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NEET Biology: Reproduction · Chapter 1

Sexual Reproduction in Flowering Plants

What to remember

  • A flower is the site of sexual reproduction. The stamen (male) makes pollen grains by microsporogenesis, and the pistil (female) makes the embryo sac by megasporogenesis. The mature embryo sac is 7-celled and 8-nucleate (Polygonum type, monosporic).
  • Double fertilisation is unique to angiosperms. One male gamete fuses with the egg (syngamy, gives the 2n zygote). The other fuses with the two polar nuclei (triple fusion, gives the 3n primary endosperm nucleus).
  • After fertilisation: zygote → embryo, primary endosperm nucleus → endosperm, ovule → seed, ovary → fruit, integuments → seed coat.
  • Pollination types: autogamy (same flower), geitonogamy (another flower of the same plant), xenogamy (flower of a different plant of the same species). Only xenogamy brings genetically different pollen.

The flower and the male side: stamen, anther and pollen grain

A flower has four whorls: calyx, corolla, androecium and gynoecium. The androecium is made of stamens. The gynoecium is made of one or more pistils (carpels).

A typical stamen has a long, slender filament and a terminal anther. The proximal end of the filament is attached to the thalamus or the petal. A typical anther is bilobed. Each lobe has two theca, so the anther is dithecous. A transverse section of an anther is four-sided (tetragonal) and shows four microsporangia, one at each corner. Each microsporangium develops into a pollen sac, and pollen grains fill the sacs.

Wall layers of a microsporangium. The wall has four layers, from outside to inside:

LayerPositionFunction
EpidermisOutermostProtection
EndotheciumBelow the epidermisHygroscopic; helps the anther to dehisce and release pollen
Middle layersBetween endothecium and tapetumProtection; they degenerate in the mature anther
TapetumInnermostNourishes the developing pollen grains; its cells have dense cytoplasm and more than one nucleus

At the centre of a young microsporangium there is a compact mass of homogeneous cells called sporogenous tissue.

Microsporogenesis. This is the formation of microspores from a pollen mother cell (microspore mother cell, PMC). As the anther matures, the sporogenous cells undergo meiosis and form microspore tetrads. Each cell of the sporogenous tissue can give rise to a tetrad, so every PMC (2n) forms four haploid microspores (n). When the anther is mature and dehydrated, the microspores separate from each other and develop into pollen grains. The anther then dehisces and releases the pollen.

The pollen grain. Pollen grains represent the male gametophyte. They are generally spherical and measure about 25–50 micrometres in diameter.

PartNatureFeatures
ExineHard outer layerMade of sporopollenin, one of the most resistant organic materials known. It withstands high temperature, strong acids and alkali. No enzyme can degrade it.
Germ poresGaps in the exineSporopollenin is absent here. The pollen tube emerges from a germ pore.
IntineThin inner layerMade of cellulose and pectin
Vegetative cellLarge cellHas abundant food reserve and a large irregularly shaped nucleus
Generative cellSmall cellFloats in the cytoplasm of the vegetative cell. It is spindle-shaped with dense cytoplasm and a nucleus.

The exine is often beautifully ornamented, so pollen grains of a species can be identified as fossils. In about 60 per cent of angiosperms the pollen grain is shed at the 2-celled stage (vegetative cell and generative cell). In the remaining species (about 40 per cent) the generative cell divides before shedding and the grain is shed at the 3-celled stage (one vegetative cell and two male gametes).

Pollen viability. The period for which pollen remains able to germinate differs between species. In rice and wheat the pollen loses viability within about 30 minutes of release. In many members of Rosaceae, Leguminosae and Solanaceae it stays viable for months. Pollen can be stored for years in liquid nitrogen at –196 °C. This is called cryopreservation, and the stored pollen is used as pollen banks.

