Questions of Assertion Reason Chapter 1 Sexual Reproduction in Flowering Plants biology CBSE Class 12 are very simple to understand as this chapter deals with Sexual Reproduction in Flowering Plants means reproduction in plants which every student is very much familiar with. To solve assertion reason type questions of science, deeper understanding of concept about Sexual Reproduction in Flowering Plants is required. In order to help the student in solving Assertion Reason type of questions, detailed process is explained.
How to solve Assertion Reason Type Questions?
In Assertion-Reason type of question, two statements are given, first is Assertion and second is called Reason. Student must have to think critically about both the statements in Assertion Reason Questions, since it combines multiple choice questions and true/false type of questions which requires a higher level of understanding.
How many types are there of Assertion Reason Type Questions?
Assertion-Reason type of questions can be asked either with four MCQ options or with five MCQ options. First four options are same in both the cases only one more options is being provided i.e. last one. One extra option increases the difficulty level of the questions.
In assertion reason type of questions, all 4 or 5 options are same for each question, which are as:
(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).
(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).
(c) Assertion (A) is true but reason (R) is false.
(d) Assertion (A) is false but reason (R) is true.
(e) Both Assertion and Reason are false.
Then a question haunts in every student’s mind, which option is correct and when?
This can be understood clearly with the following table:
|Assertion (A)||Reason (R)||MCQ Options (Fixed for all questions)|
|If True||True||(a) Both assertion (A) and reason (R) are true and reason (R) is the correct explanation of assertion (A).|
|If True||True||(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).|
|If True||False||(c) Assertion (A) is true but reason (R) is false.|
|If False||True||(d) Assertion (A) is false but reason (R) is true.|
|If False||False||(e) Both Assertion and Reason are false.|
Now, lets practice some Assertion Reason Questions of Science Chapter: 15 Our environment.
Read instructions carefully before answering the questions.
For question given below, two statements are given- one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:
(a) Both A and R are true and R is correct explanation of the assertion.
(b) Both A and R are true but R is not the correct explanation of the assertion.
(c) A is true but R is false.
(d) A is false but R is true.
Assertion: Perisperm is protective covering of seed and helps in dispersal and nutrition.
Reason: Pericarp is covering of fruit which is non-functional.
Perisperm is unused nucellus in the seed. It is often non functional for seed. Pericarp is the covering of fruit that develops from ovary wall. It is protective covering and also helps in dispersal and nutrition.
Assertion: Ubisch bodies are produced by glandular tapetum.
Reason: Ubisch bodies participated in the thickening of exine.
The Ubisch bodies are produced only by the glandular tapetum. Ubisch bodies get covered with sporopollenin and thus increase thickening of exine. The Ubisch bodies are involved in the external thickening of the exine, whose pattern is laid down by the spore cytoplasm in the tetrad stage.
Assertion: One pollen mother cell forms four microspores.
Reason: Microspores are formed due to reduction division.
The sporogenous cells of anther may directly function as microspore mother cells (also called pollen mother cells or PMCs) or they may undergo a few mitosis to add up to their number before entering meiosis. Each PMC, by a meiotic division, gives rise to a group of four haploid microspores. The aggregates of four microspores are referred to as microspore tetrads.
Assertion: Mostly in a tetrad, all microspores are free.
Reason: Compound pollen grain and pollinium are formed by grouping of microspores.
Mostly all the four spores within a tetrad are completely isolated from one another and from the spores in other tetrads of the locule. Usually the microspores separate from one another shortly after meiosis. However, in some plants the spores tend to remain together in tetrads for longer period and develop into compound pollen grains. In many members of Orchidaceae and Asclepiadaceae all the microspores in a sporangium remains together to form what is called a pollinium.
Assertion: Pollen wall is made up of two walls the intine and the exine.
Reason: Both the walls have depositions of sporopollenin.
The pollen wall comprises two principal layers, the inner one is called intine and the outer exine. The intine is pecto-cellulosic in nature as is the primary wall of the somatic cells. The exine is composed chiefly of a class of material called sporopollenin.
Assertion: Nucellus functions as a nutritive tissue.
Reason: Nucellus is always exhausted completely during development of embryo sac.
The body of the ovule consists of a mass of parenchymatous cells named nucellus. The nucellus is mostly consumed by the developing embryo sac or endosperm. But in some plants it persists in the mature seed as a nutritive tissue. The persistent nucellus is called perisperm.
Assertion: Placenta is tissue present inside the ovary.
Reason: Placenta bears ovules.
