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XII. 1. Sexual Reproduction in Flowering Plants: Assertion Reason

1. Assertion : An angiospermous flower represents the modified condensed shoot which performs the function of sexual reproduction. Reason : The fertile leaves of the shoot become modified into microsporophylls and megasporophylls which bear ovules and anthers respectively.
(a) Both assertion and reason are correct statements and reason is the correct explanation of the assertion	(b) Both assertion and reason are correct statements and reason is an incorrect explanation of the assertion	(c) Only assertion is correct	(d) Both assertion and reason are incorrect
c
A flower is a modified condensed shoot specialised to carry out the function of sexual reproduction in angiosperms. Like a branch, it arises in the axil of a small leaf like structure called bract. The receptable (thalamus or torus) of a flower supports all the floral appendages (i.e., sepals, petals, stamens and carpels). The receptacle consists of several crowded nodes which are separated by condensed internodes. The fertile leaves of the shoot become microsporophylls (=stamens) and megasporophylls (= carpels) which bear anthers and ovules respectively. The anthers produce pollen grains and the ovules possess eggs

2. Assertion : A typical microsporangium of angiosperms is generally surrounded by four wall layers – epidermis, endothecium, middle layers and tapetum. Reason : The outer three wall layers perform the function of protection and help in dehiscence of anther to release the pollen.
(a) Both assertion and reason are correct statements and reason is the correct explanation of the assertion	(b) Both assertion and reason are correct statements and reason is an incorrect explanation of the assertion	(c) Only assertion is correct	(d) Both assertion and reason are incorrect
b
The microsporangium is a part of the anther that produces microspores, which develop into male gametophytes. The microsporangium has four wall layers: epidermis, endothecium, middle layers, and tapetum. The outer three layers protect the microsporangium in the young anther and help release the pollen in the ripe anther through a process called dehiscence. Dehiscence is when a plant structure splits along a built-in line of weakness to release its contents. The innermost layer, the tapetum, nourishes the developing pollen grain

3. Assertion : In a microsporangium, the tapetal cells possess little cytoplasm and generally have a single prominent nucleus. Reason : During microsporogenesis, the microspore mother cells (M M Cs) undergo mitotic divisions to produce haploid microspore tetrads.
(a) Both assertion and reason are correct statements and reason is the correct explanation of the assertion	(b) Both assertion and reason are correct statements and reason is an incorrect explanation of the assertion	(c) Only assertion is correct	(d) Both assertion and reason are incorrect
d
Tapetum is the innermost wall layer of a microsporangium. It nourishes the developing pollen grains. The tapetal cells enlarge radically and become filled with dense protoplasmic contents as well as nutrients. Tapetal cells are generally multinucleate or their nucleus become polyploid due to endoplodiy. Microsporogenesis refers to the process of formation of haploid microspores mother cell (M MC) or pollen mother cell (PMC) through meiosis (and not mitosis)

4. Assertion : In most angiosperms, microspores of a tetrad grow and separate from one another shortly after meiosis. Reason : In the members of families Orchidaceae and Asclepiadaceae, all the pollen grains of a sporangium remain united to form a compact structure called pollinium.
(a) Both assertion and reason are correct statements and reason is the correct explanation of the assertion	(b) Both assertion and reason are correct statements and reason is an incorrect explanation of the assertion	(c) Only assertion is correct	(d) Both assertion and reason are incorrect
b
In most angiosperms, microspores of a tetrad grow and separate from one another shortly after meiosis. However, in some plants, the spores tend to remain together in tetrads for longer periods and develop into compound pollen grains (e.g., Drimys, Drosera). A pollinium is a compact structure of pollen grains that are produced by a single anther in plants like orchids and milkweeds. During pollination, the pollinium is transferred as a single unit

