Ans.The post-fertilisation events in angiosperms include: 17.With the help of an example of each explain the following Apomixis, parthenocarpy, polyembryony.  [All India 2012 c] (ii) List the differences between the embryos of dicot (pea) and monocot (grass family). (ii)Maturation of ovule(s) into seed(s). Give one example of each of these seeds. It is covered by a hollow foliar sheath called coleoptile. (ii) Zygote divides by mitosis to form a proembryo. between a male gamete and two polar nuclei. The role of endosperm in mature albuminous seeds is storage of reserve food for growing embryo. Polar nuclei            —Endosperm This may also lead to formation of more than one embryos in an embryo sac or ovule, leading to condition called polyembryony, e.g. (ii) Zygote divides by mitosis to form a proembryo. 24. Synergid                 —Degenerate (e.g. (iv)They can be used in favourable seasons depending on their viability. (a)Agamospermy In which the seed or embryo is derived from diploid egg ceil, formed without meiosis and syngamy. NCERT Solutions for Class 6, 7, 8, 9, 10, 11 and 12. (ii)They generate new combinations leading to variations. The ovary of the gynoecium produces one or more ovules and ultimately becomes the fruit wall. Milky water of green tender coconut is … Ans.In cpconut, cell formation occurs and the endosperm becomes cellular. (ii) Give reason for each of the following: (iv)Integuments of an ovule hardens and the water content is highly reduced as the seed matures. (i)Draw a labelled longitudinal view of an albuminous seed. The PEN undergoes successive nuclear divisions to give rise to free nuclei and this stage of endosperm development is called free nuclear endosperm. e.g. At this stage, it is called free nuclear endosperm. (a)outer —Testa (ii)True fruits These fruits develop from ovary, e.g. hence, in amphitropous the anatropous arrangement is tilted 90 degrees and in orthotropus it is completely inverted) . Different patterns of ovule attachment, or placentation, can be found among plant species, these include:[1]. (iii)How are pea seeds different from castor seeds with respect to endosperm? (i)Endosperm and embryo development. Citrus,Opuntia. Subsequently, cell wall is formed and endosperm becomes cellular. (a)Agamospermy In which the seed or embryo is derived from diploid egg ceil, formed without meiosis and syngamy. 2. The evolutionary origin of the inner integument (which is integral to the formation of ovules from megasporangia) has been proposed to be by enclosure of a megasporangium by sterile branches (telomes). A few angiosperms produce vascular tissue in the outer integument, the orientation of which suggests that the outer surface is morphologically abaxial. 7.Draw a labelled diagram of a matured embryo of a dicotyledonous plant. Polyembryony The occurrence of more than one embryo in a seed is known as polyembryony, e.g. (ii)Non-albuminous seeds have no residual endosperm as it is completely consumed in embryo development, e.g. (ii)This results in the formation of globular and heart-shaped embryo that finally becomes horse shoe-shaped (mature embryo) having cotyledon. The number (and position) of surviving megaspores, the total number of cell divisions, whether nuclear fusions occur, and the final number, position and ploidy of the cells or nuclei all vary. (ii) Describe any two modes by which apomictic seeds can be produced. [Delhi 2014 C] It is an adaptation for assured nutrition of the developing embryo. So, the main difference between apomixis and parthenocarpy is that seeds are formed in former, while absent in later. 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The plant stores nutrients such as starch, proteins, and oils in the endosperm as a food source for the developing embryo and seedling, serving a similar function to the yolk of animal eggs. (i)Sepals fall down or persist in few. Ans.Apomixis is the mechanism responsible for the formation of seeds without fertilisation in angiosperms, e.g. The wall of the ovary develops into the fruit wall called Ovules are initially composed of diploid maternal tissue, which includes a megasporocyte (a cell that will undergo meiosis to produce megaspores). Nuclear endosperm formed with the help of mitotic free nuclear divisions without the formation of the wall. [Delhi 2014 C] (ii)Explain the two ways by which seeds develop without fertilisation. In many Citrus and mango varieties, some of the nucellar cells surrounding the embryo sac start dividing, protrude into the embryo sac and develop into embryos. So, apples are called false fruits. This diploid egg cell develops into embryo without undergoing fertilisation, e.g. apple, strawberry, cashewnuts, etc. Nutrients from the plant travel through the phloem of the vascular system to the funiculus and outer integument and from there apoplastically and symplastically through the chalaza to the nucellus inside the ovule. It consists of three parts: the integument, forming its outer layer, the nucellus (or remnant of the megasporangium), and the female gametophyte (formed from a haploid megaspore) in its center. (v)Cells of the endosperm store food materials. This suggests that cupules of the kind produced by the Caytoniales or Glossopteridales may have evolved into the outer integument of angiosperms.