Pollen products. Pollen grains are rich in nutrients. Pollen tablets and syrups are used as food supplements. Pollen is also used in some sports and for racehorses. Pollen of some plants (for example Parthenium, or carrot grass) causes allergy and respiratory problems.

The female side: pistil, ovule and embryo sac

The pistil has three parts: the stigma (landing platform for pollen), the style (the elongated slender part below the stigma) and the ovary (the swollen basal part). Inside the ovary is the ovarian cavity (locule). The placenta is located inside the locule, and ovules arise from it.

Structure of an ovule (megasporangium).

PartDescription
FunicleStalk of the ovule
HilumJunction between the ovule and the funicle
IntegumentsOne or two protective envelopes that surround the ovule
MicropyleSmall opening at the tip where the integuments do not reach
NucellusMass of cells inside the integuments, with reserve food
ChalazaBasal part of the ovule, opposite the micropyle
Embryo sacFemale gametophyte, located in the nucellus

Megasporogenesis. This is the formation of megaspores from a megaspore mother cell (MMC). The MMC is a large cell with dense cytoplasm and a prominent nucleus. It is found in the micropylar region of the nucellus. The MMC (2n) undergoes meiosis and produces four haploid megaspores. In most flowering plants only one megaspore is functional, and the other three degenerate. The functional megaspore develops into the female gametophyte (embryo sac). Because only one megaspore forms the embryo sac, this is called monosporic development.

Embryo sac (Polygonum type). The nucleus of the functional megaspore divides mitotically to form two nuclei, which move to opposite poles. Two more mitotic divisions give four nuclei at each pole, so there are 8 nuclei in all. Cell walls then form, but not around all nuclei.

LocationCellsNuclei
Micropylar endEgg apparatus: one egg cell and two synergids3
Chalazal endThree antipodal cells3
CentreOne large central cell with two polar nuclei2

The synergids have special cellular thickenings at the micropylar tip called the filiform apparatus. It guides the entry of the pollen tube. A typical angiosperm embryo sac is therefore 7-celled but 8-nucleate.

Pollination

Pollination is the transfer of pollen grains from the anther to the stigma.

TypeMeaningGenetic result
AutogamyPollen from an anther goes to the stigma of the same flowerGenetically similar
GeitonogamyPollen goes to the stigma of another flower of the same plantFunctionally cross-pollination (it needs an agent) but genetically like autogamy
XenogamyPollen goes to the stigma of a flower of a different plantBrings genetically different pollen

For autogamy a flower must have anthers and stigma at the same stage and close together. Chasmogamous flowers open and expose anthers and stigma. Cleistogamous flowers never open. In them the anthers and stigma lie close, and the anthers dehisce inside the closed flower, so pollination is always autogamous. Cleistogamous flowers assure seed set even without pollinators. Examples are Viola (common pansy), Oxalis and Commelina. Some species bear both chasmogamous and cleistogamous flowers.

Agents of pollination. Plants use wind, water or animals (most often insects).

AgentFeatures of the plant or pollenExamples
WindPollen is light and non-sticky. Stamens are well exposed. Stigma is large and often feathery. Flowers are packed in inflorescences. The ovary often has a single ovule.Maize (corn cob; the tassels are the stigmas and styles), grasses
WaterRare, found in about 30 genera, mostly monocots. Pollen is often protected by a mucilaginous covering.Vallisneria, Hydrilla, Zostera
InsectsFlowers are large, colourful, fragrant and rich in nectar. Pollen is sticky. Small flowers form clusters.Amorphophallus, Yucca (moth lays eggs in the ovary locule)

In Vallisneria the female flower reaches the water surface by its long stalk. Male flowers or pollen are released on the surface and are carried passively by water currents to the female flower. Not all aquatic plants use water for pollination. Most aquatic plants such as water hyacinth and water lily are pollinated by insects or wind.

Outbreeding devices. Most flowering plants produce hermaphrodite flowers, so self-pollination is likely. Plants therefore use devices to promote cross-pollination.

