Please refer to VBQs for Class 12 Biology Sexual Reproduction in Flowering Plants. All value based questions for Biology Class 12 have been provided with solutions. We have provided below important values questions and answers. Students should learn these solved VBQs for Class 12 Biology as these will help them to gain more marks and help improve understanding of important topics.
Sexual Reproduction in Flowering Plants VBQs Class 12 Biology with Answers
Very Short Answer Type Questions
Question. These pictures show the gynoecium of
(i) Papaver and (ii) Michellia flowers. Write the difference in the structure of their ovaries.
Answer : (i) Multicarpellary ovary showing fused syncarpous pistil.
(ii) Multicarpellary ovary showing free apocarpous pistil.
Question. Why do cleistogamous flowers assure seed sets ?
Answer : Cleistogamous flowers are invariably autogamous as there is no chance of cross pollination.
Question. How do the pollen grains of Vallisneria protect themselves ?
Why do the pollen grains of Vallisneria have mucilage covering ?
Answer : The pollen grains of most of the water pollinated species have a mucilaginous covering to protect from wetting.
Question. How many pollen grains and ovules are likely to be formed in the anther and ovary of an angiosperm bearing 25 microspore mother cells and 25 megaspore mother cells respectively.
Answer : 100 pollen grains, 25 ovules.
Short Answer Type Questions
Question. Write the differences between wind–pollinated and insect–pollinated flowers. Give an example of each type.
|S.No.||Wind pollinated flowers||Insect pollinated flowers|
|(i)||Pollen grains are light and non-sticky so that they can be transported in wind currents.||The flowers are arge, colourful, fragrant and rich in nectar. Pollens are generally sticky, so that they can stick on the insects body.|
|(ii)|| They possess well exposed stamens so that the pollen grains are easily dispersed into wind currents and large feathery stigma to easily trap air-borne pollen grains. Wind pollinated flowers often have a single ovule in each ovary and numerous flowers packed into an inflorescence.|
|A number of flowers are clustered into an inflorescence. The flowers pollinated by flies and beetles secrete foul odours to attract these animals.|
Question. Geitonogamous flowering plants are genetically autogamous but functionally cross-pollinated. Justify.
Answer : Geiotonogamy is cross-pollination involving a pollinating agent, it is genetically similar to autogamy since the pollen grains come from the same plant.
Question. (i) How does cleistogamy ensure autogamy ?
(ii) State one advantage and one disadvantage of cleistogamy to the plant.
Answer : (i) The cleistogamous flowers remain closed and never open. They are bisexual. Therefore, this condition of flowers i.e., cleistogamy ensures autogamy i.e., they ensure the transfer of pollen from the anther to the stigma of the same and single bisexual flower e.g., Commelina and Viola.
(ii) The main advantage of cleistogamy is guaranteed or assured pollination and therefore, fertilization and seed setting.
The main disadvantage of cleistogamy is that variants cannot be produced due to autogamy.
It results in poor crop yield and poor resistance to environmental stresses.
Question. How does the study of different parts of a flower help in identifying wind as its pollinating agent ?
Answer : Wind pollinating flowers has the following characteristics :
(i) Pollen grains are light and non sticky.
(ii) The flowers often possess well-exposed stamen and large feathery stigma.
(iii) Wind-pollinated flowers have a single ovule in each ovary.
(iv) These flowers have small calyx and corolla.
Question. Why is fertilization in angiosperms referred to as double fertilization ? Explain.
Answer : Fertilization in angiosperms is referred as double fertilization, because two male gametes of a single male gametophyte fuse differently with two different cells/nuclei of the same embryo sac to produce two different structures. One male gamete fuses with the egg to form diploid zygote which gives rise to diploid embryo and another male gamete fuses with two haploid polar nuclei or diploid secondary nucleus to form triploid primary endosperm nucleus (3n) which gives rise to triploid endosperm. Hence, the phenomenon of two fusions (syngamy and triple fusion occur) in an embryo sac is known as double fertilization.
Question. Flowering plants have developed many devices to discourage self-pollination and to encourage cross-pollination. Explain three such devices.
Answer : (i) Pollen release and stigma receptivity are not synchronized. Either the pollen is released before the stigma becomes receptive or stigma becomes receptive much before the release of pollen.
