Bihar Board Class 12 Biology Solutions Chapter 2 Sexual Reproduction in Flowering Plants Textbook Questions and Answers, Additional Important Questions, Notes.
BSEB Bihar Board Class 12 Biology Solutions Chapter 2 Sexual Reproduction in Flowering Plants
Bihar Board Class 12 Biology Sexual Reproduction in Flowering Plants Text Book Questions and Answers
Name the parts of an angiosperm flower in which development of male and female gametophyte take place.
In an angiosperm flower the male gametophyte is represented by pollen grains. Pollen grains develop inside the microsporangia. In angiosperms female gametophyte or embryosac is formed from a megaspore through reduction division. It lies inside the nuceilus of ovule.
Differentiate between microsporogenesis and mega- sporogenesis. Which type of ceil division occurs during these events? Name the structures formed at the end of these two events.
|(1) The process of formation of microspores from megaspores mother cells.||(1) Its the formation of from mega- microspore spore mother cells.|
|(2) This process occurs inside the anthers.||(2) This process occurs inside the nuceilus of developing ovule of angiosperms.|
|(3) It leads to the formation of several thousands of microspores and pollen grains.||3. Initially four mega-spores are formed but generally only one megaspore is functional
and rest three degene-rate.
Both microsporogenesis and megasporogenesis takes place by meiosis i.e. reduction cell division.
Microsporogenesis leads to the formation of male gametophyte i.e. pollen grains whereas at t! e end of megasporogenesis female gametophyte or embryosac is formed.
Arrange the following terms in a correct developmental sequence :
Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.
The correct development sequence for the above terms is Sporogenous tissue, microspore tetrad, pollen mother cell, pollen grain, male gametes.
With a neat, labeled diagram, describe the parts of a typical angiosperm ovule.
Figure showing longitudinal section of an amatropous ovule with the two integuments and micropyle.
What is meant by monosporic development of female gametophytes?
During mega sporogenesis, one megaspore mother (MMC) divides mitotically to produce four megaspores. In majority of angiosperms, only one megaspore is functional (situated towards chalazal end) and develops into female gametophyte. The rest three degenerate. This is called as monosporic development of female gametophyte, e.g. polygonum.
With a neat diagram explain the 7-celled, 8-nucleate mature female gametophyte.
Figure showing: The embryosac contaihs an egg, two synergids, three antipodals and two polar nuclei.
What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.
Chasmogamous flowers: These are flowers with exposed anthers and stigma. These may be cross-pollinated or self-pollinated. Whereas cleistogamous flowers are bisexual and do not open at all to ensure complete self-pollination. In cleistogamous flowers there is no scope of cross-pollination because (i) flowers do not open at all (ii) anthers and stigma lie close to each other for self-pollination to occur. So they are antogamous and cannot be cross-pollinated.
Mention two strategies evolved to prevent self-pollination in flowers.
Flowers adopt various strategies to avoid self-pollination. Two of these are
- Dichogamy: Where pollen and stigma of the flower mature at different times to avoid self-pollination. It can be protogyny when gynoecium matures earlier than androecium e.g. Bajra; and protandry, when androecium matures and shed pollen before gynoecium matures e.g. Maize.
- Self-incompatibility: It is a genetic mechanism in which pollen from same flower or from same plant fails to fertilize the ovules either by inhibition of germination or pollen tube growth in the pistil.
What is self-incompatibility? Why does self-pollination not lead to seed rmation in self-incompatible species?
(i) Self-incompatibility or self-sterility is the inability of certain gametes even from genetically similar plant species to fertilize with each other. It occurs due to prevention of some physiological or morphological mechanisms. Self-incompatibility is a natural barrier to prevent self-pollination.
It means even if the pollen grains come in contact with stigma of the same flower or flowers of same plant, they are unable to grow and produce their own clones without any genetic variations. It includes several complex mechanisms related with interactions of pollen and stigmatic tissues. It can be sporophytic or gametophytic incompatibility. It occurs due to prevent of pollen germination, retardation of growth, deorientation of pollen tube. It may take place due to failure of nuclear fusion. Due to which there is no seed formation in self-incompatible species.