  • Pollen release and stigma receptivity are not synchronised.
  • Anther and stigma are placed at different positions, so pollen does not reach the stigma of the same flower.
  • Self-incompatibility: a genetic mechanism that prevents self-pollen from fertilising the ovules of the same flower.
  • Unisexual flowers: monoecious plants (castor, maize) have both sexes on one plant, so geitonogamy can occur but autogamy cannot. Dioecious plants (papaya) have male and female flowers on separate plants, so both autogamy and geitonogamy are prevented.

Pollen-pistil interaction. The pistil recognises the pollen. If the pollen is of the right type (compatible), the pistil accepts it and promotes post-pollination events. If it is of the wrong type (incompatible), the pistil rejects it by preventing germination or growth of the pollen tube. The pollen grain germinates on the stigma, and the pollen tube grows through the style. The tube enters the ovule through the micropyle and then enters one synergid through the filiform apparatus. The two male gametes are discharged into the synergid.

Artificial hybridisation. This is used in crop improvement to obtain desired characters. Two steps are needed:

  • 1. Emasculation: the anthers are removed from the bisexual flower of the female parent with forceps before they dehisce.
  • 2. Bagging: the emasculated flower is covered with a bag of suitable size (usually butter paper) to prevent contamination by unwanted pollen. When the stigma is receptive, pollen from the chosen male parent is dusted on it and the flower is rebagged. If the female parent bears unisexual flowers, emasculation is not needed and only bagging is done before the flowers open.

Double fertilisation

After entry into the synergid, one male gamete moves toward the egg and fuses with its nucleus (syngamy) to form the diploid zygote. The other male gamete moves toward the two polar nuclei and fuses with them to form the triploid primary endosperm nucleus (PEN). This is triple fusion, because three haploid nuclei are involved. The central cell becomes the primary endosperm cell (PEC). The two fusion events together are called double fertilisation. The synergids and antipodals degenerate after fertilisation.

Post-fertilisation: endosperm and embryo

Endosperm. Endosperm develops before the embryo, so that nutrition is ready for the growing embryo. The PEN divides repeatedly to form free-nuclear endosperm: many nuclei lie in the cytoplasm without walls. This is the common type. Later, cell walls form and the endosperm becomes cellular. Tender coconut water is free-nuclear endosperm, and the surrounding white kernel is cellular endosperm. Endosperm cells store reserve food. Some are used by the developing embryo, and in some seeds the endosperm persists.

Embryo. The embryo develops at the micropylar end of the embryo sac, where the zygote is located. The zygote divides only after some endosperm has formed. The stages in a dicot are: proembryo → globular → heart-shaped → mature embryo.

FeatureDicot embryoMonocot embryo
CotyledonsTwoOne (the scutellum, lying on one side of the embryonal axis)
Embryonal axisEpicotyl (ends in the plumule) and hypocotyl (ends in the radicle with a root cap)Short axis with radicle and plumule
SheathsNoneRadicle and root cap enclosed in coleorhiza; plumule enclosed in coleoptile
ExamplePea, beanMaize, wheat, rice

Seed and fruit

Seed. A seed contains the seed coat (from the integuments), cotyledon(s) and an embryonal axis. The seed coat has an outer testa and an inner tegmen. The micropyle remains as a small pore. It helps in the entry of oxygen and water during germination.

  • Albuminous (endospermic) seeds keep some endosperm because it is not completely used up by the embryo. Examples are wheat, maize, barley, castor.
  • Ex-albuminous (non-endospermic) seeds have no residual endosperm, because it is completely consumed. Examples are pea and groundnut.
  • Perisperm is the residual, persistent nucellus. Examples are black pepper and beet.

As the seed matures it loses water and becomes dry (about 10–15 per cent moisture). The embryo becomes dormant, which is a state of reduced metabolism. Dormancy ends when conditions such as water, oxygen and suitable temperature are present.

