1. Flowering plants reproduce sexually through a process involving stamens, which produce pollen grains containing male gametes, and pistils, which contain female gametes within ovules.
2. Pollen grains contain two cells - a vegetative cell and a generative cell that will form sperm. Pollen lands on the stigma of a pistil and a pollen tube grows to deliver the sperm to the egg cell.
3. Fertilization occurs when one sperm cell fuses with the egg cell to form a zygote, while the other fuses with the central cells to form endosperm tissue to nourish the developing seed.
Class 12||Chapter 2|| Sexual Reproduction in flowering plantsPrathamBiology
This chapter includes flowers, their detailed structure and developmental processess which took place durin sexual reproduction. Helpful for Board and NEET students.
Fell free for any query or suggestion
Mail us on: biologypratham@gmail.com
Website : www.prathambiology.in
Pollination, transfer of pollen grains from the stamens, the flower parts that produce them, to the ovule-bearing organs or to the ovules (seed precursors) themselves. In plants such as conifers and cycads, in which the ovules are exposed, the pollen is simply caught in a drop of fluid secreted by the ovule. In flowering plants, however, the ovules are contained within a hollow organ called the pistil, and the pollen is deposited on the pistil’s receptive surface, the stigma. There the pollen germinates and gives rise to a pollen tube, which grows down through the pistil toward one of the ovules in its base. In an act of double fertilization, one of the two sperm cells within the pollen tube fuses with the egg cell of the ovule, making possible the development of an embryo, and the other cell combines with the two subsidiary sexual nuclei of the ovule, which initiates formation of a reserve food tissue, the endosperm. The growing ovule then transforms itself into a seed.
Class 12||Chapter 2|| Sexual Reproduction in flowering plantsPrathamBiology
This chapter includes flowers, their detailed structure and developmental processess which took place durin sexual reproduction. Helpful for Board and NEET students.
Fell free for any query or suggestion
Mail us on: biologypratham@gmail.com
Website : www.prathambiology.in
Pollination, transfer of pollen grains from the stamens, the flower parts that produce them, to the ovule-bearing organs or to the ovules (seed precursors) themselves. In plants such as conifers and cycads, in which the ovules are exposed, the pollen is simply caught in a drop of fluid secreted by the ovule. In flowering plants, however, the ovules are contained within a hollow organ called the pistil, and the pollen is deposited on the pistil’s receptive surface, the stigma. There the pollen germinates and gives rise to a pollen tube, which grows down through the pistil toward one of the ovules in its base. In an act of double fertilization, one of the two sperm cells within the pollen tube fuses with the egg cell of the ovule, making possible the development of an embryo, and the other cell combines with the two subsidiary sexual nuclei of the ovule, which initiates formation of a reserve food tissue, the endosperm. The growing ovule then transforms itself into a seed.
Reproduction ensures continuity of species generation after generations as the older individuals undergo senescence and die. Flowering plants shows sexual mode of reproduction and bears complex reproductive units as male and female reproductive units along with accessary structures.
Flower is a modified stem which functions as a reproductive organ and produces ova and/or pollen. A typical angiospermic flower consists of four whorls of floral appendages attached on the receptacle: calyx, corolla, androecium (male reproductive organ consisting of stamens) and gynoecium (composed of ovary, style and stigma) .
Table of Contents:
a. Structure
b. Reproductive Structure
c. Androecium
d. Microsporogenesis
e. Gynoecium
f. Megasporogenesis
g. Pollination
h. Fertilization
i. Functions
Explore sexual reproduction in flowering plants notes to learn about the reproductive structure of the flower and the process of pollination.
Introduction to Sexual Reproduction in Flowering Plants, Flower, Structure of Flower, Male Reproductive Part of Flower (Stamens), Development of Anther walls, Anther Walls, Microsporangium (Pollen Sac)
Presentation on Gymnosperms. Prepared by Rahmat Alam Puniyali, Student of BS IV at Karakoram International University Gilgit, Pakistan. Photos of related plants are taken by the creator at KIU (Karakoram International University) campus.
