VBQs Class 12 Biology Sexual Reproduction in Flowering Plants

VBQs For Class 12

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


Tese pictures show the gynoecium of (A) Papaver and (B) Michelia flowers. Write the difference in the structure of their ovaries.
Answer.The gynoecium of Papaver is multicarpellary and syncarpous (pistils fused together) whereas the gynoecium of Michelia is multicarpellary and apocarpous (pistils free). In Papaver ovary is unilocular to multilocular whereas in Michelia ovary is always unilocular.

Question. Name the part of the flower which the tassels of the corn-cob represent. 
Answer.Tassels of corn cob represent staminate inflorescence (cluster of male flowers), so they represent androecium (male reproductive part) of the flower.

Question. Give an example of a plant which came into India as a contaminant and is a cause of pollen allergy. 
Answer.Parthenium or carrot grass is an example of a plant which came to India as a contaminant and is a major contributor to pollen allergy.

Question. What is pollen-pistil interaction and how is it mediated? 
Answer.Pollen-pistil interaction is the group of events that occur from the time of pollen deposition over the stigma to the time of pollen tube entry into ovule. The dialogue between pollen grain and the pistil is mediated by chemical components of the pollen interacting with those of the pistil.
The pistil has the ability to recognise the pollen,whether it is of the right type (compatible) or of the wrong type (incompatible). This is followed by its acceptance or rejection.

Question. State the function of filiform apparatus found in mature embryo sac of an angiosperm.
Answer.Filiform apparatus refers finger-like projections which arise from cell wall of the synergid and penetrate into the cytoplasm of the central cell. These are present at the micropylar tip of synergids. They play an important role in distribution of nutrients in the embryo sac, secretion of substances that attract pollen tube thereby guiding the pollen tube into synergid and also provide mechanical strength to synergids.

Question. Differentiate between xenogamy and geitonogamy.
Answer.Differences between xenogamy and geitonogamy are as follows:

Question. An anther with malfunctioning tapetum often fails to produce viable male gametophytes. Give any one reason. 
Answer.Tapetum is the microsporangial layer that provides nourishment to the developing microspores. In an anther with malfunctioning tapetum, microspores do not get suffcient nutrition and hence viable male gametophytes are often not produced.

Question. How do the pollen grains of Vallisneria protect themselves?
Answer.Vallisneria is a water pollinated plant. Pollen grains of Vallisneria have a protective mucilaginous coat that prevents the water from damaging the pollen grains.

Question. Write the function of tapetum in anthers.
Answer.(i) Tapetum nourishes the developing microspores.
(ii) It produces lipid rich ubisch granules containing sporopollenin, pollenkitt, compatibility recognising proteins etc.
(iii) It secretes enzyme callase for the separation of microspores.

Question. Explain the function of germ pores.
Answer.Germ pores are prominent apertures of pollen grain where exine is thin or absent hence, sporopollenin is absent and intine is thickened.These are the regions where intine comes out to form a pollen tube after pollination.

Question. Write the characteristic features of anemophilous flowers. 
Answer.The characteristic features of anemophilous flowers are well exposed stamens light, small, winged or dusty pollen grains and large, often-feathery and exposed stigma to trap air-borne pollen grains.

Question. Give reason why anthers of angiosperm flowers are described as dithecous. 
Answer.Anthers of most angiosperms (flowering plants) contain two anther lobes, hence are called dithecous.

Question. Mention any one application of a pollen bank.
Answer.Pollen banks are used to store pollen grains for long time, which can be used in plant breeding programmes. In pollen banks, pollens are stored in liquid nitrogen at a temperature of –196°C.

Question. All papaya plants bear flowers but fruits are seen in some. Explain. 
Answer.Papaya plant is dioecious plant and bears male and female flowers on different plants i.e., male plant and female plant. Fruit is formed by the female part of the flower after fertilisation. Following double fertilisation, i.e., fusion of one male gamete with egg cell and the other male gamete with secondary nucleus. Ovules turn into seeds and ovary turns into fruits.
As these female structures are found only on female papaya plants hence fruits are present only on female papaya plant whereas male papaya plant only produces gametophytes, i.e., pollen grains which bear male gametes.

Question. Write the characteristic features of anther, pollen and stigma of wind pollinated flowers.
Answer.In wind pollinated flowers, anthers are exserted and versatile. In some cases like Urtica, the anthers burst suddenly to throw the pollen grains (gun powder mechanism).
Pollens of wind pollinated flowers are light, small,winged, dry, smooth, non-sticky, unwettable and are produced in very large number.
Stigma of wind pollinated flower is exserted, hairy, feathery or branched to catch the wind borne pollen grains. The large thread-like stigmas and styles of cob of maize hang in air to catch wind borne pollens.

