NCERT Exemplar for Class 12 Biology Chapter 2

NCERT Exemplar for Class 12 Biology will help students to deepen their knowledge related to the topic of Sexual Reproduction in Flowering Plants. This provided exemplar by SimplyAcad allows students to cover all the areas and sections comprising the chapter 2 of the biology textbook. Students can easily access this NCERT exemplar for class 12 biology in this article below to perform incredibly well in their upcoming 12th board examinations.

Apart from these there are several NCERT exemplar for class 12 science of all the chapters provided in a detailed manner.

 

Access the NCERT Exemplar Class 12 Biology Chapter 2 Sexual Reproduction In Flowering Plants

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 and iv (d) i and ii
Answer. (c)
• 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
Answer. (c)
• 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
Ans 5. The correct option is D Epidermis and tapetum

Microsporangium

Male reproductive organ in plants is the androecium which is made up of units called stamen.

Stamen is made up of anther and filament. Anther is a bilobed and each lobe has two pollen sacs that consist of a tissue called microsporangia. It produces male gametophytes (pollen grains).

Wall layers of microsporangium

Wall layers of microsporangium-

* Outer single layer is called epidermis.

* Second layer is called endothecium, which is thick and fibrous.

* Third layer is called middle layers which disintegrates after maturation.

* Innermost layer is called tapetum which is nucleated tapetal cells with dense cytoplasm.

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, embryo 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 is 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
Answer. (b)
• 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
(c) Emasculation
(d) Collection of pollen
Answer. (c)
• 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
Answer. (b)
• 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 the 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
(a) Haploid
(b) Diploid
(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
(a) Parthenocarpy
(b) Apomixis
(c) Asexual reproduction
(d) Sexual reproduction’
Answer. (a) If a fruit is formed without fertilisation of the ovary, it is called a parthenocarpic fruit, e.g., banana and grape.

Very Short Answer Type Questions: NCERT Exemplar For Class 12 Biology

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:

Pollen mother cell → Pollen tetrad ⟶Pollen grain ⟶vegetative cell and_

Solution: Development of male gametophyte

The following events take place during the formation of pollen grains:-

* Pollen mother cells divide by meiosis and produce haploid pollen tetrads or microspore tetrads.

* The tetrads further give rise to four individual microspores.

* The nucleus of the microspores divide by mitosis and produce two daughter cells-one smaller generative cell and one larger vegetative cell. Most of the pollen grains shed off at the 2 celled stage.

Generative cell

Generative cell is a small cell having only a few cellular organelles. It lies freely in the cytoplasm of the vegetative cell. It further divides to give rise to the two male gametes.

Vegetative cell

Vegetative cell is a large cell with a nucleus that is lobed and a cytoplasm with vacuoles.

Final answer

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

Solution

Formation of megapores

* Megaspore mother cells are the diploid sporogenous cells present in the megasporangium (ovules).

* These cells divide by meiosis and produce four megaspores.

Formation of embryo sac

* Out of the four megaspores formed, three megaspores degenerate and disappear while one megaspore is functional and attaches to the chalazal end.

* The megaspore then divides by mitotic division and produces two cells that move to the opposite ends of the micropylar and chalazal end of the embryo sac.

* Now these two cells divide by mitotic division again, giving rise to four cells at the micropylar end and chalazal end.

Formation of egg

At the micropylar end, these four cells develop into an egg apparatus made up of an egg and two synergid cells.

Final answer

Megaspore mother cells divide by meiosis to produce megaspores and these megaspores divide by mitosis to produce cells of the embryo sac. Cells of the embryo sac divide by mitosis to give egg apparatus and accessory cells.

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.

Solution

Path of a pollen tube into the embryo sac.

Path of a pollen tube into the embryo sac is as follows:

* The pollen tube grows through the tissues of the stigma and the style

* It then enters through the micropylar end into the ovule.

* Synergid cell of the egg apparatus secrete chemicals and direct the movement of the pollen tube inside the synergid through the filiform apparatus.

* Pollen tube penetrates and releases two male gametes into synergid cells.

Diagram

Components of egg apparatus.

The egg apparatus is composed of one egg and two synergid cells. It is present at the micropylar end of the embryo sac.

Question.7. Name the parts of pistil which develop into fruit and seeds.
Answer. Ovary 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-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 of pollen tube growth in the pistil.

Question.12.Name the type of pollination in self-incompatible plants.
Answer.Xenogamy

NCERT Exemplar For Class 12 Science

Students must practise these additional questions for their own benefits, the ncert exemplar are curated by the best subject-matter experts to boost your knowledge on the presented topic. Students can easily access the ncert exemplar for class 12 science by visiting our website SimplyAcad and solve all the questions listed to secure maximum marks.

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