(Some of the pictures and diagrams are taken from the websites of their resembling organizations (The McGraw-Hill Companies))
Sexual and Asexual reproduction in plants with pollination and development of gametophytes and double fertilization with embryo and endosperm formation.
This chapter was really heavy
Divided it in three parts ,
1. Roots, Stem , leaves
2.Flowers, Fruits ,seed
Two parts are included, third part will be uploaded soon.
~Please comment ~ Feel free to Suggest~♥
Fertilization is the process of fusion of the female gamete, the ovum or egg and the male gamete produced in the pollen tube by the pollen grain. Fertilization in flowering plants was discovered by Strassburger in 1884.
Flowers are the reproductive structures of angiosperms. They vary greatly physically and are of great diversity in methods of reproduction. The process of fertilization in plants occurs when gametes in haploid conditions meet to create a zygote which is diploid.
The male gametes of the flower are transferred on to the female reproductive organs through pollinators. The final product of this process is the formation of embryo in a seed.
In this lesson you will learn about :
1) What is Fertilization?
2) The Pollen Grain (Male Gamete)
3) The Ovule (Containing Female Gamete)
4) Microsporogenesis and Megasporogenesis
5) Germination of Pollen Grain
6) Double Fertilization
7) Post Fertilization Events
I hope this document is helpful to you. Please share the document with your friends if you think this will benefit them. Get ready for the next lesson. Thanks.
Biological Classification
This ppt shows the details of biological classification. it gives a brief idea about the five kingdom classification with a detailed description of kingdoms monera, protista and fungi. a detailed description of viruses, viroids, prions and lichens have also been given....
For more details visit my youtube channel: (VIHIRA ACADEMY)
https://www.youtube.com/channel/UCxo06Nj-QWo_7SNvMyDnJCQ?view_as=subscriber
Reproduction ensures continuity of species generation after generations as the older individuals undergo senescence and die. Flowering plants shows sexual mode of reproduction and bears complex reproductive units as male and female reproductive units along with accessary structures.
Flower is a modified stem which functions as a reproductive organ and produces ova and/or pollen. A typical angiospermic flower consists of four whorls of floral appendages attached on the receptacle: calyx, corolla, androecium (male reproductive organ consisting of stamens) and gynoecium (composed of ovary, style and stigma) .
Table of Contents:
a. Structure
b. Reproductive Structure
c. Androecium
d. Microsporogenesis
e. Gynoecium
f. Megasporogenesis
g. Pollination
h. Fertilization
i. Functions
Explore sexual reproduction in flowering plants notes to learn about the reproductive structure of the flower and the process of pollination.
Introduction to Sexual Reproduction in Flowering Plants, Flower, Structure of Flower, Male Reproductive Part of Flower (Stamens), Development of Anther walls, Anther Walls, Microsporangium (Pollen Sac)
Presentation on Gymnosperms. Prepared by Rahmat Alam Puniyali, Student of BS IV at Karakoram International University Gilgit, Pakistan. Photos of related plants are taken by the creator at KIU (Karakoram International University) campus.
(Some of the pictures and diagrams are taken from the websites of their resembling organizations (The McGraw-Hill Companies))
Sexual and Asexual reproduction in plants with pollination and development of gametophytes and double fertilization with embryo and endosperm formation.
This chapter was really heavy
Divided it in three parts ,
1. Roots, Stem , leaves
2.Flowers, Fruits ,seed
Two parts are included, third part will be uploaded soon.
~Please comment ~ Feel free to Suggest~♥
Fertilization is the process of fusion of the female gamete, the ovum or egg and the male gamete produced in the pollen tube by the pollen grain. Fertilization in flowering plants was discovered by Strassburger in 1884.
Flowers are the reproductive structures of angiosperms. They vary greatly physically and are of great diversity in methods of reproduction. The process of fertilization in plants occurs when gametes in haploid conditions meet to create a zygote which is diploid.