(ii) Anther and stigma are placed at different positions in such a way that pollen cannot come in contact of stigma of the same flower.
(iii) Self incompatibility which inhibits the pollen germination/pollen tube growth in the pistil of same flower or another flower of same plant.
(iv) Production of unisexual flowers. This condition prevents both autogamy and geitonogamy.
Question. Explain the steps that ensures cross-pollination in an autogamous flower.
Answer : (i) Pollen release and stigma receptivity are not synchronized, i.e., either the anther matures earlier or stigma.
(ii) The anther and the stigma are placed at different positions so that pollens cannot come in contact with the stigma of the same flower.
(iii) Certain plants produce unisexual flowers, i.e., male and female flowers are present on different plants.
Question. Explain the process of pollination in Vallisneria. How is it different in water-lily, which is also an aquatic plant ?
Answer : In Vallisneria, pollination takes place through water, the female flower reach the surface of water by long stalk, male flowers / pollen grain released on to the surface of water, carried passively by water current reaching the female flowers / stigma
In Water lily, pollination takes place through wind or insect, female flower emerges above the surface of water and gets pollinated
Question. Enumerate any six adaptive floral characteristics of a wind – pollinated flower.
Answer : (i) Large production of pollen grains.
(ii) Anther is well exposed.
(iii) Flowers are not attractive and scent emitting.
(iv) Feathery and sticky stigma.
(v) The pollen grains are light and non-sticky so that they can be transported in wind currents.
(vi) Flowers do not possess nectar.
Question. Explain the process of emasculation and bagging of flowers. State their importance in breeding experiments.
Answer : Emasculation: If the female parent bears bisexual flowers, removal of anthers from the flower’s bud before the anther dehiscence, using a pair of forceps is referred to as emasculation.
Bagging: Emasculated flowers have to be covered with a bag of suitable size, generally made up of butter paper, to prevent contamination of its stigma with unwanted pollen. This process is called bagging.
Importance: When the stigma of bagged flower attains receptivity, mature pollen grains collected from anthers of the male parents are dusted on the stigma, the flowers are rebagged and the fruits are allowed to develop.
If the female parent produces unisexual female flowers, there is no need of emasculation. The female flower buds are bagged before the flowers open. When the stigma becomes receptive, pollination is carried out using the desired pollen and the flower is rebagged.
Question. What does an interaction between pollen grains and its compatible stigma result in after pollination ? List two steps in sequence that follow after the process.
Answer : There is continuous interaction between pollen grain and pistil which is mediated by the chemical components of pollen.
Two steps :
Pollen grain germinates on the stigma to produce pollen tube and the contents of the generative cell move into the pollen tube. Pollen tube grows through the tissue of stigma and style by secreting enzyme.
Long Answer Type Questions
Question. (i) As a senior biology student you have been asked to demonstrate to the students of secondary level in your school, the procedure(s) that shall ensure cross-pollination in a hermaphrodite flower. List the different steps that you would suggest and provide reasons for each one of them.
(ii) Draw a diagram of a section of a megasporangium of an angiosperm and label funiculus, micropyle, embryo sac and nucellus.
Answer : (i) Emasculation, removal of anthers from the flower bud before the anther dehisce to avoid self pollination.
Bagging, to prevent contamination of its stigma with unwanted pollen grains.
Rebagging, the stigma of the mature ovary are dusted with desired pollen grains and rebagged to allow the fruit to develop.
Detailed Answer :
(i) Cross pollination of a hermaphrodite flower can be achieved by :
(a) Emasculation : It is the process of removal of anthers (using forceps) from the bisexual flower bud without affecting the female reproductive part, i.e., pistil.
(b) Bagging : The emasculated flower is then covered with a suitable bag so as to prevent contamination of the stigma with unwanted pollen grains.
When the stigma of the bagged flower becomes receptive, the pollen grains collected from the other flower are dusted onto the stigma and then the flower is re-bagged and allowed to develop the fruits.
Question. (i) State one difference and one similarity between geitonogamy and xenogamy.
(ii) Explain any three devices developed in flowering plants to discourage self pollination and encourage cross pollination.
Answer : (i) Difference : In geitonogamy, pollen grains from one flower are transferred to the stigma of another flower on the same plant whereas in xenogamy the pollen grains are transferred to the stigma of a flower on another plant (of the same species) which is genetically different.