5. Assertion : Exine of a pollen grain is made up of sporopollenin which is resistant to high temperature, strong acid or alkali as well as enzymatic degradation. Reason : Sporopollenin is absent in the region of germ pores.
(a) Both assertion and reason are correct statements and reason is the correct explanation of the assertion	(b) Both assertion and reason are correct statements and reason is an incorrect explanation of the assertion	(c) Only assertion is correct	(d) Both assertion and reason are incorrect
b
Wall of a pollen grain consists of two layers– outer exine and inner intine. Exine is the hard outer layer which is made up of sporopollenin. Sporopollenin is one of the most resistant organic material known. It can withstand high temperature, strong acids or alkali and is not degraded by enzymes. Because of the presence of sporopollenin, pollen grains are well preserved as fossils. At certain places, the exine is thin or absent, these areas may have thickened intine or deposition of callose. They are called germ pores (if rounded) or germinal furrows (if elongated). Sporopollenin is absent in the region of germ pores or germinal furrows

6. Assertion : The method of development of embryo sac from a single functional megaspore is termed as monosporic development. Reason : In monosporic (Polygonum) type of embryo sac development, usually the megaspore which is situated towards micropylar end remains functional.
(a) Both assertion and reason are correct statements and reason is the correct explanation of the assertion	(b) Both assertion and reason are correct statements and reason is an incorrect explanation of the assertion	(c) Only assertion is correct	(d) Both assertion and reason are incorrect
c
In monosporic (Polygonum) type of development of embryo sac, only one megaspore situated towards chalazal end remains functional. The remaining three megaspores gradually degenerate and finally disappear. The functional haploid megaspore enlarges in size and by means of three successive mitotic divisions, gives rise to an eight-nucleate embryo sac. This type of embryo sac development occurs in a majority of flowering plants and the common example is Polygonum

7. Assertion : Although geitonogamy is functionally crosspollination involving a pollinating agent, genetically it is similar to autogamy. Reason : In geitonogamy, pollen grains from the anthers of one flower are transferred to the stigma of another flower borne on the same plant.
(a) Both assertion and reason are correct statements and reason is the correct explanation of the assertion	(b) Both assertion and reason are correct statements and reason is an incorrect explanation of the assertion	(c) Only assertion is correct	(d) Both assertion and reason are incorrect
a
Geitonogamy 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. It usually occurs in plants which show monoecious condition (unisexual male and female flowers are borne on the same plant). Thus, geitonogamy is functionally cross pollination as it involves the pollinating agent to carry out pollination, but genetically it is similar to autogamy (self-pollination) since the pollen grains come from the genetically same plant

8. Assertion : Hydrophily constitutes a major mode of pollination in most of the aquatic angiospermous plants. Reason : Almost all the aquatic dicot and monocot plants require water for the transport of male gametes and for fertilisation.
(a) Both assertion and reason are correct statements and reason is the correct explanation of the assertion	(b) Both assertion and reason are correct statements and reason is an incorrect explanation of the assertion	(c) Only assertion is correct	(d) Both assertion and reason are incorrect
d
Hydrophily is the made of pollination (transfer of pollen grains from the mature anther of a flower to the stigma of another flower) which is accomplished through the agency of water. Pollination by water is quite rare in flowering plants and is limited to only about 30 genera, mostly monocotyledons e.g. Vallisneria, Zostera, Ceratophyllum, etc. in may aquatic plants with emergent flowers, pollination occurs by wind or insects, e.g., lotus , water lily, water hyacinth, etc

9. Assertion : Only the pre-pollination growth of male gametophyte occurs inside the microsporangium whereas the remaining growth occurs over the female reproductive organs. Reason : Whole of the growth of female gametophyte occurs inside the megasporangium.
(a) Both assertion and reason are correct statements and reason is the correct explanation of the assertion	(b) Both assertion and reason are correct statements and reason is an incorrect explanation of the assertion	(c) Only assertion is correct	(d) Both assertion and reason are incorrect
b
Pollen grain or microspore is the first cell of male gametophyte generation and represents immature male gametophyte generation and represents immature male gametophyte. Development of male gametophyte is precocious, that is, it begins inside the microsporangium or pollen sac. The pollen grain is shed at 2 or 3 celled stage. The liberated pollen grains are transferred to the receptive surface of the carpel (i.e., stigma) through pollination. Growth of the pollen grain further occurs over the female reproductive organs. Female gametophyte or embryo sac is an oval multicellular haploid structure which is embedded in the nucellus towards micropylar end of the ovule (or integumented megasporangium). Whole of the development of female gametophyte occurs inside the megasporangium