Fruit. The ovary develops into the fruit, and the ovary wall becomes the pericarp (wall of the fruit). In most plants the fruit develops from the ovary alone. In some, such as apple, strawberry and cashew, other parts of the flower (such as the thalamus) also form part of the fruit. Such fruits are called false fruits. Fruits formed only from the ovary are true fruits.

Parthenocarpy. Development of fruit without fertilisation is called parthenocarpy. Such fruits are seedless. Banana is a common example. Parthenocarpy can be induced by growth regulators.

Apomixis and polyembryony

Apomixis is the production of seeds without fertilisation. It is a form of asexual reproduction that mimics sexual reproduction. It occurs in some species of Asteraceae and grasses. The ways are:

  • A diploid egg cell is formed without reduction division (meiosis) and develops into an embryo without fertilisation.
  • In many species (for example citrus and mango) some cells of the nucellus protrude into the embryo sac and develop into embryos.

Polyembryony is the occurrence of more than one embryo in a seed. It is common in citrus and mango, where nucellar embryos form. Apomixis is valuable because hybrid seeds can keep their character for generations, so farmers need not buy fresh hybrid seeds every year.

NEET traps

  • 1. Geitonogamy vs xenogamy: geitonogamy is between flowers of the same plant, so it is genetically autogamy even though it needs an agent. Xenogamy needs different plants.
  • 2. Endothecium vs tapetum: endothecium is hygroscopic and helps dehiscence. Tapetum is the innermost layer and nourishes pollen.
  • 3. Exine vs intine: exine is sporopollenin (outer, resistant). Intine is cellulose and pectin (inner).
  • 4. Egg apparatus vs embryo sac: egg apparatus is only the egg and two synergids (3 cells). The embryo sac has 7 cells and 8 nuclei.
  • 5. Chalazal vs micropylar end: antipodals are at the chalazal end. The egg apparatus is at the micropylar end.
  • 6. Syngamy vs triple fusion: syngamy gives 2n zygote. Triple fusion gives 3n PEN.
  • 7. Cleistogamous vs chasmogamous: cleistogamous flowers never open and are always autogamous. Chasmogamous flowers open.
  • 8. Monoecious vs dioecious: monoecious (castor, maize) still allows geitonogamy. Dioecious (papaya) prevents both autogamy and geitonogamy.
  • 9. Albuminous vs ex-albuminous: castor and wheat are albuminous. Pea and groundnut are ex-albuminous.
  • 10. Perisperm vs endosperm: perisperm is leftover nucellus (2n). Endosperm is from triple fusion (3n).

One-liners

  • 1. The anther is bilobed, dithecous and tetragonal in section, with four microsporangia.
  • 2. The wall layers of the microsporangium from outside are epidermis, endothecium, middle layers and tapetum.
  • 3. Microspore tetrads are formed by meiosis of the pollen mother cell.
  • 4. The exine of pollen is made of sporopollenin, which no known enzyme degrades.
  • 5. A pollen grain is about 25–50 micrometres in diameter.
  • 6. Pollen of rice and wheat stays viable for only about 30 minutes.
  • 7. Pollen is stored in liquid nitrogen at –196 °C.
  • 8. The ovule is attached to the placenta by the funicle at the hilum.
  • 9. Only one of the four megaspores is functional in monosporic development.
  • 10. The mature embryo sac has 3 + 3 + 2 nuclei, in the egg apparatus, antipodals and central cell.
  • 11. Cleistogamous flowers (Viola, Oxalis, Commelina) assure seed set.
  • 12. Emasculation removes anthers, and bagging uses butter paper.
  • 13. The male gamete that fuses with the egg and the one that fuses with the polar nuclei come from the same pollen tube.
  • 14. Coconut water is free-nuclear endosperm.
  • 15. Apomixis and polyembryony are seen in citrus and mango, and banana shows parthenocarpy.

