NCERT Exemplar Sexual Reproduction in Flowering Plants - 1 - Biology Class 12 - NEET

Multiple-Choice Questions

Q.1. Among the terms listed below, those that are not technically correct names for a floral whorl are:
i. Androecium
ii. Carpel
iii. Corolla
iv. Sepal

(a) i and iv
(b) iii and iv
(c) ii and iv
(d) i and ii
Ans. (c)

Sol.

• There are four floral whorls: calyx, corolla, androecium and gynoecium.
• Calyx and corolla are accessory (non-essential) whorls; androecium and gynoecium are reproductive whorls.
• The members of calyx are called sepals and members of gynoecium are carpels. Thus carpel and sepal are names of members, not names of whorls; they are not technically names of a floral whorl.

Different floral whorls

Q.2. The embryo sac is to ovule as _______ is to an anther.
(a) Stamen
(b) Filament
(c) Pollen grain
(d) Androecium
Ans. (c)

Sol.

• Embryo sac (female gametophyte) is contained within the ovule (megasporangium).
• Pollen grain (male gametophyte) is contained within the anther (microsporangium).

Q.3. In a typically complete, bisexual and hypogynous flower, the arrangement of floral whorls on the thalamus from the outermost to the innermost is:
(a) Calyx, corolla, androecium and gynoecium
(b) Calyx, corolla, gynoecium and androecium
(c) Gynoecium, androecium, corolla and calyx
(d) Androecium, gynoecium, corolla and calyx
Ans. (a)

Sol. Arrangement of floral whorls on the thalamus from the outermost to the innermost is : Calyx → Corolla → Androecium → Gynoecium.

Q.4. A dicotyledonous plant bears flowers but never produces fruits and seeds. The most probable cause for the above situation is:
(a) Plant is dioecious and bears only pistillate flowers.
(b) Plant is dioecious and bears both pistillate and staminate flowers.
(c) Plant is monoecious.
(d) Plant is dioecious and bears only staminate flowers.
Ans. (d)

Sol. If a plant bears only staminate (male) flowers, fertilisation cannot occur and no fruits or seeds will be produced. A dioecious plant with only staminate flowers therefore will not set fruit or seeds.

Q.5. The outermost and innermost wall layers of microsporangium in an anther are respectively:
(a) Endothecium and tapetum
(b) Epidermis and endodermis
(c) Epidermis and middle layer
(d) Epidermis and tapetum
Ans. (d)

Sol. Wall layers of microsporangium in an anther are:

Microsporangium

Q.6. During microsporogenesis, meiosis occurs in:
(a) Endothecium
(b) Microspore mother cells
(c) Microspore tetrads
(d) Pollen grains
Ans. (b)

Sol.

• Microsporogenesis is the formation of microspores from diploid microspore mother cells (microsporocytes).
• Meiosis (reduction division) occurs in the microspore mother cells to produce haploid microspores which may remain in tetrads initially and later separate to form pollen grains.

Q.7. From Among the sets of terms given below, identify those that are associated with the gynoecium.
(a) Stigma, ovule, embryo sac, placenta
(b) Thalamus, pistil, style, ovule
(c) Ovule, ovary, embryo sac, tapetum
(d) Ovule, stamen, ovary, embryo sac
Ans. (a)

Sol.

• Stigma is the receptive surface of the pistil where pollen lands.
• Ovule is present within the ovary and contains the embryo sac (female gametophyte).
• Embryo sac (female gametophyte) develops inside the ovule.
• Placenta is the tissue or ridge inside the ovary to which ovules are attached.
• Thalamus bears the floral appendages but is not part of the gynoecium; tapetum is part of microsporangium (anther) and stamen is part of androecium.

Q.8. Starting from the innermost part, the correct sequence of parts in an ovule is:
(a) Egg, nucellus, embryo sac, integument
(b) Egg, embryo sac, nucellus, integument
(c) Embryo sac, nucellus, integument, egg
(d) Egg, integument, embryo sac, nucellus
Ans. (b)

Sol. The correct sequence of parts in an ovule (from inside out) is :

Ovule

• The egg is present within the embryo sac (female gametophyte).
• The embryo sac develops within the nucellus (megasporangium tissue).
• The integuments surround the nucellus; at the micropyle they leave a small opening.
• Therefore, from innermost to outermost: egg → embryo sac → nucellus → integument.

