Practice Corner MCQ

Hint

(b)

Hint

(c)

Hint

(a) : Anther and filament are the parts of male reproductive organ of flower called stamen whereas stigma, style and ovary are parts of female reproductive organ of flower called carpel. They are called essential floral organs. Sepals and petals are accessory or non-essential floral organs as they have only supportive role.

Hint

(d)

Hint

(d) : The given figure is three dimensional cut section of anther. A typical angiosperm anther is bilobed with each lobe having two theca i.e., they are dithecous. Here P, Q and R are pollen sacs, pollen grains and filament respectively.

Hint

(a) : A typical angiosperm anther is bilobed with each lobe having two theca, i.e., dithecous and a dithecous anther is tetrasporangiate having four microsporangia two in each lobe.

Hint

(c) : A typical angiosperm anther is bilobed with each lobe having two theca, i.e., dithecous and a dithecous anther is tetrasporangiate having four microsporangia two in each lobe.

Hint

(c)

Hint

(b)

Hint

(c) : The tapetal layer is of great physiological significance as all the food material entering into the sporogenous tissue diffuses through this layer. Ultimately the cells of tapetal layer disorganise. Thus, tapetum makes a nutritive layer for the developing microspores or pollen grains.

Hint

(a) : A microsporangium or future pollen sac is a cylindrical sac which appears circular in transverse section. It consists of two parts, outer wall and central homogeneous sporogenous tissue. Microsporangial wall has four types of layers – epidermis, endothecium, 1-3 middle layers and tapetum. The outer three layers perform the function of protection in the young anther and mechanism of dehiscence in the ripe anther.

Hint

(b) : Tapetum secretes Ubisch bodies which get covered with sporopollenin and so increase thickness of exine of pollen grain wall. Tapetum provides nourishment to developing microspores. It also secretes callase enzyme which dissolves callose substances by which four pollens of a pollen tetrad are united, hence separating microspores or pollens of a tetrad.

Hint

(d) : Tapetum secretes Ubisch bodies which get covered with sporopollenin and so increase thickness of exine of pollen grain wall. Tapetum provides nourishment to developing microspores. It also secretes callase enzyme which dissolves callose substances by which four pollens of a pollen tetrad are united, hence separating microspores or pollens of a tetrad.

Hint

(a) : Meiosis takes place in reproductive organs of plants and young anthers are the best material to study meiosis.

Hint

(c)

Hint

(c) : In Calotropis and related plants of Family Asclepiadaceae, all the pollen grains of an anther lobe remain united in a single sac called pollinium.

Hint

(b)

Hint

(c) : Each pollen mother cell (PMC), by a meiotic division, gives rise to a group of four haploid microspores. Thus, 16 pollen mother cells undergo meiotic divisions to produce 64 pollen grains.

Hint

(c) : Each microspore mother cell or pollen mother cell (PMC) on reduction division (meiosis) gives rise to 4 pollen grains. Hence, to form 100 pollen grains, 25 meiotic divisions are required.

Hint

(b) : Outer layer (exine) of pollen grain is made of a highly resistant substance called sporopollenin. It is not degraded by any enzyme and not affected by high temperature, strong acid or strong alkali.

Hint

(c) : One or more thin areas present in the exine of pollen grains are known as germ pores. The germ pores are apertures in the exine layer of the pollen grain where the sporopollenin is absent. The germ pore helps in the formation of the pollen tube and the release of the male gametes during fertilisation. There are usually three germ pores in dicots (tricolpate) and one in monocots (monocolpate).

Hint

(c) :  One or more thin areas present in the exine of pollen grains are known as germ pores. The germ pores are apertures in the exine layer of the pollen grain where the sporopollenin is absent. The germ pore helps in the formation of the pollen tube and the release of the male gametes during fertilisation. There are usually three germ pores in dicots (tricolpate) and one in monocots (monocolpate).

Hint

(b): The development of the male gametophyte in angiosperms is called as microgametogenesis. Pollen grain is the first cell of a male gametophyte. This cell undergoes only two divisions, with the result of first division two cells are formed – a large vegetative cell (with abundant food reserve) and a small generative. The second division is concerned with generative cell only. This division may take place either in pollen grain or in the pollen tube and gives rise to two male gametes.

