cleistogamous flowers are those that never open, ensuring self-pollination.
37. Geitonogamy is the transfer of pollen from the anther of one flower to the stigma of another flower on the same plant.
38. Xenogamy is cross-pollination between flowers of two different plants.
39. Anemophily is pollination by wind.
40. Hydrophily is pollination by water.
41. Entomophily is pollination by insects.
42. Ornithophily is pollination by birds.
43. Chiropterophily is pollination by bats.
44. Dichogamy is a condition where the anthers and stigma of a flower mature at different times to prevent self-pollination.
45. Protandry is a type of dichogamy where the anthers mature before the stigma.
46. Protogyny is a type of dichogamy where the stigma matures before the anthers.
47. Herkogamy is a physical barrier between the anther and stigma of a flower to prevent self-pollination.
48. Heterostyly is the presence of different lengths of styles and stamens in flowers of the same species to promote cross-pollination.
49. Self-incompatibility is a genetic mechanism that prevents self-pollen from fertilizing the ovules.
50. Monoecious plants have both male and female flowers on the same individual plant.
51. Dioecious plants have male and female flowers on separate individual plants.
52. Emasculation is the removal of anthers from a bisexual flower before they mature to prevent self-pollination in artificial hybridization.
53. Bagging is the covering of an emasculated flower with a bag to prevent contamination from foreign pollen.
54. Artificial hybridization is the process of cross-pollinating two different varieties or species to create a hybrid.
55. Double fertilization is a unique process in angiosperms involving two fusion events: syngamy and triple fusion.
56. Syngamy is the fusion of one male gamete with the egg cell to form the diploid zygote.
57. Triple fusion is the fusion of the second male gamete with the two polar nuclei to form the triploid primary endosperm nucleus.
58. The primary endosperm nucleus (PEN) is the triploid nucleus formed by triple fusion, which develops into the endosperm.
59. The endosperm is the nutritive tissue that provides food for the developing embryo.
60. Nuclear endosperm is a type of endosperm where the primary endosperm nucleus undergoes free nuclear divisions without immediate cell wall formation.
61. Cellular endosperm is a type of endosperm where cell walls are formed immediately after each nuclear division.
62. Helobial endosperm is an intermediate type of endosperm development found in some monocots.
63. Embryogeny is the process of development of an embryo from a zygote.
64. The suspensor is a structure in the developing embryo that pushes the embryo proper into the endosperm.
65. The hypophysis is the last cell of the suspensor which forms the radicle tip.
66. The plumule is the embryonic shoot, which develops into the future shoot system.
67. The radicle is the embryonic root, which develops into the future root system.
68. The hypocotyl is the part of the embryonal axis below the cotyledons.
69. The epicotyl is the part of the embryonal axis above the cotyledons.
70. The scutellum is the large, shield-shaped single cotyledon of a monocot embryo.
71. The coleoptile is a protective sheath covering the plumule in a monocot embryo.
72. The coleorhiza is a protective sheath covering the radicle in a monocot embryo.
73. The seed coat is the protective outer layer of a seed, developed from the integuments of the ovule.
74. The testa is the outer layer of the seed coat.
75. The tegmen is the inner layer of the seed coat.
76. A true fruit develops solely from the ovary of a flower.
77. A false fruit (pseudocarp) develops from the ovary along with other floral parts like the thalamus.
78. Albuminous (or endospermic) seeds are those that retain endosperm at maturity.
79. Non-albuminous (or exalbuminous) seeds are those where the endosperm is completely consumed by the embryo, and food is stored in the cotyledons.
80. Apomixis is a form of asexual reproduction that mimics sexual reproduction, producing seeds without fertilization.
81. Parthenocarpy is the development of fruit without fertilization, resulting in seedless fruits.
82. Polyembryony is the occurrence of more than one embryo in a single seed.
83. Anemochory is seed dispersal by wind.
84. Hydrochory is seed dispersal by water.
85. Zoochory is seed dispersal by animals.
86. Epizoochory is seed dispersal where seeds attach to the exterior of an animal.
87. Endozoochory is seed dispersal where seeds are consumed and passed through an animal's digestive tract.
88. Autochory is self-dispersal of seeds, often by an explosive mechanism.
89. Porogamy is the entry of the pollen tube into the ovule through the micropyle.
90. Chalazogamy is the entry of the pollen tube into the ovule through the chalaza.
91. Mesogamy is the entry of the pollen tube into the ovule through the integuments.
92. Recurrent apomixis is a type of apomixis where the embryo develops from a diploid cell, resulting in a diploid embryo.
93. Non-recurrent apomixis is a type of apomixis where the embryo develops from a haploid cell, resulting in a haploid embryo.
94. Parthenogenesis is the development of an embryo from an unfertilized egg.
95. The wall layers are Epidermis, Endothecium, Middle layers, and Tapetum.
96. Sporogenous tissue is the diploid tissue in the center of a young microsporangium that develops into microspore mother cells.
97. The exine is made of sporopollenin.
98. The raphe is a ridge on the ovule formed by the fusion of the funicle with the body of the ovule.
99. An integument is the outer protective layer(s) of an ovule which develops into the seed coat.
100. The endosperm provides nourishment to the developing embryo.

Section C: 2 Marks Questions

1. A typical flower consists of four whorls of floral appendages—calyx, corolla, androecium, and gynoecium—attached to a central axis called the thalamus or receptacle. The calyx and corolla are accessory whorls, while the androecium and gynoecium are the reproductive whorls.
2. A stamen consists of two main parts: the anther, which is a bilobed structure containing pollen sacs where pollen grains are produced, and the filament, which is a long, slender stalk that supports the anther.
3. The gynoecium is the female reproductive part, composed of one or more carpels. Each carpel has three parts: the ovary at the base containing ovules, the style which is a long tube connecting the ovary to the stigma, and the stigma which is the receptive tip for pollen grains.
4. The microsporangium wall has four layers: the outermost epidermis (protective), the endothecium (helps in dehiscence), the middle layers (short-lived, nutritive), and the innermost tapetum (provides nourishment to developing pollen grains).
5. Microsporogenesis is the process where diploid microspore mother cells (MMCs) within the anther undergo meiosis. Each MMC divides to form a tetrad of four haploid microspores, which then mature into pollen grains.
6. A pollen grain has a two-layered wall: a tough outer exine made of sporopollenin and a thin inner intine made of cellulose and pectin. Inside, it contains a large vegetative cell and a smaller generative cell.
7. A microspore develops into a pollen grain by undergoing an unequal mitotic division. This forms a large vegetative cell (tube cell) and a small, spindle-shaped generative cell that floats in the cytoplasm of the vegetative cell.
8. An anatropous ovule is inverted such that the micropyle lies close to the funicle. It has a stalk (funicle), a point of attachment (hilum), a basal part (chalaza), protective layers (integuments), a nutritive tissue (nucellus), and the female gametophyte (embryo sac).