Practice questions

  1. Which is the innermost wall layer of a microsporangium?

    1. Endothecium
    2. Epidermis
    3. Tapetum
    4. Middle layer
    Answer

    C. Tapetum

    The tapetum is the innermost layer and nourishes the developing pollen grains.

  2. The exine of a pollen grain is made of

    1. pectin
    2. sporopollenin
    3. cellulose
    4. chitin
    Answer

    B. sporopollenin

    Exine is sporopollenin, a highly resistant organic material; cellulose and pectin form the intine.

  3. How many cells are present in a mature Polygonum-type embryo sac?

    1. 7
    2. 8
    3. 6
    4. 4
    Answer

    A. 7

    Three antipodals, one egg, two synergids and one central cell make 7 cells (8 nuclei).

  4. Pollen grains of rice and wheat remain viable for only about

    1. 3 hours
    2. 30 days
    3. 3 days
    4. 30 minutes
    Answer

    D. 30 minutes

    In rice and wheat pollen loses viability within about 30 minutes of release.

  5. The filiform apparatus is a cellular thickening present in the

    1. synergids
    2. antipodal cells
    3. central cell
    4. egg cell
    Answer

    A. synergids

    Synergids have the filiform apparatus at the micropylar tip, which guides the pollen tube.

  6. Which of the following bears cleistogamous flowers?

    1. Zostera
    2. Papaya
    3. Vallisneria
    4. Viola
    Answer

    D. Viola

    Viola, Oxalis and Commelina bear cleistogamous flowers that never open.

  7. Tender coconut water is an example of

    1. nucellar tissue
    2. cellular endosperm
    3. free-nuclear endosperm
    4. perisperm
    Answer

    C. free-nuclear endosperm

    Coconut water is free-nuclear endosperm; the white kernel is cellular endosperm.

  8. The scutellum of a monocot embryo represents the

    1. coleorhiza
    2. single cotyledon
    3. coleoptile
    4. epicotyl
    Answer

    B. single cotyledon

    The scutellum is the single cotyledon of a grass embryo, on one side of the axis.

  9. Perisperm, the persistent remnant of nucellus in a seed, is seen in

    1. wheat
    2. black pepper
    3. pea
    4. castor
    Answer

    B. black pepper

    Black pepper and beet retain perisperm; wheat and castor have endosperm; pea has none.

  10. Triple fusion results in the formation of

    1. diploid primary endosperm nucleus
    2. diploid zygote
    3. triploid zygote
    4. triploid primary endosperm nucleus
    Answer

    D. triploid primary endosperm nucleus

    One male gamete fuses with two polar nuclei, giving a 3n primary endosperm nucleus.

  11. The endothecium of an anther wall mainly

    1. nourishes the pollen grains
    2. produces sporopollenin
    3. helps in dehiscence of the anther
    4. forms the microspore tetrads
    Answer

    C. helps in dehiscence of the anther

    Endothecium is hygroscopic and helps release of pollen by dehiscence.

  12. Development of fruit without fertilisation is seen in

    1. banana
    2. apple
    3. strawberry
    4. cashew
    Answer

    A. banana

    Banana is parthenocarpic; apple, strawberry and cashew are false fruits.

  13. Polyembryony is commonly seen in

    1. citrus
    2. wheat
    3. maize
    4. pea
    Answer

    A. citrus

    Nucellar cells form extra embryos in citrus and mango.

  14. Geitonogamy is genetically equivalent to

    1. parthenocarpy
    2. autogamy
    3. apomixis
    4. xenogamy
    Answer

    B. autogamy

    Pollen comes from the same plant, so it is genetically like autogamy though it needs an agent.

  15. The pollen tube enters the embryo sac through the

    1. chalazal end
    2. hilum
    3. filiform apparatus of a synergid
    4. antipodal cells
    Answer

    C. filiform apparatus of a synergid

    The tube enters via the micropyle and then one synergid through the filiform apparatus.

