2nd PUC Biology Question Bank Chapter 2 Sexual Reproduction in Flowering Plants

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Karnataka 2nd PUC Biology Question Bank Chapter 2 Sexual Reproduction in Flowering Plants

2nd PUC Biology Sexual Reproduction in Flowering Plants One Mark Questions and Answers

Question 1.
Name the protective substance present on the pollen envelop to tide over adverse condition.
Answer:
Sporopollenin.

Question 2.
Name the stage of the occurrence of more than one embryo in a seed.
Answer:
Polyembiyony.

Question 3.
Define fertilisation in angiosperms.
Answer:
It is the fusion of one male gamete with egg cell and the second gamete with the polar nuclei in angiosperm.

Question 4.
Name the parts of an angiosperm i.c. flower in which development of male and female gametophyte takes place.
Answer:
Male gametophyte develops in pollen grain, whereas female gametophyte develops in the ovule.

Question 5.
What is meant by monosporic development of female gametophyte?
Answer:
The formation of female gametophyte or embryo sac from a single functional megaspore is called monosporic development of female gametophyte.

Question 6.
What type of pollination is seen in cleistogamous flower?
Answer:
Self pollination.

Question 7.
What is apomixis?
Answer:
Apomixis is the phenomenon of production of seeds without fertilization.

Question 8.
What is microsporogenesis?
Answer:
The process that leads to the formation of microspores from a pollen mother cell through meiosis is referred to as microsporogenesis.

Question 9.
What is sporopollenin?
Answer:
The exine of pollen grain is composed of a highly resistant organic chemical called sporopollenin.

Question 10.
Name one plant each where pollination occurs with the help of (a) Water, (b) Bats.
Answer:
Water pollinated: vallisneria and hydrilla. Bat pollinated: Anthocephalous and Bauhinia megalandra.

Question 11.
What is polyembryony?
Answer:
Polyembryony is the phenomenon of formation of more than one embryo during the development of a seed.

Question 12.
How many haploid nuclei and haploid cells are present in the female gametophyte of angiosperm?
Answer:
8 – haploid nuclei and 7 – haploid cells.

Question 13.
Mention the scientific term for the type of pollination which ensures Genetic
recombination.
Answer:
Xenogamy or Allogamy.

Question 14.
Which are the’ nuclei that fuse to form endosperm?
Answer:
The second male gamete fuses with the secondary nucleus (which is formed by fusion of two polar nuclei) to form a triploid primary endosperm [PEN],

Question 15.
Name the part of plant producing seed and fruit after fertilization.
Answer:
After fertilization, ovule develops into seed and ovary develops into fruit.

Question 16.
What is pericarp?
Answer:
The wall of fruit developed by the wall of the ovary is called pericarp.

2nd PUC Biology Sexual Reproduction in Flowering Plants Two Marks Questions and Answers

Question 1.
What is a false fruit? Give an Example.
Answer:
A fruit which is formed by any floral parts of the flower other than ovary, eg. apple, pear, cashew nut, etc.

Question 2.
Arrange the following terms in the correct development sequence:
pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.
Answer:
Sporogenous tissue → pollen mother cell → microspore tetrad → pollen grain → male gametes.

Question 3.
What are the parthenocarpic fruits?
Answer:
The fruits which are formed without fertilization.
Example: Seedless fruits like banana.

Question 4.
What is double fertilization?
Answer:
One male gamete fuses with an egg (syngamy) to form a zygote and a second male gamete fuses with two polar nuclei to form a primary endosperm nucleus (triple fusion). Both these steps together represent double fertilization.,

Question 5.
What is Apomixis? What is its importance?
Answer:
The phenomenon of asexual reproduction that mimics sexual reproduction by formation of seed without fertilisation is called apomixis.

Importance: Apomixis has the potential to maintain hybrid vigour indefinitely even in those crop plants where vegetative reproduction is not possible.

Question 6.
Draw a diagram of pollen grain with germ tube and two male gametes with labelling.
Answer:

Question 7.
What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
Answer:
The inability of certain gametes even from genetically similar plant species, to fuse with each other is called self incompatibility. It is because of a continuous dialogue between pollen grain and pistil which is mediated by their chemical components.

Question 8.
What is bagging technique? How is it useful in plant breeding programme?
Answer:
The process of covering the emasculated flowers or the female flowers after dusting with the desired pollen with bags made of butter paper.
Bagging protects the stigmas from further pollination (from unwanted pollen).

Question 9.
What is triple fusion? Where and how does it takes place? Name the nuclei involved in triple fusion.
Answer:
The process of fusion of haploid or diploid nuclei three times is called triple fusion.