9. Megasporogenesis is the process where a diploid megaspore mother cell (MMC) in the nucellus of an ovule undergoes meiosis. This results in the formation of four haploid megaspores, typically arranged in a linear tetrad.
10. In most angiosperms (Polygonum type), the megaspore mother cell divides meiotically to form four haploid megaspores. The megaspore at the chalazal end remains functional, while the other three degenerate. The functional megaspore then develops into the embryo sac through three successive free nuclear mitotic divisions.
11. A mature embryo sac is a 7-celled, 8-nucleate structure. It contains an egg apparatus (one egg cell and two synergids) at the micropylar end, three antipodal cells at the chalazal end, and a large central cell with two polar nuclei.
12. Pollination is of two main types: self-pollination (autogamy and geitonogamy) and cross-pollination (xenogamy). Self-pollination involves the transfer of pollen within the same flower or to another flower on the same plant, while cross-pollination involves transfer to a flower on a different plant.
13. Chasmogamous flowers are open flowers with exposed anthers and stigma, which can undergo self- or cross-pollination. Cleistogamous flowers never open, so their anthers and stigma are not exposed, which ensures self-pollination (autogamy).
14. Wind-pollinated (anemophilous) flowers have adaptations like being small, inconspicuous, and lacking nectar or fragrance. They produce large quantities of light, non-sticky pollen and have large, feathery stigmas to trap airborne pollen.
15. Water-pollinated (hydrophilous) flowers are typically small and inconspicuous. In many species, pollen grains are long and ribbon-like and are protected from wetting by a mucilaginous covering.
16. Insect-pollinated (entomophilous) flowers are usually large, colorful, fragrant, and rich in nectar to attract insects. Their pollen grains are often sticky or spiny, and the stigma is also sticky to ensure pollen adheres to it.
17. Animal-pollinated (zoophilous) flowers have various adaptations depending on the pollinator. For example, bird-pollinated flowers are often brightly colored (red, orange) and produce copious nectar, while bat-pollinated flowers are often large, dull-colored, and open at night.
18. Dichogamy is the maturation of anthers and stigma at different times. It includes protandry, where anthers mature first (e.g., sunflower), and protogyny, where the stigma matures first (e.g., Ficus). This promotes cross-pollination.
19. Herkogamy is a spatial separation of anthers and stigma, creating a physical barrier to self-pollination (e.g., Hibiscus). Heterostyly is the presence of different floral forms (e.g., long and short styles) in the same species to encourage cross-pollination.
20. Self-incompatibility is a genetic mechanism that prevents the germination of self-pollen on the stigma or inhibits pollen tube growth in the style. This is controlled by multiallelic S-genes and is an effective way to enforce cross-pollination.
21. Unisexuality, or dicliny, is the presence of either male (staminate) or female (pistillate) reproductive organs in a flower. This can occur in monoecious plants (both flower types on one plant, e.g., maize) or dioecious plants (flower types on separate plants, e.g., papaya), promoting cross-pollination.
22. Pollen-pistil interaction involves all events from pollen deposition on the stigma until the pollen tube enters the ovule. It is a dynamic process involving pollen recognition, followed by promotion or inhibition of the pollen. The pistil has the ability to recognize the pollen, whether it is of the right type (compatible) or of the wrong type (incompatible).
23. Artificial hybridization involves: 1. Emasculation: removal of anthers from a bisexual flower bud. 2. Bagging: covering the emasculated flower to prevent unwanted pollen contamination. 3. Pollination: dusting the stigma with desired pollen. 4. Rebagging: covering the flower again until the fruit develops.
24. Double fertilization is a unique event in angiosperms. It involves two fusions: one male gamete fuses with the egg cell (syngamy) to form the diploid zygote, and the other male gamete fuses with the two polar nuclei in the central cell (triple fusion) to form the triploid primary endosperm nucleus (PEN).
25. The significance of double fertilization is twofold. Syngamy leads to the formation of the embryo, which develops into the new plant. Triple fusion leads to the formation of the endosperm, a nutritive tissue that provides nourishment to the developing embryo, increasing the viability of the seed.
26. There are three main types of endosperm development: 1. Nuclear type: The PEN undergoes repeated free nuclear divisions, followed later by cell wall formation (e.g., coconut water). 2. Cellular type: Cell wall formation occurs after every nuclear division (e.g., Petunia). 3. Helobial type: An intermediate type where the first division is cellular, followed by free nuclear divisions in the larger chamber.
27. In dicots, the zygote divides into a suspensor cell and an embryonal cell. The embryonal cell develops into a globular, then heart-shaped, and finally a mature embryo with a radicle, plumule, and two cotyledons. The suspensor pushes the embryo into the endosperm.
28. In monocots, the zygote divides to form an embryo, but it develops only a single large cotyledon called the scutellum. The embryo also has a coleoptile (sheath covering the plumule) and a coleorhiza (sheath covering the radicle).
29. A mature dicot embryo consists of an embryonal axis and two cotyledons. The portion of the axis above the cotyledons is the epicotyl (terminating in the plumule), and the portion below is the hypocotyl (terminating in the radicle).
30. A mature monocot embryo has one large cotyledon (scutellum), an embryonal axis with a plumule protected by a coleoptile, and a radicle protected by a coleorhiza.
31. After fertilization, the ovule develops into a seed. A seed consists of a seed coat (developed from integuments), cotyledon(s), and an embryonal axis. The seed coat provides protection to the embryo within.
32. True fruits develop exclusively from the ovary (e.g., mango, pea). False fruits (pseudocarps) develop from the ovary as well as other floral parts like the thalamus (e.g., apple, strawberry).
33. Albuminous (endospermic) seeds retain a part of the endosperm at maturity as a food reserve (e.g., wheat, maize, castor). Non-albuminous (exalbuminous) seeds have their endosperm completely consumed during embryo development, and food is stored in the cotyledons (e.g., pea, bean, groundnut).
34. Apomixis is the production of seeds without fertilization. It is a form of asexual reproduction that mimics sexual reproduction. Types include recurrent apomixis (diploid embryo) and non-recurrent apomixis (haploid embryo). It is significant for producing hybrid seeds with desirable traits year after year.
35. Parthenocarpy is the formation of fruit without fertilization. This results in seedless fruits, which is commercially valuable in crops like bananas, grapes, and oranges. It can be induced by the application of growth hormones.
36. Polyembryony is the occurrence of more than one embryo in a seed. It can be caused by the fertilization of more than one egg, the development of multiple embryo sacs, or the proliferation of cells in the nucellus or integuments. It is common in citrus fruits.
37. Seed dispersal is crucial for the survival and distribution of a plant species. It prevents overcrowding, reduces competition for resources (light, water, nutrients) between the parent and offspring, and allows the colonization of new habitats.
