NCERT Based KT’s PowerNotes
NEET 2022
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Sexual Reproduction In Flowering Plants
Male reproductive structure of flower
Female reproductive structure of flower
Stamen
• Stamen has two parts, anther and filament
• Anther is bilobed structure.
• Each lobe has two pollen sac (theca)  dithecous
anther
• The anther is a four-sided (tetragonal) structure
consisting of four microsporangia located at the
corners, two in each lobe.
• The microsporangia develop further and become
pollen sacs.
• The gynoecium represents female reproductive part of flower.
• Gynoecium may consist of a single pistil (monocarpellary) or
may have more than one pistil (multicarpellary)
• Multicarpellary Syncarpus : Papaver
• Muticarpellary Apocarpus : Michelia
• Fused pistil: Syncarpus gynoecium
• Free pistil : Apocarpus gynoecium
• Pistil is composed of Stigma, Style and Ovary
• One ovule in one ovary: wheat, paddy, mango
• Many ovules in single ovary: Papaya, Water melon, Orchids
Structure of microsporangium
• It is surrounded by four wall layers epidermis, endothecium,
middle layers and the tapetum.
• The outer three wall layers perform the function of protection
and help in dehiscence of anther to release the pollen.
• The innermost wall layer is the tapetum. It nourishes the
developing pollen grains
• Sporogenous tissue occupies the centre of each
microsporangium.
Structure of ovule
• Placenta connects ovules to ovary through stalk called funicle
• Ovule has hilum, ovule fuses with funicle in region called hilum.
• Each ovule has protective envelopes called integuments. I
• Small opening where integuments are absent : Micropyle
• Basal part of ovule, opposite to micropyle : Chalaza
Microsporogenesis
• Cells of the sporogenous tissue undergo meiotic divisions to
form microspore tetrads
• Each cell of the sporogenous tissue give rise to a microspore
tetrad. Each one is a potential pollen or microspore mother cell.
The process of formation of microspores from a pollen mother
cell (PMC) through meiosis is called Microsporogenesis
• Microspores formed, are arranged in a cluster of four cells–the
microspore tetrad
• Microspores dissociate from each other and develop into pollen
grains
Pollen grain
• Hard outer layer is exine and inner layer is intine
• Exine is made up of spropollenin
• Sporopollenin is one of the most resistant organic material
known.
• It can withstand high temperatures and strong acids and alkali.
• No enzyme that degrades sporopollenin is so far known.
• Pollen grain exine has prominent apertures called germ pores
where sporopollenin is absent
• The inner wall of the pollen grain is called the intine
• When the pollen grain is mature it contains two cells, the
vegetative cell and generative cell
• Vegetative has abundant food reserve
• Generative cell divide mitotically to give two male gamete on
pollination.
• Pollen grains also causes pollen allergy in some individual
• Used as nutritional supplement by athletes
• Can be stored grains of a large number of species for years in
liquid nitrogen (-1960C) : cryopreservation
Megasporogenesis
• The process of formation of megaspores from the megaspore
mother cell is called Megasporogenesis
• One of the cell of nucellus differentiate into megaspore mother
cell. It undergoes meiosis form 4 megaspores. one of the
megaspores is functional while the other three degenerate
• Functional megaspore develops into the female gametophyte
(embryo sac) – 7 celled 8 nucleated structure
Pollination
Transfer of pollen grains to the stigma of a pistil is termed
pollination.
Autogamy
• Transfer of pollen grains from the anther to the stigma of the
same flower
• requires synchrony in pollen release and stigma
• Some plants such as Viola (common pansy), Oxalis, and
Commelina produce two types of flowers –
• Chasmogamous flowers which are similar to flowers of other
species with exposed anthers and stigma, and cleistogamous
flowers which do not open at all
Geitonogamy
• Transfer of pollen grains from the anther to the stigma of another
flower of the same plant.
• Genetically it is similar to autogamy since the pollen grains
come from the same plant.
Xenogamy
• Transfer of pollen grains from anther to the stigma of a different
plant
• Brings genetically different types of pollen grains to the stigma.
Biology BOMB
NCERT Based KT’s PowerNotes
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Agents of Pollination
Majority of plants use biotic agents (eg honeybee) for pollination
Abiotic pollinating agent
Wind Pollination
• Pollination by wind is more common amongst abiotic
pollinations
• Requirements for wind pollination
 Light non sticky pollen
 Well exposed stamens
• Wind pollinated flowers often have a single ovule in each ovary
and numerous flowers packed into an inflorescence; a familiar
example is the corn cob
Pollination by water
• Shown by Vallisneria and Hydrilla and sea-grasses such as
Zoster
• In Vallisneria , pollen grains are released on to the surface of
water
• In sea-grasses such as Zoster , pollens are released inside water
• In most of the water-pollinated species, pollen grains are
protected from wetting by a mucilaginous covering
Both wind and water pollinated flowers are not very colourful and
do not produce nectar.