Q.9. From the statements given below, choose the option that are true for a typical female gametophyte of a flowering plant:
i. It is 8-nucleate and 7-celled at maturity.
ii. It is free-nuclear during the development.
iii. It is situated inside the integument but outside the nucellus.
iv. It has an egg apparatus situated at the chalazal end.
(a) i and iv
(b) ii and iii
(c) i and ii
(d) ii and iv
Ans. (c)

Sol.

• A typical angiosperm embryo sac (Polygonum type) is formed from a functional megaspore which undergoes three mitotic divisions producing 8 nuclei that are arranged into 7 cells at maturity: three antipodals (chalazal), two polar nuclei (central cell), three cells at micropylar end forming the egg apparatus (one egg + two synergids).
• During its development the embryo sac is free-nuclear (nuclei divide without immediate cell wall formation), followed by cellularisation to form the seven cells.
• The embryo sac is situated inside the nucellus, which in turn is enclosed by integuments; statement iii is incorrect.
• The egg apparatus is situated at the micropylar end, not at the chalazal end; statement iv is incorrect.

Q.10. Autogamy can occur in a chasmogamous flower if:
(a) Pollen matures before the maturity of an ovule.
(b) Ovules mature before the maturity of pollen.
(c) Both pollen and ovules mature simultaneously.
(d) Both anther and stigma are of equal lengths.
Ans. (c)

Sol.

• Autogamy means self-pollination within the same flower.
• In chasmogamous flowers (flowers open and expose their organs) autogamy requires synchrony: pollen release and stigma receptivity must coincide and the anthers and stigma must be positioned so pollen can reach the stigma.
• Therefore, autogamy is most likely when both pollen and ovules mature simultaneously.

Q.11. Choose the correct statement from the following:
(a) Cleistogamous flowers always exhibit autogamy.
(b) Chasmogamous flowers always exhibit geitonogamy.
(c) Cleistogamous flowers exhibit both autogamy and geitonogamy.
(d) Chasmogamous flowers never exhibit autogamy.
Ans. (a)

Sol.

• Cleistogamous flowers remain closed and do not open; hence they undergo invariable autogamy (selfing within the closed flower), ensuring seed set even without pollinators.
• Examples of cleistogamous plants: Viola, Oxalis, Commelina, Arachis hypogaea, Oryza sativa.

Q.12. A particular species of the plant produces light, non-sticky pollen in large numbers and its stigmas are long and feathery. These modifications facilitate pollination by:
(a) Insects
(b) Water
(c) Wind
(d) Animals
Ans. (c)

Sol.

• Pollination by wind is called anemophily.
• Anemophilous flowers are usually small, inconspicuous, lack nectar, scent and bright colours, and produce a very large number of light, dry, non-sticky pollen grains.
• Such flowers often have long, feathery stigmas to catch airborne pollen, matching the description; so pollination is by wind.

Q.13. From among the situations given below, choose the one that prevents both autogamy and geitonogamy.
(a) Monoecious plant bearing unisexual flowers.
(b) Dioecious plant bearing only male or female flowers.
(c) Monoecious plant with bisexual flowers.
(d) Dioecious plant with bisexual flowers.
Ans. (b)

Sol.

• Autogamy = selfing within the same flower. Geitonogamy = transfer of pollen between different flowers of the same plant.
• In a dioecious species individual plants are either male (only staminate flowers) or female (only pistillate flowers); therefore, a plant bearing only male or only female flowers cannot self-fertilise and cannot receive pollen from its own flowers - both autogamy and geitonogamy are prevented.

Q.14. In a fertilised embryo sac, the haploid, diploid and triploid structures are:
(a) Synergid, zygote and primary endosperm nucleus.
(b) Synergid, antipodal and polar nuclei.
(c) Antipodal, synergid and primary endosperm nucleus.
(d) Synergid, polar nuclei and zygote.
Ans. (a)

Sol.