• Triple fusion occurs, in the embryo sac.
• It involves the fusion of two polar nuclei to form a secondary nucleus, one male gamete with egg to form a zygote and further diploid secondary nucleus with another male gamete to form PEN.

Question 10.
Why do you think the zygote is dormant for sometime in a fertilized ovule?
Answer:
The zygote divides only after a certain amount of endosperm is formed. This is an adaptation to provide assured nutrition to the developing embryo. Therefore, the zygote is dormant for some time in a fertilized ovule.

Question 11.
Differentiate between:
(a) hypocotyl and epicotyl;
(b) coleoptile and coleorrhiza;
(c) integument and testa ;
(d) perisperm and pericarp.
Answer:
(a) The portion of embryonal axis above the cotyledon is called epicotyl, while the portion of embryonal axis below the cotyledon is called hypocotyl.

(b) Coleoptile is a conical protective sheath over the plumule, while coleorhiza is a protective sheath over the root tip in monocotyledonous seeds.

(c) Integument is the protective covering of ovule, while testa is the protective outer seed coat of the seed developed from the outer integuments.

(d) Perisperm is the residual persistant nucellus, while pericarp is the fruit wall derived from the ovary wall.

Question 12.
Why is apple called a false fruit? Which parts of the flower forms the fruit?
Answer:
In apple, thalamus of the flower also contributes in the formation of fruit along with the ovary, hence it is called a false fruit.
Thalamus of the flower is mainly involved in the formation of pulp of the apple.

Question 13.
What is meant by emasculation? When and why does a plant breeder employ this technique?
Answer:
The process of removal of anthers from the flower buds of a bisexual flower, before the anther dehiscense in order to avoid self pollination.
Plant breeders employ this technique for artificial hybridization for crop improvement programme.

Question 14.
Explain the role of tapetum in the formation of a pollen grain wall.
Answer:
Tapetum produce ubisch granules for the formation of exine of pollen grain and also secrete pollenkitt in case of entomophilous pollen grain. It also supplies nutrients for the developing pollengrain.

Question 15.
Write the characters of a wind pollinated flower?
Answer:
Characters of anemophilous flowers :

• The flowers are small and do not have colour and scent.
• Anthers are versatile swinging freely in the air.
• Pollen grains are dry, light, smooth powdery and produced in large quantity, so that they can be easily carried by wind.
• Stigmas may be feathery or long branched and bushy, so that they can catch the pollens from air easily.

Question 16.
Distinguish between protandry and protogyny.
Answer:
(a) Protandry: Anthers mature earlier than the carpels, e.g. sunflower, cotton.
(b) Protogyny: Carpels mature earlier than anthers, e.g. michelia, Ficus.

Question 17.
What are cleistogamous flowers? Can cross pollination occur in cleistogamous flowers? Give reasons for your answer.
Answer:
Cleistogamous flowers have exposed anthers and stigma. Cross pollination cannot occur in cleistogamous flowers, as such flowers do not open at all.

Question 18.
Mention two strategies evolved to prevent self-pollination in flowers.
Answer:
1. Dicliny : It is the condition where one of the two sexes is absent in the flower and the flower becomes a unisexual male or female (diclinous). Such diclinous flowers may be borne either on the same plant or on the two different plants. In such cases, cross pollination, is the rule. e.g. maize, cucurbita.

2. Herkogamy: (Herkos = barrier) It is the condition where style of the gynoecium extend far beyond the anthers or stamens may face outward or pollens may aggregate into pollinia. In such cases, self pollination is impossible, e.g. gloriosa, calotropis.

Question 19.
Write the significance of double fertilization.
Answer:
Importance of double fertilization is the production of seeds from ovules and fruits from ovaries. Double fertilization also signifies the formation of nutritive tissue endosperm in the seeds.

Question 20.
Differentiate Geitonogmy from Xenogamy.
Answer:
Geitonogamy is the transfer of pollen grains from the anther of a flower to the stigma of another flower of the same plant. (Genetically it is similar to autogamy)

Xenogamy is the transfer of pollen grains from anther of a flower on one plant to the stigma of a flower on a different plant. (Brings genetically different pollen grains to the stigma).

Question 21.
What is xenogamy? Mention its importance.
Answer:
Xenogamy: Cross pollination which takes place between two flowers borne on two different plants of the same species is called xenogamy.
Importance: Characters of the two plants can be combined.

Question 22.
What is artificial hybridization? Explain emasculation and bagging techniques used in artificial hybridisation for crop improvement programme.
Answer:
It is one of the major approaches of crop improvement programme. It is a crossing experiment 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.

