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|Chapter Name||Sexual Reproduction in Flowering Plants|
NCERT Exemplar Class 12 Biology Chapter 2 Sexual Reproduction in Flowering Plants
Multiple Choice Questions
Single Correct Answer Type
Question.1. Among the terms listed below, those that are of 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 andiv (d) i and ii
• There are 4 floral whorls viz., calyx, corolla, androecium and gynoecium. Calyx and corolla are accessory organs or non-essential whorl, while androecium and gynoecium are reproductive organs.
• The calyx is the outermost whorl of the flower and the members are called sepals.
• Gynoecium is the female reproductive part of the flower and is made up of one or more carpels.
Question.2. Embryo sac is to ovule as is to an anther.
(a) Stamen .(b) Filament
(c) Pollen grain (d) Androecium
• Embryo sac (female gametophyte) • Ovule (megasporangium)
• Pollen grain (male gametophyte) • Anther (microsporangium)
Question.3. In a typical 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
Answer. (a) Arrangement of floral whorls on the thalamus from the outermost to the innermost is calyx, corolla, androecium and gynoecium.
Question.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.
Answer. (d) A dicotyledonous plant bears flowers but never produces fruits and seeds because plant is dioecious and bears only staminate flowers.
Question.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
Answer. (d) Wall layers of microsporangium in an anther are:
Question.6. During microsporogenesis, meiosis occurs in
(a) Endothecium (b) Microspore mother cells
(c) Microspore tetrads (d) Pollen grains
Answer. (b) During microsporogenesis, meiosis occurs in microspore mother cells.
Question.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, qpibryo sac
Answer. (a) Stigma, ovule, embryo sac and placenta are associated with the gynoecium.
Question.8. Starting from the innermost part, the correct sequence of parts in an ovule are
(a) Egg, nucellus, embryo sac, integument .
(b) Egg, embryo sac, nucellus, integument.
(c) Embryo sac, nucellus, integument, egg
(d) Egg, integument, embryo sac, nucellus
Answer. (b) The correct sequence of parts in an ovule are
Question.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
Answer. (c) A typical female gametophyte of a flowering plant is 8-nucleate and 7-celled at maturity and free-nuclear during the development.
Question.10. Autogamy can occur in a chasmogamous flower if
(a) Pollen matures before maturity of ovule
(b) Ovules mature before maturity of pollen
(c) Both pollen and ovules mature simultaneously
(d) Both anther and stigma are of equal lengths
Answer. (c) In a normal flower which opens and exposes the anthers and stigma complete autogamy is rather rare. Autogamy in such flowers requires synchrony in pollen release and stigma receptivity and also, the anthers and the stigma should lie close to each other so that self-pollination can occur.
Question.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
Answer. (a) Cleistogamous flowers are invariably autogamous as there is no chance of cross-pollen landing on the stigma. Cleistogamous flowers produce assured seed-set even in absence of pollinators.
E.g. of cleistogamous flowers are Viola (common pansy), Oxalis, Commelina, Arachis hypogea and Oryza sativa.
Question.12. A particular species of 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
Answer. (c) Pollination by wind is called anemophily. Anemophilous flowers are small, in conspicuous non-scented without bright colours, nectar and fragrance. Wind pollination also requires that the pollen grains are light and non-sticky which is in large numbers and its stigmas are long and feathery.
Question.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
• Autogamy (same flower); geitonogamy (different flowers of same plants; xenogamy (different plant’s flower)
• Dioecious plant bearing only male or female flowers prevents both autogamy and geitonogamy.
Question.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
Answer. (a) In a fertilised embryo sac, the haploid, diploid and triploid structures are synergid, zygote and primary endosperm nucleus, respectively.
Question.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
Answer. (b) In an embryo sac, synergids and antipodals degenerate after fertilisation.
Question.16. While planning for an artificial hybridization programme involving dioecious plants, which of the following steps would not be relevant?
(a) Bagging of female flower
(b) Dusting of pollen on stigma
(d) Collection of pollen
• Artificial hybridisation is one of the major approaches of crop improvement programme. In such crossing experiments it is important to make sure that only the desired pollen grains are used for pollination and the stigma is protected from contamination (from unwanted pollen). This is achieved by emasculation and bagging techniques.
• Emasculation is relevant in monoecious plants.
Question.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
Answer. (c) Cotyledons of the typical dicot embryo are simple structures generally thick and swollen due to storage of food reserves (as in legumes) and embryo of monocots consists of one large and shield shaped cotyledon known as scutellum situated towards one side (lateral) of the embryonal axis. E.g.: Grass family, Sorghum.
Question.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
• Apomixis is the special mechanism, to produce seed without fertilisation. It is observed in few flowering plants such as some species of asteraceae and grasses.
• Apomixis is a form of asexual reproduction that mimics sexual reproduction. If a fruit is formed without fertilisation of ovary, it is called a parthenocarpic fruit, e.g., banana and grape.
