Chap 2 - SEXUAL REPRODUCTION IN PLANTSFlower is a modified shoot (stem bearing leaves) which functions as a reproductive organ and produces ova and/or pollen.

STAMENSStamen consists of long and slender stalk called filament and generally bilobed an-thers.Each lobe contains two theca (dithecious).Theca of an angiosperm consists of a pair of microsporangia that are adjacent to each other.Microsporangium is generally surrounded by four layered walls- the epidermis, endothecium, middle layer and tapetum. Innermost layer tapetum nourishes the developing pollen grains.

Flower is a modified stem which functions as a repro-ductive organ and produces ova and/orpollen. A typical angiospermic flower consists of four whorls - calyx, corolla, and gynoeciumCALYX made of sepals – green – protects flower at bud stageCOROLLA made of petals – multicoloured – attracts insects for pollinationANDROECIUM made up of stamens/male part of the flower/consists filament, anthers with pollen grains in them – function: to produce pollen grainsGYNOECIUM made up of pistils or carpels/part of the flower/consists ovary, style and stigma/female - function: produce egg cell/ova insie the ovaryStamen consists of long and slender stalk called fila-ment and generally bilobed anthers.Each lobe contains two theca (dithecious).

• In flowers, male (androecium) and female (gynoecium) differentiate and develops in which male and female gametes are produced. Stamen, Microsporangium and Pollen Grain :• Stamen consists of long and slender stalk called filament and generally bilobed anthers. Each lobe contains two theca (dithecious).• The anther is four-sided structure consisting of four microsporangia, two in each lobes.• Microsporangia develop further and become pollen sacs which contain pollen grains.Microsporangium consists of four layers of cells: Epidermis/Endodermis/Tapetum/Microspore mother cellsMicrosporogenesis- The process of the formation and differentiation of microspores (pollen) will delt in class.Page 1 SAS Class 12 Biology notes 2020

I understand that most would want the next chapter to be started - rep in humans - but we can-not skip this one. So here are some notes you can start with. Some parts of it need to discussed in class, so i will leave those portions.

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Pollen grainThey have two layered walls which covers the cell membrane of pollen grain - (i) Exine :- Made of sporopollenin- most resistant organic matter known - withstands high temperatures and strong acids and alkali and enzymes cannot break it. (ii)Intine :- it is a thin continuous layer made up of cellulose. Pollen grain appears like a golf ball. The depressions of the ball are the GERM PORES where the sporolollenin is absent.Mature pollen grains contain two cell each with its own nucleus - Vegetative and the GenerativeVEGETATIVE CELL: Bigger/bundant food reserve/Large irregular nucleus/Responsible for the development of pollen grain itselfGENERATIVE CELL: Small/Involves in syngamy (fuse with an egg)Pollen grains of many species e.g Parthenium cause severe allergies and bronchialdiseases in some people and leads to chronic respiratory disorders– asthma, bronchitis, etc.They are rich in nutrients and can be used as food supplements and can be stored in liquid nitrogen.

Gynoecium may consists of pistil - com-prised of stigam, style and ovary.Single pistil (monocarpellary)More than one pistil (polycarpellary)Polycarpellary can be of two types again:Fused - Syncarpous: examples -Tomato, tulip or Free Apocarpous: Magnolia, Strawberry, Rose

PYASTOL PISTIL or PYASTOL

PISTIL OR CARPEL

OVULE or MEGASPORANGIUMOvule is a small structure attached to placenta.Funicle – stalk by which ovule is attached to placentaHilum- junction between ovule and funicleInteguments- protective envelopsMicropyle- small opening at the tip of ovule into where pollen tube enters.Chalaza- basal part of ovuleNucellus (2n)-mass of cells enclosed in integu-ments. Has abundant food reserve.Megasporogenesis- The process of formation of megaspore from megaspore mother cell bymeiotic division is known as megasporogenesis. This topic I want to deal with in the class - needs some expla-nation. I will try and explain while some of you are bound to sleep. Well guess what it puts me to sleep!!But will try to make it as interesting as possicle.

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I. Wind Pollination> Pollen grains :– light, non- sticky, winged> Anther :- well exposed> Stigma :- large and feathery> Flower :- one ovule, arranged as inflorescence> Each lobe contains two theca (dithecious). > Examples: wheat, rice, corn, rye, barley, and oats.II. Water Pollination- Bryophytes, Pteridophytes, Algae. Pollen grains : protected by mucilaginous covering.Examples: pond weed, eel-grass, hydrilla, coontail etc.Main features of wind and water pollinated plants- produce pollen grains in large no.- do not produce nectar.III. Insect Pollination- Flowers : large, colourful, fragrant, rich in nectar- Pollen grains : sticky- Stigma : stickyExamples: Magnolia, Aster, Lithops, etcinflorescence.

