Exam Question for Class 12 Biology Chapter 2 Sexual Reproduction in Flowering Plants
Please refer to below Exam Question for Class 12 Biology Chapter 2 Sexual Reproduction in Flowering Plants. These questions and answers have been prepared by expert Class 12 Biology teachers based on the latest NCERT Book for Class 12 Biology and examination guidelines issued by CBSE, NCERT, and KVS. We have provided Class 12 Biology exam questions for all chapters in your textbooks. You will be able to easily learn problems and solutions which are expected to come in the upcoming class tests and exams for standard 12th.
Chapter 2 Sexual Reproduction in Flowering Plants Class 12 Biology Exam Question
All questions and answers provided below for Exam Question Class 12 Biology Chapter 2 Sexual Reproduction in Flowering Plants are very important and should be revised daily.
Very Short Answer Type Questions
Question. Name the component cells of the ‘egg-apparatus’ in an embryo sac.
Answer. The component cells of the ‘egg-apparatus’ in an embryo sac include, two synergids, one egg cell and the filiform apparatus.
Question. Name the part of gynoecium that determines the compatible nature of pollen grain.
– Thinking Process
Stigma is a part of pistil. So, somewhere it is also mentioned as the part of gynoecium that determines the compatible nature of pollen grain.
Answer. The pistil has the ability to recognise, the pollen, whether it is of the right type (compatible) or of the wrong type (incompatible). If it is of the right type, the pistil accepts the pollen and promotes post-pollination events that lead to fertilisation. If the pollen is of wrong type, the pistil rejects the pollen.
The ability of the pistil to recognise the pollen is followed by its acceptance or rejection. It is the result of a continuous dialogue between pollen grain and the pistil mediated by chemical components of the pollen interacting with those of the pistils.
Question. Name the common function that cotyledons and nucellus perform.
Answer. The common functions that cotyledons and nucellus perform are as follows
(i) Storage of reserve food material.
(ii) Nourishment Cotyledons nourishes embryo and nucellus nourishes embryo sac.
Question. Complete the following flow chart
The process of formation of microspores from a Pollen Mother Cell (PMC) through meiosis is called microsporogenesis. The microspores, as they are formed, are arranged in a cluster
of four cells i e . ., the microspore tetrad.
As the anthers mature and dehydrate, the microspores dissociate from each other and develop into pollen grains (male gametophyte). When the pollens mature, it contains two cells the vegetative cell (bigger) and generative cell (smaller)
Question. Indicate the stages where meiosis and mitosis occur (1, 2 or 3) in the flow chart.
Megaspore mother cell →1 Megaspores →2 Embryo sac →3 Egg
The diploid Megaspore Mother Cell (MMC) undergo meiosis and forms a linear tetrad of four haploid megaspores. Three mitotic divisions, inside the functional (one) megaspore form
the embryo sac (eight haploid nuclei), while the other three megaspores degenerate.
The embryo sac is a seven-celled and eight nucleated structure. Three micropylar, Three chalazal and one central. The three micropylar cells are collectively known as egg-apparatus, which, consists of two synergids and one egg cell.
While three chalazal cell form antipodal cell. The central cell is in the form of two nucleated cell till the fertilisation occurs and called as polar nuclei.
Question. 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. Following compatible pollination, the pollen grain germinates on the stigma to produce a pollen tube through one of the germ pores. The contents of the pollen grain (2 mole nuclei) move into the pollen tube. Pollen tube grows through the tissues of the stigma and reaches the ovary.
After reaching the ovary, pollen tube, enters the ovule through the micropyle and then enters the embryo sac by passing into one of the synergids through the filiform apparatus. It leads to the degeneration of that synergid.
The pollen tube breaks to release its contents (2 male nuclei). Out of the two male gametes one fuses with egg and the other fuses with central cell and fertilise.
The component cells of the egg-apparatus in an embryo sac include, two synergids, one egg cell and the filiform apparatus.
