CBSE Class 12 Biology Sexual Reproduction In Flowering Plants Worksheet Set C

MULTIPLE CHOICE QUESTIONS

Question.Asexual reproduction is called as 
(a) apomixis
(b) fragmentation
(c) self fertilization
(d) cross fertilization
Answer. C

Question. Pollination by snail and slug is called as
(a) entomophilous
(b) malacophilous
(c) ornithophilous
(d) chiropterophilous
Answer. B

Question. In angiosperm, the endosperm is 
(a) diploid
(b) triploid
(c) haploid
(d) polyploid
Answer. B

Question. Female gametophyte of angiosperm is
(a) 7 celled
(b) 8 celled
(c) 11 celled
(d) 5 celled
Answer. A

Question. The pollen tube usually enters the embryo sac
(a) between the egg cell and synergid
(b) by directly penetrating the egg
(c) between one synergid and antipodal cell
(d) by knocking off the antipodal cells
Answer. A

Question. Double fertilization involves
(a) fertilization of egg by two male gametes
(b) fertilization of two eggs in the same embryo sac by two sperms brought by one pollen tube
(c) fertilization of the egg and the central cell by two sperms brought by different pollen tubes
(d) fertilization of the egg and the central cell by two sperms brought by the same pollen tube
Answer. D

Question. In which one of the following combinations (a - d) the number of chromosomes of the present day hexaploid wheat is correctly represented?
Comb-     Mono-    Haploid    Nulli-    Triination
ination    somic                     somic     somic
(a)          21            28            42          43
(b)          7             28             40          42
(c)          21            7              42          43
(d)          41           21             40          43
Answer. D

Question. Apomixis is 
(a) formation of seeds by fusion of gametes.
(b) formation of seeds without syngamy and meiosis.
(c) formation of seeds with syngamy but no meiosis.
(d) None of the above
Answer. B

Question. The plant part which consists of two generations one within the other, is
(a) germinated pollen grain
(b) embryo
(c) unfertilized ovule
(d) seed
Answer. B

Question. Geitonogamy involves:
(a) fertilization of a flower by the pollen from another flower of the same plant.
(b) fertilization of a flower by the pollen from the same flower.
(c) fertilization of a flower by the pollen from a flower of another plant in the same population.
(d) fertilization of a flower by the pollen from a flower of another plant belonging to a distant population. 
Answer. A

Question. Which of the following statement is correct?
(a) Sporopollenin can withstand high temperatures but not strong acids.
(b) Sporopollenin can be degraded by enzymes.
(c) Sporopollenin is made up of inorganic materials.
(d) Sporopollenin can withstand high temperature as well as strong acids and alkalis.
Answer. D

Very Short Answer Questions

Question. Draw a diagram of a matured microspore of an angiosperm. Label its cellular components only. 
Answer.

Question. A bilobed, dithecous anther has 100 microspore mother cells per microsporangium. How many male gametophytes this anther can produce? 
Answer. The bilobed anther can produce 1600 male gametophytes.

Question. The diploid number of chromosomes in an angiospermic plant is 16. What will be the number of chromosomes in its endosperm and antipodal cells? 
Answer. Endosperm—24 chromosomes, Antipodals—8 chromosomes.

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.

Question. Name the part of the flower which the tassels of the corn-cob represent. 
Answer. Style and stigma

Question. Write the function of coleoptile. 
Answer. It protects the plumule of the monocot embryo.

Question. The microscopic pollen grains of the past are obtained as fossils. Mention the characteristic of the pollen grains that makes it happen.
Answer. The exine of pollen grains have an outermost hard layer composed of a chemical, sporopollenin.
It is highly resistant to high temperature, strong acids and alkali. So, pollen grains are obtained as fossils.

Question. Define parthenocarpy.
Answer. Parthenocarpy is an economically important process in which seedless fruit is formed without fertilisation, for example, banana.