2nd PUC Biology Sexual Reproduction in Flowering Plants Three Marks Questions and Answers

Question 1.
Differentiate between non-albuminous and albuminous seeds with examples.
Answer:
Non albuminous seeds have no residual endosperm as it is completely consumed during embryo development.
e.g.: pea, groundnut.

Albuminous seeds retain a part of endosperm as it is not completely used up during embryo development,
e.g.: wheat, maize, barley, castor.

Question 2.
Differentiate between anemophilous and entomophilus flowers?
Answer:
Characters of anemophilous flowers :

• The flowers are small and do not have colour and scent.
• Anthers are versatile swinging freely in the air.
• Pollen grains are dry, light, smooth powdery and produced in large quantity, so that they can be easily carried by wind.
• Stigmas may be feathery or long branched mid bushy, so that they can catch the pollens from air easily.

Characters of Entamophilous Flowers :
In majority of the plants cross pollination takes place through the agency of insects and such flowers are called entomophilous flowers. These show the following characters.

Colour: Normally petals of a flower are brightly coloured to attract insects for the purpose to carryout cross pollination. In some plants, Other parts of the flower are also modified into petaloid structure, e.g. In bougainvellia, bracts are brightly coloured, in canna stamens are petaloid.

Nector: It is the sugary substance secreted by gamopetalous corolla of entomophilous flowers. Insects while collecting nector unknowingly bring-about cross pollination. In some plants, nectary glands are developed on involucre of cyathium inflorescence, e.g. poinsettia.

Scent: Some entomophilous flowers emit strong scent during night to attract the insects and take their service in cross pollination, e.g. nightqueen, jasmine.

Question 3.
What is apomixis and what is its importance?
Answer:
Apomixis :
1. It is a form of asexual reproduction, that mimics sexual reproduction, where seeds are formed without fertilisation. It is also known as agamospermy.

2. Apomictic seeds may be formed in one or more of the following ways:
(a) A diploid egg cell (formed without meiosis during megasporogenesis) may develop in an embryo without fertilisation.
(b) Cells of the nucellus (diploid) surrounding the embryo sac may develop into embryos and become pushed into the embryo sac. e.g., Citrus, mango.

Question 4.
Differentiate between microsporogenesis and megasporogenesis.
Answer:
Microsporogenesis,]

• It refers to the process of formation of microspores from a microspore mother cell.
• It occurs in micro sporangia present in anther.
• The microspores are arranged in a tetrad manner.

Megasporogenesis

• It refers to the process of formation of megaspores from a megaspore mother cell.
• It occurs in nucellus part of the ovule.
• Megaspores are arranged in a linear row.

Question 5.
Explain the structure of a mature female gametophyte in flowering plants.
Answer:

• The female gametophyte develops from a single megaspore and hence is described as monosporic development.
• The functional megaspore is the first cell of female gametophyte of angiosperms.
• It enlarges to form the female gametophyte, also called embryo sac.
• Its nucleus undergoes a mitotic division and the two nuclei move to the opposite poles, forming the 2-nucleate embryo sac.
• Two successive mitotic divisions in each of these two nuclei result in the formation of an 8- nucleate embryo sac.
• Cell wall formation starts at the eight-nucleus stage, resulting in the formation of a typical female gamêtophyte.
• Three nuclei are grouped together at the micropylar end to form the egg apparatus, consisting of two synergids and a femãle gamete/egg cell by wall formation.
• The remaining two nuclei are called polar nuclei, they move to the centre of the embryo sac and fuse to from a diploid secondary nucleus. The remaining three nuclei aggregate at the chalazal end to form three antipodal cells.
• Thus a typical angiosperm embryo sac is 8-nucleate and celled.

Question 6.
What is apomixis? Mention its significance in agriculture.
Answer:
1. It is a form of asexual reproduction, that mimics sexual reproduction, where seeds are formed without fertilisation. It is also known as agamospermy.

2. Apomictic seeds may be formed in one or more of the following ways:
(a) A diploid egg cell (formed without meiosis during megasporogenesis) may develop in an embryo without fertilisation.
(b) Cells of the nucellus (diploid) surrounding the embryo sac may develop into embryos and become pushed into the embryo sac. e.g., Citrus, mango.

Question 7.
With a neat labelled diagram, explain the structure of a pollen grain.
Answer:
Structure of pollen grain : Pollen grain is the haploid unicellular, uninucleated spherical shaped body bounded by outer thick, spiny or reticulate callose wall called exine and inner thin, smooth cellulose wall called intine. In the exine, thin areas called germ pores are present. Intine encloses peripheral cytoplasm and central nucleus.