• Synergids are haploid (n) cells at the micropylar end of the embryo sac.
• The zygote (fusion of egg and male gamete) is diploid (2n).
• The primary endosperm nucleus (PEN) formed by fusion of two polar nuclei and one male gamete is triploid (3n).
• Thus, haploid = synergid; diploid = zygote; triploid = primary endosperm nucleus.

Mature embryo sac of an angiosperm

Q.15. In an embryo sac, the cells that degenerate after fertilisation are:
(a) Synergids and primary endosperm cell
(b) Synergids and antipodals
(c) Antipodals and primary endosperm cell
(d) Egg and antipodals
Ans. (b)

Sol.

• After fertilisation the synergids usually degenerate once the pollen tube has entered and released male gametes.
• The antipodals typically degenerate after fertilisation; their persistent function is limited or variable across species.
• The primary endosperm cell (PEN) does not degenerate; it divides to form endosperm tissue. The egg fuses to form zygote, so it does not degenerate.

The following conversion takes place:

Q.16. While planning for an artificial hybridization programme involving dioecious plants, which of the following steps would not be relevant:
(a) Bagging of a female flower.
(b) Dusting of pollen on the stigma.
(c) Emasculation
(d) Collection of pollen.
Ans. (c)

Sol.

• Artificial hybridisation is a human-performed controlled cross between two selected parents to combine desirable traits.
• Important precautions include bagging (to prevent unwanted pollen) and collection and dusting of pollen from the chosen male parent into the receptive stigma of the chosen female parent.
• Emasculation (removal of anthers from bisexual flowers) prevents self-pollination but is not required in dioecious species because male and female flowers occur on separate plants.

Q.17. In the embryos of a typical dicot and a grass, true homologous structures are: 
(a) Coleorhiza and coleoptile
(b) Coleoptile and scutellum
(c) Cotyledons and scutellum
(d) Hypocotyl and radicle
Ans. (c)

Sol.

• In dicots the embryo has two cotyledons which often store food and may become photosynthetic after germination.
• In monocots of the grass family the single cotyledon is modified into a scutellum, a specialised structure for absorbing nourishment from endosperm during germination.
• Therefore, cotyledons (dicot) and scutellum (monocot) are homologous structures derived from the same embryonic organ.
• Example: scutellum is seen in grasses such as sorghum, maize, rice.

Q.18. The phenomenon observed in some plants wherein parts of the sexual apparatus is used for forming embryos without fertilisation is called:
(a) Parthenocarpy
(b) Apomixis
(c) Vegetative propagation
(d) Sexual reproduction
Ans. (b)

Sol.

• Apomixis is the formation of seeds without fertilisation; embryos arise from somatic cells of the ovule (e.g., nucellus) or from unfertilised egg cells, producing offspring genetically identical to the mother.
• Parthenocarpy refers to development of fruit without fertilisation; parthenocarpic fruits are typically seedless (examples: banana, some grapes).

Q.19. In a flower, if the megaspore mother cell forms megaspores without undergoing meiosis and if one of the megaspores develops into an embryo sac, its nuclei would be:
(a) Haploid
(b) Diploid
(c) A few haploid and a few diploid
(d) With varying ploidy
Ans. (b)

Sol.

• Meiosis reduces chromosome number from diploid (2n) to haploid (n). If the megaspore mother cell (MMC) does not undergo meiosis, it remains diploid.
• If such a diploid MMC directly forms an embryo sac, the nuclei in that embryo sac will be diploid (2n), not haploid.

Q.20. The phenomenon wherein the ovary develops into a fruit without fertilisation is called:
(a) Parthenocarpy
(b) Apomixis
(c) Asexual reproduction
(d) Sexual reproduction
Ans. (a)

Sol. Parthenocarpy is development of fruit without fertilisation of the ovary and therefore usually results in seedless fruits. Examples include certain varieties of banana and some grapes.

Very Short Answer Type Questions

Q.1. Name the component cells of the 'egg apparatus' in an embryo sac.
Ans. Egg apparatus has three cells-one egg cell and two synergids.