[4]. 82(4):547-64, Frohlich and Chase, 2007. In flowering plants, the ovule is located inside the portion of the flower called the gynoecium. Ann Bot (2011) 107 (9): 1465-1489. doi: 10.1093/aob/mcr120, International Code of Nomenclature for algae, fungi, and plants, International Code of Nomenclature for Cultivated Plants, International Association for Plant Taxonomy, https://en.wikipedia.org/w/index.php?title=Ovule&oldid=1009081779, Articles with unsourced statements from April 2016, Articles with Spanish-language sources (es), Creative Commons Attribution-ShareAlike License. 5.Dicot embryo consists of two cotyledons and an embryonal axis between them: J. Bot. (i) Describe the endosperm development in coconut. (d)Produce genetic variations. (i) Draw a labelled diagram of LS of an embryo of grass (any six labels). It is rich in nutrients like fats, proteins, carbohydrates, minerals, vitamins, etc. (b)Adventive embryony The method in which diploid cells surrounding the embryo sac, e.g nucellus and integument protrude into the sac and develops into embryo. (c)Wall formation takes place from the periphery and proceeds towards the centre and the endosperm becomes cellular. grasses. (vi) On the availability of favourable conditions, seeds germinate and later dispersed by abiotic and biotic agents. (ii) The introduction of apomixis genes into hybrid seeds results in apomictic seeds, which results in asexual reproduction or production of cloned seed. The endosperm in pea seeds is consumed completely during embryo development, but endosperm is not utilised in castor seeds. (e)In exalbuminous seeds, the endosperm is completely consumed by the developing embryo before seed maturation, 4.Embryo formation occurs when certain amount of endosperm is formed. Give the characteristic features of endosperm of coconut. wall formation takes place following the first division. (i) Post-fertilisation events can be traced as: Embryo development in dicot plant Ans. grapes, cucumber, etc. Simple or compound ovary. Name the process. Development of endosperm, enlargement of seeds and fruit formation. (v)The portion of embryonal axis above the level of attachment of cotyledons is epicotyl and terminates in the plumule. 1.After double fertilisation, the following changes occur: How are they different from each other with respect to seeds? (iv)Cell wall formation starts from the periphery and the endosperm becomes completely cellular, e.g. The nucellus (plural: nucelli) is part of the inner structure of the ovule, forming a layer of diploid (sporophytic) cells immediately inside the integuments. The origin of the ovule. So, they need to be produced every year and cannot be stored. 2009 C) ... Cytoplasm undergoes cleavage after each nuclear division. (iii) Micropyle allows entry of water and oxygen during seed germination. Overview of developmental events and signalling during central cell maturation and early endosperm development with a focus on mechanisms of sexual and autonomous endosperm initiation. The number of free nuclei formed before cellularisation varies greatly. [All India 2009,2008] The cupules of some extinct taxa have been suggested as the origin of the outer integument. 1. Gymnosperms typically have one integument (unitegmic) while angiosperms typically have two integuments (bitegmic). After fertilization, the nucellus may develop into the perisperm that feeds the embryo. May persist or get consumed. Location within the plant. (b)The embryonic stages during the development of mature embryo sac are: (i)Embryo development occurs after endosperm development in angiosperms. (iv)Cell wall formation starts from the periphery and the endosperm becomes completely cellular, e.g. There is some amount of endosperm left in the seeds always. B — Scutellum (cotyledon) (a)Primary endosperm cell divides repeatedly and forms triploid endosperm nucleus. (iii) Formation of globular and heart-shaped embryo occurs which finally becomes horse shoe-shaped mature embryo. Then the cell wall formed. Ans. Here PEN divides repeatedly (mitotic division) without cytokinesis. 8.Ovary develops into a fruit. (iii)Albuminous seeds retain a part of endosperm as it is not completely used up during embryo development, e.g. (iv)In some seeds such as black pepper and beet, remnants of nucellus are also persistent (perisperm). The endosperm is also called the albumen of the seed. (ii)Mention one advantage of apomictic seeds to farmers. (iii)Maturation of ovary into fruit. This diploid egg cell develops into embryo without undergoing fertilisation, e.g. Prepare the mount at the demonstration table using a depression slide. (ii)Advantages of seeds to flowering plants are: (i)The embryonic stages during the development of mature embryo sac are: Nature 450:1184-1189 (20 December 2007) |, Kotpal, Tyagi, Bendre, & Pande. rice, maize plants, etc. It is an adaptation for assured nutrition of the developing embryo. (v) Why is the given structure called a grain?

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