Hint

(c) : The development of the male gametophyte in angiosperms is called as microgametogenesis. Pollen grain is the first cell of a male gametophyte. This cell undergoes only two divisions, with the result of first division two cells are formed – a large vegetative cell (with abundant food reserve) and a small generative. The second division is concerned with generative cell only. This division may take place either in pollen grain or in the pollen tube and gives rise to two male gametes. 

Hint

(b) : A pollen grain with pollen tube carrying male gametes represents mature male gametophyte. It is 3 -celled (one tube cell + 2 male gametes) and 3 -nucleated (one tube nucleus + two nuclei of each male gamete) structure.

Hint

(c) : A pollen grain with pollen tube carrying male gametes represents mature male gametophyte. It is 3 -celled (one tube cell + 2 male gametes) and 3 -nucleated (one tube nucleus + two nuclei of each male gamete) structure.

Hint

(b) : The given figure shows multicarpellary, syncarpous pistil of Papaver. Here \(X\) is stigma and \(Y\) is syncarpous ovary.

Hint

(b)

Hint

(a)

Hint

(b)

Hint

(b) : Depending upon the configuration and orientation of the body of ovule in relation to funiculus, there are six types of ovule orthotropous (atropous, erect), anatropous (inverted), hemitropous (half inverted), campylotropous (body curved), amphitropous (both body and embryo sac curved) and circinotropous (funiculus is coiled around the ovule).Anatropous or inverted ovule is the most common type of ovule found in angiosperms (in \(80 \%\) of angiosperm families). Here, body of the ovule gets inverted and micropyle is on lower side. Further micropyle and funiculus lie side by side and micropyle is close to hilum.

Hint

(b) : Orthotropous or atropous ovule is the most primitive and simplest type of ovule in angiosperms. It is erect (i.e., micropyle at upper end) and here micropyle, chalaza and funiculus lie in a same straight line, e.g., Family Polygonaceae and Piperaceae.

Hint

(c) : The body of the ovule consists of a mass of parenchymatous cells named nucellus. It is equivalent to megasporangium (2n). Megaspore mother cell or megasporocyte is a diploid (2n) cell which undergoes meiosis to form a linear tetrad of four haploid megaspores ( \(n\) ). Normally, the chalazal megaspore is the functional megaspore while the other three degenerate.

Hint

(c): The functional megaspore is the first cell of female gametophyte. The cell enlarges and undergoes three free nuclear mitotic divisions. The first division produces two nucleate embryo sac. The two nuclei shift to the two ends and divide twice forming four nucleate and then eight nucleate structure. One nucleus from each side moves to the middle, they are called polar nuclei. The remaining three nuclei form cells at the two ends, 3 celled egg apparatus at the micropylar end and three antipodal cells at the chalazal end. The middle binucleate part organises itself into central cell. Embryo sac developed from a single megaspore is called monosporic.

Hint

(a) : The synergids have special cellular thickenings at the micropylar tip called filiform apparatus, which play an important role in guiding the pollen tube into the synerqid.

Hint

(c) : In angiosperms, the female gametophyte (or embryo \(\mathrm{sac}\) ) is an oval multicellular haploid structure which is embedded in the nucellus towards micropylar half of the ovule.

A typical and most common type of embryo sac, found in \(80 \%\) flowering plants is called Polygonum type of embryo sac. It contains 8 nuclei but 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. The three chalazal cells of the embryo sac are called antipodal cells.

Hint

(b) : The synergids have special cellular thickenings at the micropylar tip called filiform apparatus, which play an important role in guiding the pollen tube into the synergid.

Hint

(b) 

In angiosperms, the female gametophyte (or embryo \(\mathrm{sac}\) ) is an oval multicellular haploid structure which is embedded in the nucellus towards micropylar half of the ovule.

A typical and most common type of embryo sac, found in \(80 \%\) flowering plants is called Polygonum type of embryo sac. It contains 8 nuclei but 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. The three chalazal cells of the embryo sac are called antipodal cells.