Question. Name the parts of pistil which develop into fruit and seeds.
Answer. Pistil is the female reproductive organ that receives pollen to fertilise the egg located in ovary. A pistil has three parts, i e . ., stigma (receives pollen), which grows down through style to ovary. Ovary contains ovules, which contain an egg. The ovary develops into the fruit and ovule develops into a seeds.
Question. In case of polyembryony, if an embryo develops from the synergid and another from the nucellus which is haploid and which is diploid?
– Thinking Process
Presence of more than one embryo in a seed is called polyembryony. e.g., lemon, groundnut, etc.
Answer. Embryo developed from the synergid is haploid as the ploidy of the synergid is haploid.
Embryo developed from the nucellus is diploid as the ploidy of the nucellus is diploid.
Question. Can an unfertilised, apomictic embryo sac give rise to a diploid embryo? If yes, then how?
Answer. Yes, if megaspore develops into embryo sac without meiotic division egg will be diploid.
Diploid egg develops into embryo by mitotic divisions.
Note Apomixis is a form of asexual reproduction to produce seeds without fertilisation.
Question. Which are the three cells found in a pollen grain when it is shed at the three celled stage?
Answer. In over 60% of angiosperms, pollen grains are shed at the two cell further stage (vegetative cell and generative cell). In the remaining species, the generative cell divides mitotically to give rise to the two male gametes before pollen grains are shed at the (three-celled stage (are vegetative cell and two male gametes).
Question. What is self-incompatibility?
Answer. It is a genetic mechanism which prevents self-pollen from fertilising the ovules by inhibiting pollen germination or pollen tube growth in the pistil.
Question. Name the type of pollination in self-incompatible plants.
Answer. In self-incompatible plants, (while self-pollination is incompatible) cross-pollination is occurs.
Note Self-incompatibility is a genetic mechanism which prevents self-pollen from fertilising the ovules by inhibiting pollen germination or pollen tube growth in the pistil.
Question. Draw the diagram of a mature embryo sac and show its eight-nucleate,seven-celled nature. Show the following parts-antipodals, synergids, egg,central cell, polar nuclei.
Question. Which is the triploid tissue in a fertilised ovule? How is the triploid condition achieved?
Answer. Endosperm is the triploid tissue. It results from triple fusion involving union of one male gamete and two haploid polar nuclei.
Question. Are pollination and fertilisation necessary in apomixis? Give reasons.
– Thinking Process
The phenomenon of asexual reproduction that mimics sexual reproduction by formation of seed without fertilisation is called apomixis.
Answer. Pollination and fertilisation are not necessary for apomixis. The reasons in support of this are given below
(i) Embryo sac can develop from megaspore without reduction division the egg is diploid and develops into embryo.
(ii) Embryo sac can also develop from diploid nucellus cells in which case egg is diploid that develop into embryo parthogenetically.
Question. Identify the type of carpel with the help of diagrams given below
– Thinking Process
The gynoecium represents the female reproductive part of the flower and may consist of a single pistil (monocarpellary) or many pistils (multicarpellary).
Answer. (a) If a gynoecium has multiple carpels fused into a single structure, it is syncarpous. In this given diagram, the type of carpel is syncarpous (e.g.,poppy).
(b) If a gynoecium has multiple carpels in free form, it is apocarpous. In this given diagram, the type of carpel is apocarpous. (e.g., michelia)
Question. How is pollination carried out in water plants?
Answer. (a) In many aquatic plants with emergent flowers, pollination occurs by wind and insects.
(b) In water plants if pollination occurs below the surface of water is called hypohydrophilly, e.g., Ceratophyllum.
(c) In water plants if pollination takes place over the surface of water is called epihydrophily, e.g., Vallisneria spiralis.
Question. What is the function of the two male gametes produced by each pollen grain in angiosperms.
– Thinking Process
Mature pollen grain contains two cells, the vegetative cell and generative cell. Generative cell is the generation cell that divides mitotically to give rise to the two male gametes .