Assertion: Megaspore mother cell undergoes meiotic division.
Reason: All four megaspores form female gametophyte.
One hypodermal nucellar cell of the micropylar region differentiates into sporogenous cell. It forms a diploid megaspore mother cell or megasporocyte. The megaspore mother cells undergo meiosis and forms a row of four haploid megaspores. Only the chalazal megaspore remains functional while the other three degenerate. The functional megaspore enlarges and gives rise to female gametophyte, also called embryo sac.
Assertion: The egg apparatus, consists of two synergids and one egg cell.
Reason: Filiform apparatus play an important role in guiding the pollen tubes into the synergids.
Assertion: Chasmogamous flowers require pollinating agents.
Reason: Cleistogamous flowers do not expose their sex organs.
The majority or angiosperms bear chasmogamous flowers, which means the flowers expose their mature anthers and stigma to the pollinating agents. There is another group of plants which set seeds without exposing their sex organs. Such flowers are called cleistogamous and the phenomenon is cleistogamy. Such flowers show self pollination.
Assertion: Cross pollination is the only means of pollination in unisexual flowers.
Reason: Self-sterility is the only way to prevent self-pollination in bisexual flowers.
In plants such as hemp and willow where the flowers are unisexual cross pollination becomes obligatory. However, in plants with bisexual flowers legitimate self-pollination is prevented through the various adaptations, such as self-sterility, dichogamy, herkogamy and heterostyly. All those plants in which pollen from a flower is incapable of bringing about fertilization in the same flower are said to be self sterile or self-incompatible.
Assertion: Allogamy includes both geitonogamy and xenogamy.
Reason: Allogamy needs abiotic or biotic external agencies for pollination.
Cross pollination is the transfer of pollen grains from the anther of one flower to the stigma of another flower, i.e., allogamy. Cross pollination is further classified depending on whether the pollination has occurred between two flowers on the same plant (geitonogamy) or between two flowers on different plants (xenogamy). Cross pollination (allogamy) is performed with the help of an external agency. The latter may be abiotic (e.g., wind, water) or biotic (e.g., insects, birds, bats, snails).
Assertion: Most of entomophilous pollination is done by bees.
Reason: Bee-pollinated flowers are highly coloured.
Of the various insects, bees are the main flower visitors. Bees handle up to 80% of all pollination done by insects. All the bee pollinated flowers are brightly coloured, possess sweet fragrance, and / or produce nectar. Bees are colour blind for red and are fond of yellow, violet and purple. The bees visit flowers to collect their food (pollen and nectar) and in the process prove instrumental in bringing about pollination.
Assertion: Colpa aurea is a specialised pollinating agent of orchid Ophrys speculum.
Reason: Male Colpa mistakes the Ophrys flowers for female partner.
For its pollination the orchid Ophrys speculum has picked on the most selective attraction in the entire animal kingdom. It is pollinated by a hairy wasp, Colpa aurea. The wasp has a fixed habit whereby its males leave the burrows for above – ground existence about four weeks before the females emerge for the open air mating. The orchid opens its flowers about the same time the males appear and they possess an appearance and odour similar to those possessed by the female wasp. The inexperienced males mistake the Ophrys flowers for their female counterparts and land to perform the act of pseudo-copulation. The insect repeats the act with a number of orchid flowers and carries pollinia from one flower to another.
Assertion: Self-sterility inhibits self pollination.
Reason: Dichogamy is the condition in which only self pollination occurs.
Self-sterility is the condition in which the pollen of a flower has no fertilizing effect on the stigma of the same flower. Cross-pollination is thus the only method in them for the production of seeds. In many bisexual flowers the anther and stigma often mature at different times. This condition is known as dichogamy. Dichogamy often stands as a barrier to self pollination. There are two conditions of dichogamy.
(i) protogyny when the gynoecium matures earlier than the anthers of the same flowers
(ii) protandry – when the anthers mature earlier than the stigma of the same flower.
In both cases only cross pollination is possible.
Assertion: Double fertilization is unique to angiosperms.
Reason: Triple fusion occurs in both fertilization, i.e. first and second.
S.G. Nawaschin (1898) was the first to show that both the sperms released by a pollen tube are involved in fertilization. They fertilize two different elements of the embryo sac. The phenomenon is unique The nucleus of one of the sperms fuses with the egg to angiosperms and is called double fertilization. nucleus (syngamy) and that of the other migrates to the central cell where it fuses with two polar nuclei or their fusion product, the secondary nucleus. The second fertilization involves the fusion of three nuclei (sperm with two polar nuclei). This phenomenon is called triple fusion.
