Sexual Reproduction in Flowering Plants: Class 12 Biology NCERT Chapter 2
Key Features of NCERT Material for Class 12 Biology Chapter 2– Sexual Reproduction in Flowering Plants
In the last chapter 1: Reproduction in Organisms, you learned about how the living organisms cop with reproduction method. In this chapter: Sexual Reproduction in Flowering Plants, you will learn about reproduction and that this type of reproduction is seen in the two plants and creatures. In plants, sexual reproduction happens in flowering plants.
Sexual reproduction is the kind of reproduction that includes two unique guardians that have a place with the other gender. Before becoming familiar with sexual reproduction in flowering plants, we should comprehend the life structures of a flower.
Quick Revision Notes
Reproduction guarantees congruity of species age after ages as the more seasoned people experience senescence and bite the dust. Flowering plants show the sexual reproduction method and bear sophisticated conceptive units as male and female regenerative units alongside accessory structures.
A flower is a changed stem which capacities as a contraceptive organ and produces ova or potentially pollen. A run of the mill angiosperms flower comprises four whorls of botanical members connected on the container: calyx, corolla, androecium (male regenerative organ consisting of stamens) and gynoecium (made out of the ovary, style, and stigma).
(Class 12 Biology Notes of Sexual Reproduction in Flowering Plants)
Pre-treatment: Structures and Events
• Several auxiliary and hormonal changes lead to the arrangement and advancement of the botanical primordium. The inflorescence is shaped that bears botanical buds and afterward flowers.
• In flowers, male (androecium) and female (gynoecium) separate and create in which male and female gametes are delivered.
Stamen, Microsporangium and Pollen Grain :
• Stamen comprises long and thin tails called fiber and by and large bilobed anthers. Every projection contains two thecae (dioecious).
• The anther is a four-sided structure consisting of four microsporangia, two in every projection.
• Microsporangia grow further and become pollen sacs which contain pollen grains.
(Class 12 Biology Notes of Sexual Reproduction in Flowering Plants)
• Microsporangium is commonly encircled by four-layered dividers, the epidermis, endothecium, center layer, and tapetum. The deepest layer tapetum feeds the creating pollen grains.
• Sporogenous tissues- It is minimalistically organized homogenous cells present at the focal point of every microsporangium when the anther is youthful.
The microsporogenesis – The procedure of the arrangement and separation of microspores (pollen grains) from microspore mother cells (MMC) by reductional division is called microsporogenesis.
• The cells of sporogenous tissues experience meiotic division to shape microspore quadruplicate. As the anthers develop and dry out, the microspore separates and forms into pollen grains.
The male gametophytes are represented by the pollen grains. They are made of 2 layered Wall,
1. Exine:- Made of a sporopollenin-most safe, natural issue known. It can withstand high temperatures and solid acids and soluble base. No catalyst can debase sporopollenin
2. Intine:-
– Thin and constant layer
– Made of cellulose and gelatin
3. Germ pores
– openings on exine where sporopollenin is missing
– structures pollen tube.
4. A plasma layer encompasses the cytoplasm of the pollen grain.
Develop POLLEN
— A develop pollen comprises of 2 cells with a nucleus (Vegetative and Generative)
VEGETATIVE CELL
Greater
Plentiful food save
Huge, unpredictable nucleus
Answerable for the advancement of pollen grain
GENERATIVE CELL
Little
Includes in syngamy (combine with an egg)
Thick cytoplasm and nucleus
Pollen grains of numerous species, e.g Parthenium, cause serious hypersensitivities and bronchial illnesses in certain individuals and prompt interminable respiratory issues such as asthma, bronchitis, and so on.
• Pollen grains are wealthy in supplements and are utilized as pollen tablets as food supplements.
• Viability of pollen grain fluctuates with species to species and should arrive on stigma before this period to germinate. Pollen grains of an enormous number of species are put away in liquid nitrogen at temperature – 1960, called pollen bank.
The Pistil, Megasporangium (Ovule) and Embryo sac
• Gynoecium may comprise of the single pistil (monocarpellary) or more than one pistil (polycarpellary), which might be melded (syncarpous) or free (apocarpous).
e.g., Multicarpellary and syncarpous pistil-Papaver
Multicarpellary and apocarpous pistil-Michelia
• Each pistil has three sections: the stigma, style, and ovary. Inside the ovary is ovarian depression (locule). The placenta is situated inside the ovarian depression. Megasporangia (ovules) emerge from the placenta.
Megasporangium (ovule)
The ovule is a little structure connected to the placenta.
Funicle – tail by which ovule is connected to the placenta
Hilum-intersection among ovule and funicle
Integuments-defensive wraps
Micropyle-little opening at the tip of ovule into where pollen tube enters
Chalaza-basal piece of ovule
Nucellus (2n)– a mass of cells encased in integuments. Has plentiful food save.
The megasporogenesis-The procedure of development of megaspore from megaspore mother cell by meiotic division is known as megasporogenesis. This procedure happens in an ovule.
Ovule separates a solitary megaspore mother cell (MMC) in the micropylar area of the nucleus. MMC experiences meiotic division that outcomes into the creation of four megaspores.
• In a large portion of the flowering plants, three megaspores degenerate. 1megaspore forms into the female gametophyte (embryo sac).
• The nucleus of useful megaspore separates mitotically to frame two nuclei, which move to inverse posts to shape the 2-nucleate embryo sac. Two more successive mitotic divisions result in the 8-nucleate embryo sac.
• Six of the eight nuclei encompassed by the cell divider and staying two nuclei (polar nuclei) are arranged beneath the egg mechanical assembly.
• Three cells are assembled at the micropylar end to comprise egg contraption and three cells at chalazal end structures antipodal cells. At development, embryo sac is 8-nucleate and seven celled
Pollination – move of pollen grains from the anther to stigma.
