Sexual Reproduction in Flowering Plants

Deus Learnings -
0
Botany Question Paper - Reproduction in Flowering Plants

Reproduction in Flowering Plants

Class: XII | Subject: Biology

Section A
(Multiple Choice Questions - 1 mark each)

  1. The innermost wall layer of a microsporangium that nourishes the developing pollen grains is the:



  2. The hard outer layer of a pollen grain, the exine, is composed of which resistant organic material?



  3. A typical angiosperm embryo sac at maturity is:



  4. The phenomenon of formation of an embryo sac from a single megaspore is termed:



  5. Which of the following plants produces two types of flowers: chasmogamous and cleistogamous?



  6. The part of the pistil that serves as a landing platform for pollen grains is:



  7. The fusion of a male gamete with the two polar nuclei in the embryo sac is known as:



  8. In a fertilised embryo sac, the zygote is __________ and the Primary Endosperm Nucleus (PEN) is __________.



  9. Fruits that develop from parts other than the ovary, such as the thalamus, are called:



  10. The water of a tender coconut represents the:



  11. The protective sheath covering the radicle in a monocot embryo is called the:



  12. The transfer of pollen grains from the anther to the stigma of another flower of the same plant is called:



  13. A dioecious plant, such as papaya, prevents:



  14. The filiform apparatus, which guides the entry of the pollen tube into the synergid, is a characteristic feature of:



  15. For questions 15 and 16, two statements are given—one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
    a) Both A and R are true and R is the correct explanation of A.
    b) Both A and R are true but R is not the correct explanation of A.
    c) A is true but R is false.
    d) A is false but R is true.

    Assertion (A): Continued self-pollination leads to inbreeding depression.
    Reason (R): Flowering plants have developed devices like self-incompatibility to encourage cross-pollination.
  16. Assertion (A): Pollen grains can be well-preserved as fossils.
    Reason (R): The inner wall of the pollen grain, the intine, is made of cellulose and pectin.

Section B
(Very Short Answer Questions - 2 marks each)

  1. Differentiate between the vegetative cell and generative cell of a mature pollen grain.
  2. What are 'pollen banks'? State their significance in crop breeding programmes.
  3. Why is bagging of the emasculated flower essential during artificial hybridisation experiments?
  4. Explain the function of the following parts of a typical angiosperm ovule:
    a) Nucellus
    b) Integuments
  5. What is meant by 'inbreeding depression'? Name any two devices that flowering plants have developed to discourage self-pollination.

Section C
(Short Answer Questions - 3 marks each)

  1. Draw a neat, labelled diagram of a mature embryo sac of an angiosperm.
  2. With reference to a typical dicot embryo, explain the terms epicotyl, hypocotyl, and radicle.
  3. What is pollination? Differentiate between geitonogamy and xenogamy.
  4. List the characteristic features of wind-pollinated flowers.
  5. Why does endosperm development precede embryo development in angiosperms? Differentiate between albuminous and non-albuminous seeds with one example of each.
  6. "The pistil has the ability to recognise the compatible or incompatible pollen." Explain this statement with reference to the pollen-pistil interaction.
    OR
    What is triple fusion? Where and how does it take place? Name the nucleus formed as a result of this fusion.
  7. Describe the structure of a typical stamen with the help of a well-labelled diagram showing a three-dimensional cut section of an anther.

Section D
(Case-based Questions - 4 marks each)

  1. Read the following and answer the questions that follow:
    In a majority of flowering plants, one of the megaspores is functional while the other three degenerate. The functional megaspore develops into the female gametophyte. The nucleus of the functional megaspore divides by mitosis to form two nuclei which move to opposite poles, forming a 2-nucleate embryo sac. Two more sequential mitotic divisions result in an 8-nucleate stage. These divisions are strictly free-nuclear. After the 8-nucleate stage, cell walls are laid down, leading to the organisation of a typical female gametophyte. Three cells are grouped at the micropylar end to form the egg apparatus, three cells at the chalazal end are the antipodals, and the remaining two nuclei, called polar nuclei, are situated in the large central cell.

