Chapter 1: Sexual Reproduction in Flowering Plants (Reproduction)
Exam-ready answers to all 18 exercises of Chapter 1, Sexual Reproduction in Flowering Plants (NCERT Class 12 Biology, 2026-27): microsporogenesis and megasporogenesis, the ovule and embryo sac, pollination and outbreeding devices, self-incompatibility, bagging and emasculation, double fertilisation and triple fusion, seed and fruit parts, false fruits, parthenocarpy, tapetum and apomixis. All 18 questions are answered, with the key answer highlighted.
Differentiate between microsporogenesis and megasporogenesis. Which type of cell division occurs during these events? Name the structures formed at the end of these two events.
Solution
Microsporogenesis
Megasporogenesis
Formation of microspores from the pollen mother cell (microspore mother cell)
Formation of megaspores from the megaspore mother cell
Occurs in the microsporangium (pollen sac) of the anther
Occurs in the nucellus of the ovule
All four microspores of the tetrad are functional
Usually only one of the four megaspores is functional; three degenerate
Ends with a microspore tetrad, which forms pollen grains
Ends with megaspores; the functional one forms the embryo sac
Both involve meiosis (reduction division), so the spores are haploid. The end products are microspore tetrads (pollen grains) and megaspores (a linear tetrad).
Microsporogenesis gives four functional microspores (pollen) in the anther; megasporogenesis gives one functional megaspore in the ovule. Both are by meiosis.
Arrange the following terms in the correct developmental sequence: Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.
With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.
Solution
The ovule is attached to the placenta by a stalk, the funicle. The point where the funicle joins the body of the ovule is the hilum. The ovule has:
Integuments (one or two protective layers) that cover the ovule except at a small opening, the micropyle.
Chalaza, the basal part opposite the micropyle, where the integuments and nucellus meet.
Nucellus, a mass of nutritive tissue inside the integuments.
Embryo sac (female gametophyte), located inside the nucellus, usually towards the micropylar end; it contains the egg apparatus, the central cell with polar nuclei, and antipodal cells.
Labels for the diagram (anatropous ovule): funicle, hilum, micropyle, outer integument, inner integument, nucellus, embryo sac, chalaza.
An ovule = funicle and hilum, integuments with a micropyle, chalaza, nucellus and the embryo sac (labels as listed).
What is meant by monosporic development of female gametophyte?
Solution
The embryo sac (female gametophyte) develops from a single functional megaspore; the other three megaspores of the tetrad degenerate. This is called monosporic development (seen in most flowering plants, e.g. the Polygonum type).
Development of the embryo sac from only one functional megaspore.
With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.
Solution
The nucleus of the functional megaspore divides mitotically three times (free nuclear divisions), giving 8 nuclei: four go to each pole. Then cell walls form:
Micropylar end: three cells form the egg apparatus: one egg cell and two synergids (with filiform apparatus).
Chalazal end: three cells form the antipodals.
Centre: the two remaining nuclei (one from each pole), the polar nuclei, stay in one large central cell.
So the mature embryo sac has 3 + 3 + 1 = 7 cells but 8 nuclei (the central cell has two).
Labels for the diagram: micropylar end, filiform apparatus, synergids, egg cell, central cell, polar nuclei, antipodals, chalazal end.
Three mitoses give 8 nuclei; walls form around 6 (egg, 2 synergids, 3 antipodals) and the central cell keeps 2 polar nuclei: 7 cells, 8 nuclei.
What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.
Solution
Chasmogamous flowers have exposed anthers and stigma, like other flowers, and open normally (e.g. Viola, Oxalis and Commelina also produce them).
No, cross-pollination cannot occur in cleistogamous flowers. These flowers never open; the anthers and stigma lie close together inside the closed flower. When the anthers dehisce, pollen falls directly on the stigma, so only self-pollination (autogamy) is possible.
Chasmogamous flowers open with exposed anthers and stigma; cleistogamous flowers never open, so only self-pollination is possible.
What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
Solution
Self-incompatibility is a genetic mechanism that prevents pollen from fertilising the ovules of the same flower or of other flowers on the same plant, by inhibiting pollen germination or pollen tube growth in the pistil.
In such species the pistil "recognises" its own pollen and stops it from germinating or stops the pollen tube from growing in the stigma or style. Since the male gametes never reach the egg, fertilisation does not happen, and no seed is formed.
A genetic block to fertilisation by the plant's own pollen; the pollen does not germinate or its tube stops growing, so there is no fertilisation and no seed.
What is bagging technique? How is it useful in a plant breeding programme?
Solution
Bagging is covering an emasculated flower (or a flower of a female plant) with a bag, usually of butter paper, to protect its stigma from contamination by unwanted pollen.