10. Assertion : Self-incompatibility is a genetic mechanism which prevents self-pollination and thereby fertilisation by inhibiting either pollen germination or pollen tube growth in the pistil. Reason : In gametophytic self-incompatibility, the incompatibility reaction is determined by the genotype of the sporophytic tissue of the plant from which the pollen is derived.
(a) Both assertion and reason are correct statements and reason is the correct explanation of the assertion	(b) Both assertion and reason are correct statements and reason is an incorrect explanation of the assertion	(c) Only assertion is correct	(d) Both assertion and reason are incorrect
C
Self-Incompatibility prevents Inbreeding in Flowering Plants. Genetic diversity is important for maintaining the health and survival of species. By selecting their traits of interest humans often unwittingly reduce genetic diversity in domesticated crops and animals. The self-incompatibility system comprises the recognition of self-related pollen by cells of the pistil which is followed by rejection of the incompatible pollen. The mechanism of self-incompatibility (SI) prevents self-fertilization and thus encourages outcross and allogamy which shouldn’t be confused with genetically controlled physical or temporal mechanisms (prevent self-pollination), such as heterostyly and sequential hermaphroditism (dichogamy) . In plants with SI, when a pollen grain produced in a plant reaches a stigma of the same plant or another plant with a matching allele or genotype, the process of germination of pollens, pollen tube growth, ovule fertilization, and embryo development is halted at one of its stages and consequently, no seeds are produced. To prevent inbreeding and promote the generation of new genotypes in plants, SI is one of the most important mechanisms which is considered as one of the causes for the spread and success of angiosperms on the earth. Self-incompatibility is a device to prevent inbreeding. This is a genetic mechanism and prevents self-pollination (from the same flower or other flower of the same plant) by inhibiting pollen germination or pollen tube growth in pistil. Two categories of self-incompatibility have been recognized depending on the origin of factors determining the mating types: (i) Gametophytic self-incompatibility (GSI). The incompatibility process is determined by the genotype of male gametophyte (pollen) itself, e.g., Liliaceae, Poaceae, Solanaceae. (ii) Sporophytic self-incompatibility (SSI). The incompatibility process is controlled by the genotype of the sporophytic tissue of the plant from which the pollen is derived, e.g., Asteraceae, Brassicaceae Note: The mechanism, self-Incompatibility is very important in plant breeding so that self-incompatibility effectively prevents self-pollination; as a result, it has a profound effect on plant breeding approaches and objectives. (1) In the production of hybrid seeds, self-incompatibility is used. For that, two self-incompatible but cross-compatible lines are to be interpolated; seeds obtained from both the lines would be a hybrid seed. (2) Without emasculation and without resorting to genetic or cytoplasmic male sterility, self-incompatibility provides a way for hybrid seed production. (3) The combining of desirable genes in a single genotype from two or more different sources through natural cross-pollination is allowed by the self-incompatibility system which is not possible in self-compatible species. (4) In the case of pineapple, commercial clones are self- incompatible which results in their fruits developing parthenocarpic ally & are seedless.