38. The main agents of seed dispersal are wind (anemochory), water (hydrochory), and animals (zoochory). Some plants also have self-dispersal mechanisms (autochory), such as explosive fruits.
39. Seeds dispersed by wind are typically light, small, and may have specialized structures like wings (e.g., Moringa, maple) or hairy pappus (e.g., dandelion, cotton) to aid in flotation and travel long distances.
40. Seeds dispersed by water usually have buoyant and waterproof coverings. For example, the coconut has a fibrous mesocarp that helps it float in water for long periods, allowing it to be carried to distant shores.
41. Animal dispersal can be external (epizoochory), where seeds have hooks or barbs to attach to fur (e.g., Xanthium), or internal (endozoochory), where animals eat fleshy fruits and excrete the hard seeds elsewhere (e.g., berries).
42. The tapetum is the innermost wall layer of the anther. Its cells are nutritive and provide nourishment to the developing microspore mother cells and pollen grains. They also secrete enzymes and hormones essential for pollen development.
43. The filiform apparatus is a mass of finger-like projections in the synergid cells of the embryo sac. It plays a crucial role in guiding the pollen tube towards the egg cell, ensuring successful fertilization.
44. The antipodal cells are three cells located at the chalazal end of the embryo sac. While their exact function can vary, they are generally thought to play a nutritive role, supporting the development of the embryo sac and the early embryo.
45. The polar nuclei are the two nuclei located in the large central cell of the embryo sac. They fuse with one of the male gametes during double fertilization (triple fusion) to form the triploid primary endosperm nucleus (PEN).
46. A microspore is the haploid cell formed from meiosis of a microspore mother cell. A pollen grain is the mature male gametophyte that develops from the microspore; it is a two- or three-celled structure.
47. The suspensor is a stalk-like structure that develops from the zygote in the early stages of embryogeny. Its primary function is to push the developing embryo proper deep into the endosperm tissue to ensure it receives adequate nutrition.
48. The endosperm is a nutritive tissue unique to angiosperms, formed as a result of triple fusion. Its primary significance is to provide food reserves (in the form of starch, proteins, and oils) for the developing embryo and, in some cases, for the seedling during germination.
49. The seed coat develops from the one or two integuments of the ovule after fertilization. It serves as a protective outer covering for the seed, safeguarding the embryo and endosperm from mechanical damage, desiccation, and pathogens.
50. The testa is the outer layer of the seed coat, which is typically thick and protective. The tegmen is the inner layer of the seed coat, which is usually thin and membranous. Both develop from the outer and inner integuments of the ovule, respectively.
51. The grass embryo (a monocot) is characterized by a large, shield-shaped cotyledon called the scutellum. The embryonal axis has a plumule covered by a protective sheath called the coleoptile and a radicle covered by a sheath called the coleorhiza.
52. Cotyledons are the embryonic leaves. In non-albuminous seeds (like beans), they store food reserves for the embryo. In albuminous seeds (like castor), they are thin and help in transferring nutrients from the endosperm to the growing embryo during germination.
53. In nuclear endosperm formation, the primary endosperm nucleus (PEN) undergoes numerous mitotic divisions without immediate cell wall formation (cytokinesis). This results in a large number of free nuclei suspended in the cytoplasm of the central cell, as seen in coconut water.
54. In cellular endosperm formation, the first and all subsequent divisions of the primary endosperm nucleus are immediately followed by cell wall formation. This results in a completely cellular endosperm tissue from the beginning, as seen in Petunia.
55. Helobial endosperm is an intermediate type. The first division of the PEN is followed by cell wall formation, creating two chambers. Subsequent divisions are free-nuclear, primarily in the larger micropylar chamber, before cell walls eventually form.
56. The integuments are the protective outer layers of the ovule. After fertilization, they harden and develop into the seed coat (testa and tegmen), which protects the embryo and endosperm within the mature seed.
57. In an anatropous ovule, the funicle (stalk) is fused with the body of the ovule along one side. This line of fusion forms a distinct ridge known as the raphe.
58. The micropyle is a small opening in the integuments at the apex of the ovule. It serves as the primary site for the entry of the pollen tube to deliver the male gametes for fertilization and also facilitates the absorption of water during seed germination.
59. The chalaza is the basal region of the ovule where the nucellus and integuments originate. It is located opposite the micropyle and is the site where vascular tissues enter the ovule to provide nourishment.
60. The nucellus is the central mass of tissue within the ovule that surrounds and nourishes the developing embryo sac. In some seeds (perispermic seeds like black pepper), remnants of the nucellus persist as a nutritive tissue.
61. The generative cell inside the pollen grain divides by mitosis to form two non-motile male gametes. This division can occur either before the pollen is shed (3-celled stage) or after the pollen has landed on the stigma and the pollen tube has started to grow.
62. The pollen tube, after growing through the style, typically enters the ovule through the micropyle (porogamy). It then grows through the nucellus and penetrates the embryo sac, usually entering one of the synergids.
63. Upon reaching the embryo sac, the pollen tube ruptures at its tip, releasing the two male gametes into the cytoplasm of the synergid. The synergid then degenerates, allowing the gametes to move.
64. The zygote is formed by the process of syngamy, which is the fusion of one of the haploid male gametes with the haploid egg cell inside the embryo sac. The resulting zygote is diploid (2n) and develops into the embryo.
65. The primary endosperm nucleus (PEN) is formed by the process of triple fusion. This involves the fusion of the second haploid male gamete with the two haploid polar nuclei located in the central cell. The resulting PEN is triploid (3n).
66. After fertilization, the flower undergoes significant changes: the sepals, petals, and stamens usually wither and fall off. The ovary develops into the fruit, the ovules develop into seeds, the zygote develops into the embryo, and the primary endosperm nucleus develops into the endosperm.
67. After fertilization, the ovary wall develops into the pericarp, which is the wall of the fruit. The pericarp can differentiate into three layers: the outer epicarp, the middle mesocarp, and the inner endocarp.
68. After fertilization, the integuments of the ovule develop into the seed coat (testa and tegmen). The zygote develops into the embryo, and the primary endosperm nucleus develops into the endosperm, which provides nourishment.
69. Cross-pollination introduces genetic variation into a population, which is essential for adaptation to changing environments. It can lead to healthier, more vigorous offspring (hybrid vigor) and reduces the chances of expressing harmful recessive alleles.
70. Continuous self-pollination can lead to inbreeding depression, which is the reduction in fitness and vigor of the offspring due to the accumulation of harmful recessive alleles. It also limits genetic variation, making the population more vulnerable to diseases and environmental changes.
71. Adaptations for wind pollination include the production of large amounts of lightweight, non-sticky pollen, inconspicuous flowers without nectar or fragrance, and large, feathery stigmas to effectively trap airborne pollen.