Question. In a case of polyembryony, if an embryo develops from the synergid and another from the nucellus, which is haploid and which is diploid? 
Answer. Synergid embryo is haploid and nucellar embryo is diploid.

Short Answer Questions

Question. In the T.S. of a mature anther given below, identify “a” and “b” and mention their function. (1)
Answer. a—Sporogenous tissue: It forms pollen grains.
b—Tapetum: It provides nourishment to the developing pollen grains.

Question. Name the organic materials the exine and intine of an angiosperm pollen grains are made up of. Explain the role of exine.
Answer. Exine is made up of sporopollenin and intine is made up of cellulose and pectin. Exine is the most resistant organic material and can withstand high temperature, acidic and alkali environment.

Question. “Pollen grains in wheat are shed at 3-celled stage while in peas they are shed at 2-celled stage.”Explain. Where are germ pores present in a pollen grain? 
Answer. At the time of shedding wheat pollen consists of one vegetative and two male gametes, which is the 3-celled stage. While pea pollen consists of one vegetative and one generative cell which is the 2-celled stage. Germ pores are present on the exine where sporpollenin is absent.

Question. Gynoecium of a flower may be apocarpous or syncarpous. Explain with the help of an example each. 
Answer. The gynoecium represents the female reproductive part of the flower. When there are more than one pistil, if the pistils are fused together, the flower is said to be syncarpous and if the pistils are free, it is said to be apocarpous. For example, pistil of Papaver is syncarpous and that of Michelia is apocarpous.

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. The haploid cells in an unfertilised mature embryo sac are: egg cell, synergids, antipodals and central cell. There are 7 cells in total.

Question. Draw a diagram of pollen grain with germ tube and two male gametes. (8)
Answer.

Question. Which is the triploid tissue in a fertilised ovule? How is the triploid condition achieved?
Answer. The triploid tissue in the ovule is the endosperm. Its triploid condition is achieved by the fusion of two polar nuclei and one nucleus of male gamete, referred to as triple fusion.

Question. Fill in the following labels with the type of cell function.

Answer. X—Meiosis (Reduction division); A—Mitosis; B—Mitosis; C—Mitosis; D—Cells reorganised as polar nuclei, antipodals and egg apparatus.

Question. Differentiate between albuminous and non-albuminous seeds, giving one example of each.
Answer. Albuminous seeds have residual endosperm in them. For example, maize.
Non-albuminous seeds do not have any residual endosperm. For example, pea.

Question. The flower of brinjal is referred to as chasmogamous while that of beans is cleisto- gamous. How are they different from each other? 
Answer. Differences between  flowers of  brinjal  and beans are as follows  :

Flower of brinjal (Chasmogamous flower)	Flower of beans (Cleistogamous flower)
Open flowers with exposed anthers and stigma	Closed flowers in which anthers and stigma lie close to each other and anthers dehisce within flower buds.

Require pollinating agents.	Do not require pollinating agents.
These flowers favour cross pollination.	These flowers ensure self pollination.

 

Question. Make a list of any three outbreeding devices that flowering plants have developed and explain how they help to encourage cross-pollination.
OR
Why are angiosperm anthers called dithecous? Describe the structure of its microsporangium. 
Answer.  The three outbreeding devices that flowering plants have developed are as follows:
(i) Dicliny (Unisexuality) : Flowers are unisexual so that self pollination is not possible. The plants may be monoecious (bearing both male and female flowers, e.g., maize) or dioecious (bearing male and female flowers on different plants, e.g., mulberry, papaya).
(ii) Dichogamy : Anthers and stigmas mature at different times in a bisexual flower so as to prevent self pollination. (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.
(iii) Heterostyly : There are 2 or 3 types of flowers
with different heights of styles (and stamens), e.g.,
In   diheterostyly  (dimorphic   heterostyly),  there are two types of flowers, pin eyed (long style and short  stamens)  and  thrum  eyed (short  style and long stamens),  e.g., Primula (primrose),  jasmine. Pollination occurs between anthers and stigmas of the same height present in different flowers.
Angiosperm anthers consist of two anther lobes therefore are called dithecous.
A typical angiospermic microsporangium appears near circular in outline. It consists of two parts, outer wall and central homogenous tissue. Microsporangial wall has four types of layers:
– Epidermis of single layer for protection.
– Endothecium of single layer for dehiscence of anther.
– Middle layers are 1-4 in number.
– Tapetum, the innermost parietal layer with cells having dense cytoplasm and large nuclei.