What is bagging technique? How is it useful in a plant breeding programme?
Bagging is a technique, for artificial hybridization. In it already emasculated flowers are covered with a butter paper of suitable size, to prevent contamination of its sitgma with unwanted pollen. This technique is very’ useful for plant breeding programmes as it prevents unwanted cross-pollination.
What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
Triple fusion is fusion of three haploid nuclei during double fertilization. It takes place between one male gamete with the two polar nuclei located in the centra! cell. It leads to the formation of a triploid primary endosperm nucleus (PEN).
Why do you think the zygote is dormant for sometime in a fertilized ovule?
Mostly zygote remains dormant for sometime in a fertilized ovuie because endosperm development preceedes embryo development (embryo develops from zygote). The endosperm tissue provides nutrition to the developing embryo.
Differentiate between :
(a) hypocoty! and epicotyl;
(b) coleoptile and coleorrhiza;
(c) integument and testa;
(d) perisperm and pericarp.
(a) Hypocotvt and Epicotyl :
|(1) Hypocotyl is the cylindrical portion below the level of cotyledons.||(1) Epicotyl is the portion of ernbryonal ads above the level of cotyledons.|
|(2) Hypocotyl terminates with root cap called radical.||(2) Eicotyl terminates with stern tip or plumule|
(b) Coleoptile and Coleorrhiza :
|1. Along with shoot apex the epicoryl has a few leaf primordia n a hollow foliar structure called coleoptile.||1. Embryonal axis at its lower end has radical and root cap enclosed in an undifferentiated sheath which is called as coleorhiza.|
(c) integument and Testa:
|(1) integuments are the protective covering of the ovules.||(1) Testa is the outer seed coat. It is actually the integument of ovule which harden to form tough seed coat.|
|(2) It encircle the ovule completely except at micropylar end. They are protective in nature.||(2) Testa is hard and provides protection to the young embryo. Micropyle is also present here.|
(d) Perisperm and Pericarp :
|(1) Perisperm is the residual persistent nucellus, e.g. black pepper.||(1) Pericarp is the wall of fruit, which is developed from the wall of ovary.|
|(2) It is a single layer to store food.||(2) It may be divided into three layers viz exocarp, mesocarp and endocarp.|
Why is the apple called a false fruit? Which parts of the flower forms the fruit?
A fruit is a matured ovary with of without seeds. It may be defined as a structure made up of one or more matured ovaries together with any accessory structures closely associated with them, which may degenerate and fall off.
Apple is called a false fruit because its fleshy edible part is composed of thalamus. The true fruit lies within it. It has got an inferior ovary, two or more seeded and fleshy syncarpous fruit surrounded by thalamus. It is known as pome.
What is meant by emasculation? When and why does a plant breeder employ this technique?
Emasculation is technique of removal of anthers from the flower bud before the anther dehisces. It is done manually by using forceps. It is used widely by plant breeders to produce commercially superior varieties of plants. It is done to produce desired cross-pollination between different species or general to combine desirable characters. It is followed by bagging.
If one can induce parthenocarpy through the application of growth substances, which fruits you would select to induce parthenocarpy and why?
Parthenocarpy is the process of production of fruits by application of growth substances such as auxins and gibberellins. It can be natural or induced. Parthenocarpic fruits are produced without fertilization. E.g. Seedless grapes, oranges, lemons and tomatoes etc. can be produced by this process and they are very successful commercially.
Explain the role of tapetum in the formation pollen-grain wail.
Tapetum is the innermost wall of the microsporangium. The tapetal cells may be uni-, bi-, or multinucleate and possess dense cytoplasm. The various roles played by tapetum are as such :
- Secretion of hormones and various enzymes,
- Transportation of nutrients in another locule during meiosis in spore mother cells,
- Production of Ubisch bodies coated with sporopollenin to cause exine thickening,
- Secretion of pollen kitt (oily substance) outside mature pollen,
- Secretion of proteins for pollen to be compatible during recognition.
What is apomixes and what is its importance?