The male gametes of the flower are transferred on to the female reproductive organs through pollinators. The final product of this process is the formation of embryo in a seed.
In this lesson you will learn about :
1) What is Fertilization?
2) The Pollen Grain (Male Gamete)
3) The Ovule (Containing Female Gamete)
4) Microsporogenesis and Megasporogenesis
5) Germination of Pollen Grain
6) Double Fertilization
7) Post Fertilization Events
I hope this document is helpful to you. Please share the document with your friends if you think this will benefit them. Get ready for the next lesson. Thanks.
Biological Classification
This ppt shows the details of biological classification. it gives a brief idea about the five kingdom classification with a detailed description of kingdoms monera, protista and fungi. a detailed description of viruses, viroids, prions and lichens have also been given....
For more details visit my youtube channel: (VIHIRA ACADEMY)
https://www.youtube.com/channel/UCxo06Nj-QWo_7SNvMyDnJCQ?view_as=subscriber
The Slides contains are Female Reproductive part of Flower (Carpels/Pistils), Structure of Ovule, Types of Ovules, Microsporogenesis, Megasporogenesis, Structure of Pollen Grain, Structure of Embryo Sac
Are we not lucky that plants reproduce sexually? The myriads of flowers that we enjoy gazing at, the scents and the perfumes that we swoon over, the rich colours that attract us, are all there as an aid to sexual reproduction. Flowers do not exist only for us to be used for our own selfishness. All flowering plants show sexual reproduction.
in this slide the chapter explanation is according to NCERT Syllabus which would be helping students in every field..
This seeks to throw light on the process by which organisms give rise to offspring of their kind and all forms of mechanisms and structures in plants that are directly and indirectly involve in that process
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
The increased availability of biomedical data, particularly in the public domain, offers the opportunity to better understand human health and to develop effective therapeutics for a wide range of unmet medical needs. However, data scientists remain stymied by the fact that data remain hard to find and to productively reuse because data and their metadata i) are wholly inaccessible, ii) are in non-standard or incompatible representations, iii) do not conform to community standards, and iv) have unclear or highly restricted terms and conditions that preclude legitimate reuse. These limitations require a rethink on data can be made machine and AI-ready - the key motivation behind the FAIR Guiding Principles. Concurrently, while recent efforts have explored the use of deep learning to fuse disparate data into predictive models for a wide range of biomedical applications, these models often fail even when the correct answer is already known, and fail to explain individual predictions in terms that data scientists can appreciate. These limitations suggest that new methods to produce practical artificial intelligence are still needed.
In this talk, I will discuss our work in (1) building an integrative knowledge infrastructure to prepare FAIR and "AI-ready" data and services along with (2) neurosymbolic AI methods to improve the quality of predictions and to generate plausible explanations. Attention is given to standards, platforms, and methods to wrangle knowledge into simple, but effective semantic and latent representations, and to make these available into standards-compliant and discoverable interfaces that can be used in model building, validation, and explanation. Our work, and those of others in the field, creates a baseline for building trustworthy and easy to deploy AI models in biomedicine.
Bio
Dr. Michel Dumontier is the Distinguished Professor of Data Science at Maastricht University, founder and executive director of the Institute of Data Science, and co-founder of the FAIR (Findable, Accessible, Interoperable and Reusable) data principles. His research explores socio-technological approaches for responsible discovery science, which includes collaborative multi-modal knowledge graphs, privacy-preserving distributed data mining, and AI methods for drug discovery and personalized medicine. His work is supported through the Dutch National Research Agenda, the Netherlands Organisation for Scientific Research, Horizon Europe, the European Open Science Cloud, the US National Institutes of Health, and a Marie-Curie Innovative Training Network. He is the editor-in-chief for the journal Data Science and is internationally recognized for his contributions in bioinformatics, biomedical informatics, and semantic technologies including ontologies and linked data.
Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released.