Question. Describe the structure of a mature micros- porangium of an angiosperm
Answer. A microsporangium or pollen sac is a cylindrical sac which appears circular in transverse section. It consists of two parts, outer wall and central homogenous sporogenous tissue. Microsporangial wall has four types of layers - epidermis (common anther covering), endothecium, 1-3 middle layers and tapetum. The outer three perform the function of protection in the young anther and dehiscence 
of the mature anther. Both endothecium and tapetum consist of larger cells. In a typical anther the endothecial cells develop fibrous thickenings of -cellulose on the inner and radial walls. In the shallow groove present between the two microsporangia of an anther lobe, the hypodermal cells lying at the level of endothecium remain thin walled. They constitute the stomium or line of dehiscence. The sporogenous tissue gives rise to microspores.

Question. Explain the process of megasporogenesis in angiosperms.
Answer. Megasporogenesis is the formation of megaspore (n) from megaspore mother cell (2n) inside the ovule by the process of meiosis. In the hypodermal region of nucellus towards the micropylar end develops a primary archesporial cell. The primary archesporial cell divides periclinally to form outer parietal cell and inner sporogenous cell. The sporogenous cell functions as megaspore mother cell (MMC),which undergoes reduction division to form four haploid megaspores. Only one megaspore (usually the chalazal one) remains functional and the other three degenerate. Different stages in the development of linear tetrad of megaspores are shown as follows :

Question. Describe the process of megasporogenesis in angiosperms until 8 nucleate stage.
Answer. Megasporogenesis is the formation of megaspore (n) from megaspore mother cell (2n) inside the ovule by the process of meiosis. In the hypodermal region of nucellus towards the micropylar end develops a primary archesporial cell. The primary archesporial cell divides periclinally to form outer parietal cell and inner sporogenous cell. The sporogenous cell functions as megaspore mother cell (MMC). The MMC undergoes meiotic division and produce four haploid megaspores. One of the megaspore is functional while other three degenerate. Different stages in the formation of embryo sac from functional megaspore are represented diagrammatically as follows :
he functional megaspore is the first cell of female gametophyte or embryo sac. The nucleus of megaspore divides by mitosis into eight daughter nuclei. Two polar nuclei are present in centre which further fuse to form a secondary nucleus. After fertilisation with a male gamete it produces triploid endosperm. Three nuclei at the base of embryo sac form antipodal cells. The remaining three nuclei at the micropylar end constitute egg apparatus, which consists of two cells known as synergids or help cells and an egg cell or oosphere. The egg cell on fusing with one male gamete (fertilisation) gives rise to zygote.

Question. Describe the structure of a 3-celled pollen grain of an angiosperm.
Answer.Pollen grain is the first cell of male gametophyte. The 3-celled pollen grain of an angiosperm consists of one tube or vegetative cell and two male gametes.
The tube cell has a vacuolated cytoplasm which is rich in the food reserves (starch, protein, fat with mostly unsaturated fatty acids) and cell organelles. Its nucleus is large and irregular. Male gametes are formed by division of generative cell. Each male gamete is lenticular to spherical in outline. It has a large nucleus which is surrounded by a thin sheath of cytoplasm.