Apomixes: The process of development of seeds without fertilization is called as apomixis. This form of asexual reproduction mimics sexual reproduction. It’s characteristic of some grasses and Asteraceae. Apomixis is very important for hybrid seed industry. Hybrid seeds need to be produced year after year, thus making it Very costly. If hybrids are made apomicts there won’t be any segregation of characters as in hybrids. Thus these hybrids seeds can be used year after year without spending extra money to buy new hybrids. Thus it is very economical.
Bihar Board Class 12 Biology Sexual Reproduction in Flowering Plants Additional Important Questions and Answers
Very Short Answer Type Questions
Name two essential parts of flower.
These are stamen and carpel.
Define anemophily. (Haryana board 2001)
Anemophily is the pollination by wind.
What is double fertilization? (Haryana Board 2001)
Fusion of one male gamete with the egg cell, and the union of second male gamete to polar nuclei in angiosperms.
Give an example of bat pollinated flower.
Name three types of incompatibility.
- Gametophytic incompatibility.
- Sporophytic incompatibility.
Why is grafting not possible in monocot plants?
Monocots do not have cambium.
Name various types of vegetative reproduction in flowering plants.
By modified tuberous roots which have adventitious buds, underground modified stems, creeping stems,’leaves, bulbils and turions.
Give the characters of flowers pollinated by insects.
They are usually large, brightly coloured, scented and produce nectar to attract insects.
The undifferentiated mass of cells is called callus.
What is funiculus?
Funiculus is the stalk of ovule.
What is nucellus?
Nucellus is the mass of parenchymatous tissue surrounded by integuments in an ovule. It encloses embryo sac and provides nourishment to the developing embryo.
One of the plants bearing anemophilous flowers is :
(d) Maize (C.B.S.E. 2003)
Why grafting is not possible in monocot plants? (P.S.E.B. 1998)
Grafting is not possible in monocot plants because they do not possess cambium.
Why are cucurbits referred to as monoecious? (C.B.S.E. 2001)
Cucurbits are unisexual i.e. male and female flowers are borne on the same plant so they are referred to as monoecious.
Why are flowers of cucumber referred to as epigynous? (C.B.S.E. 2001)
The female flowers of cucumber are referred to as e.pigynous because their ovary is inferior and other floral parts appear to arise above its level.
Why are date palm plants referred to as dioecious? (C.B.S.E. 2001)
Date palms are unisexual where male and female flowers are borne on different plants so they are called dioecious.
Which technique can be used for imprpved varieties of rose?
What do you mean by hydrophily? (H.P.S.E.B. 1996)
Its a mode of pollination that occurs through water.
Name a cultivated plant in which neither fruits nor seeds are formed.
Where are the pollen grains formed in a plant?
Pollen grains are formed inside the pollen sacs in anthers.
Short Answer Type Questions
Why is endosperm in angiosperms ovule considered as more efficient? (Maharashtra Board 2001)
In angiosperms, the cells of endosperm are triploid due to double fertilization. Thus they are considered more efficient in supplying food materials to the developing embryo.
Why is the process of fertilization in a flowering plant referred to as double fertilization? Explain. (C.B.S.E. Delhi 2004)
Fertilization in flowering plants is referred to as double fertilization because two male gametes from the same microspore takes part infusion. One male gamete fuses with the egg to form a diploid zygote and the other male gamete fuses with the two polar nuclei or secondary nucleus to form the triploid primary endosperm nucleus.
Write the functions of flowers. (P.S.E.B. 2001)
Functions of a flower are as follows :
- Flowers are modified to perform the function of sexual reproduction.
- They are shaped variously to help in pollination.
- They provide seat for germination of pollen, development of pollen tube, formation of gametes and fertilization.
- Some floral parts help in dispersal of fruits and seeds.
- The ovary transforms into fruit and ovules into seeds after fertilization in flowers.
Differentiate between self-pollination and cross-pollination.
|Self pollination||Cross pollination|
|(1) Migration of pollen grains from anther to the stigma of the same flower (or same plant) is called self-pollination.||(1) Migration of pollen grains from anther to the stigma of another flower of another plant is called cross-pollination.|
|(2) Mode of pollination is always winded or by touch.||(2) Modes of pollination are external e.g. wind, water or animals.|
|(3) Anthers and stigma mature at same time and lie close to each other.||(3) Anthers and stigma may mature at different times and not essentially lie in proximity.|
|(4) No chances of new varieties.||(4) Variations occurs at every new generation and thus leads to evolution.|
Draw a labelled diagram of the longitudinal section of a maize grain to show the structure of mature embryo.