Question. A bilobed, dithecous anther has 100 microspore mother cells per microsporangium. How many male gametophytes this anther can produce?
Answer.Dithecous anther has four microsporangia or pollen sacs. This anther will have 400 microspore mother cells. As each microspore mother cell forms 4 pollen grains, 400 microspore mother cells will form 1600 pollen grains (male gametophytes).

Question. The microscopic pollen grains of the past are obtained as fossils. Mention the characteristic of the pollen grains that makes it happen.
Answer.Sporopollenin is a major component of the hard outer layer called exine of pollen grains. It is chemically very stable and is usually well preserved in soils and sediments. Hence, pollen grains of the part are well preserved as fossils.

Question. Name the type of flower which favours cross pollination.
Answer.Unisexual flowers favour cross pollination

Question. Why is bagging of the emasculated flowers essential during hybridisation experiments?
Answer.Bagging of the emasculated flowers is essential to prevent the landing of unwanted pollen on the stigma of flowers during hybridisation experiments.

Question. The following statements (a), (b) and (c) seem to describe the water-pollinated submerged plants.
Which one of these statements is incorrect?
(a) Thee flowers do not produce nectar.
(b) The pollen grains have mucilaginous covering.
(c) The brightly coloured female flowers have long stalk to reach the surface.
Answer.Statement (c) is incorrect. In submerged waterpollinated plants, the flowers are small, inconspicuous and generally dull coloured not brightly coloured.

Question. How can pollen grains of wheat and rice which tend to lose viability within 30 minutes of their release be made available months later for breeding programmes? 
Answer.In some cereals such as wheat and rice, pollen grains lose viability within 30 minutes of their release. They can be made available months later by means of cryopreservation i.e., storing them in liquid nitrogen at a very low temperature (–196°C).

Question. List the different types of pollination depending upon the source of pollen grain.
Answer.Based on the source of pollen grain, pollination can be of following three types:
(i) Autogamy : Autogamy (self pollination) is the transfer of pollen grains from anther to the stigma of the same flower.
(ii) Geitonogamy : It is the transfer of pollen grains from the anther of one flower to the stigma of another flower on the same plant. Geitonogamy is functionally cross-pollination involving a pollinating agent but genetically it is equivalent to autogamy since the pollen grains come from the same plant.
(iii) Xenogamy : It is the transfer of pollen grains from anther to the stigma of different plants of same species. It brings genetically different types of pollen grains to the stigma.

Question. Angiosperms bearing unisexual flowers are said to be either monoecious or dioecious. Explain with the help of one example of each.
Answer.Unisexual flowers are flowers bearing either male or female reproductive structures. Male flower is staminate, i.e., bearing stamens while female flower is pistillate i.e., bearing pistils.
In some flowering plants, both male and female Fowers are present on same plant. Such plants are referred to as monoecious e.g., cucurbits. In some plants, unisexual male and female flowers are present on separate plants. Such plants are referred to as dioecious e.g., papaya.

Question. A single pea plant in your kitchen garden produces pods with viable seeds, but the individual papaya plant does not. Explain.
Answer.Pea plant is monoecious plant i.e., bearing both male and female flowers on same plant. Thus, a single pea plant can produce viable seeds after pollination and fertilisation. However, a papaya plant is dioecious plant i.e., bearing male and female flowers on different plants and requires cross pollination for production of viable seeds. Thus, in absence of either stamens or pistils, fertilisation will not take place and hence viable seeds will not be produced.

Question. Gynoecium of a flower may be apocarpous or syncarpous. Explain with the help of an example each.
Answer.Gynoecium represents the female reproductive part of a flower. Gynoecium is called apocarpous if the carpels are free, e.g., Michelia. It is called syncarpous if the carpels are fused, e.g., Papaver (poppy).

Question. Why do hermaphrodite angiosperms develop outbreeding devices? Explain any two such devices with the help of examples.
Answer.Hermaphrodite angiosperms develop out breeding devices to avoid self pollination and encourage cross pollination. Two outbreeding devices
which ensure cross pollination are as follows:
(i) Dichogamy : Anthers and stigmas mature at different times in a bisexual flower. It is of two types:
(a) Protandry : Anthers mature earlier than stigma of the same flower. Their pollen grains become available to stigmas of the older flowers, e.g., Sunflower, Salvia.
(b) Protogyny : Stigmas mature earlier so that they get pollinated before the anthers of the same flower develop pollen grains, e.g., Mirabilis jalapa, Gloriosa,Plantago.
(ii) Self sterility (Self incompatibility) : Pollen grains of a flower do not germinate on the stigma of the same flower due to presence of similar self sterile gene (S1S3 in pistil and S1 or S3 in pollen grain) e.g.,tobacco, potato, crucifers.