Hint

(a)

In angiosperms, the female gametophyte (or embryo \(\mathrm{sac}\) ) is an oval multicellular haploid structure which is embedded in the nucellus towards micropylar half of the ovule.

A typical and most common type of embryo sac, found in \(80 \%\) flowering plants is called Polygonum type of embryo sac. It contains 8 nuclei but 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. The three chalazal cells of the embryo sac are called antipodal cells.

Hint

(b) : Commelinaproduces two types of flower-chasmogamous flowers which are similar to flowers of other species with exposed anthers and stigma, and cleistogamous flowers which 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 effect pollination. Thus, cleistogamous flowers are invariably autogamous as there is no chance of crosspollen landing on the stigma. Cleistogamous flowers assure seedsetting even in the absence of pollinators.

Hint

(a) : Commelina produces two types of flower-chasmogamous flowers which are similar to flowers of other species with exposed anthers and stigma, and cleistogamous flowers which 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 effect pollination. Thus, cleistogamous flowers are invariably autogamous as there is no chance of crosspollen landing on the stigma. Cleistogamous flowers assure seedsetting even in the absence of pollinators.

Hint

(d)

Hint

(c) : Autogamy (Gk. autos-self, gamos-marriage) is a type of self pollination in which an intersexual or perfect flower is pollinated by its own pollen, Geitonogamy (Gk. geiton-neighbour, gamos-marriage) is a type of pollination in which pollen grains of one flower are transferred to the stigma of another flower belonging to either the same plant or genetically similar plant. In geitonogamy, the flowers often show modifications similar to ones found in xenogamy or cross pollination. Xenogamy (Gk. xenos – strange, gamos – marriage) or cross pollination is the transfer of pollen grains from anther of one flower to the stigma of a genetically different flower of same species.

Hint

(a) : The plants in which male and female flowers are borne on separate individuals, are referred to as dioecious plants, e.g., papaya, date palm. Dioecious plants exhibit xenogamy.

Hint

(d) : Xenogamy or cross pollination is the transfer of pollen grains from the anther of one flower to the stigma of a genetically different flower of same species. Cross pollination is performed with the help of an external agency.

Hint

(b) : Wheat is an anemophilous plant. Its flowers are not very showy. They do not have petals or sepals. Each female flower consists of an ovary from which two styles emerge, with two feathery sticky stigmas to catch pollen grains.

Hint

(d) : Wind pollinated flowers often have a single ovule in each ovary and numerous flowers packed into an inflorescence.

Hint

(a)

Hint

(d) : Cannabis is a wind pollinated plant.

Hint

(d) : Chiropterophily is pollination by bats.

Hint

(b) : Entomophily type of pollination takes place through the agency of insects. The entomophilous flowers are brightly coloured and fragranted to attract the insects. Their pollen grains are sticky or spiny to easily get attached with the body of pollinators. When the insects visit the flowers, their body gets dusted with pollen grains, and when they fly and visit other flowers, they brush against the stigma which being sticky, at once receives the pollen grains from their body. Thus, cross-pollination is achieved.

Hint

(c) : Entomophilous flowers produce an odour which may be pleasant (e.g., jasmine) or foul (e.g., Aristolochia, Arum, Rafflesia). Smell and nectar attract flies and other insects.

Hint

(b) : Pollination by ants is known as myrmecophily.

Hint

(c) : In Kigelia pinnata (sausage tree).

Hint

(d) : In Adansonia, cross pollination takes place through bat. This type of pollination is called chiropterophily.

Hint

(a)

Hint

(b) : In the pollen grains of an insect pollinated plant, the exine is covered by a yellowish, viscous, sticky and oily layer called pollenkitt. It is made up of lipids and carotenoids. Pollenkitt is secreted by tapetum.

Hint

(a)

Hint

(b) : Monoecious plant species have separate male and female flowers on the same plant. Some examples of monoecious plants are maize, birch, coconut and cucurbits. The plants in which male and female flowers are borne on separate individual are referred to as dioecious plants, e.g., papaya, date palm.