Question. Explain the processes of emasculation and bagging of flowers. State their importance in breeding experiments.
Answer. Emasculation is the removal of the anthers of a bisexual flower in order to prevent self-pollination. Bagging involves covering of emasculated flowers by butter paper or polythene in order to protect them from contamination by foreign or undesirable pollen.
Emasculation and bagging are important steps of artificial hybridisation technique used in crop improvement programmes.

Question. Explain the  characteristic features of flowers that facilitate wind-pollination.  
 Answer.The characteristic features of flowers that facilitate wind pollination are as follows:
(i) Both the stigmas and anthers are exserted
(ii) Pollen grains are light, small and winged or dusty. They can be blown by wind to distances of upto 1300 km.
(iii) Pollen grains are dry, smooth, non-sticky and unwettable.
(iv) Stigma is hairy, feathery or branched to catch the wind-borne pollen grains. The large thread-like
stigmas and style of maize cob hang in air to catch wind borne pollens.
(v) Pollen grains are produced in very large number. For example, a single flower of Cannabis produces 5,00,000 pollen grains. Consequently, the pollen grains spread over large tracts so that even isolated plants get pollinated.
(vi) Calyx and corolla are either reduced or absent. Anthers are usually versatile.
(vii) Flowers are small and inconspicuous. (viii)When flowers are unisexual, male flowers are more abundant than female flowers. In bisexual flowers, the stamens are generally numerous.

Question. Describe the Polygonum type of embryo sac.
Why is it generally referred to as monosporic?
Answer. The most common type of embryo sac, found in 80% flowering plants is called Polygonum type of embryo sac. It contains 8 nuclei and 7 cells – 3 micropylar, 3 chalazal and one central. It is formed by one meiosis and three mitosis. The three micropylar cells are collectively known as egg apparatus. One middle cell is larger and is called egg or oosphere. The remaining two cells are called synergids or cooperative cells or help cells. The three chalazal cells of the embryo sac are called antipodal cells. The central cell contains two polar nuclei which often  fuse to from a single diploid secondary nucleus or definitive nucleus. Polygonum type of embryo sac is developed from a single megaspore (rest three degenerate) and so it is called monosporic type of embryo sac.

Question. Angiosperm flowers may be monoecious, cleistogamous or show self-incompatibility. Describe the characteristic features of each one of them and state which one of these flowers promotes inbreeding and outbreeding respectively.
Answer. Monoecious flowers are bisexual i.e., they bear both male and female reproductive organs, e.g., pea. Cleistogamous flowers are those flowers which 
do not open at all. These flowers are intersexual and remain closed causing self pollination. In cleistogamous flowers, the anthers dehisce inside closed flowers. Growth of style brings the pollen grains in contact with stigma. Pollination and seed setting are assured. Pollinators are not required. E.g. Commelina benghalensis, balsam.
Self incompatibility is inability of pollen of a plant to fertilise the pistil of the same plant, e.g., Primula. Monoecious and cleistogamous flowers promote inbreeding whereas self incompatibility in plants promotes outbreeding.

Question. A non biology person is quite shocked to know that apple is a false fruit, mango is a true fruit and banana is a seedless fruit. As a biology student how would you satisfy this person?
Answer. A fruit is a seed containing part of a plant that develops from a fertilised ovary. Apple is a false fruit because in apple apart from the ovary, thalamus also contributes to fruit formation.
Mango is a true fruit as it develops only from the ovary after fertilisation.
Banana is a seedless fruit or parthenocarpic fruit because it develops without fertilisation.

Question. Banana fruit is said to be parthenocarpic whereas turkey is said to be parthenogenetic why?
Answer. Banana fruit is a seedless fruit which is developed without pollination and fertilisation hence is referred to as parthenocarpic fruit, whereas in turkey the unfertilised egg develops into complete individual after fertilisation hence turkey is referred to as parthenogenetic.