Question.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
(c) A few haploid and a few diploid
(d) With varying ploidy
Answer. (b) 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 diploid.
Question.20. The phenomenon wherein, the ovary develops into a fruit without fertilisation is called
(c) Asexual reproduction
(d) Sexual reproduction’
Answer. (a) If a fruit is formed without fertilisation of ovaty, it is called a parthenocarpic fruit, e.g., banana and grape.
Very Short Answer Type Questions
Question.1. Name the component cells of the ‘egg apparatus’ in an embryo sac.
Answer. Egg apparatus have three cells—one egg cell and two synergids.
Question.2. Name the part of gynoecium that determines the compatible nature of pollen grain.
Answer. Compatible nature of pollen grain is determined by the stigma of carpel/ pistil.
Question.3. Name the common function that cotyledons and nucellus perform.
Answer. Both cotyledons and nucellus provide nourishment.
Question.4.Complete the following flow chart:
Question.5.Indicate the stages where meiosis and mitosis occur (1, 2 or 3) in the flow ?
Question.6. In the diagram given below, show the path of a pollen tube from the pollen on the stigma into the embryo sac. Name the components of egg apparatus.
Answer. Components of egg apparatus: one egg cell and two synergids.
Question.7. Name the parts of pistil which develop into fruit and seeds.
Answer. Ovaiy of pistil develops into fruit while ovules develop into seeds.
Question.8.In case of polyembryony, if an embryo develops from the synergid and another from the nucellus which is haploid and which is diploid?
Answer.Synergid embryo is haploid and nucellar embryo is diploid.
Question.9.Can an unfertilised, apomictic embryo sac give rise to a diploid embryo? If yes, then how?
Answer.Yes, if the embryo develops from the cells of nucellus or integument it will be diploid.
Question.10.Which are the three cells found in a pollen grain when it is shed at the three- celled stage?
Answer.One vegetative cell and two male gametes.
Question.11.What is self-incompatibility?
Answer.The device to prevent inbreeding is self-incompatibility or self-sterlity. This is a genetic mechanism and prevents self-pollen (from the same flower or other flowers of the same plant) from fertilising the ovules by inhibiting pollen germination or pollen tube growth in the pistil.
Question.12.Name the type of pollination in self-incompatible plants.
Question.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.
Question.14. Which is the triploid tissue in a fertilised ovule? How is the triploid condition achieved?
Answer. The triploid tissue in the ovule is the endosperm. Its triploid condition is . attained due to the fusion of two polar nuclei and one nucleus of male gamete (also referred to as triple fusion).
Question.15. Are pollination and fertilization necessary in apotnixis? Give reasons.
Answer. No, they are not necessary. Apomixis is actually an alternative to sexual
reproduction although the female sexual apparatus is used in the process. In apomicts, embryos can develop directly from the nucellus or synergid or egg. Therefore, there is no need for either pollination or fertilisation.
Question.16.Identify the type of carpel with the help of diagrams given below:
Question.17. How is pollination carried out in water plants?
Answer. Pollination by water is called hydrophily. Some examples of water pollinated plants are Vallisneria and Hydrilla (both are angiospermic hydrophytes) which grow in fresh water and several marine sea-grasses such as Zostera. Not all aquatic plants use water for pollination. In a majority of aquatic plants such as water hyacinth and water lily, the flowers emerge above the level of water and pollinated by insects or wind as in most of the land plants.
Question.18. What is the function of the two male gametes produced by each pollen grain in angiosperms?
Answer. After entering one of the synergids, the pollen tube releases the two male gametes into the cytoplasm of the synergid. One of the male gametes moves towards the egg cell or oosphere and fuses with its nucleus, thus completing the syngamy. This results in the formation of a diploid cell, the zygote. The other male gamete moves towards the two polar nuclei located in the central cell and fuses with them to produce a triploid primary endosperm nucleus (PEN).
Short Answer Type Questions
Question.1. List three strategies that a bisexual chasmogamous flower can evolve to prevent self-pollination (autogamy).
Answer. Flowering plants have developed many devices to discourage self-pollination and to encourage cross-pollination.
• First device: In some species, pollen release and stigma receptivity are not synchronised. Either the pollen is released before the stigma becomes receptive or stigma becomes receptive much before the release of pollen. This condition is called dichogamy in which stigma and anther matures at different time.
• Second device: In some species, the anther and stigma are placed at different positions so that the-pollen cannot come in contact with the stigma of the same flower. This condition is called heterostyly.
• Herkogamy: Non-transfer of pollen from anther to stigma of the same flower due to a mechanical barrier is present between anther and stigma. E.g.: Calotropis (Asclepiadaceae), Aristolochia, Gloriosa superba.