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules - a chemical called pyruvate. A small amount of ATP is formed during this process.
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to “burn” the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP. Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 – 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
6. Stamen, Microsporangium and Pollen
grain:
• Typical stamen consists of two parts, long
and slender stalk called filament and
terminal bilobed structure called anther.
• A typical angiosperm anther is bilobed.
• Each lobe have two theca i.e. dithecous.
• Each anther contains four microsporangia
located at the corners, two in each lobe.
• Microsporangia become pollen sacs and
are packed with pollen grains.
7. Structure of microsporangium:
• Each microsporangium surrounded by four wall layers
i) Epidermis
ii) Endothecium
iii)Middle layer.
iv) Tapetum.
• The outer three layers perform the function of• The outer three layers perform the function of
i) protection & ii) dehiscence of anther to release pollen.
• The inner most layer is tapetum which is multinucleated,
with dense cytoplasm; it nourishes the developing pollen
grain.
• The centre of each microsporangium contain homogenous
cells called sporogenous tissues.
8.
9. Microsporogenesis:
• The process of formation of microspores from pollen
mother cell through meiosis is called microsporogenesis.
• The sporogenous tissue of microsporangium differentiated
into microspore mother cell or pollen mother cell.
• Each microspore mother cell undergoes meiosis and gives
rise to haploid microspore tetrad.
• On dehydration microspore tetrad dissociated to form four
microspores.
• Each microspore developed into a pollen grain.
10. Pollen grain:
• Pollen grain represents the male
gametophytes.
• It is spherical and measuring about 25-50
micrometer in diameter.
• It is covered by two layers.
i) The hard outer layer called the exine is made
up of sporopollenin,up of sporopollenin,
• Is the most resistant organic materials known.
• It can withstand high temperature and strong
acids and alkali.
• No enzyme can degrade sporopollenin
The exine has prominent apertures called germ
pore where sporopollenin is absent.
11. ii)The inner wall of pollen grain is called intine.
It is thin and continuous layer
made of cellulose and pectin.
• On maturity the pollen grain contains two cells, the
vegetative cell and generative cell.
• The vegetative cell is bigger, has abundant food reserve and a• The vegetative cell is bigger, has abundant food reserve and a
large irregularly shaped nucleus.
• The generative cell is small and floats in the cytoplasm of
vegetative cell.
• In 60% of angiosperms, pollen grains are shed at this 2-celled
stage.
• In others the generative cell divides mitotically to form two
male gametes before pollen grain are shed (3-celled stage).
12.
13. Problems
• Pollen grains of many species cause severe
allergies and bronchial
afflictions often leading to asthma, bronchitis.
• Parthenium or carrot grass came as a• Parthenium or carrot grass came as a
contaminant with imported wheat causes
pollen allergy.
14. Use
• Pollen grains are rich in nutrients, we now use
pollen tablets as food supplements.
• In western countries pollen products in the form of
tablets and syrups are available in the market.
• Pollen consumption increases the performance of
athletes and race horses.athletes and race horses.
15. Viability of pollen grains
• Viability depends on
i) Prevailing temperature
ii) Humidity
• Viability of pollens varies in different species.
• In some cereals eg rice and wheat pollen grains
lose viability within 30 minutes of their release.
• In members of Rosaceae, Leguminoseae and
Solanaceae they maintain viability for months.
16. Cryopreservation
Storing Pollen grains
• Cryopreservation (liquid
nitrogen -196oC.
• Stored pollen can be Cryopreservation
Pollen Bank
• Stored pollen can be
used as pollen banks
in crop breeding
programmes.
17. The Pistil, Megasporangium (ovule) and Embryo Sac:
• The Gynoecium represents the female reproductive part of the flower.
• The Gynoecium may contain single pistil (monocarpellary) or may
have more than one pistil (multicarpellary).
• Fused pistils are called syncarpous and free pistils are called
apocarpous.
• Each pistil has three parts the stigma, style and ovary.