Hint

(d) : Cleistogamous flowers are intersexual. They remain closed causing self pollination. Cleistogamy occurs late in the flowering season in some plants, e.g., Commelina, balsam, Oxalis, Viola. These plants possess both chasmogamous and cleistogamous flowers. In cleistogamous flowers, the anthers dehisce inside closed flowers. Growth of style brings the pollen grains in contact with stigma. Cleistogamy ensures self-pollination autogamy.

Hint

(c) : Cleistogamous flowers are intersexual. They remain closed causing self pollination. Cleistogamy occurs late in the flowering season in some plants, e.g., Commelina, balsam, Oxalis, Viola. These plants possess both chasmogamous and cleistogamous flowers. In cleistogamous flowers, the anthers dehisce inside closed flowers. Growth of style brings the pollen grains in contact with stigma. Cleistogamy ensures self-pollination autogamy.

Hint

(c) : Heterostyly is the presence of 2.3 types of flower with different heights of styles and stamens. In diheterostyly (dimorphic heterostyly), there are two types of flower, pin eyed (long style and short stamens) and thrum eyed (short style and long stamens), e.g., Primula vulgaris (primrose), jasmine.

Hint

(b)

Hint

(a) : Stigma is the terminal receptive part of the pistil which functions as landing platform for the pollen grains. It also determines the compatibility of the pollen grains.

Hint

(b) : Stigma is the terminal receptive part of the pistil which functions as landing platform for the pollen grains. It also determines the compatibility of the pollen grains.

Hint

(c) : In the given figure, A-central cell, B-egg nucleus, C-plasma membrane, D-synergid, E-filiform apparatus, F-male gametes, G-vegetative nucleus.

Hint

(a) : The pollen tube paves its way through the solid part of the stigma and style by secreting pectinases and hydrolytic enzymes. Pollen tube travels intercellularly and chemotropically along the concentration gradient of calcium-boron-inositol sugar complex.

Hint

(b)

Hint

(d) : After arriving at the wall of the ovary, the pollen tube enters the ovule either through the micropyle or by some other route. The entrance of the pollen tube through the micropyle is the normal condition and is known as porogamy. In some cases the pollen tube enters the ovule through the chalaza (chalazogamy, e.g. Casuarina) or through integuments (mesogamy, e.g. Cucurbita).

Hint

(d)

Hint

(c) : Fusion of egg with male gamete is called syngamy. The point at which funicle touches the ovule is hilum.

Hint

(d) : Double fertilisation is an event unique to angiosperms. It involves fusion of one male gamete (haploid) with egg (haploid) to form zygote (diploid) that gives rise to embryo accompained with fusion of other male gamete (haploid) with two polar nuclei (secondary nucleus) to form primary endosperm nucleus (PEN) that gives rise to a nutritive tissue called endosperm. Hence total of five haploid nuclei are involved in double fertilisation process.

Hint

(d) : Options (a), (b) and (c) represent the events that take place before fertilisation. Primary endosperm nucleus (PEN) is formed after double fertilisation and develops into endosperm.

Hint

(c)

Hint

(a)

Hint

(b) : In many aquatic plants with emergent flowers, pollination occurs by wind or insects, e.g., lotus, water lily, water hyacinth.

Hint

(b) : In coconut (Cocos nucifera), the surrounding white kernel called coconut meal is cellular endosperm and the coconut water (also called coconut milk) in the centre is free nuclear endosperm made up of thousands of nuclei.

Hint

(b) : Nuclear endosperm \((X)\) is the most common type of endosperm. It is named so because it contains free nuclei in the beginning. The primary endosperm nucleus divides repeatedly without wall formation to produce a large number of free nuclei. Meanwhile central vacuole appears in the central cell and pushes the cytoplasm containing the nuclei to the periphery. The cytoplasm thickens so that the vacuole decreases in size. It ultimately disappears with the exception of a few cases. The multinucleate cytoplasm undergoes cleavage and gives rise to a multicellular tissue, e.g., maize, wheat, rice, sunflower, Capsella bursa-pastoris.