Assertion: In angiosperms, the first fertilization is called syngamy.
Reason: Second fertilization is called vegetative fertilization.
Fusion of the egg nucleus with sperm nucleus is called syngamy. As, in this process fusion product is diploid zygote or oospore, it is called generative fertilization. It is also called first fertilization as the first sperm fuses with the egg. The second male gamete fuses with the diploid secondary nucleus of the central cell to form a triploid primary endosperm cell. It is known as vegetative fertilization.
Assertion: Helobial endosperm is found in monocots.
Reason: Two chambers are formed in this endosperm.
Helobial endosperm is restricted largely to the monocotyledons. The primary endosperm nucleus moves to the chalazal end of the embryo sac where it divides forming a large micropylar chamber and a small chalazal chamber.
Assertion: Autogamy is a transfer of pollen grains from an anther to the stigma of the same flower on the same plant.
Reason: Xenogamy is pollination between two flowers on different plants.
Based on the destination of pollen grains, two types of pollination are recognised. When pollen grains are transferred from an anther to the stigma of the same flower the process is called self-pollination or autogamy. Cross-pollination is further classified depending on whether the pollination has occurred between two flowers on the same plant (geitonogamy) or between two flowers on different plants (xenogamy).
Assertion: Insects visit flower to gather honey.
Reason: Attraction of flowers prevents the insects from damaging other parts of the plant.
Assertion: Pollen mother cells (PMCs) are the first male gametophytic cells.
Reason: Each PMC gives rise to two pollens.
Primary sporogenous cell gives rise to microspore mother cells or pollen mother cells (PMCs). They are sporophytic in nature i.e., diploid. These cells undergo meiosis (reduction division) which gives rise to 4 microspores or pollens and this formation of microspores or pollens is called microsporogenesis. Microspores represent the beginning of the gametophytic phase and they are haploid in nature.
Assertion: Gynoecium consists of pistil.
Reason: It represents the male reproductive part in flowering plants.
Assertion: Flowers are the structures related to sexual reproduction in flowering plants.
Reason: Various embryological processes of plants occur in a flower.
Assertion: Geitonogamy is genetically similar to autogamy.
Reason: The pollen grains come from same plant.
Assertion: Cleistogamous flowers produce assured seed set in the absence of pollinators.
Reason: These flowers do not open at all.
Assertion: A typical microsporangium of angiosperms is generally surrounded by four wall layers.
Reason: The outer three wall layers perform the function of protection and help in dehiscence of anther to release the pollen.
A typical microsporangium 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 wall layers perform the function of protection in the young anther and mechanism of dehiscence in the ripe anther.
Assertion: Exine of a pollen grain is made up of sporopollenins which are resistant to high temperatures, strong acids or alkali as well as enzymatic degradation.
Reason: Sporopollenins are absent in the region of germ pores.
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.
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
magasporophylls which bear ovules and anthers respectively.
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 receptalce (thalamus or torus) of a flower supports all the floral appendages (i.e., sepals, petals, stamens and carpels). The receptalce consists of several crowded nodes which are separated by condensed internodes. The fertile leaves of the shoot become microsporophylls (stamens) and megasporo phylls ( carpels) which bear anthers and ovules respectively. The anthers produce pollen grains and the ovules possess eggs.
Assertion: Although geitonogamy is functionally cross-pollination involving a pollinating agent, genetically it is similar to autogamy since the pollen grains come from the same parent.
Reason: In getionogamy, pollen grains from the anthers of one flower are transferred to the stigma of another flower borne on the same plant.
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 monoeciouscondition (unisexual male and female flowers borne on the same plant. Thus, geitonogamy is functionally cross pollination as it involves 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.
Assertion: The pre-pollination growth of male gametophyte occurs inside the microsporangium whereas the rest of the growth occurs over the female reproductive organs.
Reason: Growth of the entire female gametophyte occurs inside the megasporangium.
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.
Assertion: Hydrophily is a major mode of pollination in most of the aquatic plants in angiosperms.
Reason: Almost all the aquatic dicot and monocot plants require water for the transport of male gametes and for fertilisation.
Hydrophily is the mode of pollination 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 many aquatic plants with emergent flowers, pollination occurs by wind or insects, e.g., Lotus, Water Lily, Water Hyacinth, etc.
Assertion: Pollen grains from male parent are mostly transferred to the stigma in the female parent by some external agency.
Reason: This is because the male flowers or male organs have no internal device to reach the female organs in another flower.