    a) What is this method of embryo sac formation from a single megaspore called?
    b) Why are the mitotic divisions during embryo sac development referred to as 'free-nuclear'?
    c) How many cells and nuclei are present in a typical mature embryo sac?
    d) What is the function of the filiform apparatus in the egg apparatus?
  2. Read the following and answer the questions that follow:
    Artificial hybridisation is a major approach in crop improvement. To ensure desired pollination, two techniques, emasculation and bagging, are employed. If the female parent bears bisexual flowers, the anthers are removed from the flower bud before they dehisce. This step is called emasculation. The emasculated flowers are then covered with a bag to prevent contamination of its stigma with unwanted pollen. This is called bagging. When the stigma becomes receptive, mature pollen grains from the desired male parent are dusted on it, and the flower is rebagged. If the female parent is unisexual, emasculation is not needed.

    a) Why is emasculation necessary in a bisexual flower for artificial hybridisation?
    b) What is the purpose of bagging the flower after emasculation?
    c) Why is there no need for emasculation if the female parent produces unisexual flowers?
    d) Name the type of paper generally used for making the bags.

Section E
(Long Answer Questions - 5 marks each)

  1. a) What is double fertilisation? Describe the process in flowering plants.
    b) Name the cells and nuclei involved in this process.
    c) What is the fate of the zygote and the primary endosperm cell after fertilisation?
    OR
    a) Draw a longitudinal section of a flower and label the following parts:
        i. The part that develops into a fruit.
        ii. The part that produces pollen grains.
        iii. The part that receives pollen grains.
        iv. The part that develops into a seed.
    b) Describe the structure of the part that contains the female gametophyte.
  2. a) Define pollination.
    b) Explain the different types of pollination depending on the source of pollen.
    c) Describe the adaptations seen in flowers pollinated by water.
  3. a) Trace the development of a microspore into a mature pollen grain. Illustrate the stages with labelled diagrams.
    b) Mention the functions of the two cells present in a mature pollen grain.

Answer Key and Marking Scheme

Section A

  1. d) Tapetum
  2. c) Sporopollenin
  3. b) 8-nucleate and 7-celled
  4. a) Monosporic development
  5. c) Commelina
  6. b) Stigma
  7. c) Triple Fusion
  8. c) diploid, triploid
  9. d) False fruits
  10. b) Free-nuclear endosperm
  11. c) Coleorrhiza
  12. b) Geitonogamy
  13. c) Both autogamy and geitonogamy
  14. b) Synergids
  15. a) Both A and R are true and R is the correct explanation of A.
  16. c) A is true but R is false. (Reason R is a true statement about the intine, but it does not explain why pollen is preserved. The preservation is due to sporopollenin in the exine).

Section B

  1. Vegetative Cell: Larger, has abundant food reserve, large irregularly shaped nucleus.
    Generative Cell: Small, floats in the cytoplasm of the vegetative cell, spindle-shaped with dense cytoplasm and a nucleus. (1 mark for each)
  2. Pollen Banks: Facilities where pollen grains of a large number of species are stored for years in liquid nitrogen (-196°C).
    Significance: Used in crop breeding programmes to cross plants with desirable characteristics, preserving genetic diversity.
  3. Bagging prevents contamination of the stigma of the emasculated flower with unwanted pollen from other sources. This ensures that pollination occurs only with the desired pollen grains collected from the chosen male parent.
  4. a) Nucellus: It is a mass of cells with abundant reserve food materials that provides nutrition to the developing embryo sac.
    b) Integuments: They are protective envelopes that encircle the nucellus and later harden to form the seed coat.
  5. Inbreeding Depression: The reduction in fitness and vigour of a population due to continued self-pollination.
    Devices: (Any two)
    • Non-synchronisation of pollen release and stigma receptivity.
    • Anther and stigma are placed at different positions.
    • Self-incompatibility.
    • Production of unisexual flowers.