In plant breeding (artificial hybridisation), it ensures that only the desired pollen reaches the stigma. After the stigma becomes receptive, pollen from the chosen male parent is dusted on it and the flower is bagged again until the fruit develops.
Covering the emasculated flower with a bag so that only the chosen pollen pollinates it during hybridisation.
What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
Solution
Triple fusion is the fusion of a male gamete with the two polar nuclei (or the secondary nucleus) in the central cell, forming the triploid primary endosperm nucleus (PEN).
It takes place in the central cell of the embryo sac. The pollen tube releases two male gametes into a synergid; one fuses with the egg (syngamy) and the other moves to the central cell and fuses with the two polar nuclei. Since syngamy and triple fusion both occur, the process is called double fertilisation.
Nuclei involved: one male gamete nucleus and two polar nuclei.
Fusion of a male gamete with the two polar nuclei in the central cell, giving the triploid primary endosperm nucleus.
Why do you think the zygote is dormant for sometime in a fertilised ovule?
Solution
The zygote waits until some endosperm has formed. The endosperm develops first so that it can supply nourishment to the developing embryo. Once enough food is available, the zygote starts dividing to form the embryo.
Endosperm forms first, to provide nutrition to the embryo that will develop from the zygote.
Differentiate between: (a) hypocotyl and epicotyl; (b) coleoptile and coleorrhiza; (c) integument and testa; (d) perisperm and pericarp.
Solution
(a)Hypocotyl: part of the embryonal axis below the cotyledons, ending in the radicle (root tip). Epicotyl: part of the embryonal axis above the cotyledons, ending in the plumule (shoot tip).
(b)Coleoptile: a hollow foliar sheath enclosing the plumule (shoot apex) in monocot embryos (grass). Coleorrhiza: an undifferentiated sheath enclosing the radicle and root cap.
(c)Integument: the protective layer(s) of the ovule. Testa: the outer seed coat that develops from the outer integument after fertilisation.
(d)Perisperm: residual, persistent nucellus in some seeds (e.g. black pepper, beet). Pericarp: the fruit wall, developed from the ovary wall.
(a) Below vs above the cotyledons. (b) Sheath over the shoot vs over the root (monocots). (c) Ovule coat vs seed coat. (d) Leftover nucellus in the seed vs fruit wall.
Why is apple called a false fruit? Which part(s) of the flower forms the fruit?
Solution
In a true fruit, only the ovary develops into the fruit. In apple, the fleshy edible part develops mainly from the thalamus (receptacle), and the ovary forms only the core. Since parts other than the ovary contribute, apple is a false fruit. (Strawberry and cashew are other examples.)
Its fleshy part develops from the thalamus, not only from the ovary; the ovary forms the core.
What is meant by emasculation? When and why does a plant breeder employ this technique?
Solution
Emasculation is the removal of the anthers from a bisexual flower bud before the anthers dehisce, using forceps.
A plant breeder uses it in artificial hybridisation, when the female parent has bisexual flowers, to prevent self-pollination. The emasculated flower is then bagged and later pollinated with pollen from the chosen male parent.
Removing anthers from a flower bud before they shed pollen; used in hybridisation to prevent self-pollination.
If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?
Solution
Parthenocarpy produces seedless fruits without fertilisation. It is useful for fruits where seeds are undesirable and the fleshy part is eaten, such as banana, grapes, orange, watermelon, guava and pineapple. Seedless fruits are easier to eat and process (juice, canning) and fetch a better price.
Fruits eaten for their pulp where seeds are a nuisance, e.g. banana, grapes, oranges, watermelon, guava.
Explain the role of tapetum in the formation of pollen-grain wall.
Solution
The tapetum is the innermost wall layer of the microsporangium. Its cells are dense, often multinucleate, and nourish the developing pollen grains. It secretes:
the material for sporopollenin, which forms the tough outer pollen wall (exine), and
Ubisch bodies and the sticky pollenkitt that coat the pollen.
It also provides enzymes (e.g. callase) that release the microspores from the tetrad.
It nourishes the developing pollen and supplies sporopollenin (exine), pollenkitt and enzymes for wall formation.
Apomixis is the formation of seeds without fertilisation, a kind of asexual reproduction that mimics sexual reproduction (seen in some grasses and Asteraceae).
Importance: apomictic seeds are genetically identical to the parent. If hybrid varieties are made apomictic, farmers can keep using the seeds of hybrids year after year, because the hybrid characters do not segregate in the next generation. This would reduce the cost of buying hybrid seeds every year.
Seed formation without fertilisation; apomictic hybrids would keep their hybrid characters, so farmers could reuse their seeds.
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For NCERT Biology Class 12 (2026-27 edition) - all 13 chapters, CBSE board 2027
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