Sexual Reproduction in Flowering Plants
1. The reproductive structure of a plant is the flower containing 2 types of sporophyll - (i) micro sporophyll (stamen) and (ii) megasporophyll (carpel)
2. Pedicel is the stalk of the flower which contains the floral parts - (i) sepals (collectively called as calyx) (ii) Petals (coralla), which are sterile parts.
3. The fertile parts are androecium (male) and gynoecium (female) reproductive organs.
4. Stamen consists of an anther and a filament, in which an anther is bilobed and encloses 4 microsporangia (or) pollen sac, that contains a number of pollen grains.
5. One cell thickness of epidermis, cellulose thickened endothecium, 1-6 layers of middle layer and innermost tapetum are the 4 wall layers of an anther.
6. Tapetum surrounds the sporogenous tissue in which sporopollenin (hardest substance) is secreted by ubisch bodies (deposited is the exine of the pollen wall).
7. The pollen mother cells divide meiotically to form tetrad of pollen grains (microspores) which gets surrounded by outer exine and inner intine and the process is termed as microsporogenesis.
8. The thin areas over the wall of exine are called as germ pores through which pollen tube germinates.
9. Pistil consists of stigma, stalk-like style and a ovary which may possess one (or) many ovules which are attached to the placenta through funicle.
10. The ovules contain a mass of thin walled parenchymatous cells called nucellus that is protected by integuments with a basal portion – chalaza.
11. A small opening is left at the apex of integuments known as micropyle.
12. Different types of ovules with examples are as follows.
(i) Orthotropous (erect) : Polygonum
(ii) Anatropous (inverted) : Angiospermes (most common type)
(iii) Hemi-anatropous (Nucellus and integuments right angled) : ES : Ranunculus.
(iv) Campylotropous : Cruciferae, Chenopodiaceae.
(v) Amphitropous : horse-shoe shaped, Papaveraceae.
(vi) Circinotropous : Ovule turns more than 360° : Cactaceae.
13. The process of haploid megaspores from 2n megaspore mother cell through meiosis is called megasporogenesis, where it is arranged is a linear tetrad.
14. Usually the lowermost megaspore enlarges to become functional megaspore and the upper three degenerates.
Watch this video for the topic from 0:54 to 48:44
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