The third device to prevent inbreeding is self-incompatibility or self-sterility. This is a genetic mechanism and prevents self-pollen (from the same flower or other flowers of the same plant) from fertilising the ovules by inhibiting pollen germination or pollen tube growth in the pistil.
Question.2. Given below are the events that are observed in an artificial hybridization programme. Arrange them in the correct sequential order in which they are followed in the hybridisation programme.
(a) Re-bagging, (b) Selection of parents, (c) Bagging, (d) Dusting the pollen on stigma, (e) Emasculation, (f) Collection of pollen from male parent.
Answer. (b) Selection of parents –>(e) Emasculation —> (c) Bagging –> (f) Collection of pollen from male parent –>(d) Dusting the pollen on stigma –>(e) Rebagging.
Question.3. Vivipary automatically limits the number of offspring in a litter. How?
Answer. In viviparous animals (majority of mammals including human beings), the
zygote develops into a young one inside the body of the female organism. After attaining a certain stage of growth, the young ones are delivered out of the body of the female organism. Vivipary automatically limits the number of offspring in a litter because female have limited space for the development of embryo.
Question.4. Does self-incompatibility impose any restrictions on autogamy? Give reasons and suggest the method of pollination in such plants.
Answer. Self-incompatibility imposes restriction to autogamy. The device to prevent inbreeding is self-incompatibility or self-sterility. This is a genetic mechanism and prevents self-pollen (from the same flower or other flowers of the same plant) from fertilising the ovules by inhibiting pollen germination or pollen tube growth in the pistil. Self-incompatiblity is overcome by mixed pollination.
Question.5. In the given diagram, write the names of parts shown with lines.
Question.6. What is polyembryony and how can it be commercially exploited?
Answer. As in many Citrus and Mango varieties some of the nucellar cells surrounding the embryo sac start dividing, protrude into the embryo sac and develop into the embryos. In such species each ovule contains many embryos. Occurrence of more than one embryo in a seed is referred as polyembryony.
If hybrids are made into apomicts, there is no segregation of characters in the hybrid progeny. Then the farmers can keep on using the hybrid seeds to raise new crop year after year and he does not have to buy hybrid seeds every year.
Question.7. Are parthenocarpy and apomixis different phenomena? Discuss their benefits.
Answer. Yes, they are different. Parthenocarpy leads to development of seedless fruits.
Apomixis leads to embryo development.
Question.8. Why does the zygote begin to divide only after the division of Primary Endosperm Cell (PEC)?
Answer. The zygote needs nourishment during its development. As the mature, fertilised embryo sac offers very little nourishment to the zygote, the PEC divides and generates the endosperm tissue which nourishes the zygote. Hence, the zygote always divides after division of PEC.
Question.9. The generative cell of a two-celled pollen divides in the pollen tube but not in a three-celled pollen. Give reasons.
Answer. In a 3-celled pollen, as the generative cell has already been divided and formed 2 male gametes, it will not divide again in the pollen tube. But in a 2-celled pollen, as the generative cell has not divided, it divides in the pollen tube.
Question.10. In the figure given below, label the following parts: male gametes, egg cell, polar nuclei, synergid and pollen tube
Long Answer Type Questions
Question.1. Starting with the zygote, draw the diagrams of the different stages of embryo development in a dicot.
Question.2. What are the possible types of pollinations in chasmogamous flowers? Give reasons.
Answer. A bisexual flower which normally open is called chasmogamous flower.
Kinds of Pollination
1. Autogamy: In this type, pollination is achieved within the same flower. Transfer of pollen graift from the anther to the stigma of the same flower. In a normal flower which opens and exposes the anthers and stigma complete autogamy is rather rare.
Majority of flowering plants produce hermaphrodite flowers and pollen grains are likely to come in contact with the stigma of the same flower. Continued self-pollination result in inbreeding depression. Flowering plants have developed many devices to discourage self-pollination and to encourage cross-pollination.
2. Geitonogamy: Transfer of pollen grains from the anther to the stigma of another flower of the same plant.
3. Xenogamy: Transfer of pollen grains from anther to the stigma of a different plant.
Question.3. With a neat, labelled diagram, describe the parts of a mature angiosperm embryo sac. Mention the role of synergids.
Filiform apparatus present at the micropylar part of the synergids guides the entry of pollen tube.
Question.4. Draw the diagram of a microsporangium and label its wall layers. Write briefly on the role of the endothecium.
Endothecium performs the function of protection and help in dehiscence of anther to release the pollen.
Question.5. Embryo sacs of some apomictic species appear normal but contain diploid cells. Suggest a suitable explanation for the condition.
Answer. It is true that many apomicts possess normal looking embryo sacs. The only possibility of the embryo sac possessing diploid cells is due to failure of meiotic division at the megaspore mother cell stage. Since, the megaspore mother cell has a diploid nucleus, if it undergoes mitosis instead of meiosis, all the resulting nuclei and cells will be diploid in nature.
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