72. Adaptations for insect pollination include large, colorful, and fragrant flowers to attract insects, the presence of nectar as a reward, sticky pollen grains that adhere to the insect's body, and a sticky stigma to receive the pollen.
73. Self-incompatibility is a genetic mechanism where the pistil recognizes and rejects pollen from the same plant. This is often controlled by S-genes. If the S-allele in the pollen matches one of the S-alleles in the pistil, pollen tube growth is arrested, preventing self-fertilization.
74. The genetic basis of self-incompatibility is typically controlled by a single locus (S-locus) with multiple alleles. In gametophytic self-incompatibility, the pollen's S-allele determines its compatibility. In sporophytic self-incompatibility, the diploid genotype of the pollen-producing plant determines compatibility.
75. Emasculation is the process of removing the anthers from a bisexual flower before they release pollen. This is a crucial step in artificial hybridization to prevent unwanted self-pollination and ensure that the flower can be cross-pollinated with desired pollen.
76. Bagging is the technique of covering an emasculated flower with a bag (usually made of butter paper) to prevent contamination of its stigma with foreign or unwanted pollen. The bag is removed only for hand-pollination and then replaced.
77. Artificial hybridization is a key technique in plant breeding programs. It allows breeders to combine desirable characters from two different parent plants into a single hybrid offspring, leading to the development of new crop varieties with improved yield, disease resistance, or other valuable traits.
78. Parthenocarpy, the production of fruit without fertilization, is commercially important because it results in seedless fruits like bananas, grapes, and navel oranges. Seedlessness is a desirable trait for consumers, making the fruits more palatable and easier to process.
79. Polyembryony in citrus is significant because the embryos that arise from the nucellar cells are genetically identical to the parent plant. This allows for the production of uniform, true-to-type rootstocks for grafting, which is a common practice in the citrus industry.
80. Apomixis allows for the fixation of desirable traits, including hybrid vigor, in plants. If a hybrid variety can be made to reproduce via apomixis, farmers can replant the seeds from their own crop year after year without losing the hybrid characteristics, which is not possible with sexually reproducing hybrids.
81. Some plants, like peas and beans, have fruits (pods) that dry out and create tension in the fruit wall. When the tension is high enough, the pod splits open explosively, flinging the seeds away from the parent plant. This is a form of autochory (self-dispersal).
82. Adaptations for animal dispersal include fleshy, edible fruits that attract animals to eat them and disperse the seeds in their droppings (endozoochory). Other plants have seeds with hooks, barbs, or sticky substances that attach to an animal's fur or feathers (epizoochory).
83. Winged seeds, such as those of maple and moringa, have wing-like extensions of the seed coat. These structures increase the seed's surface area and air resistance, allowing them to be carried over long distances by the wind, which is a form of anemochory.
84. The coconut fruit is adapted for water dispersal (hydrochory). Its fibrous and buoyant mesocarp (the husk) allows it to float on water for extended periods, enabling it to be carried by ocean currents to colonize new islands and coastlines.
85. The fruit of Xanthium has hooks or spines on its surface. These structures readily attach to the fur of passing animals. The animal then carries the fruit away, eventually dislodging it in a new location, effectively dispersing the seed. This is a form of epizoochory.
86. Fleshy fruits are an adaptation for endozoochory. They are typically brightly colored, aromatic, and contain sugars to attract animals. The animal consumes the fruit, and the hard, indigestible seeds pass through its digestive tract and are excreted in a different location, often with a bit of fertilizer.
87. Accessory fruits, also known as false fruits or pseudocarps, are fruits that develop from tissues other than the ovary, such as the thalamus or receptacle. Examples include apples, pears, and strawberries, where the fleshy part is derived from the thalamus.
88. The endosperm is a specialized nutritive tissue that provides essential food reserves (starch, proteins, oils) for the developing embryo. In albuminous seeds, it also nourishes the seedling during the initial stages of germination until it can photosynthesize.
89. The seed coat, derived from the ovule's integuments, provides a protective barrier for the embryo and endosperm. It guards against mechanical injury, desiccation (drying out), and attack by pathogens like bacteria and fungi.
90. Seed germination is the process by which a dormant seed resumes growth and develops into a seedling. It typically requires favorable external conditions, including adequate water, oxygen, and a suitable temperature. The seed absorbs water, swells, and the embryo becomes metabolically active.
91. The micropyle, the small pore in the seed coat, plays a crucial role in germination. It is the primary site for the entry of water, which is essential for rehydrating the seed's tissues and activating the metabolic processes required for growth.
92. The hilum is the scar on the seed coat that marks the point where the seed was attached to the fruit stalk (funicle). It is simply a scar and does not have a direct function in the mature seed, but it is a visible landmark.
93. The plumule is the part of the embryo that develops into the shoot system of the plant. It consists of the embryonic leaves (leaf primordia) and the shoot apical meristem, which is responsible for all future shoot growth.
94. The radicle is the part of the embryo that develops into the primary root of the plant. It is the first part of the embryo to emerge from the seed during germination and anchors the seedling in the soil, absorbing water and nutrients.
95. The scutellum is the large, shield-shaped single cotyledon in a monocot (like grass). Its primary role is to secrete enzymes that digest the stored food in the endosperm and transfer the nutrients to the growing embryo during germination.
96. The coleoptile is a protective, cap-like sheath that covers the plumule (embryonic shoot) in monocot seedlings. It protects the delicate shoot tip as it pushes through the soil during germination.
97. The coleorhiza is a protective sheath that covers the radicle (embryonic root) in monocot seedlings. It provides protection to the root tip as it grows downwards into the soil.
98. The epicotyl is the region of the embryonal axis that is above the point of attachment of the cotyledon(s). It develops into the upper part of the stem and leaves. The hypocotyl is the region of the axis below the cotyledons, which connects the cotyledons to the radicle.
99. Cotyledons are the embryonic leaves that are part of the embryo. They are formed from the proembryo during embryogenesis. In dicots, there are two cotyledons, and in monocots, there is one.
100. Sexual reproduction in plants is significant because it creates genetic variation through the recombination of genes from two parents. This variation is the raw material for natural selection and evolution, allowing plant populations to adapt to changing environmental conditions and survive over the long term.

Section D: 3 Marks Questions

1. A typical flower is a reproductive shoot with four main whorls arranged on a receptacle. The outermost whorl is the calyx (sepals), which is protective. Inside this is the corolla (petals), which attracts pollinators. The third whorl is the androecium (stamens), the male part, which produces pollen. The innermost whorl is the gynoecium (carpels), the female part, which contains ovules. (A labeled diagram showing these parts would be included).