Similarity : In both types of pollination, pollen grains from the anther are transferred to the stigma of another flower of the same species
(ii) (a) Pollen release & stigma receptivity not synchronised / hence the maturity of stigma and pollen are different / Protandry / Protogyny
(b) Anther and Stigma are placed at different positions so that pollen cannot come in contact with stigma of the same flower.
(c) Self incompatibility / Self sterility.
(d) Production of unisexual flowers
Question. A flower of tomato plant following the process of sexual reproduction produces 240 viable seeds.
Answer the following questions giving reasons :
(i) What is the minimum number of pollen grains that must have been involved in the pollination of its pistil ?
(ii) What would have been the minimum number of ovules present in the ovary ?
(iii) How many megaspore mother cells were involved ?
(iv) What is the minimum number of microspore mother cells involved in the above case ?
(v) How many male gametes were involved in this case ?
Answer : (i) 240, one pollen grain participates in fertilization of one ovule.
(ii) 240, one ovule after fertilization forms one seed.
(iii) 240, each MMC forms four megaspores out of which only one remain functional.
(iv) Atleast 60, as each microspore mother cell meiotically divides to form four pollen grains
(v) 480, each pollen grain carries two male gametes (which participate in double fertilization)
Question. (i) Draw a labelled schematic diagram of the transverse section of a mature anther of an angiosperm plant.
(ii) Describe characteristic features of an insect pollinated flower.
Answer : (i)
(ii) Characteristic features of insect pollinated flowers :
(a) The flowers are brightly coloured, showy, large and if small they becomes conspicuous by grouping as in capitulum and umbel etc.
(b) The flowers are sweetly scented so as to attract the insects for pollination.
(c) The flowers have nectar secreting glands which secrete abundant nectar which attract the pollinating insects.
(d) Flowers may have edible pollen e.g., rosa and clematis.
(e) The flowers have stamens and stigma inserted.
(f) Flowers possesses pollen kit as an yellowish sticky substance.
Question. (i) Can a plant flowering in Mumbai be pollinated by pollen grains of the same species growing in New Delhi ? Provide explanations to your answer.
(ii) Draw the diagram of a pistil where pollination has successfully occurred. Label the parts involved in reaching the male gametes to its desired destination.
Answer : (i) Yes, By artificial means (any relevant explanation)
(ii) Diagram with following labellings
Stigma, Pollen tube, Synergid / Filiform Apparatus, Micropyle
Question. (a) Describe any two devices in a flowering plant which prevent both autogamy and geitonogamy.
(b) Explain the events upto double fertilisation after the pollen tube enters one of the synergids in an ovule of an angiosperm.
Answer : (a) (i) Dioecy/Production of unisexual flowers (in different plants)
(ii) Self incompatibility
(b) (i) Pollen tube releases 2 male gametes in the cytoplasm of synergids.
(ii) One male gamete fuses with egg cell, syngamy, resulting in diploid zygote.
(iii) Other male gamete fuses with polar nuclei /triple fusion, to form triploid PEN (Primary endosperm nucleus)/PEC (Primary endosperm cell).
(i) Production of unisexual flowers: Presence of male and female flowers on different plants such that each plant is either male or female (dioecy). In dioecious plants (e.g. papaya), male and female flowers are present on different plants (dioecy). This prevents both autogamy and geitonogamy.
(ii) Self-incompatibility: It is a genetic mechanism to prevent self-pollen (from the same flower or other flowers of the same plant) from fertilization by inhibiting pollen germination or pollen tube growth in the pistil.
(b) Events which occur during double fertilisation are:
(i) Two male gametes are released by the pollen tube into the cytoplasm of synergid.
(ii) Out of the two male gametes, one gametes fuses with the nucleus of the egg cell and forms the zygote, which forms an embryo. The process is known as syngamy.
(iii) The other male gamete fuses with the two polar nuclei located in the central cell to form a triploid primary endosperm nucleus (PEN).
(iv) Since, the process involves the fusion of three haploid nuclei, it is known as triple fusion.
After triple fusion, the central cell becomes the primary endosperm cell (PEC).
(v) Since two types of fusions (syngamy and triple fusion) take place in an embryo sac it is known as double fertilisation.