Name the pollinating agents of flowers like maize and wheat. Give any two favourable features of such a flower. (C.B.S.E. 1997)
In case of maize, the pollinating agent is wind. These flowers are unisexual, small, colourless, inconspicuous and odourless. Whereas in wheat, its self-pollination. Both anthers and stigma of bisexual flowers from the same plant mature before the bud opens, thus to ensure complete self-pollination.
Name a plant where vegetative propagation occurs from reproductive organs. What is the special name of the reproductive part of this plant. (C.B.S.E. 1995)
In Agave sp. (century plant), the floral buds get modified into bulbils. When these bulbils get detached from the mother plant, they form a new plant. Thus its a form of vegetative propagation which occurs from reproductive organs (flower).
Draw a labelled diagram of the longitudinal section of a pistil showing pollen germination. (C.B.S.E. 1996, P.S.E.B. 1995)
What are the advantages of using plant tissue culture for propagation?
Plant tissue culture is a technique employed for quick multiplication of plants. It is also used in producing virus-free plants, disease-free plants and homozygous diploids. This technique is highly useful in commercial micropropagation of orchids, carnation, gladiolus, chrysonthemum and some ornamental plants.
What are the characteristics of wind-pollinated flowers? (P.S.E.B. 1997, 2001)
Pollination by wind is called Anemophilous. It happens in coconut palm, date palm, maize, grasses etc. Their some characters are as such :
- Flowers are inconspicuous and not showy.
- They are colourless and odourless.
- Produce large quantities of dusty pollens.
- Flowers grow in large groups:
- Stigmas are sticky, hairy, feathery or branched.
Some crop plants can be grown from a seed as well as vegetatively from stem cutting. List any four advantages of vegetative propagation in such cases. (C.B.S.E. 1998)
Plants which are grown vegetatively from stem cuttings have following advantages than those produced from seeds.
- They mature early and grow very fast.
- They are healthy and robust.
- The produce flowers and fruits much early.
- They characteristics of parent plant are preserved in them as no recombination occurs.
Draw a labelled sketch of the section of a mature pollen grain.
Trace the development of microsporocyte in the anther to a mature pollen grain. (C.B.S.E. 2000)
Microsporocyte or microspore mother cells are polygonal and closely packed initially. Pollen grains develop from them in pollen sacs of anthers. As anther enlarges, pollen sac becomes loosely arranged. A few microsporocytes become non-functional and are absorbed by developing microspores. Each microsporocyte undergoes meiosis and form four haploid nuclei (microspores or pollen grains). They arrange in a tetrahedral manner. Later on each microspore separates and develops into a mature pollen grain.
Trace the development of a mature ovule from a megaspore mother cell. (C.B.S.E. 2004)
The process of formation of megaspores from megaspore mother cell is called as megasporogenesis. Megaspore mother cell undergoes meiosis to form four haploid megaspores. They arrange in a linear tetyrad. usually the upper three degenerate and lowermost becomes a functional megaspore. This functional megaspore forms female gametophyte or embryo sac.
Name one example for each of the following :
(a) A plant in which both male and female sex organs occur in the same flower.
(b) A plant in which separate male and female mowers are borne on the same individual at different positions.
(c) A cultivated plant which neither fruits nor seeds are formed.
(d) A species in which the individual plant is either male or female.
(a) Hibiscus rosa-sinensis,
(b) Zea-mays (maize),
(c) Sugar cane,
Long Answer Type Questions
Write short notes on the following :
(a) Nuclear type endosperm
(b) Dicot non-endospermic seed
(c) Seed dormancy
(a) Nuclear type endosperm: During the development of nuclear type endosperm, the primary endosperm nucleus divides mitotically into free nuclear divisions without wall formation. It results into a large number of free nuclei in the central cell of embryo sac. A big central vacuole is developed into embryo sac pushing all the nuclei to the periphery. In the second phase the cleavage of multinucleate peripheral cytoplasm results in centripetal cell wall formation. Finally, all the endosperm is converted into a cellular tissue e.g., Coconut.