Pollen grain represents the first stage of male gametophyte. Development by pollen grain takes place when it is still present in the anther locule. During the development it divides unequally into a large vegetative cell and a small generative cell. Generative cell then divides and give rise to two non-motile male gametes. This takes place either in the pollen grain or in the pollen tube after pollination.

1. Pollen grains of many species cause severe allergies and chronic respiratory disorders like asthma, bronchitis, etc. e.g. parthenium (carrot grass)

2. Pollen grains are rich in nutrients. Thus pollen tablets are used as nutrient supplements.

2nd PUC Biology Sexual Reproduction in Flowering Plants Five Marks Questions and Answers

Question 1.
Draw the T.S. of mature anther and explain briefly.
Answer:
(a) Structure of a mature anther :
A mature anther internally contains four microsporangia, two in each anther lobe. Each microsporangium consists of an outer anther wall and inner anther locule

(i) Anther wall: It is the protective covering of anther or microsporangium. It is composed of epidermis, endothecium, middle layer and tapetum.
1. Epidermis: It is the outermost protective layer of anther composed of single layer of cells. The cells are often stretched and flattened in a mature anther.

2. Endothecium : It is the uniseriate layer composed of radially elongated cells with callose thickening on their inner tangential walls. Along the line of dehiscence of anther lobe, endothecium is composed of thin walled cells called stomium.

3. Middle layers: These are 2-3 concentric layers of cells present in between the endothecium and tapetum. In mature anther the cells of middle layers are flattened and collapsed due to the pressure exerted in the anther locule.

4. Tapetum: This i$ the innermost layer of anther wall composed of secretory cells. These cells secrete nutrients for developing microspore mother cells/ pollen grains in the anther locale.

(ii) Anther locule: It is the sporangial cavity containing a number of microspore tetrads/pollen grains formed from microspore mother cells by meiosis. (Microspores after the separation from tetrad are called pollen grains)

Question 2.
Show a diagrammatic representation of the mature embryo sac..
Answer:

Question 3.
What is triple fusion and double fertilisation write the significance of double fertilisation?
Answer:
Triple fusion: One of the two male gametes fuses with the egg cell. This is known as syngamy and the fused product is called an oospore. The other male gamete unites with the secondary nucleus. This is known as triple fusion (as this involves the fusion of 1 male nucleus and 2 polar nuclei) and the fused product is called primary endosperm nucleus. (PEN).
After fertilization the following changes takes place.

• Oospore develops into embryo and PEN develops into endosperm.
• Ovule develops into seed and integuments of ovule develop into seed coat.
• The outer integument of the ovule forms the testa or outer seed coat.
• The inner integument forms the tegmen or inner seed coat.
• Ovary develops into fruit and ovary wall develops into fruit wall called pericarp.
• Style, stamens, calyx and corolla wither off.

Significance of double fertilization :
Importance of double fertilization is the production of seeds from ovules and fruits from ovaries. Double fertilization also signifies the formation of nutritive tissue endosperm in the seeds.

Question 4.
How are seeds advantageous to angiosperms?
Answer:
Significance of seeds:
Seeds offer the following advantages to plants:

• Since reproductive processes such as pollination and fertilization are dependent on water, seed formation is more dependable.
• Seeds have adaptation for dispersal to new habitats and help the species to colonize in other areas.
• Seeds have enough food reserves to nourish seedlings until they are capable of photosynthesis on their own.
• The hard seed coat provides protection to the young embryo.
• Seeds are the product of sexual reproduction, hence they generate new genetic combinations leading to variations.
• Seed is the basis of our agriculture. Dehydration and dormancy of mature seeds are crucial for storage of seeds, which can be used as food through out the year and also raise crop in the next season.

Question 5.
Draw a neat labelled diagram of an anatropous ovule and label its parts.
Answer:

Question 6.
Define the post-fertilization events in a flower and also include their functions.
Answer:
Post fertilization events in a flower:
After fertilization the following events take place.

• Oospore develops into embryo and PEN develops into endosperm.
• Ovule develops into seed and integuments of ovule develop into seed coat.
• The outer integument of the ovule forms the testa or outer seed coat.
• The inner integument forms the tegmen or inner seed coat.
• Ovary develops into fruit and ovary wall develops into fruit wall called pericarp.
• Style, stamens, calyx and corolla wither off.

Question 7.
Differentiate between microsporogenesis and megasporogenesis. Which type of cell division occurs during these events? Name the structures formed at the end of these two events.
Answer:
Microsporogenesis,

• It refers to the process of formation of microspores from a microspore mother cell.
• It occurs in micro sporangia present in anther.
• The microspores are arranged in a tetrad manner.

