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XII Botany New Chap 01 Sexual Reproduction in Flowering Plants 80
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https://t.me/R_Inayathullah_Best_Wishes XII_Botany _ New Chap-01 Sexual Reproduction in Flowering Plants (Assertion and Reason Statements)XII_BOTANY_NEW_CHAPTER-01: SEXUAL REPRODUCTION IN FLOWRING PLANTS _ A&R TEST ITEMS
# Correct Assertion Correct Reason
1.2 PRE-FERTILISATION: STRUCTURES AND EVENTS
Hormonal and structural changes initiate flower These changes lead to inflorescence formation, bearing floral
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differentiation. buds and subsequently developing flowers.
Androecium and gynoecium differentiate in the Androecium represents male reproductive organs, while
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flower. gynoecium represents female reproductive organs.
Stamens consist of a filament and bilobed anther. Filament attaches to the thalamus or petal; anther contains
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microsporangia, the pollen-producing structures.
Angiosperm anther is bilobed with dithecous theca. A longitudinal groove often separates the theca, and a
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transverse section reveals four microsporangia in the anther.
Microsporangium has four wall layers: epidermis, Tapetum nourishes developing pollen grains; sporogenous
5 endothecium, middle layers, and tapetum. tissue in the microsporangium undergoes meiotic divisions for
microsporogenesis.
Microspore tetrads formed by meiotic divisions in Each microspore tetrad is a potential pollen or microspore
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sporogenous tissue. mother cell.
Microspores released with anther dehiscence develop Pollen grains, male gametophytes, exhibit diverse architecture
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into pollen grains. with a two-layered wall (exine and intine).
Pollen grain exine, made of sporopollenin, is resistant The exine's germ pores allow pollen germination; the intine is a
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to high temperatures and chemicals. thin layer surrounding the cytoplasm.
Mature pollen grain contains vegetative and The vegetative cell is larger with abundant food reserve; the
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generative cells. generative cell divides to form male gametes.
Pollen grains shed at 2-celled or 3-celled stage Some pollen grains, causing allergies, must land on the stigma
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depending on the species. for fertilization within variable viability periods.
Pollen grains' viability varies with temperature and Stored pollen grains in liquid nitrogen can be used in breeding
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humidity. programs, akin to seed banks
Microsporangia in anther develop into pollen sacs. Microsporangia, initially located in the anther, extend
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longitudinally, eventually becoming packed with pollen grains.
Transverse section of microsporangium shows circular Wall layers - epidermis, endothecium, middle layers, and
13 outline with four wall layers. tapetum - surround the microsporangium and play specific
roles.
Sporogenous tissue undergoes meiotic divisions for Microspore tetrads, potential pollen or microspore mother
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microsporogenesis. cells, form during the development of anther cells.
Microspores dissociate from each other and mature Anthers mature and dehydrate, leading to the release of
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into pollen grains. individual pollen grains.
Sporogenous tissue undergoes meiotic divisions to Each tetrad cell is potentially a pollen or microspore mother
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form microspore tetrads. cell, initiating microsporogenesis.
Pollen grains retain viability for variable periods, Viability duration ranges from minutes in some cereals to
17 influenced by temperature and humidity. months in certain Rosaceae, Leguminoseae, and Solanaceae
species.
The microsporangium undergoes meiotic divisions for Sporogenous tissue cells, initially compactly arranged, become
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microsporogenesis. microspore tetrads.
Microspores within a microsporangium form a cluster As anthers mature, microspores dissociate and develop into
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(tetrad). pollen grains.
Pollen grains are shed at either 2-celled or 3-celled Generative cell division determines whether pollen grains are
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stages in different species. shed in a 2-celled or 3-celled state.
Ploidy of cells in the microspore tetrad is haploid. The cells of the sporogenous tissue undergo meiosis to produce
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microspores in the microsporangium.
Pollen grain exine's sporopollenin provides resistance Sporopollenin's resistance allows pollen grains to be well-
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to environmental factors. preserved as fossils and withstand harsh conditions.
The generative cell in the mature pollen grain can In over 60% of angiosperms, pollen grains are shed at the 2-
23 divide mitotically. celled stage, with the generative cell dividing before shedding in
some species.
Viability period of pollen grains is highly variable and In some cereals, pollen grains lose viability within 30 minutes,
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influenced by temperature. while in certain species, viability is maintained for months.
1.2.2 The Pistil, Megasporangium (ovule) and Embryo sac
Gynoecium, the female reproductive part, may have Pistils can be fused (syncarpous) or free (apocarpous), each
25 one (monocarpellary) or more pistils (multicarpellary). consisting of stigma, style, and ovary.
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