Question. Name the organic materials exine and intine of an angiosperm pollen grain are made up of.Explain the role of exine. 
Answer.Exine is the outer tough and resistant layer of pollen grains made up of sporopollenin. Intine is thin continuous and inner wall of the pollen grain
which is made up of cellulose and pectin.
Exine provides protection to pollen grain during its hazardous journey from anther of one flower to the stigma of another flower. Due to presence of sporopollenin in exine, pollens of past are will preserved as fossil in soil and sediments elabling the scientists to study pollen structure and pollination pattern of angiosperms of past.

Question. Draw a diagram of a matured microspore of an angiosperm. Label its cellular components only. 
Answer.Labelled diagram of mature microspore (or pollen grain) is as follows:

Question. (a) How does cleistogamy ensure autogamy?
(b) State one advantage and one disadvantage of cleistogamy to the plant.
Answer.(a) Cleistogamy is the condition where pollination occurs in closed flowers that do not open at all. In such flowers, the anthers and stigma lie close to each other. When anthers dehisce in the flower buds, pollen grains come in contact with the stigma to efect pollination. Thus, cleistogamous flowers are invariably autogamous as there is no chance of cross-pollen landing on the stigma.
(b) One advantage of cleistogamy is that seed setting is assured even in the absence of pollinators as pollen on maturity will always reach the stigma due to their close placement.
One disadvantage of cleistogamy is that it does not allow cross pollination, thereby restricting chances of genetic variability.

Question. Geitonogamous flowering plants are genetically autogamous but functionally cross-pollinated. Justify. 
Answer.Geitonogamy is the transfer of pollen grains from the anther of one flower to the stigma of another flower of the same plant. It is functionally cross pollination involving pollinating agent but genetically it is similar to autogamy since the pollen grains come from the same plant.

Question. Name all the haploid cells present in an unfertilised mature embryo-sac of a flowering plant. Write the total number of cells in it.
Answer.In an unfertilised mature embryo sac of flowering plant, six haploid cells are present i.e., two synergids, one egg, three antipodals. The total number of cells in an unfertilised mature embryo sac is seven i.e., two haploid synergids, one haploid egg, three haploid antipodals and one central cell (containing two polar nuclei).

Question. Differentiate between the two cells enclosed in a mature male gametophyte of an angiosperm.
Answer.Two cells enclosed in a mature male gametophyte of an angiosperm are : a smaller generative cell and a much larger vegetative cell (or tube cell). Generative cell is spindle shaped to spherical in outline with thin dense cytoplasm surrounding a prominent nucleus. Vegetative cell has a lobed central nucleus that lies in vacuolated cytoplasm packed with, starch grains, lipids and proteins.

Question. Draw a labelled diagram of a mature pollen grain. 
Answer.Labelled diagram of mature pollen grain is as follows:

Question. Explain the sequence of events in pollen-pistil interaction. 
Answer.Pollen pistil interaction is the group of events that occur from the time of pollen deposition over the stigma to the time of pollen tube entry into ovule.
As soon as a pollen grain lands on the stigma, it is hydrated. As a result of hydration, the exine and intine proteins are released on the stigmatic surface.
The pollen wall proteins bind to the stigma surface pellicle (receptor site for the pollen wall proteins) within few minutes of the contact.
When pollen is compatible, erosion of the cuticle of the stigma papilla begins beneath the emerging pollen tube. This is the essential preliminary requirement for the penetration of the pollen tube.
In case of incompatible pollination, a callosic plug develops between the plasma membrane and pectocellulosic layer of the stigmatic papillae just below the point of contact with the pollen and the growth of pollen tube ceases.

Question. Draw labelled diagram of a mature ovule and embryo sac with its contents.

Question. List the adaptive features of water pollinated flowers like Vallisneria. 
Answer.Vallisneria is a submerged dioecious aquatic plant in which pollination takes place by the agency of water. The adaptive features of water pollinated flowers of Vallisneria are as follows:
(i) The male plants produce a large number of male flowers. The male flowers abscise and rise to the surface where they float.
(ii) The male flowers have two fertile stamens. Two of their tepals form a boat-shaped structure while the third one functions as a sail.
(iii) The female plants bear long stalked solitary pistillate flowers. The mature female flowers are brought to the surface of water by the elongation of their stalks. They have large sticky trifid stigmas.
(iv) While floating, the male flowers are drawn in the depression surrounding each female flower.
One anther of a male or staminate flower comes in contact with the stigma of the female flower. The anther bursts and pollination is performed.
(v) Pollen grains are covered by mucilage which helps them in sticking to stigma as well as protects them from wetting by water.
(vi) After pollination, the female flower is pulled inside water by the coiling of its stalk.