Question. Write the difference between the tender coconut water and the thick white kernel of a mature coconut and their ploidy.
Answer. The tender coconut water is free nuclear endosperm i.e., during development the primary endosperm nucleus divides by repeated mitotic free nuclear division without formation of wall. White kernel of coconut is cellular endosperm i.e., during development first nuclear division of the primary endosperm nucleus is followed by the formation of either a longitudinal or transverse cell wall in the central cell. Both tender coconut water and white kernel of coconut are triploid (3n) but coconut water is multinucleated structure whereas in kernel of coconut each cell is uninucleated.

Question. Some angiosperm seeds are said to be
‘albuminous’, whereas few others are said to have a perisperm. Explain each with the help of an example. 
Answer. The seeds in which endosperm persists as food storage tissue are called endospermic or albuminous, seeds, e.g., castor, maize, wheat, barley, rubber, coconut.
In some seeds remains of nucellus persist. The residual nucellus which persists in the seed is called perisperm, e.g., black pepper, coffee, castor, cardamum, Nymphaea.

Question. Describe the development of endosperm after double fertilisation in an angiosperm. Why does endosperm development precedes that of zygote? 
Answer. Endosperm is the food laden tissue formed after double fertilisation. It provides essential nutrients to the growing embryo and also the young seedling at the time of seed germination. In angiosperms, the endosperm develops from triploid (3n) primary endosperm nucleus which is formed as a result of vegetative fertilisation or triple fusion i.e., fusion of a male gemete with secondary nucleus of the central cell. Based on the first and subsequent divisions of primary endosperm nucleus, the development of endosperm takes place in different ways and accordingly endosperm is of three types – nuclear, cellular and helobial.
Nuclear type : In the nuclear type of endosperm the first division of primary endosperm nucleus and few subsequent nuclear divisions are not accompanied by wall formation. The nuclei produced are free in the cytoplasm of the embryo sac and they may remain free indefinitely or wall formation takes place later. The multinucleate cytoplasm undergoes cleavage, and gives rise to multicellular tissue, maize, wheat, rice.
Cellular type : In this case, there is cytokinesis after each nuclear division of endosperm nucleus. The endosperm, thus, has a cellular form, from the very beginning because first and subsequent divisions are all accompanied by wall formation. e.g., Petunia, Datura, Adoxa etc.
Helobial type: It is an intermediate type between the nuclear and cellular types. The first division is accompanied by cytokinesis but the subsequent ones are free nuclear. The chamber towards micropylar end of embryo sac is usually much larger than the chamber towards chalazal end. A large number of nuclei are formed in the micropylar chamber by free nuclear divisions while the nucleus of the chamber towards chalazal end divides to form a fewer free nuclei or may not divide at all, e.g., Order Helobiales and most monocots.
Endosperm provides nourishment to the zygote. So, endosperm development precedes that of zygote.

Question. Explain the development of a mature embryo from the embryo sac of dicot flower.
Answer. In a typical dicot flower, after double fertilisation, the zygote elongates and then divides by a transverse wall into two unequal cells. The larger basal cell is called suspensor cell. The other towards the antipodal end is termed as terminal cell or embryo cell. The suspensor cell divides transversely a few times to produce a filamentous suspensor of 6–10 cells. The suspensor helps in pushing the embryo in the endosperm. The first cell of the suspensor towards the micropylar end becomes swollen and functions as a haustorium. The last cell of the suspensor is known as hypophysis. Hypophysis later gives rise to the radicle and root cap. The embryo cell undergoes two vertical divisions and one transverse division to form eight cells arranged in two tiers– epibasal (terminal) and hypobasal (near the suspensor). The epibasal cells eventually form the two cotyledons and the plumule. The hypobasal cells produce the hypocotyl except its tip.
Initially the embryo is globular and undifferentiated.
Early embryo with radial symmetry is called proembryo. It is transformed into embryo with the development of radicle, plumule and cotyledons. At this time the embryo becomes heart-shaped. The rate of growth of the cotyledons is very high so that they elongate tremendously while the plumule remains as a small mound of undifferentiated tissue.

 

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