Section C

  1. Diagram of Mature Embryo Sac:
    • Correct diagram showing 7 cells and 8 nuclei. (1 mark)
    • Correct labelling: Egg apparatus (Egg cell, Synergids, Filiform apparatus), Central Cell (with Polar nuclei), and Antipodals. (2 marks)
  2. Epicotyl: The portion of the embryonal axis above the level of the cotyledons, which terminates in the plumule (stem tip).
    Hypocotyl: The cylindrical portion of the embryonal axis below the level of the cotyledons, which terminates in the radicle.
    Radicle: The part of the embryo that develops into the root tip.
  3. Pollination: The transfer of pollen grains from the anther to the stigma of a pistil.
    Geitonogamy: Transfer of pollen from the anther to the stigma of another flower of the same plant. Genetically it is self-pollination.
    Xenogamy: Transfer of pollen from the anther to the stigma of a flower on a different plant. It brings genetically different pollen to the stigma.
  4. Features of wind-pollinated flowers:
    • Pollen grains are light and non-sticky.
    • Stamens are well-exposed for easy dispersal of pollen.
    • Stigma is large and often feathery to trap airborne pollen.
    • Flowers often have a single ovule in each ovary and are packed into an inflorescence.
    • Flowers are not very colourful and do not produce nectar. (Any three points)
  5. Endosperm development precedes embryo development because the endosperm tissue provides nutrition to the developing embryo. This is an adaptation to ensure the embryo gets assured nourishment.
    • Albuminous seeds: Retain a part of the endosperm in the mature seed. Example: Wheat, maize, castor.
    • Non-albuminous seeds: Have no residual endosperm as it is completely consumed during development. Example: Pea, groundnut.
  6. The pistil can recognise the pollen through a continuous dialogue mediated by chemical components.
    • Compatible Pollen: The pistil accepts the pollen, promoting post-pollination events like pollen germination and pollen tube growth.
    • Incompatible Pollen: The pistil rejects the pollen by preventing germination on the stigma or inhibiting pollen tube growth in the style.
    OR
    • Triple Fusion: Fusion of the second male gamete with the two polar nuclei in the central cell.
    • Takes place in the central cell of the embryo sac.
    • Forms the triploid Primary Endosperm Nucleus (PEN).
  7. Diagram of Stamen and Anther T.S.:
    • Correct diagram of a stamen showing filament and anther. (1 mark)
    • Correct 3D cut-section diagram of anther showing bilobed, dithecous nature, pollen sacs, and line of dehiscence. (2 marks)

Section D

  1. a) Monosporic development.
    b) Because the nuclear divisions are not immediately followed by cell wall formation.
    c) A mature embryo sac is 7-celled and 8-nucleate.
    d) It has special cellular thickenings that play an important role in guiding the pollen tube into the synergid.
  2. a) To prevent the stigma from being pollinated by the pollen from the same flower (self-pollination).
    b) To prevent contamination of the stigma with any unwanted pollen from other flowers or plants.
    c) Because unisexual female flowers do not have anthers, so there is no risk of self-pollination.
    d) Butter paper.

Section E

  1. a) Double Fertilisation: A phenomenon unique to flowering plants where two fusions occur — syngamy and triple fusion.
    • Syngamy: One male gamete fuses with the egg to form a diploid zygote.
    • Triple Fusion: Other male gamete fuses with two polar nuclei to form triploid PEN.
    b) Cells involved: Egg cell, Central cell, Synergid. Nuclei: Egg nucleus, two polar nuclei, two male gametes.
    c) Zygote → Embryo; PEN → Endosperm.
    OR
    a) Diagram: Ovary → Fruit; Anther → Pollen; Stigma → Receives pollen; Ovule → Seed.
    b) Structure of ovule: Attached via funicle; parts: nucellus, integuments, micropyle, chalaza, embryo sac.
  2. a) Pollination: Transfer of pollen from anther to stigma.
    b) Types: Autogamy (same flower), Geitonogamy (same plant), Xenogamy (different plant).
    c) Adaptations: Ribbon-like pollen, mucilaginous coating, female flowers reach surface (e.g., Vallisneria).
  3. a) Microspore → Mitosis → Vegetative cell (large) + Generative cell (small) → (in some) generative cell divides into two male gametes.
    Diagrams showing microspore → 2-celled → 3-celled pollen grain.
    b) Vegetative cell: forms pollen tube and nourishes.
    Generative cell: divides to form two male gametes.
Previous Post Next Post