2. A microsporangium (pollen sac) is surrounded by four wall layers: epidermis (outermost, protective), endothecium (fibrous thickenings aid in anther dehiscence), middle layers (1-3 layers, nutritive, degenerate at maturity), and tapetum (innermost, provides vital nutrition to developing pollen). The center contains the sporogenous tissue, which forms microspore mother cells.
3. Microsporogenesis begins with the diploid microspore mother cells (MMCs) in the sporogenous tissue. Each MMC undergoes meiosis I and meiosis II, a reductional division, to produce a cluster of four haploid cells called a microspore tetrad. As the anther matures, the tetrads separate, and each microspore develops into a pollen grain. (A diagram showing MMC -> Meiosis I -> Dyad -> Meiosis II -> Tetrad would be included).
4. The haploid microspore undergoes an unequal mitotic division to form a large, irregularly shaped vegetative cell and a small, dense generative cell. The generative cell then divides mitotically to form two male gametes. This entire structure, enclosed by the exine and intine, is the mature male gametophyte or pollen grain, which is shed at either the 2-celled or 3-celled stage.
5. An anatropous ovule is inverted with the micropyle facing the placenta. It consists of a funicle (stalk), hilum (attachment point), raphe (ridge), chalaza (basal part), nucellus (nutritive tissue), and an embryo sac (female gametophyte). It is protected by two layers called integuments, which leave a small opening called the micropyle. (A labeled diagram would be included).
6. Megasporogenesis occurs inside the nucellus of the ovule. A single diploid megaspore mother cell (MMC) differentiates and undergoes meiosis. This produces a linear tetrad of four haploid megaspores. Typically, the three megaspores towards the micropylar end degenerate, while the one at the chalazal end remains functional and develops into the embryo sac.
7. The functional haploid megaspore enlarges, and its nucleus undergoes three successive free-nuclear mitotic divisions. This results in an 8-nucleate stage. Cell walls then form, organizing the nuclei into a 7-celled structure: an egg apparatus (one egg, two synergids), three antipodal cells, and a large central cell with two polar nuclei. This is the mature female gametophyte.
8. A mature embryo sac (Polygonum type) is a 7-celled, 8-nucleate structure. At the micropylar end is the egg apparatus (egg cell for fertilization, synergids to guide the pollen tube). At the chalazal end are three antipodal cells (nutritive). The large central cell contains two polar nuclei, which fuse with a male gamete to form the endosperm.
9. Pollination is the transfer of pollen to the stigma. It can be: 1. Autogamy (self-pollination in the same flower, e.g., pea). 2. Geitonogamy (pollen transfer to another flower on the same plant, e.g., maize). 3. Xenogamy (cross-pollination between different plants, e.g., papaya). Autogamy and geitonogamy are genetically similar to self-pollination, while xenogamy brings genetic diversity.
10. Agents of pollination include wind, water, insects, birds, and bats. Wind-pollinated flowers are small and produce abundant, light pollen. Water-pollinated flowers have pollen protected by mucilage. Insect/animal-pollinated flowers are large, colorful, fragrant, and offer nectar as a reward to attract their specific pollinators, showing co-evolution.
11. Outbreeding devices are mechanisms that plants use to discourage self-pollination and encourage cross-pollination. These include: 1. Unisexuality (dioecy), where male and female flowers are on different plants. 2. Dichogamy (protandry or protogyny), where anthers and stigma mature at different times. 3. Self-incompatibility, a genetic mechanism to reject self-pollen. 4. Herkogamy, a physical barrier between reproductive parts.
12. Self-incompatibility is a genetic mechanism to prevent inbreeding. It is controlled by S-genes. If the S-allele of the pollen matches an S-allele in the pistil, the pollen is recognized as "self" and its germination or pollen tube growth is inhibited. This ensures that only genetically different (non-self) pollen can achieve fertilization.
13. Artificial hybridization is a crop improvement technique. It involves: 1. Emasculation: Removing anthers from a bisexual flower bud to prevent self-pollination. 2. Bagging: Covering the flower to prevent contamination by unwanted pollen. 3. Pollen Collection: Collecting pollen from the desired male parent. 4. Pollination: Dusting the collected pollen onto the stigma of the emasculated flower. 5. Rebagging: Covering the flower again to allow the fruit and seeds to develop without contamination.
14. Double fertilization is a process unique to angiosperms. When the pollen tube enters the embryo sac, it releases two male gametes. One male gamete fuses with the egg cell (syngamy) to form the diploid (2n) zygote. The other male gamete fuses with the two polar nuclei in the central cell (triple fusion) to form the triploid (3n) primary endosperm nucleus (PEN).
15. Double fertilization is highly significant. The formation of the zygote ensures the creation of a new individual, carrying genetic information from both parents. The formation of the triploid endosperm provides a dedicated, highly nutritious food source for the developing embryo, increasing the chances of the seed's survival and successful germination.
16. Endosperm development can be of three types: 1. Nuclear: The PEN divides repeatedly without cell wall formation, creating a free-nuclear endosperm (e.g., coconut water). Walls form later. 2. Cellular: Each nuclear division is immediately followed by cell wall formation, resulting in a cellular tissue from the start (e.g., Datura). 3. Helobial: An intermediate type where the first division is cellular, but subsequent divisions in one chamber are free-nuclear.
17. In dicots, the zygote divides to form a proembryo and a suspensor. The embryo proper develops from the proembryo, passing through globular and heart-shaped stages. The mature embryo consists of an embryonal axis with a plumule (future shoot), a radicle (future root), and two prominent cotyledons that often store food. (A diagram showing these stages would be included).
18. In monocots, the zygote also divides to form an embryo, but its development is slightly different. It forms a single large, shield-shaped cotyledon called the scutellum. The embryonal axis is protected by sheaths: the coleoptile covers the plumule, and the coleorhiza covers the radicle. The endosperm is the primary food source.
19. A mature dicot embryo has an embryonal axis and two cotyledons. The epicotyl is the region above the cotyledons, and the hypocotyl is the region below. A monocot embryo has a single cotyledon (scutellum), a coleoptile, and a coleorhiza protecting the plumule and radicle, respectively. (Diagrams comparing the two would be included).
20. After fertilization, major changes occur: the ovary develops into the fruit, and the ovary wall becomes the pericarp. The ovules mature into seeds. The integuments of the ovule form the seed coat. The zygote develops into the embryo, and the PEN develops into the endosperm. The sepals, petals, stamens, style, and stigma typically wither and fall off.
21. A seed is a mature ovule containing an embryo and, in most cases, a food reserve (endosperm or food-storing cotyledons), all enclosed within a protective seed coat. The seed coat develops from the integuments. The seed is the unit of propagation for angiosperms.
22. True fruits develop solely from the mature ovary of a flower (e.g., mango, grape, tomato). False fruits, or pseudocarps, develop from the ovary along with other accessory floral parts, most commonly the thalamus. In apples and strawberries, for instance, the fleshy, edible part is the enlarged thalamus, not the ovary wall.