  16. In a monocot embryo the plumule is enclosed in the

    1. scutellum
    2. testa
    3. coleorhiza
    4. coleoptile
    Answer

    D. coleoptile

    Coleoptile covers the plumule; coleorhiza covers the radicle and root cap.

  17. Given below are two statements: Statement I: The tapetum nourishes the developing pollen grains. Statement II: The endothecium is the innermost layer of the anther wall. Choose the correct answer.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    C. Statement I is correct but Statement II is incorrect

    Tapetum is the innermost layer; the endothecium lies below the epidermis.

  18. Given below are two statements: Statement I: The generative cell of a pollen grain is large and has an irregularly shaped nucleus. Statement II: The vegetative cell has abundant food reserve. Choose the correct answer.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    D. Statement I is incorrect but Statement II is correct

    The vegetative cell is large with an irregular nucleus; the generative cell is small and spindle-shaped.

  19. Given below are two statements: Statement I: Geitonogamy requires a pollinating agent. Statement II: Geitonogamy is genetically a type of autogamy. Choose the correct answer.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    A. Both Statement I and Statement II are correct

    Pollen moves between flowers of one plant, so an agent is needed, but the genetic result is like autogamy.

  20. Given below are two statements: Statement I: Cleistogamous flowers set seeds even without pollinators. Statement II: In cleistogamous flowers the anthers and stigma are exposed to the outside. Choose the correct answer.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    C. Statement I is correct but Statement II is incorrect

    Cleistogamous flowers never open, so pollination occurs inside the closed flower.

  21. Given below are two statements: Statement I: Papaya, being dioecious, prevents both autogamy and geitonogamy. Statement II: Castor, being monoecious, prevents geitonogamy. Choose the correct answer.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    C. Statement I is correct but Statement II is incorrect

    Monoecious plants like castor prevent autogamy but still allow geitonogamy.

  22. Which of the following statements are correct? 1. Emasculation is the removal of anthers before they dehisce. 2. Bagging prevents contamination by unwanted pollen. 3. Emasculation is essential when the female parent bears unisexual flowers.

    1. 1 and 2 only
    2. 2 and 3 only
    3. 1 and 3 only
    4. 1, 2 and 3
    Answer

    A. 1 and 2 only

    Unisexual female flowers have no anthers, so only bagging is needed; statement 3 is wrong.

  23. Given below are two statements: Statement I: The germ pores of the pollen grain are regions where sporopollenin is present. Statement II: The intine is made of sporopollenin. Choose the correct answer.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    B. Both Statement I and Statement II are incorrect

    Germ pores lack sporopollenin; the intine is cellulose and pectin.

  24. Which of the following statements are correct? 1. Castor seeds are albuminous. 2. Pea seeds are ex-albuminous. 3. Beet seeds show perisperm.

    1. 1 and 2 only
    2. 2 and 3 only
    3. 1 and 3 only
    4. 1, 2 and 3
    Answer

    D. 1, 2 and 3

    Castor retains endosperm, pea consumes it, and beet keeps perisperm.

  25. Given below are two statements: Statement I: In a monocot embryo the coleorhiza encloses the plumule. Statement II: In a monocot embryo the coleoptile encloses the plumule. Choose the correct answer.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    D. Statement I is incorrect but Statement II is correct

    Coleorhiza covers the radicle and root cap; coleoptile covers the plumule.

  26. Given below are two statements: Statement I: All aquatic plants are pollinated by water. Statement II: In Vallisneria, pollen is carried passively on the water surface to the female flower. Choose the correct answer.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    D. Statement I is incorrect but Statement II is correct

    Water lily and water hyacinth are insect or wind pollinated; Vallisneria uses surface water currents.