An Autogamy –move of a pollen grain from the anther to the stigma of the same flower.
I. The cleistogamous – flower which doesn’t open. Cleistogamous flowers are autogamous as there is zero chance of cross-pollen arriving on the stigma. Cleistogamous flowers produce guaranteed seed-set even without pollinators: e.g., Viola (normal pansy), Oxalis, and Commelina.
ii. Chasmogamous–uncovered anther and stigma.
b) Geitonogamy – move of pollen grains from the anther to the stigma of the various flowers of the same plant. Geitonogamy is practically cross-pollination including a pollinating operator, and hereditarily it is like autogamy since the pollen grains originate from a similar plant
c) Xenogamy–move of a pollen grain from the anther to the stigma of various plant’s flower of the same species.
Operators of pollination incorporate abiotic (water, wind) and biotic (bugs, butterfly, bumblebee, and so on. An enormous number of pollen grains are created by plants utilizing an abiotic method of pollination as the majority of pollen grains are squandered during a move.
Transformations in flowers for Pollination
I. Wind Pollination
pollen grains:– light, non-clingy, winged
another:- very much uncovered
stigma:- enormous and fluffy
flower:- one ovule, organized as inflorescence
Ex : corn cob, cotton, date palm
Water Pollination
– Bryophytes, Pteridophytes, Algae
pollen grains: secured by adhesive covering
Ex: Freshwater plants-Vallisneria, Hydrilla
Ocean grass-Zostera
Principle highlights of wind and water pollinated plants
– produce pollen grains in huge no.
– don’t create nectar
III. Creepy crawly Pollination
– Flowers: huge, vivid, fragrant, wealthy in nectar
– Pollen grains: clingy
– Stigma: clingy
Certain compensations to pollinators:
nectar and (consumable) pollen grains as nourishments
give the safe spot to laying eggs
Ex : Amorphophallus, Yucca
Outbreeding Devices –the different instruments take debilitate self-pollination and support cross-pollination as proceeded with self-pollination prompts inbreeding depression. It incorporates
- Pollen delivery and stigma receptivity not synchronized.
- Anther and stigma are put at the various positions.
- Inhibiting pollen germination in the pistil.
- Production of unisexual flowers.
Pollen pistil connection – the pistil has the capacity to perceive the good pollen to start post pollination occasions that prompt fertilization. Pollen grain produces pollen tubes through germ pores to encourage the movement of male gametes to embryo sac.
Fake Hybridization
Crossing diff assortments of species-half and half individual-with attractive characters of the parent plants
wanted pollen grains for pollination-stigma shielded from pollution
Emasculation: the expulsion of anther
Sacking: flower concealed pack made of spread prevent the defilement of stigma from undesirable pollen
Packed away flower-accomplishes receptivity-develop pollen grains-cleaned on the stigma – rebagged-natural products permitted to create
Twofold Fertilization -in In the wake of entering one of the synergids, every pollen grain discharges two male gametes. One male gamete melds with an egg (Syngamy) and other male gametes combine with two polar nuclei (triple combination) to create a triploid essential endosperm nucleus (PEN). Since two kinds of combinations happen in an embryo sac, the phenomenon is called twofold fertilization —the PEN forms into the endosperm, and zygote forms into an embryo.
Post fertilization occasions incorporate endosperm and embryo improvement, developing ovules into seeds, and ovaries into organic products.
Endosperm–the essential endosperm cell partitions many opportunities to structure triploid endosperm tissue having hold food materials.
Two kinds of endosperm improvement :
(I) Free atomic sort (basic technique)
(ii) Cellular sort
(a) Non-albuminous -endosperm is used before the development of seeds. e.g., pea, groundnut
(b) Albuminous -a part of endosperm stays in developing seeds. e.g., wheat, maize, castor
Embryo -Embryo creates at the micropylar finish of the embryo sac where the zygote is found.
Embryogeny – beginning phases of embryo development. The zygote ascends to the proembryo and along these lines to the globular, heart-formed, and developing embryo.
Embryo comprises of:
– embryonal pivot
– cotyledons
– plumule
– radicle
Monocotyledonous Seed
– Scutellum = Cotyledon
– Coleorhiza: undifferentiated sheath covering radical and root top
– Coleoptile: sheath covering plumule
Seed
– Fertilized and developed ovule forms into the seed.
Seed comprises of:
– cotyledon(s)
– embryonal hub
– Seed coat-twofold layered-framed by integuments
Testa (external coat)
Tegmen (internal coat)
– Micropyle:- little opening on the seed coat, it encourages section of H2O and O2 into seeds (for germination)
– Hilum:- scar on the seed coat
– Seed – Albuminous/Non-Albuminous
– Perisperm: leftovers of nucellus that are diligent. Ex: Black pepper
– Dormancy: the condition of idleness
- The mass of ovary forms into a mass of natural products called the pericarp. In evident natural products, just ovaries contribute to organic product arrangement by bogus natural product thalamus, which likewise contributes to natural product development.
Apomixis
– Form of asexual reproduction-emulates sexual reproduction-seed shaped without fertilization
– Formation of apomictic seeds :
- diploid cell (framed without meiosis)- form into an embryo without fertilization
- cells of nucellus (2n) encompassing embryo sac-project into embryo sac-form into embryos. Ex. Citrus and Mango.
Polyembryony
– The presence of more than a single embryo in a seed
– Often connected with apomixis. Ex: Citrus, groundnut
Questions
Q: Which of the accompanying conveys the male gamete for sexual reproduction in flowering plants?
- Ovary
- Ovules
- Stigma
- Pollen grain
Arrangement: Option D. Pollen grains convey the male gamete for sexual reproduction in flowering plants, wires with the ovules to frame the zygote.