(b) Dicot non-endospermic seed: The seeds which store their food in cotyledons are called non-endospermic seed or exalbuminous seeds, e.g. bean, gram etc. The seeds of bean are formed within pod, which is a ripened ovary. The seed is attached by funiculus or seed stalk. When seeds the funiculus breaks off leaving a prominent stalk, hilum. Below the Helium lies micropyle. The seed coats have characteristic colours.
In these seeds there is no endosperm, it’s already consumed by developing embryo. Most of the food is stored in cotyledons which never function as true leaves.
(c) Seed dormancy: The dormancy of seed is the condition of seed when it fails to germinate even though the environmental conditions which are considered favourable for active growth. Seed dormancy may be due to seed coats, condition of embryo, due to specific light requirement, due to germination inhibitors. Seed dormancy is beneficial in various ways as it is a adaptation to ensure germination only under favourable conditions. It unables the seeds to be disseminated in time and space. Seed dormancy can be broken by softening or breaking of seed coats (scarification), by shaking (impaction), altering the temperature, treatment of seeds with growth promoters,
(d) Geitonogamy: Geitonogamy is the kind of self-pollination. It takes place when pollen grains are transferred from anther of a flower to the stigma of the same flower. The flowers are essentially bisexual, e.g. Pea, Wheat, rice etc.
(a) Describe with the help of a sketch the structure of a maize grain.
(b) How does it differ from been seed?
(a) Structure of maize grain: Maize grain is endospermic grain, it is a one-seeded fruit called caryopsis. The pericarp is fused with testa. It consists of following parts :
- Seed coat: The outer brownish layer. In this, seed and fruit are fused together.
- Endosperm: Its the major part of grain and full with reserve food. Its made up of two regions : (I) Aleurone layer: outer single layer made up of aleurone proteins.
(2) Inner starcy endosperm. Endosperm is separated from embryo by epithelium.
Embryo: It is a single cotyledonous embryo called scutellum. An embroy axis with plumule and radical are present at its two ends. At the tip of radicle is present root cap, radical is surrounded by a protective layer known as coleorhiza. Plumule is protected by covered sheath called coleoptile.
(b) Difference between maize grain and bean seed :
|(1) It is single-seeded fruit called the caryopsis.||(1) It is a true seed formed inside a fruit called the pod or a legume. There – are many seeds in a pod.|
|(2) The fruit wall or the pericarp ¡s fused with testa.||(2) The pericarp is free from testa.|
|(3) There is one seed coat which is inseparably fused with pericarp.||(3) There are two seed coats called testa and tegmen. They are fused with each other.|
|(4) The nucellus persists within the seed coat. It is in the form of a single layer of cells.||(4) The nucellus is consumed during seed development.|
|(5) The grain is endospermic.||(5) The seed is non-endospermic.|
|(6) It has only one cotyledon.||(6) It has two cotyledons.|
|(7) The endosperm has a distinct layer called aleurone layer and the starchy endosperm. The aleurone layer is made up of a single, layer of cells, whose protoplasm contains aleurone grains.
The starchy endosperm is made up of many layers of cells whose protoplasm contains starch grains.
|(7) The food is stored in the cotyledons. The cells of the cotyledons are thin-walled with their protoplasm filled with protein grains, fats and starch grains.|
|(8) The grain has no hilum, micropyle and chalaza on its surface.||(8) The chalaza, hilum and micropyle are clearly visible.|
|(9) There is no ridge-like raphe.||(9) The raphe is clearly visible.|
|(10) The plumule and radicle are protected by distinct sheaths called the coleoptile and the coleorhiza, respectively.||(10) The plumule and radicle are not covered by any such protective sheaths.|
|(11) The hypocotyl is not distinct.||(11) The hypocotyl is distinct.|
|(12) The cotyledon acts as the absorbing structure that absorb food from the endosperm and transfers to the embryo.||(12) The cotyledons are merely food storage organs.|