23. Albuminous (endospermic) seeds, like castor and maize, retain the endosperm as the primary food storage tissue at maturity. Non-albuminous (exalbuminous) seeds, like pea and bean, have the endosperm completely consumed by the developing embryo, and the food reserves are instead stored in the large, fleshy cotyledons.
24. Apomixis is the production of seeds without fertilization. It is a form of asexual reproduction. Its significance lies in plant breeding, as it allows for the fixation of hybrid vigor. Desirable hybrid characteristics can be maintained indefinitely through apomictic seeds, which is not possible with sexual reproduction where traits segregate.
25. Parthenocarpy is the natural or artificially induced production of fruit without fertilization of ovules, which makes the fruit seedless. It is commercially important for producing seedless varieties of grapes, bananas, and watermelons, which are highly preferred by consumers for convenience and palatability.
26. Polyembryony is the condition where more than one embryo develops within a single seed. It can arise from various causes, such as the cleavage of a zygote or the development of embryos from nucellar or integumentary cells. It is common in citrus and is used in horticulture to produce uniform rootstocks.
27. Seed and fruit dispersal is vital for a plant's success. It allows the species to colonize new areas, reducing competition for light, water, and nutrients between offspring and the parent plant. Dispersal also helps plants escape from predators and pathogens that may be concentrated near the parent.
28. Seeds are dispersed by various methods: 1. Wind (Anemochory): Seeds are light or have wings/hairs (e.g., dandelion). 2. Water (Hydrochory): Seeds can float (e.g., coconut). 3. Animals (Zoochory): Seeds are eaten (endozoochory, e.g., berries) or attach to fur (epizoochory, e.g., burrs). 4. Explosion (Autochory): Fruits burst open to fling seeds (e.g., pea).
29. Plants adapted for wind dispersal (anemochory) produce seeds that are very small and light (like dust, e.g., orchids) or have specialized structures to increase air resistance. These include wings (e.g., maple, Moringa) or plumes of hair (e.g., cottonwood, milkweed), which allow the seeds to be carried by the wind over great distances.
30. Plants adapted for water dispersal (hydrochory) often grow near water bodies. Their seeds or fruits have adaptations for buoyancy, such as a fibrous or spongy outer coat that traps air, and a waterproof covering to prevent waterlogging. The coconut is a classic example, able to float for months in seawater.
31. Plants adapted for animal dispersal (zoochory) use two main strategies. They may produce fleshy, nutritious fruits that animals eat, with the hard seeds passing through the digestive tract unharmed (endozoochory). Alternatively, they may produce fruits or seeds with hooks, barbs, or sticky substances that cling to an animal's fur or feathers (epizoochory).
32. Insect-pollinated flowers show co-evolution with their pollinators. They are typically brightly colored, produce fragrances, and offer nectar as a reward. The flower's structure is often adapted to ensure that when an insect visits for nectar, its body is dusted with pollen, which is then transferred to the stigma of the next flower it visits.
33. Bird-pollinated (ornithophilous) flowers are usually large, robust, and brightly colored, often in shades of red or orange, as birds have good color vision. They produce large amounts of dilute nectar and typically lack a strong scent, as birds have a poor sense of smell.
34. Bat-pollinated (chiropterophilous) flowers are adapted for nocturnal visitors. They are often large, pale or dull-colored, and open at night. They emit a strong, fermenting, or musky odor to attract bats and produce copious nectar as a reward.
35. Pollen-pistil interaction is a critical step that determines compatibility. When a pollen grain lands on a compatible stigma, it absorbs water and nutrients and germinates to form a pollen tube. The pollen tube grows down through the style, guided by chemical signals from the pistil, towards the ovule.
36. Upon landing on a compatible stigma, the pollen grain is rehydrated. The vegetative cell (tube cell) emerges through a germ pore and grows into a pollen tube. The tube nucleus directs the growth of the tube down the style, and the generative cell travels down the tube, dividing into two male gametes.
37. The pollen tube grows through the tissues of the style and enters the ovary. It is chemically attracted to the ovule and typically enters through the micropyle. It then penetrates the nucellus and enters the embryo sac, usually by passing into one of the two synergid cells, guided by the filiform apparatus.
38. After entering a synergid, the pollen tube stops growing, and its tip ruptures. This releases the two non-motile male gametes into the cytoplasm of the synergid. The synergid then begins to degenerate, allowing the male gametes to move towards the egg cell and the central cell for fertilization.
39. The suspensor develops from the basal cell after the first division of the zygote. It is a multicellular, stalk-like structure. Its primary functions are to anchor the embryo and to push the developing embryo proper deep into the nutritive endosperm tissue, ensuring a constant supply of food for its growth.
40. The endosperm is the primary nutritive tissue for the embryo. It is formed from the primary endosperm nucleus and is rich in starch, proteins, and oils. In albuminous seeds, it persists and is used during germination. In non-albuminous seeds, its reserves are transferred to the cotyledons before the seed matures.
41. The seed coat develops from the integuments of the ovule. If there are two integuments, the outer one forms the thick, protective testa, and the inner one forms the thin, membranous tegmen. The seed coat protects the embryo from mechanical damage, desiccation, and pathogens.
42. Cotyledons are the embryonic leaves. In dicots, there are two, and in monocots, there is one (the scutellum). Their function varies: in non-albuminous seeds like beans, they are thick and store food. In albuminous seeds like castor, they are thin and help absorb and transfer nutrients from the endosperm to the embryo.
43. The monocot embryo has several specialized structures. The single cotyledon is called the scutellum. The embryonic shoot (plumule) is protected by a sheath called the coleoptile. The embryonic root (radicle) is protected by a sheath called the coleorhiza.
44. In a grass embryo, the coleoptile and coleorhiza are protective structures. The coleoptile is a hollow, conical sheath that encloses the plumule and the first few leaves, protecting them as they push through the soil. The coleorhiza is an undifferentiated sheath that encloses the radicle and protects it during its initial growth into the soil.
45. The primary nutritive tissue in seeds is the endosperm, which is triploid. In some seeds, like pea and bean, the endosperm is consumed, and the cotyledons (which are diploid and part of the embryo) become the nutritive tissue. In a few species, a remnant of the nucellus, called the perisperm (diploid), also acts as a nutritive tissue.
46. Seed germination is the resumption of embryonic growth after a period of dormancy. It begins with the imbibition of water, which activates enzymes and metabolic processes. The radicle is typically the first part to emerge, followed by the plumule, which grows upwards to form the shoot. This requires oxygen, favorable temperatures, and sometimes light.
47. Pollination efficiency is affected by several factors. For abiotic pollination (wind, water), efficiency depends on the density of plants and environmental conditions. For biotic pollination, it depends on the abundance and activity of pollinators, the attractiveness of the flower (color, scent, reward), and the synchrony of flowering with pollinator life cycles.