Answer. One male gamete unites with egg forming embryo.This process is called fertilisation or syngamy.
Another male gamete unite with two polar nuclei resulting in the formation of endosperm triple fusion.
Short Answer Type Questions
Question. List three strategies that a bisexual chasmogamous flower can evolve to prevent self-pollination (autogamy).
– Thinking Process
Majority of flowering plants produce hermaphrodite flowers and pollen grains are likely to come in contact with the stigma of the same flower. This self-pollination result in inbreeding depression. Flowering plants have evolved many devices to discourage self- pollination.
Answer. A bisexual chasmogamous flower can evolve the following (three) strategies to prevent self-pollination (autogamy).
(a) Dichogamy In this mechanism, pollen release and stigma receptivity are not synchronised. In sunflower, the pollen is released before the stigma becomes receptive (protandry). In Datura, Solanum, the stigma becomes receptive much before the release of pollen (protogyny) leads to cross-pollination.
(b) Herkogamy The male and female sex organs are placed at different positions or in different directions is called Herkogamy. In these plants, the pollen cannot came in contact with the stigma of the same flower. It has undergone cross pollination, e.g., Hibiscus, Gloriosa.
(c) Self-sterility It is a genetic mechanism which prevents the self-pollen from fertilising the ovules by inhibiting pollen germination or pollen tube growth in the pistil, e.g., Abotilon.
Note Another device to prevent self-pollination is the production of unisexual flowers, but this is not beneficial as above mentioned strategies. It prevents autogamy but not geitonogamy in monoecious plants such as castor and maize.
Question. Given below are the events that are observed in an artificial hybridisation 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.
– Thinking Process
One of the major approaches of crop improvement programme is ‘Artificial hybridisation’. 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).
Answer. The correct sequential order of artificial hybridisatian is as following
(a) Selection of parents.
(b) Emasculation (removal of anthers from the flower bud before the anther dehisces).
(c) Bagging (process to cover the emasculated flower with a bag made up of butter paper).
(d) Collection of pollen from other male plant.
(e) Dusting of pollen on stigma.
Note If the female parent produces unisexual flowers, there is no need of emasculation.
Question. Vivipary automatically limits the number of offsprings in a litter. How?
Answer. Vivipary is defined as the seed germination, while the fruit is still attached to the mother plant. Plants which grow in marshy places are called Mangroves. In these plants when
seeds fall on marshy places, they cannot germinate, because of high salinity and more water conditions.
So, in those plants, seeds germinate when they are still attached to the mother plant. Litter is the off spring at one birth of animal usually 3-8 in number.Vivipary automatically limits the number of offspring in litter due to the reason that limited number of egg or ovum are produced and fertilised during reproductive cycle of female.
Question. Does self-incompatibility impose any restrictions on autogamy? Give reasons and suggest the method of pollination in such plants.
Answer. Self-incompatibility imposes restrictions on autogamy. The season far this may be as Majority of flowering plants produce hermaphrodite flowers and when pollens grains comes in contact with the stigma of the same flower to continue self-pollination.
Such type of continued self-pollination result in inbreeding depression. That’s why flowering plants have developed many devices to discourage self-pollination and to encourage cross-pollination. One of the major way to prevent self-pollination is self-sterility.
Self-sterility in some bisexual flowers, if the pollen grains fall on the stigma of the same flower, germination does not occur. But the same pollen grains germinate when they fall on
the stigma of other flowers of the same species. It is a genetic mechanism to prevent self pollination.
Question. In the given diagram, write the names of parts shown with lines.
Answer. Embryos of monocotyledons possess only one cotyledon. In the grass family the cotyledon is called scutellum that is situated towards one side (lateral) of the embryonal
At its lower end, the embryonal axis has the radical and root cap enclosed in an undifferentiated sheat called coleorrhiza. The portion of the embryonal axis above the level of attachment of scutellum is the epicotyl.