Biotic pollinating agent
• Majority of flowering plants use a range of animals as
pollinating agents eg Bees, butterflies, flies, beetles, wasps, ants,
moths, birds, (lemurs), arboreal (tree-dwelling) rodents, or even
reptiles (gecko lizard and garden lizard)
• Insects, particularly bees are the dominant biotic pollinating
agents
• Requirement for biotic pollination
 Large, colourful, fragrant and rich in nectar flowers
 Secretion of foul odour to attract insect
• Special examples
 Amorphophallus (the flower itself is about 6 feet in height)
provide safe places to pollinating agent to lay eggs
 Moth and Yucca plant : cannot complete their life cycles
without each other.
Outbreeding Devices
• Continued self-pollination result in inbreeding depression, so
discourage self-pollination some plants have evolved various
mechanisms called as outbreeding devices such as :
1. Pollen release and stigma receptivity are desynchronised
2. The anther and stigma are placed at positions unfavourable
for self-pollination
3. self-incompatibility ,this is a genetic mechanism and
prevents self-pollen (from the same flower or other flowers
of the same plant) from fertilising the ovules
4. Production of unisexual flowers (seen in castor , maize etc),
it prevents autogamy but not geitonogamy
5. Dioceous plant e.g. Papaya, in this plant male and female
flowers are present on different plants
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Pollen-pistil Interaction
The pistil has the ability to recognise the pollen, whether it is of
the right type (compatible) or of the wrong type (incompatible).
Pollen grain germinates on the stigma to produce a pollen tube
through one of the germ pores.
Generative cell divides and forms two male gametes
Pollen tube enters the ovule through the micropyle
Filiform apparatus guides the entry of pollen tube
Artificial hybridisation
• This is a method where desired pollen grains are used for
pollination and the stigma is protected from contamination (from
unwanted pollen). This achieved by emasculation and bagging
• Emasculation: removal of anthers,
• Bagging: covering of flower with a bag made up of butter paper
 In Bisexual flower : Both emasculation & bagging is done
 In unisexual flower: no need for emasculation, only
bagging is done
Double fertilisation
• Pollen tube releases two male gametes into the cytoplasm of the
synergid.
• One male gamete fuses with egg cell nucleus  zygote formed
• Another male gamete fuses with central cell  k/a triple fusion
triploid primary endosperm nucleus forms
Post-fertilisation : structures and events
Endosperm
• PEN undergoes successive nuclear divisions to give rise to free
nuclei. This stage of endosperm development is called freenuclear endosperm e.g. Coconut water
Endospermic seed
• Endosperm persist in the mature seed (e.g. wheat, maize, barley
castor and coconut)
Non endospermic seed
• Also k/a non-albuminous or ex-albuminous
• Endosperm is completely consumed by the developing embryo
before seed maturation (e.g., pea, groundnut, beans)
Embryo
Zygote divide only after certain amount of endosperm is formed.
Dicotyledonous embryo
• Consists of an embryonal axis and two cotyledons.
• Epicotyl
 Portion of embryonal axis above the level
of cotyledons is  epicotyl
 Terminal part of epicotyl  Plumule or stem tip.
• Hypocotyl
 Portion below the level of cotyledons is  hypocotyl
 Terminal part of hypocotyl  radicle or root tip
 The root tip is covered with a root cap.
Monocotyledonous embryo
Embryos of monocotyledons possess only one cotyledon
• Epicotyl
 The portion above embryonal axis Epicotyl
 The terminal part of epicotyl  Plumule
 Covering of Plumule  coleoptile
• Hypocotyl
 The portion below embryonal axis hypocotyl
 The terminal part of hypocotyl  radicle and root cap
 Covering of radicle and root cap  coleorhiza
Seed
• In some seeds nucellus remains persistent k/a perisperm as in
black pepper and beet
• Wall of the ovary develops into the wall of fruit called pericarp
• Integument  seed coat, Ovule  seed
• Fleshy fruits : guava, orange, mango, etc.,
• Dry fruits : groundnut, and mustard etc.
• True fruits (Fruit which develops only from ovary)
Biology BOMB
NCERT Based KT’s PowerNotes
NEET 2022
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• False fruits (fruit develop from ovary + thalamus) : apple,
strawberry, cashew, etc.
Generally fruits develops after fertilization, when fruit develop
without fertilisation it is called as parthenocarpic fruit
E.g. Banana
Viability of seed
• Viability of seed varies greatly.
• Lupinus arcticus excavated from Arctic Tundra, germinated an
estimated record of 10,000 years of dormancy
• Seed of date palm( Phoenix dactylifera ) found viable after 2000
years in dead sea
Fruit with large number of seeds
Orchid and parasitic plants (orobrache and striga)
bear fruits with large number of seeds
Apomixis and polyembryony
Apomixis
• Development of fruit without fertilisation  Parthenocarpy
• Development of seeds without fertilisation  Apomixis
E.g. Asteraceae and grasses
• Apomixis is a form of asexual reproduction
Polyembryony
• In some plants nucellar cells surrounding the embryo sac
protrude into the embryo sac and develop into the embryos, in
such species each ovule contains many embryos 
Polyembryony e.g. citrus , mango, orange
Problems with Hybrid seed
If the seeds collected from hybrids are sown, the plants in the
progeny will segregate and do not maintain hybrid characters.
Production of hybrid seeds is costly and hence the cost of hybrid
seeds becomes too expensive for the farmers. If these hybrids are
made into apomicts, there is no segregation of characters in the
hybrid progeny.
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Biology BOMB