48. The structure of a flower is a key evolutionary innovation of angiosperms. The enclosure of the ovules within the ovary provides protection. The evolution of petals, nectar, and scents co-evolved with pollinators, leading to more efficient and targeted pollen transfer compared to the random wind pollination common in gymnosperms.
49. There is a close relationship between flower structure and its pollination method. Wind-pollinated flowers are simple and lack attractants. Insect-pollinated flowers have complex shapes, colors, and nectar guides to suit their specific pollinators. This co-evolution ensures reproductive success for the plant and provides a reliable food source for the pollinator.
50. Flower development is controlled by a set of homeotic genes, often described by the ABC model. Different combinations of these genes are expressed in the four floral whorls, determining whether a whorl develops into sepals, petals, stamens, or carpels. Mutations in these genes can lead to abnormal flower structures.
51. Fruit development is regulated by plant hormones, particularly auxins, gibberellins, and cytokinins. Fertilization triggers a surge in these hormones, promoting the growth of the ovary wall. In some cases, external application of these hormones can induce parthenocarpy (fruit development without fertilization).
52. Reproduction in plants is influenced by environmental factors like temperature, photoperiod (day length), and water availability. Many plants require specific temperature ranges or day lengths to initiate flowering. Stressful conditions, like drought, can inhibit or alter reproductive processes.
53. Flowering plants are ecologically vital as they form the base of most terrestrial food webs. They are primary producers, converting sunlight into energy. Their flowers provide food for pollinators, and their fruits and seeds provide food for a vast range of animals, making them a cornerstone of ecosystem structure and function.
54. Sexual reproduction in plants is of immense economic importance. It is the basis of agriculture, as nearly all our food crops (grains, fruits, vegetables) are the products of sexual reproduction (seeds and fruits). It is also fundamental to the production of fibers (cotton), oils, and many other plant-based products.
55. Sexual reproduction is a major driver of evolution. The genetic recombination that occurs during meiosis and fertilization creates new combinations of alleles, leading to variation within a population. Natural selection acts on this variation, allowing populations to adapt to changing environments over time.
56. The main advantage of sexual reproduction is the creation of genetic diversity, which enhances the ability of a species to adapt and survive in the long run. Asexual reproduction produces genetically identical offspring (clones), which can be advantageous in stable environments but makes the entire population vulnerable to the same diseases or environmental changes.
57. At the molecular level, fertilization involves a series of cell-cell recognition events. Proteins on the surfaces of the male and female gametes interact, allowing for species-specific fusion. After fusion, a calcium wave is triggered in the egg cell, which establishes a block to polyspermy (preventing fusion with more than one sperm) and activates the zygote to begin development.
58. During pollen tube growth, there are significant biochemical changes. The pollen grain metabolizes stored reserves (lipids, carbohydrates) to fuel the rapid, polarized growth of the tube. The tube secretes enzymes to digest the tissues of the style, and there is a steep calcium ion gradient at the growing tip, which is essential for directing its growth.
59. Embryo development involves precise patterns of cell division, differentiation, and morphogenesis. Gene expression patterns change dramatically as the single-celled zygote develops into a multicellular embryo with distinct tissues and organs (cotyledons, plumule, radicle). This process establishes the basic body plan of the plant.
60. Seed development involves the accumulation of large amounts of storage reserves (starch, proteins, oils) in the endosperm or cotyledons. This requires a major shift in the metabolism of the seed tissues. As the seed matures, it typically undergoes desiccation, losing most of its water and entering a dormant, metabolically quiescent state.
61. Fruit ripening is a complex process involving coordinated physiological and biochemical changes. These include the conversion of starches to sugars (making the fruit sweet), the breakdown of chlorophyll and synthesis of pigments (color change), and the softening of the fruit wall due to the enzymatic degradation of pectin. This process is primarily regulated by the hormone ethylene.
62. The molecular basis of self-incompatibility involves the S-locus genes, which code for proteins in both the pollen and the pistil. In many systems, the pistil expresses S-RNases that can enter a "self" pollen tube and degrade its RNA, thereby inhibiting its growth. The pollen expresses F-box proteins that can detoxify non-self S-RNases.
63. Apomixis bypasses meiosis and fertilization. In one common mechanism (apospory), a diploid cell of the nucellus develops directly into an unreduced (diploid) embryo sac. The egg cell within this sac then develops into an embryo without being fertilized, a process called parthenogenesis.
64. Parthenocarpy can be induced by applying growth hormones like auxins and gibberellins to unpollinated flowers. These hormones mimic the natural hormonal signal that is normally produced after fertilization, tricking the ovary into developing into a fruit even though fertilization has not occurred.
65. The cytological basis of polyembryony can vary. In cleavage polyembryony, the zygote divides into multiple, separate embryos. More commonly, especially in citrus, adventive embryos arise from the mitotic division of diploid cells of the nucellus or integuments surrounding the embryo sac.
66. The diversity of fruit types reflects different strategies for seed dispersal. Fleshy fruits are adapted for consumption by animals. Dry, dehiscent fruits (like pods) are adapted for explosive self-dispersal. Dry, indehiscent fruits with wings or plumes are adapted for wind dispersal. This diversity enhances the reproductive success of plants in various ecological niches.
67. The relationship between flowers and their pollinators is a classic example of co-evolution. Plants evolve floral traits (color, shape, scent) that attract specific pollinators, and pollinators evolve physical and behavioral traits (beak shape, foraging patterns) that make them efficient at exploiting those flowers. This mutualism benefits both partners.
68. Sexual reproduction is the foundation of plant breeding. By selectively cross-pollinating plants with desirable traits (e.g., high yield, disease resistance), breeders can create new hybrid varieties that combine the best characteristics of both parents. This process of selection and hybridization has been responsible for dramatic improvements in crop productivity.
69. Biotechnology offers powerful tools for plant reproduction. Techniques like in vitro fertilization, embryo rescue (culturing immature embryos), and genetic engineering (inserting specific genes) can overcome breeding barriers, speed up the breeding process, and create novel plant varieties with traits that are difficult to achieve through conventional breeding.
70. Conservation of plant reproduction is crucial for maintaining biodiversity. This involves protecting natural habitats to preserve plant-pollinator relationships. It also includes ex-situ conservation methods like creating seed banks and pollen banks to store the genetic material of endangered species for future use.
71. Tissue culture involves growing plant cells, tissues, or organs in a sterile, nutrient-rich medium. In reproduction, it is used for micropropagation (cloning large numbers of plants), producing disease-free plants, and for techniques like embryo rescue, where embryos that would abort in the seed are cultured to maturity in vitro.