• Inside the ovary is the ovarian cavity (locule).
• The placenta located inside the ovarian cavity.
• Megasporongia or ovules arise from the placenta.
• The number of ovule inside the ovary may be single or many.
18.
19. Megasporangium (Ovule):
• Ovule is a small structure attached
to the placenta of locule with a stalk
called funicle.
• The body of the ovule fused
with the funicle in the region called hilum.
• Hilum is the junction between the funicle
and ovule.and ovule.
• Each ovule has one or two protective envelops called integuments.
• Integument covered the ovule except an opening at the top called
micropyle.
• Opposite of the micropylar end, is the chalaza, representing the
basal part of the ovule.
20. Megasporogenesis:
• The process of formation of megaspores from the
megaspore mother cell is called Megasporogenesis.
• In the centre of the ovule there is a mass of tissue called
nucellus.
• Cells of nucellus have abundant reserve food materials.
• One cell of the nucellus towards micropylar end
differentiated into megaspore mother cell (MMC).
• It is a large diploid cell, dense cytoplasm with prominent
nucleus.
• The MMC undergo meiotic division resulting four haploid
megaspores.
21. Female gametophyte:
• Out of four megaspores, one megaspore is functional and other three
degenerates.
• The functional megaspore developed into the female gametophyte.
• Female gametophyte is known as the embryo sac.
• Development of embryo sac from a single megaspore is called as
monosporic type of embryo sac.
• The nucleus of the functional megaspore divided by mitotic division
to form two nuclei which move to the opposite pole, 2-nucleated
embryo sac.
• Two successive mitotic division leads to formation of 4-nucleate and
later 8-nucleate stages of the embryo sac.
• All mitotic divisions are free nuclear type; karyokinesis is not followed
by cytokinesis.
22. • Six of the eight nuclei are surrounded by cell walls and
organized into cells.
• Three cells are grouped together at the micropylar end,
constitute the egg apparatus.
• The egg apparatus, in turn consists of two synergids and
one egg cell.
• Synergids have special filiform apparatus, which play an
important role in guiding the entry of pollen tube into theimportant role in guiding the entry of pollen tube into the
synergids.
• Three cells arranged towards chalazal end are called
antipodal cells.
• The large central cell has two polar nuclei.
• A typical angiosperm embryo sac at maturity is 8- nucleated
and 7-celled.
23.
24.
25.
26.
27. Pollination:
Transfer of pollen grains from the anther to the stigma of a pistil is
termed as pollination.
Both male and female gametes are non-motile.
Kinds of pollination:
Autogamy:
• Pollination within same flower.• Pollination within same flower.
• In open and exposed anthers and stigma autogamy is rare.
• Viola, Oxalis and Commelina produce two types of flowers:
i) Chasmogamous: exposed anther and stigma
ii) Cleistogamous: closed anther and stigma.
Cleistogamous flower is invariably autogamous and assured seed set
even in the absence of the pollinator.
30. Geitonogamy:
• Pollination between two flowers of the same plant.
• Pollination by pollinating agent.
• Genetically similar to the autogamy.
Xenogamy:Xenogamy:
• Transfer of pollen grains from the anther to the
stigma of different plant.
• It is commonly called as cross-pollination.
• It brings genetically different types of pollen grains
to the stigma.
31. Agents of pollination:
• Plant use two abiotic agent i.e. wind and
water for pollination.
• One biotic agent for pollination such as
animals.animals.
• Majority of plant use biotic agent for
pollination.
• Few plant use abiotic pollinating agent.
32. Anemophily:
• Pollinating agent is wind.
• Plants produces enormous amount of pollen when
compared to the number of ovules available for pollination
to compensate the uncertainties of pollination.
• Flowers with well exposed stamens.• Flowers with well exposed stamens.
• Large feathery stigma to trap air-borne pollen grains.
• Most wind pollinated flower contains single ovule in one
ovary and numerous flower packed into an inflorescence
e.g. corn cob.