Question. Where is sporopollenin present in plants? State its significance with reference to its chemical nature. 
Answer.Sporopollenin is present in exine layer of pollen grains. Sporopollenin is highly resistant fatty substance not degraded by any enzyme and not affected by high temperature, strong acid or strong alkali therefore pollen grains can be well preserved as microfossils.

Question. How does the study of different parts of a flower help in identifying wind as its pollinating agent?
Answer.In a wind pollinated flower, following characteristics are present which help to identify that wind is its pollinating agent:
(i) Flowers are small and inconspicuous.
(ii) Non-essential parts are either absent or reduced.
(iii) The flowers are colourless, odourless and nectarless.
(iv) In case of unisexual flowers, the male flowers are more abundant. In bisexual flowers, the stamens are generally numerous.
(v) Flowers are produced above the foliage, before the appearance of new foliage or placed in hanging position.
(vi) Both the stigmas and anthers are exserted.Anthers are versatile.
(vii) Pollen grains are light, small, dusty, dry and unwettable.
(viii) Stigma is hairy, feathery or branched to catch the wind borne pollen grains.

Question. Trace pollen grain development from sporogenous tissue in the anther. 
Answer.In an anther, each cell of the sporogenous tissue is a potential pollen or microspore mother cell (PMC).Each PMC divides by meiosis to form a microspore tetrad. This process is called microsporogenesis. As the anthers mature and dehydrate, the microspores dissociate from each other and develop into pollen grains. The hard outer layer called the exine is made up of sporopollenin. The inner wall of the pollen grain is called the intine. When the pollen grain is mature it contains two cells, the vegetative cell and the generative cell. Different stages of microsporogenesis are shown below.

Question. What is the role of endothecium and tapetum in an anther? 
Answer.Endothecium performs the function of protection in the young anther and is involved in dehiscence of the mature anther.
Role of tapetum in an anther is as follows:
(i) Nourishment of the developing microspore mother cells and pollen grains.
(ii) It produces lipid rich ubisch granules containing sporopollenin for exine formation, pollenkitt in case of entomophilous plants, special proteins for the pollen grains to recognise compatibility and hormone IAA.
(iii) It secretes enzyme callase responsible for the degradation of callose wall around pollen tetrad.

Question. Differentiate between autogamy, geitonogamy and xenogamy. 
Answer.Difference between autogamy, geitonogamy and xenogamy is as follows:

Question. Why does a breeder need to emasculate a bisexual flower? Mention a condition in a flower where emasculation is not necessary.
Answer.Emasculation is removal of stamens from the floral buds of female parent. A breeder needs to
emasculate a bisexual flower to eliminate the chances of self pollination. Emasculation is not required if the flowers are unisexual. However, flowers must be kept covered by bags to protect them from contamination by unwanted pollen grains.

Question. (a) Mention any four strategies adopted by flowering plants to prevent self-pollination.
(b) Why is geitonogamy also referred to as genetical autogamy? 
Answer.(a) In self pollination, the pollen grains are transferred from the anther of a flower to the stigma of either the same or genetically similar flower. In this process the parental characters are sustained and new useful characters are seldom introduced in next generation. So, to prevent this, some strategies
are adopted by the flowering plants. ese are as follows:
– Dichogamy : Male and female sex organs of a bisexual flower mature at different times.
– Self sterility : The pollen of a flower has no fertilising effect on the stigma of the same flower.
– Pollen prepotency : In some plants when the stigma receives pollen from the same flower as well as from the other flower simultaneously the foreign pollen germinates quickly and fertilises the ovule.
– Herkogamy : It is the presence of natural and physical barriers between androecium and gynoecium which help in avoiding self pollination.
(b) In geitonogamy pollen grains of one flower are transferred to the stigma of another flower belonging to either the same plant or genetically similar plant.
Thus, geitonogamy is also referred to as genetical autogamy.

Question. Explain the process of artificial hybridisation to get improved crop variety in (a) plants bearing bisexual flowers (b) female parent producing unisexual flowers. 
Answer.In bisexual flowers, hybridisation involves emasculation i.e., removal of male reproductive parts (stamens) followed by artificial pollination.
(b) In unisexual flowers the procedure is rather simple. Unopened floral buds are covered with cellophane bags. When the stigma attains receptivity pollens from the male parent are dusted on it, and the pollinated flowers are rebagged.