72. Molecular markers are specific DNA sequences that can be used to identify genetic variation between individuals. In plant breeding, they are used to quickly screen large populations for desirable genes (marker-assisted selection), assess genetic diversity, and verify the parentage of hybrids, making the breeding process more efficient.
73. Genetic engineering allows for the direct transfer of specific genes into a plant's genome. This can be used to introduce traits like herbicide resistance, pest resistance (e.g., Bt cotton), or improved nutritional quality. It offers a way to modify plant reproduction and traits with high precision.
74. Cryopreservation is the storage of biological material at ultra-low temperatures (typically in liquid nitrogen at -196°C). Pollen and seeds of many species can be cryopreserved, which halts their metabolic activity and allows for long-term storage of genetic resources without degradation. This is vital for gene banks and conservation efforts.
75. In vitro fertilization (IVF) in plants involves the direct fusion of isolated male and female gametes in a test tube. This technique is used to overcome pre-fertilization barriers, such as pollen-stigma incompatibility, allowing breeders to create hybrids between species that cannot be crossed conventionally.
76. Somatic hybridization involves the fusion of somatic cells (non-reproductive cells) from two different plant species to create a hybrid. The cell walls are first removed to create protoplasts, which are then induced to fuse. This technique allows for the creation of hybrids between sexually incompatible species.
77. Protoplast fusion is a key step in somatic hybridization. After removing the cell walls with enzymes, the resulting protoplasts are treated with chemicals (like polyethylene glycol) or an electric field to induce them to fuse. The fused protoplast contains the genetic material from both parent cells.
78. Chromosome engineering involves manipulating the chromosomes of a plant to achieve desired outcomes. This can include inducing polyploidy (increasing the number of chromosome sets) or transferring specific chromosome segments from a wild relative into a crop species to introduce traits like disease resistance.
79. Polyploidy, the condition of having more than two sets of chromosomes, can be induced by treating plant cells with chemicals like colchicine, which disrupts mitosis. Polyploid plants are often larger and more robust than their diploid counterparts and are common in many crop species.
80. Mutation breeding involves inducing mutations in a plant's DNA using mutagens like radiation or chemicals. This creates a large pool of random genetic variation. Breeders can then screen the mutated population to find individuals with desirable new traits that have arisen from these mutations.
81. Hybrid vigor, or heterosis, is the phenomenon where hybrid offspring exhibit superior qualities (e.g., faster growth, higher yield) compared to their inbred parents. Plant breeders utilize this by creating F1 hybrid varieties, which are widely used in agriculture (e.g., hybrid corn) to maximize productivity.
82. Heterosis is commercially exploited by producing F1 hybrid seeds for sale to farmers. Since the F2 generation (seeds from the F1 hybrid) will show genetic segregation and lose the uniform vigor, farmers must purchase new F1 seeds each year, creating a sustainable market for seed companies.
83. Incompatibility systems are natural barriers to self-fertilization in many crop plants. Understanding these systems is crucial for breeders. They must be managed to either ensure cross-pollination for hybrid seed production or be overcome to allow for the development of inbred lines.
84. Male sterility is a condition where a plant cannot produce functional pollen. This is a valuable tool in hybrid seed production. A male-sterile line is used as the female parent, eliminating the need for costly and labor-intensive emasculation, as it cannot self-pollinate.
85. Seed production technology involves the large-scale multiplication of high-quality seeds of improved crop varieties. It requires careful management of genetic purity, isolation from other varieties to prevent cross-pollination, and optimal growing conditions to ensure high yield and seed quality.
86. Quality control in seed production is essential to ensure that the seeds sold to farmers are of high genetic purity, have a high germination rate, are free from diseases and pests, and are of the correct variety. This involves field inspections, laboratory testing, and certification processes.
87. Seed testing involves laboratory analysis to determine the quality of a seed lot, including its germination percentage, moisture content, and physical and genetic purity. Seed certification is a legal system to verify that a seed lot meets the established standards of quality, ensuring that farmers receive reliable seeds.
88. Proper seed storage is crucial to maintain seed viability (the ability to germinate) over time. Seeds must be stored in cool, dry conditions to minimize metabolic activity and prevent degradation. Viability naturally declines over time, and storage conditions significantly impact how long a seed remains viable.
89. Seed dormancy is a state where a viable seed will not germinate even under favorable conditions. This is a natural survival mechanism. Dormancy can be broken by various treatments that mimic natural conditions, such as scarification (scratching the seed coat), stratification (cold treatment), or exposure to light.
90. The primary requirements for seed germination are water, oxygen, and a suitable temperature. Water is needed for rehydration and metabolic activation. Oxygen is required for aerobic respiration to produce energy for growth. Each species has an optimal temperature range for germination.
91. Seedling establishment is the critical phase after germination where the young seedling develops roots and leaves and begins to photosynthesize. Successful establishment depends on factors like soil moisture, nutrient availability, and the absence of pests and diseases.
92. Transplantation is the process of moving a seedling from its initial location (like a nursery bed or container) to its permanent location in the field. This must be done carefully to minimize damage to the delicate root system and reduce transplant shock.
93. Nursery management involves the care of young plants in a controlled environment before they are transplanted. This includes providing optimal water, nutrients, and light, as well as protecting the seedlings from pests and diseases to ensure they are healthy and vigorous at the time of transplanting.
94. Propagation is the process of creating new plants. In horticulture, this includes sexual propagation (from seeds) and asexual (vegetative) propagation techniques like cuttings, grafting, and layering, which produce clones of the parent plant.
95. Grafting and budding are vegetative propagation techniques where a part of one plant (the scion or bud) is attached to the root system of another plant (the rootstock). This is used to combine the desirable fruit or flower characteristics of the scion with the robust root system of the rootstock.
96. Layering is a technique where a stem attached to the parent plant is induced to form roots while still attached. A cutting is a piece of a stem or root that is cut from the parent plant and induced to form roots, creating a new, independent plant.
97. Micropropagation is a tissue culture technique for producing a large number of plants from a small piece of parent tissue (explant). It allows for the rapid cloning of plants and the production of disease-free planting material in a sterile, laboratory environment.
98. Organogenesis is the process of forming organs (like shoots and roots) from a mass of undifferentiated cells (callus) in tissue culture. Embryogenesis is the process of forming embryos from somatic cells (somatic embryogenesis), which can then develop into whole plants. Both are key pathways in micropropagation.
99. Somaclonal variation is the genetic variation that arises in plants regenerated from tissue culture. While often undesirable, it can also be a source of novel traits. Breeders can screen these somaclones to find individuals with beneficial new characteristics, like disease resistance.
100. Future research in plant reproduction will likely focus on improving crop resilience to climate change, enhancing nutritional value, and developing more sustainable agricultural practices. This will involve advanced genetic tools like CRISPR gene editing, a deeper understanding of the molecular control of reproductive processes, and the development of crops that can thrive with fewer inputs.