• Pollen grains are light and non-sticky.
33. In corn the tassels we see are stigma and style which wave in the
wind to trap pollen grains.
34. Hydrophily:
• Pollination by abiotic agent like water.
• This type of pollination is very rare, about 30 genera,
mostly monocot.
• Vallisneria, Hydrilla and Zostera are the common example
for Hydrophily.
• All aquatic plants are not Hydrophily.eg Water Lily• All aquatic plants are not Hydrophily.eg Water Lily
• Pollen grains released into the surface of water and
carried to the stigma by air current as in Vallisneria.
• In sea grass the flowers remained submerged.
• Pollen grains are long, ribbon like and carried passively
inside the water
• Pollen grains are protected from wetting by mucilaginous
covering.
36. Pollination by biotic agent:
• Majority of flowering plants use a range of animals as pollinating
agents.
• Among the animal, insect particularly bees are the dominant biotic
agents for pollination.
• Insect pollinating flowers are very large, colourful, fragrant and rich in
nectar.
• Small flowers present in cluster to make them conspicuous.
• Flower pollinated by flies and beetles secrete foul odours.• Flower pollinated by flies and beetles secrete foul odours.
37. • Nectar and pollen grains are the usual floral
rewards for insects.
• In some species floral rewards are in providing safe
places to lay eggs: e.g. Amorphophallus.
• A species of moth and Yucca plant cannot complete• A species of moth and Yucca plant cannot complete
their life cycle without each other. The moth
deposits its eggs in the locule of the ovary and the
flower in turn get pollinated by the moth.
• Many insects may consume pollen or nectar
without bring about pollination. Such floral visitors
are referred as pollen/nectar robbers.
38. Outbreeding Devices:
• Majority of the flowering plants produce hermaphrodite
flower and undergo autogamy.
• Continuous autogamy or self-pollination results in
inbreeding depression.
• Flowering plants have developed many devices to avoid
self pollination and to encourage cross-pollination. Suchself pollination and to encourage cross-pollination. Such
devices are called Outbreeding devices.
Pollen released and stigma receptivity is not
synchronized.
Spatial separation of anthers and stigmas
Anther and stigma are placed at different positions.
Self incompatibility.
Production of unisexual flowers.
39. Pollen pistil Interaction:
• All the events – from pollen deposition on the stigma until
pollen tubes enter the ovule – are together referred as
pollen-pistil interaction.
• Pollination does not guarantee the transfer of the right
type of pollen grain to the right type of stigma.
• The pistil has the ability to recognize the pollen whether it• The pistil has the ability to recognize the pollen whether it
is compatible or incompatible.
• If it is right type the stigma allow the pollen to germinate.
• If it is wrong type the stigma rejects the pollen, preventing
germination.
• The ability of the pistil to recognize the pollen by
continuous dialogue mediated by chemical like Boron,
Inositol and sucrose level.
40.
41. • Following compatible pollination, the pollen grain produce
pollen tube through one of the germ pore.
• Content of the pollen grain move into the pollen tube.
• Pollen tube grows through the tissues of the stigma and
style and reaches the ovary.
• If the pollen grain is in 2-celled stage the generative cell
divides and forms two male gametes inside the pollen tube.divides and forms two male gametes inside the pollen tube.
• If the pollen grain is in 3- cell stage the pollen tube carry
two male gametes from the beginning.
• Pollen tube enters into the ovule through micropyle and
then into the embryo sac through synergids guided by
filiform apparatus.
42. Artificial hybridization:
• One of the major approaches of crop improvement programme.
• Only desired pollen grain used for pollination.
• Stigma is protected from contamination (from unwanted pollen
grain).
• Removal of anthers from the flower bud before the anther dehisces• Removal of anthers from the flower bud before the anther dehisces
is called emasculation.
• Emasculated flowers covered by bag generally made up of butter
paper, to prevent contamination of its stigma with unwanted pollen.
This step is called bagging.
• If the female flower is unisexual there is no need of emasculation.