  27. Assertion (A): Pollen grains are well preserved as fossils. Reason (R): The exine of pollen is made of sporopollenin, which resists degradation.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    A. Both A and R are true and R is the correct explanation of A

    Sporopollenin withstands heat, acids, alkali and enzymes, so pollen persists as fossils.

  28. Assertion (A): The tapetum is important for pollen development. Reason (R): The tapetum is the outermost layer of the anther wall.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    C. A is true but R is false

    Tapetum nourishes pollen but is the innermost layer, so R is false.

  29. Assertion (A): Apomixis is a form of sexual reproduction. Reason (R): In apomixis seeds are formed without fertilisation.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    D. A is false but R is true

    Apomixis is asexual reproduction that mimics sexual reproduction, so A is false; R is true.

  30. Assertion (A): Emasculation is done before the anthers dehisce. Reason (R): After emasculation the flower is covered with a bag of butter paper.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    B. Both A and R are true but R is not the correct explanation of A

    Both are true, but bagging prevents foreign pollen; it does not explain why emasculation is done early.

  31. Assertion (A): Monoecious plants prevent geitonogamy. Reason (R): Male and female flowers occur on the same plant in monoecious plants.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    D. A is false but R is true

    Monoecious plants prevent autogamy only; geitonogamy remains possible, so A is false.

  32. Assertion (A): Parthenocarpic fruits are seedless. Reason (R): The fruit develops without fertilisation, so the ovules do not form seeds.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    A. Both A and R are true and R is the correct explanation of A

    Without fertilisation the ovules do not develop into seeds.

  33. Match List I with List II. List I: a. Funicle b. Micropyle c. Chalaza d. Nucellus List II: i. Basal part of the ovule, opposite the micropyle ii. Stalk of the ovule iii. Small opening at the ovule tip iv. Tissue with reserve food

    1. a-i, b-iv, c-ii, d-iii
    2. a-ii, b-iii, c-i, d-iv
    3. a-iii, b-ii, c-i, d-iv
    4. a-iv, b-i, c-iii, d-ii
    Answer

    B. a-ii, b-iii, c-i, d-iv

    Funicle-stalk (ii), micropyle-opening (iii), chalaza-basal part (i), nucellus-reserve food (iv).

  34. Match List I with List II. List I: a. Epidermis b. Endothecium c. Middle layers d. Tapetum List II: i. Nourishes pollen grains ii. Hygroscopic, helps dehiscence iii. Outermost protective layer iv. Degenerate in the mature anther

    1. a-iv, b-ii, c-iii, d-i
    2. a-iii, b-ii, c-iv, d-i
    3. a-iii, b-i, c-ii, d-iv
    4. a-ii, b-iii, c-i, d-iv
    Answer

    B. a-iii, b-ii, c-iv, d-i

    Epidermis-iii, endothecium-ii, middle layers-iv, tapetum-i.

  35. Match List I with List II. List I: a. Viola b. Vallisneria c. Maize d. Papaya List II: i. Wind pollination ii. Dioecious iii. Cleistogamous flowers iv. Water pollination

    1. a-i, b-iv, c-iii, d-ii
    2. a-iii, b-iv, c-i, d-ii
    3. a-ii, b-iv, c-i, d-iii
    4. a-iii, b-i, c-iv, d-ii
    Answer

    B. a-iii, b-iv, c-i, d-ii

    Viola-iii, Vallisneria-iv, maize-i, papaya-ii.

  36. Match List I with List II. List I: a. Castor b. Pea c. Black pepper d. Banana List II: i. Ex-albuminous seed ii. Albuminous seed iii. Parthenocarpy iv. Perisperm

    1. a-i, b-ii, c-iv, d-iii
    2. a-ii, b-i, c-iii, d-iv
    3. a-ii, b-i, c-iv, d-iii
    4. a-iv, b-i, c-ii, d-iii
    Answer

    C. a-ii, b-i, c-iv, d-iii

    Castor-ii, pea-i, black pepper-iv, banana-iii.