Epicotyl has a shoot apex and a few leaf primordia enclosed in a hollow foliar structure, the coleoptile.
Question. What is polyembryony and how can it be commercially exploited?
Answer. Polyembryony is the occurrence of more than one embryo in a seed. 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 embryos. In such species, each ovule contains many embryos.
Polyembryony plays a main role in plant breeding and horticulture. The plantlets obtained from these embryos are virus free and has more vigour. Hybrid varieties of several food and vegetable crops are being extensively cultivated and these hybrid cultivars possess high productiviy.
Question. Are parthenocarpy and apomixis different phenomena? Discuss their benefits.
Answer. Yes, parthenocarpy and apomixis are different phenomenon.
Importance of Parthenocarpy
(i) The fruit production without fertilisation of the ovary is called parthenocarpy. This phenomenon is applied for the commercial production of seedless fruits. e.g., banana, grapes.
(ii) This is more useful far the juice industries.
Importance of Apomixis
(i) During apomixis, chromosomal segregation and recombination does not occur. So,characters are stable for several generations.
(ii) It simplifies commercial hybridised production because isolation is not necessary to produce F1 or maintain parental generation.
(iii) Adventive embryony is being used in the production of uniform root-stock and virus free varieties.
Question. Why does the zygote begin to divide only after the division of Primary Endosperm Cell (PEC)?
– Thinking Process
The zygote needs nourishment to develop.
Answer. The primary endosperm cell divides repeatedly and forms a triploid endosperm tissue. The cells of this tissue are filled with reserve food materials and are used for nutrition of the
Embryo develops at the micropylar end of the embryo sac where zygote is situated. Most zygotes divide only after certain amount of endosperm is formed. This is an adaptation to provide assured nutrition to the developing embryo.
Question. The generative cell of a two celled pollen divides in the pollen tube, but not in a three-celled pollen. Give reasons.
– Thinking Process
Pollen grain at maturity, divides and produce two unequal cells. The large cell is vegetative cells, has abundant food reserve and cantains a large irregular nucleus. The smaller cell is generative cell and floats in the cytoplasm of vegetative cell, which is spindle shaped with dense cytoplasm and a nucleus.
Answer. In over 60 % of angiosperms, pollen grains are shed at this 2-celled stage tube cell or vegetative cell generative cell. In the remaining species, the generative cell divides
mitotically to give rise to the two male gametes before pollen grains are shed tubecell or vegetative cell two male gamete 3-celled stage.
In 3 celled stage, the pollen grains further germinate on the stigma to produce pollen tube through ane of the germ pores. The contents of the pollen grains move into the tube pollen tube grows through the tissues of the stigma and style and reaches to ovary. Inplants, when pollen grain are shed at 2 celled stage the generative cell divides and form two male gametes during the growth of the pollen tube in the stigma.
Question. In the figure given below label the following parts-male gametes, egg cell, polar nuclei, synergid and pollen tube
Answer. The following are the parts of this figure
Long Answer Type Questions
Question. Starting with the zygote, draw the diagrams of the different stages of embryo development in a dicot.
– Thinking Process
The zygote gives rise to the proembryo and subsequently to the globular, heart-shaped and mature embryo
Note The early stages of embryogeny (embryo development) in both monocotyledons and dicotyledons are similar. In case of monocotyledonous embryo a single cotyledon is present.
Question. What are the possible types of pollinations in chasmogamous flowers. Give reasons.
– Thinking Process
The pollination that occurs in open flowers is called chasmogamy. It is the most common type of pollination in all types of flowers.
Answer. There are two types of pollinations (chasmogamy) in chasmogamous flowers, i e . ., self–pollination and cross-pollination.
(a) Self-pollination(Autogamy) The transfer of pollen grains from anther to stigma of the same flower is called self-pollination. It is found in both cleistogamous and chasmogamous flowers.