Pollination – transfer of pollen grains from anther to stigma.a) Autogamy- transfer of pollen grain from anther to stigma of same flower.i. Cleistogamous – flower which do not open. cleistogamous flowers are autogamous as there is no chance of cross-pollen landing on the stigma. Cleistogamous flowers produce assured seed-set even in the absence of pollinators. e.g Viola (common pansy), Oxalis, and Commelina.ii. Chasmogamous- exposed anther and stigma.b) Geitonogamy – transfer of pollen grains from anther to stigma of different flower of same plant. Geitonoga-my is functionally cross-pollination involving a pollinating agent, genetically it is similar to autogamy since the pollen grains come from the same plantc) Xenogamy- transfer of pollen grain from anther to stigma of different plant’s flower of same species. nitrogen.MODIFICATIONS OF FLOWER FOR POLLINATION

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The pistil has ability to recognize the compatible pollen to initiatepost pollination events that leads to fertilisation. Pollen grain produce pollen tube throughgerm pores to facilitate transfer of male gametes to embryo sac.

OUTBREEDING: It is cross pollination as against Inbreeding - which is Self pollinationOutbreeding Devices-structures that promote cross pollination or outbreeding. > Unisexual flowers - male and female parts present in different flowers.> Anther and stigma with varying heights> Timing of maturing of stigma and anther differentPollen pistil interaction: Pollen-pistil interaction is a sequence of events that occur from the time of pollen deposition over the stigma till the time of entry of pollen tube inside the ovule. The process has checks at several places for the promotion or inhibition of pollen growth.

Artificial HybridizationCrossing different varieties of species- hybrid individual- with desirable characters of the parent plants desired pollen grains for pollination- stigma protected from contamination Emasculation : removal of antherBagging : flower covered- bag made up of butter-prevent contamination of stigma from unwanted pollen.Double Fertilisation- after entering the one of the synergids, each pollen grain releases two male gametes. One male gametes fuse with egg (Syngamy) and other male gametes fuse with two polar nuclei (triple fusion) to produce triploid primary endosperm nucleus (PEN). Since two types of fusion takes place in an embryo sac the phenomenon is called double fertilisation. The PEN develops into the endosperm and zygote develops into embryo.Post fertilisation events include endosperm and embryo development, maturation of ovules into seeds and ovary into fruits.Endosperm- the primary endosperm cell divides many time to forms triploid endosperm tissue having reserve food materials.Two types of endosperm development :(i) Free nuclear type (common method)(ii) Cellular type(a) Non-albuminous- endosperm completely utilized- before maturation of seeds. e.g pea, groundnut.(b) Albuminous- a portion of endosperm remain in mature seeds. e.g wheat, maize, castor.Embryo- Embryo develops at the micropylar end of the embryo sac where the zygote is located.Embryogeny – early stages of embryo development .The zygote gives rise to the proembryo and subsequently to the globular, heart-shaped and mature embryo.Embryo consists of: embryonal axis/cotyledons/plumule/radicle.Monocotyledonous Seed- Scutellem = Cotyledon- Coleorrhiza: undifferentiated sheath covering radical & root cap- Coleoptile: sheath covering plumuleSeed: Fertilized and mature ovule develops into seed.Seed consists of: Cotyledon/Embryonal axis/Seed coat- double layered- formed by integuments.Testa (outer coat) Tegmen (inner coat)- Micropyle:- small opening on seed coat, it facilitates entry of water and oxygen into seeds (for germination).nitrogen.

Artificial HybridizationCrossing different varieties of species- hybrid individual- with desirable characters of the parent plants desired pollen grains for pollination- stigma protected from contamination Emasculation : removal of antherBagging : flower covered- bag made up of butter-prevent contamination of stigma from unwanted pollen.

ENDOSPERMThe endosperm makes the main source of food for the embryo.After pollination and fertilization, carpels develop into the fruit tissue we eat (ovary) and the seeds within (ovules). Fruit devel-opment is initiated by growth regulating hormones produced by developing seeds.TYPES OF ENDOSPERMThree main types of endosperm development in flowering plants are: (i) Nuclear type (ii) Cellular type and (iii) Helobial type! The for-mation of endosperm is initiated by mitotic divisions of the primary endosperm nucleus (3N).

Signification of seed and fruit formation The function of the fruit is to aid in dispersal of the seeds. Several different vectors-- wind, water, and animals--are involved in fruit and seed dispersal. Seeds and fruits are without doubt the most important source of food for people and other animals, and they always have been.

HOMEWORK:Write short notes for the following terms:Monodelphous Diadelphous Polyadelphous Syngenesious Synandrous Didynamous tetradynamous Epipetalous Epiphylous Dithecous Monothecous Adnate Basifized Dorsifixed Versatile Introrse Extrorse Unilocular Bilocular Placentation Anatropous Orthotropous

Check the School website for more uploads after a few days.Stay home - stay safe boysBe helpful at home.

- Hilum:- scar on seed coat- Seed - Albuminous / Non-Albuminous- Perisperm : remnants of nucellus that is persistent. Ex: Black pepper- Dormancy: state of inactivityThe wall of ovary develops into wall of fruit called pericarp.Apomixis: Form of asexual reproduction- mimics sexual reproduction- seed formed without fertilisationFormation of apomictic seeds :> diploid cell (formed without meiosis)- develop into embryo without fertilization> cells of nucellus (2n) surrounding embryo sac- protrude into embryo sac- develop into embryos. Ex. Citrus and Mango.Polyembryony- Occurrence of more than one embryo in a seed- Often associated with apomixes. Ex: Citrus, groundnut

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