44. Double fertilization:
After entering one of the synergids, the pollen tube releases two male
gametes into the cytoplasm of the synergids.
Syngamy: one of the male gamete fused with egg cell, to form a diploid
zygote.
Two polar nuclei of central cell fused to form a diploid secondary
nucleus.nucleus.
Triple fusion: The second male gamete fused with the secondary
nucleus to form a triploid primary endosperm nucleus.
Since two type of fusion, syngamy and triple fusion take place in the
embryo sac the phenomenon is termed as double fertilization.
The central cell after triple fusion becomes primary endosperm cell and
developed into the endosperm.
The zygote developed into an embryo.
45.
46. POST- FERTILIZATION : STRUCTURE AND EVENTS
• Events of endosperm and embryo development,
maturation of ovule into seed and ovary into fruit,
are collectively termed as post-fertilization events.
47. Endosperm:
• Development of endosperm takes place before the embryo
development.
• Primary endosperm cell divides repeatedly to form a
triploid endosperm.
• Cells are filled with reserve food material and are used for
the nutrition of the developing embryo.
• PEN undergoes successive nuclear division to give rise to• PEN undergoes successive nuclear division to give rise to
free nuclei. This is called free-nuclear endosperm.
• Subsequently cell wall formation takes place and become
cellular endosperm.
• The coconut water is free nuclear endosperm and the
white kernel is the cellular endosperm.
• Endosperm may be consumed completely during embryo
developed or it may be consumed during germination of
seed.
48. Embryo:
• Zygote formed and placed at the micropylar end of the
embryo sac.
• Zygote starts its development only after some amount of
endosperm formed.
• Embryo development takes place in following stages:
ProembryoProembryo
Globular stage
Heart shaped
Matured embryo.
49.
50.
51. Dicot embryo:
• A typical dicotyledonous embryo
consists of an embryonal axis and
two cotyledons.
• Embryonal axis above the
cotyledon is the epicotyls.
• Terminal part of the epicotyls is• Terminal part of the epicotyls is
the plumule (gives rise to the
shoot).
• Embryonal axis below the
cotyledon is the hypocotyl.
• The terminal part of the hypocotyl
is called the radicle (root tip).
• The root tip is covered by the root
cap.
52. Monocot embryo:
• Possesses only one cotyledon
• the cotyledon is called scutellum.
• Scutellum situated towards one side of the
embryonal axis.
• Radicle and the root cap enclosed by a
sheath called coleorhiza.
• The portion of the embryonal axis above
level of attachment of scutellum is called
epicotyl.epicotyl.
• Epicotyl has the shoot apex or plumule
enclosed by hollow foliar structure called
coleoptile.
• Seed is the final product of the sexual
reproduction.
• Seed consists of seed coat, cotyledon and
embryo axis.
• Cotyledon stores the reserve food material
for development and germination
53. • Matured seed without endosperm called non-albuminous.
(Ground nut)
• A part of the endosperm retained in matured seed is
Albuminous.
• Remainants of nucellus in the matured seed is called
perisperm. E.g. black pepper, beet.
• The wall of the ovary develops into the wall of fruit called
pericarp.pericarp.
• Fruit developed from the ovary is called true fruit.
• In apple, strawberry, cashew, the thalamus contributes in
the fruit formation is called false fruit.
• Fruit developed without fertilization is called
Parthenocarpic fruits.
54.
55. APOMIXIS AND POLYEMBRYONY.
Apomixis is very common in Asteraceae and grasses.
• Seeds are produced without fertilization.
• Apomixis is a type of asexual reproduction which mimics the sexual
reproduction.
• Diploid egg cell is formed without meiosis and develops into seed
without fertilization.without fertilization.
• In Citrus and Mango the nucellar cells starts dividing, protrude into
the embryo sac and develop into embryo.
• Ovule having more than one embryo is termed as polyembryony.
• Hybrid plants are developed by apomixis to maintain the genetic
identity.