Hint

(b) : Nuclear endosperm \((X)\) is the most common type of endosperm. It is named so because it contains free nuclei in the beginning. The primary endosperm nucleus divides repeatedly without wall formation to produce a large number of free nuclei. Meanwhile central vacuole appears in the central cell and pushes the cytoplasm containing the nuclei to the periphery. The cytoplasm thickens so that the vacuole decreases in size. It ultimately disappears with the exception of a few cases. The multinucleate cytoplasm undergoes cleavage and gives rise to a multicellular tissue, e.g., maize, wheat, rice, sunflower, Capsella bursa-pastoris.

Hint

(c) : In angiosperms, endosperm is a triploid (3n) structure
\(\therefore \quad 3 n=24\) (given), then \(n=8\)
Root represents the diploid structure of a plant, therefore \(2 n=16\)

Hint

(a) : In angiosperms, endosperm is a triploid structure.
\(\therefore \quad 3 n=24\) (given), then \(n=8\)
As gametes are haploid structures, therefore number of chromosomes in gametes will be 8 .

Hint

(b)

Hint

(b) : In double fertilisation, out of the two male gametes one fuses with egg or oosphere to perform generative fertilisation. Generative fertilisation is also called syngamy or true fertilisation. It gives rise to a diploid zygote or oospore.

Hint

(a)

Hint

(b)

Hint

(b) : During the development of dicot embryo, initially the dicot 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. Two cotyledons differentiate from the sides with a faint plumule in the centre. At this time the embryo becomes heart-shaped.

Hint

(c)

Hint

(a) : Endosperm represents the food storing tissue of a seed. It is produced as a result of double fertilisation in angiosperms. In most monocots and some dicot seeds, the food reserve remains in the endosperm. They are called endospermic or albuminous seeds, e.g., maize, wheat, castor bean, coconut, barley, rubber. However, in the majority of dicot seeds (e.g., pea, gram, bean, mustard, groundnut) and some monocot seeds (e.g., orchids, Sagittaria), the endosperm is consumed during seed development and the food is stored in cotyledons and other regions. They are called nonendospermic or exalbuminous seeds.

Hint

(a) : Endosperm represents the food storing tissue of a seed. It is produced as a result of double fertilisation in angiosperms. In most monocots and some dicot seeds, the food reserve remains in the endosperm. They are called endospermic or albuminous seeds, e.g., maize, wheat, castor bean, coconut, barley, rubber. However, in the majority of dicot seeds (e.g., pea, gram, bean, mustard, groundnut) and some monocot seeds (e.g., orchids, Sagittaria), the endosperm is consumed during seed development and the food is stored in cotyledons and other regions. They are called nonendospermic or exalbuminous seeds.

Hint

(d) : Endosperm represents the food storing tissue of a seed. It is produced as a result of double fertilisation in angiosperms. In most monocots and some dicot seeds, the food reserve remains in the endosperm. They are called endospermic or albuminous seeds, e.g., maize, wheat, castor bean, coconut, barley, rubber. However, in the majority of dicot seeds (e.g., pea, gram, bean, mustard, groundnut) and some monocot seeds (e.g., orchids, Sagittaria), the endosperm is consumed during seed development and the food is stored in cotyledons and other regions. They are called nonendospermic or exalbuminous seeds.

Hint

(a)

Hint

(a) : In some seeds, remains of nucellus persist. This residual nucellus which persists in the seed is called perisperm, e.g., black pepper, coffee, castor, cardamum, Nymphaea.

Hint

(d)

Hint

(b) : After fertilisation, the integuments of the ovule form the protective coats (seed coats). Outer integument develops into testa and the inner one develops into tegmen.

Hint

(a)

Hint

(d)

Hint

(b) : There are several records of very old yet viable seeds The oldest one is of a lupin (Lupinus arcticus), excavated from Arctic Tundra. Seeds of Lupinus arcticus, (atleast 10,000 years old) were found in lemming burrows deeply buried in permanently frozen silt of Pleistocene age in unglaciated central Yuzon. They readily germinated in the laboratory and have since grown into normal healthy plants.

Hint

(d) : Polyembryony refers to the phenomenon of having more than one embryo in the same seed. In Citrus, a seed has 2-40 embryos, one normal embryo and the rest adventitive embryos (mostly nucellar). In adventitive embryony, an embryo develops directly from a diploid cell other than egg like that of nucellus and integument, e.g. Citrus, Opuntia.