(b) Cross-pollination (Allogamy) The transfer of pollen grains from anther to stigma of another flower is called a cross-pollination. It is of two types
(i) Geitonogamy It is the transfer of pollen grains from anther to the stigma of another flower of the same plant. It is functionally a type of cross-pollination involving a pollinating agent, genetically. It is similar to autogamy.
(ii) Xenogamy The transfer of pollen grains from the flower of one plant to the stigma of another plant. This is the only type of pollination, which brings genetically different types of pollen grains to the stigma.
Question. With a neat, labelled diagram, describe the parts of a mature angiosperm embryo sac. Mention the role of synergids.
– Thinking Process
Megaspore is the mother cell for the development of female gametophyte (embryo sac).The nucleus of the functional megaspore divides mitotically to form two nuclei, which moves to the opposite poles forming two nucleus embryo sacs.
Two more mitotic nuclear divisions occur in two nuclei, resulting in the formation of eight-nucleate embryo sac.
Answer. After the 8-nucleate stage, cell walls are laid down leading to the organisation of the typical female gametophyte or embryo sac.
Six of the eight nuclei are surrounded by cell walls and organised into cells. Three cells present towards the micropylar end grouped together, constitute the egg apparatus. The egg apparatus, in turn consists of two synergids and one egg cell.
Three cells of the chalazal end are called the antipodals. The large central cell is formed by the fusion of 2-polar nuclei. Thus, a typical angiospermic embryo sac, at maturity consists of
eight nuclei and seven cells. This embryo sac is formed from, the single megaspore, so it is called ‘monosporic embryo sac.
Role of Synergids
The synergids have special cellular thickenings at the micropylar tip called filiform apparatus, which play an important role in guiding the pollen tubes into the synergid.
Question. Draw the diagram of a microsporangium and label its wall layers. Write briefly about the wall layers?
– Thinking Process
A typical angiospermic anther is bilobed with each lobe having two theca. The anther is a four sided structure consisting of four microsporangia located at the corners, two in each lobe.
Answer. The diagram representation of a microsporangium is shown below
In a transverse section, a typical microsporangium is circular in outline and is surrounded by four wall layers.
(a) Epidermis The epidermis is the outermost protective layer. It is composed of tangentially flattened cells. The cells are closely fitted and have thick walls which is helpful in the dehiscence of anther.
(b) Endothecium It is present below the epidermis and expands radically with fibrous thickenings, at maturity these cells loose water, at contract and help in dehiscence of pollen sac.
(c) Wall Layers It is present between well marked endothecium and tapetum. These are thin walled layers, arranged in one to five layers, which also help in dehiscence of anther.
(d) Tapetum It is the innermost wall layer with large cells, thin cell walls, abundant cytoplasm and have more than one nuclei. Tapetum is a nutritive tissue which nourishes the developing pollen grains.
The centre of the microsporangium consists of sporogenous tissue, which undergoes meiotic divisions to form microspore tetrads. This process is known as microsporogenesis.
Question. Embryo sacs of some apomictic species appear normal, but contain diploid cells. Suggest a suitable explanation for the condition.
Answer. Replacement of the normal sexual reproduction by asexual reproduction without fertilisation is called apomixis. e.g., replacement of the flower by bulbils and replacement of the seed by a plant.
Apomitically produced offsprings are genetically identical to the parent plant. In flowering plants, apomixis is used in a restricted sense to mean angiosperm, i.e., asexual
reproduction through seeds.
In some plant species it is common, e.g., Asteraceae, Poaceae. In some species, the diploid egg cell is formed without reduction division and develops into embryo without fertilisation. It is an asexual reproduction in the absence of pollinators such as in extreme environments.
In some species like citrus, some of the nucellar cells surrounding the embryo sac start dividing and develop into embryo. It occurs in the megaspore mother cell does not undergo meiosis, thus produces diploid embryo sac through mitotic divisions.
Thus, it explains that, embryo sacs of some apomictic species appear normal, but produce diploid cells.