Q.2. Name the part of gynoecium that determines the compatible nature of pollen grain.
Ans. The stigma of the carpel/pistil determines compatibility of pollen grain; it recognises compatible pollen and permits pollen germination and pollen tube growth.

Q.3. Name the common function that cotyledons and nucellus perform.
Ans. Both cotyledons and nucellus provide nourishment to the developing embryo/young seedling.

Q.4. Complete the following flow chart

Ans.

Q.5. Indicate the stages where meiosis and mitosis occur (1, 2 or 3) in the flow chart.

Ans.

Q.6. The diagram given below shows the path of a pollen tube from the pollen on the stigma into the embryo sac. Name the components of the egg apparatus.

Ans. Components of egg apparatus: one egg cell and two synergids.

Egg

Q.7. Name the parts of the pistil which develop into fruit and seeds.
Ans. The ovary develops into the fruit and the ovules develop into seeds.

Q.8. In the case of polyembryony, if an embryo develops from the synergid and another from the nucellus which is haploid and which is diploid?
Ans. A synergid-derived embryo will be haploid (develops without fertilisation unless it becomes diploid by other means), whereas a nucellar embryo (from nucellus tissue) will be diploid (somatic origin, genetically identical to the mother).

Q.9. Can an unfertilised, apomictic embryo sac give rise to a diploid embryo? If yes, then how?
Ans. Yes. If the embryo develops from diploid somatic cells of the ovule such as the nucellus or integument (apomixis by sporophytic origin), the embryo will be diploid because it arises from a somatic 2n cell.

Q.10. Which are the three cells found in a pollen grain when it is shed at the three celled stage?
Ans. One vegetative (tube) cell and two male gametes (sperm cells).

Q.11. What is self-incompatibility?
Ans. Self-incompatibility (self-sterility) is a genetic mechanism that prevents inbreeding by inhibiting germination of self pollen or growth of self pollen tubes in the pistil, thereby preventing self-fertilisation.

Q.12. Name the type of pollination in self-incompatible plants.
Ans. Xenogamy (cross-pollination between different plants) is required in self-incompatible plants.

Q.13. Draw the diagram of a mature embryo sac and show its 8-nucleate, 7-celled nature. Show the following parts: antipodals, synergids, egg, central cell, polar nuclei.
Ans.

Q.14. Which is the triploid tissue in a fertilized ovule? How is the triploid condition achieved?
Ans. The endosperm is triploid (3n). Triploidy arises by triple fusion: fusion of two haploid polar nuclei (n + n) with one haploid male gamete (n) producing the primary endosperm nucleus (3n).

Q.15. Are pollination and fertilization necessary in apomixis? Give reasons.
Ans. No. In apomixis seeds and embryos can form without pollination and fertilisation because embryos may develop directly from somatic cells of the ovule (e.g., nucellus) or from an unfertilised egg; thus sexual fusion is not required.

Q.16. Identify the type of carpel with the help of diagrams given below:

Ans.

• (a) Multicarpellary, syncarpous pistil (carpels fused) - example: Papaver.
• (b) Multicarpellary, apocarpous gynoecium (carpels free) - example: Michelia.

Q.17. How is pollination carried out in water plants?
Ans.

• Pollination by water is called hydrophily. True hydrophily occurs in some aquatic plants such as Vallisneria and Hydrilla (freshwater) and some marine seagrasses like Zostera, where pollen is transported by water currents.
• However, not all aquatic plants are hydrophilous; many aquatic flowers rise above water and are pollinated by wind or insects (e.g., water hyacinth, water lily).

Q.18. What is the function of the two male gametes produced by each pollen grain in angiosperms?
Ans.

• After the pollen tube enters the embryo sac and releases the two male gametes, one male gamete fuses with the egg cell to form the zygote (syngamy) which develops into the embryo (diploid).
• The other male gamete fuses with the two polar nuclei in the central cell to form the primary endosperm nucleus (PEN) which is triploid and develops into nutritive endosperm (triple fusion).