11. Assertion : In angiosperms, endosperm development precedes embryo development. Reason : Double fertilisation ensures that the nutritive tissue is formed before the zygotes starts cleaving so that the energy spent on the formation of endosperm does not get wasted.
(a) Both assertion and reason are correct statements and reason is the correct explanation of the assertion	(b) Both assertion and reason are correct statements and reason is an incorrect explanation of the assertion	(c) Only assertion is correct	(d) Both assertion and reason are incorrect
A
During double fertilisation in angiosperms, one male gamete fuses with the egg to form the diploid zygote (syngamy or generative fertilisation). The diploid zygote finally develops into embryo. The other male gamete fuses with the two polar nuclei (or secondary nucleus) to form the triploid primary endosperm nucleus, PEN (triple fusion or vegetative fertilisation). Endosperm provides nutrition to the developing embryo. The cells of endosperm are filled with reserve food materials. Hence the zygote starts to divide and develops into an embryo only after a certain amount of endosperm is formed, i.e., endosperm development precedes embryo development. This ensures that the developing embryo gets proper nutrition. Double fertilisation ensures that the nutritive tissue is formed before the zygote starts cleaving so that the energy spent on the formation of endosperm does not go waste in case the fertilisation fails. Angiosperms are, therefore, economical and more specialised as compared to gymnosperms where a large nutritive female gametophyte is formed long before fertilisation

12. Assertion : In Cocos nucifera coconut water represents the cellular endosperm and the surrounding white kernel represents the free-nuclear endosperm. Reason : Endosperm is always completely consumed by developing embryo before seed maturation
(a) Both assertion and reason are correct statements and reason is the correct explanation of the assertion	(b) Both assertion and reason are correct statements and reason is an incorrect explanation of the assertion	(c) Only assertion is correct	(d) Both assertion and reason are incorrect
D
In Cocos nucifera, the free water in the cavity is free nuclear endosperm and the surrounding kernel is the cellular endosperm. The primary endosperm nucleus (PEN) first undergoes a number of free nuclear divisions without wall formation to form a large number of free nuclei (free nuclear endosperm) Endosperm can be entirely consumed by the developing embryo-like in groundnut and beans or it may persist even in the mature seeds like castor and coconut and this is used for seed germination

13. Assertion : During embryo development in dicots, suspensor serves as the main nutritive tissue for the embryo. Reason : The last cell of the suspensor at the end adjacent to the embryo is known as haustorium.
(a) Both assertion and reason are correct statements and reason is the correct explanation of the assertion	(b) Both assertion and reason are correct statements and reason is an incorrect explanation of the assertion	(c) Only assertion is correct	(d) Both assertion and reason are incorrect
D
During embryo development, the endosperm serves as the main nutritive tissue for the embryo. The suspensor is a group of cells which pushes the proembryo into the embryo sac. The first cell of the suspensor at the micropylar end becomes the haustorium which helps to absorb water and nutrients for the growing embryo. The last cell of the suspensor at the end adjacent to the embryo is known as hypophysis

14. Assertion : Ex-albuminous seeds do not possess any residual endosperm, as it is completely consumed during embryo development., Reason : Wheat, castor, pea and groundnut are all the examples of ex-albuminous seeds
(a) Both assertion and reason are correct statements and reason is the correct explanation of the assertion	(b) Both assertion and reason are correct statements and reason is an incorrect explanation of the assertion	(c) Only assertion is correct	(d) Both assertion and reason are incorrect
c
In some seeds, the endosperm persists in the seed as food storage tissue. Such seeds are called endospermic or albuminous e.g., Castor, Maize, Wheat, Barley, rubber, coconut. In others the endosperm is completely of embryo is then stored in cotyledons which become massive. Such seeds are non-endospermic or ex-albuminous, e.g., gram, bean, groundnut

15. Assertion : In plants, apomixis is a form of asexual reproduction that mimics sexual reproduction. Reason : Apomixis involves the production of seeds without the fusion of gametes
(a) Both assertion and reason are correct statements and reason is the correct explanation of the assertion	(b) Both assertion and reason are correct statements and reason is an incorrect explanation of the assertion	(c) Only assertion is correct	(d) Both assertion and reason are incorrect
A
Apomixis (apo-without, mixis-fusion) is a mode of reproduction in some plants which results in the formation of seeds without gametic fusion. It is a form of asexual reproduction. In plants apomixis commonly mimics sexual some species of Asteracease and grasses. There are several methods of apomictic development in seeds.