Megasporogenesis

• It refers to the process of formation of megaspores from a megaspore mother cell.
• It occurs in nucellus part of the ovule.
• Megaspores are arranged in a linear row.

Meiosis occurs in both of the events.
Microsporogenesis gives rise to microspores (Pollen grains), while megasporogenesis gives rise to megaspores.

Question 8.
Describe the process of development of dicotyledonous embryo.
Answer:
Embryo:

• The embryo formation starts after a certain amount of endosperm is formed, as there is an assured supply of nutrition to the embryo.
• The zygote divides by mitosis to from a proembryo first.
• Later development results in the formation of globular and heart-shaped embryo, that ultimately become the horse -shoe shaped mature embryo, with one or two cotyledons.

Development of the embryo: After fertilization the diploid zygote secretes a wall around itself to become an oospore and divides itself into 2 cells. The upper cell which is away from the micropyle is called as embryonal cell and the lower cell towards the micropyle is called as the suspensor cell. The suspensor cell divides in one plane to produce a filament of cells called suspensors which elongates and thereby pushes the embryo deeper into the endosperm tissue for better nutrition. The basal cell of the suspensor is highly enlarged to form a food absorbing structure.

The embryonal cell produces a group of 4 cells called quadrant which further divides to give rise to an octant. These cells are the embryonal mass from which the future embryo develops. The cell of the suspensor adjacent to the embryonal mass is called hypophysis. It produces the apex of the radicle. The cells of the embryonal mass towards the suspensor, produce the radicle. The embryonal cells away from the suspensor produce the 2 cotyledons (embryonic leaves) and plumule (the future shoot system).

The embryo passes through the globular stage and a heart shaped embryo state where the two cotyledons are clearly visible. Then it passes through the torpedo stage (called so because the elongated cotyledons look like a torpedo). During the embryo development the endosperm is partly or completely utilized. ‘
Dicotyledonous Embryo:

Dicotyledonous Embryo:

• In dicotyledonous plants, the embryo consists of two cotyledons and the embryonal axis between them.
• The portion of embryonal axis above the level of attachment of cotyledons is the epicotyl and it terminates in the plumule (shoot meristem).
• The portion of embryonal axis below the level of attachment of cotyledons in the hypocotyls; it terminates in the radicle (root tip).

Question 9.
Explain how some plants are adapted for achieving pollination through wind. How Vallisneria and seagrasses achieve pollination.
Answer:
Types of cross pollination:
Cross pollination is always brought about by some external ágentš. Because pollen grains have no power of independent movement. Based on the agents involved ¡n cross. pollination, the following types of cross pollination are recognised.

1. Hydrophilly: Cross pollination by the agency of water is called hydrophily and such flowers are called hydrophilous flowers. Hydrophily can be seen in some submerged hydrophytes (aquatic plant) like hydrilla, elodea, vallisneria, etc.

Characters of Hydrophilous flowers:
1. Generally, the pollen grains of submerged plants like hydrilla have same specific gravity as that of water, so that pollen grains suspend and float in water at different depths.

2. In vallisneria special types of characters are developed for cross pollinauion. It is dioecious. Male plant bears smalj sessile male flowers in submerged spadix. These flowers detach and float on the surface of the water. Female plant bears solitary’female flowers on the spirally coiled stalks. When flowers mature the stalks uncoil and bring the flowers to the surface of the water. When male flowers come in contact with a female flower, the anthers burst open and sticky pollen grains deposit on the stigma. After the pollination, the stalk of the female flower coils and thus flower is brought down into water, where fruit formation takes place.

2. Anemophily : Cross pollimition by the agency of wind is called anemophily and such flowers are called anemophilous flowers. Anemophily can be seen in maize, grass and palms, etc.

Characters of anemophilous flowers :

• The flowers are small and do not have any colour or scent.
• Anthers are versatile, swinging freely in the air.
• Pollen grains are dry, light, smooth, powdery and produced in large quantity, so that they can be easily carried by wind.
• Stigmas may be feathery or long branched and bushy, so that they can catch the pollens from air easily.

3. Zoophily: Cross pollination by the agencyof animals is called zoophily and such flowers are called zoophilous flowers.
Zoophily is again sub-divided into
(a) Entomophily – pollination by insects. e.g. sunflower, canna.
(b) Ornithophily -pollination by birds. e.g. silk cotton, passion flower.
(e) Chiropterophily – pollination by bats. e.g. bauhinia, banana.