  37. Match List I with List II. List I: a. Scutellum b. Coleoptile c. Coleorhiza d. Epicotyl List II: i. Sheath over the radicle ii. Sheath over the plumule iii. Cotyledon of a monocot iv. Part of the axis above the cotyledon(s)

    1. a-iii, b-ii, c-i, d-iv
    2. a-iii, b-i, c-ii, d-iv
    3. a-iii, b-ii, c-iv, d-i
    4. a-ii, b-iii, c-i, d-iv
    Answer

    A. a-iii, b-ii, c-i, d-iv

    Scutellum-iii, coleoptile-ii, coleorhiza-i, epicotyl-iv.

  38. Match List I with List II. List I: a. Egg apparatus b. Antipodals c. Central cell d. Filiform apparatus List II: i. Three cells at the chalazal end ii. Egg cell with two synergids iii. Cell holding two polar nuclei iv. Thickening at the synergid tip

    1. a-iv, b-i, c-iii, d-ii
    2. a-ii, b-iii, c-i, d-iv
    3. a-ii, b-i, c-iii, d-iv
    4. a-i, b-ii, c-iii, d-iv
    Answer

    C. a-ii, b-i, c-iii, d-iv

    Egg apparatus-ii, antipodals-i, central cell-iii, filiform apparatus-iv.

  39. In a wild plant the anthers release pollen several days before the stigma of the same flower becomes receptive. This is an example of

    1. parthenocarpy
    2. an outbreeding device (non-synchronised pollen release and stigma receptivity)
    3. apomixis
    4. cleistogamy
    Answer

    B. an outbreeding device (non-synchronised pollen release and stigma receptivity)

    Asynchrony of pollen release and receptivity promotes cross-pollination.

  40. A breeder wants to cross two plants. The female parent has bisexual flowers. What should be done first, before the flower opens?

    1. Remove the anthers with forceps, then bag the flower
    2. Cut the stigma and bag the flower
    3. Remove the ovary and rebag it
    4. Dust pollen on the stigma and leave it open
    Answer

    A. Remove the anthers with forceps, then bag the flower

    Emasculation precedes bagging; pollen is dusted later when the stigma is receptive.

  41. A researcher wants to keep pollen alive for several years. The pollen should be stored at

    1. about 25 °C in dry air
    2. about 37 °C in water
    3. about 4 °C in a refrigerator
    4. about –196 °C in liquid nitrogen
    Answer

    D. about –196 °C in liquid nitrogen

    Cryopreservation in liquid nitrogen at –196 °C preserves viability.

  42. An anther has 100 pollen mother cells that all undergo meiosis normally. How many pollen grains can form?

    1. 200
    2. 400
    3. 100
    4. 800
    Answer

    B. 400

    Each PMC forms a tetrad of four microspores, each becoming one pollen grain.

  43. A plant has a diploid number of 24. How many chromosomes are present in a cell of its endosperm?

    1. 36
    2. 48
    3. 24
    4. 12
    Answer

    A. 36

    The primary endosperm nucleus is 3n (three sets of n = 12).

  44. A citrus seed gives rise to several seedlings, and most are identical to the mother plant. This is best explained by

    1. fusion of many polar nuclei
    2. development of several egg cells by meiosis
    3. nucellar embryos formed without fertilisation
    4. pollen tubes carrying many gametes
    Answer

    C. nucellar embryos formed without fertilisation

    Nucellar cells form embryos without meiosis or fertilisation (polyembryony with apomixis).

  45. Pollen from one species lands on the stigma of another species but fails to germinate. The most likely reason is

    1. the exine has no sporopollenin
    2. the pistil recognises it as incompatible and rejects it
    3. the pollen is always 3-celled
    4. the stigma lacks a style
    Answer

    B. the pistil recognises it as incompatible and rejects it

    The pollen-pistil interaction accepts only compatible pollen.

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