Structure of Pistil & Megasporangium ( ovule)

Good morning Children, for today's class we will do the following learning outcomes :
Students will be able to :
1) Draw & Label parts of pistil.
2) Elaborate on types of ovules found in plants.
3) Analyse the structure of Megasporangium.
4) Explain the formation of Embryo Sac with diagrams.

STRUCTURE OF PISTIL.

We know pistil is the female reproductive part of the flower. A gynoecium may consists  of a single pistil ( monocarpellary) ormay have more than one pistil ( Multicarpellary).
In multicarpellary situation pistil may be fused, then it is called syncarpous ; if pistil are free then it is called apocarpous.
Each Pistil has three parts :-
I. The stigma - it acts as a landing platform for pollen grains.
II. Style - it is elongated tube that joins stigma & the ovary.
III. Ovary - it has Ovarian cavity ( locule) . The placenta is located inside the ovarian cavity. It acts as a nutritional attachment for megasporangia, commonly called as OVULES.



THE STRUCTURE OF  MEGASPORANGIUM ( OVULE)

 1)  The ovules is small structure attached to the placenta by means of a stalk called FUNICULUS.
2)   The body of ovule fuses with funicle in the region called HILUM.
3) Each ovule has one or two protective envelopes called INTEGUMENTS.
Integuments encircle the ovule except at the tip, this small opening is called MICROPYLE.
4) Opposite the Micropyle end is the CHALAZAL END, which represents the basal part of the ovule.
5) Enclosed with integuments is a mass of cells called the NUCELLUS. This  layer has abundant Reserve Food Materials, which provides nutrition to the embryo sac / female gametophyte.

TYPES OF OVULES
( It is based on the position of the embryo sac & the funiculus)
There are total 6 types of ovules found in plants :-
A) Orthotropous / Atropous Ovule -Eg: Polygonum.
B) Anatropous Ovule - Eg : found in all Gamopetalae members
C) Hemitropous Ovule - Eg : Ranunculus
D) Campylotropous Ovule -Eg : All  Legumes family.
E) Amphitropous Ovule - Eg : Allismaceae, Butomaceae families.
F) Circinotropous Ovule - Eg : Opuntia.


P. S. Only orthotropus & Anatropous Ovule has to be done in detail for CBSE Exams. Others you will do for your NEET exams.
I am attaching a link explaining all the types of ovules along with labelled diagrams.

https://images.app.goo.gl/NQ26EYp4MLoPMZok7

Now we will do detailed study of Orthotropous & Anatropous ovules.

MEGASPOROGENESIS PROCESS

The process of formation of megaspores from the megaspore mother cells ( MMC) is called MEGASPOROGENESIS.
 MMC is in the micropyle region of the nucellus. It is Large Cell with dense cytoplasm & a prominent nucleus.

MMC _-------------->undegoes Meiosis I resulting in formation of Megaspore DYAD ----------------> undergoes Meiosis II, resulting in formation of Megaspore TETRAD ( 4 Megaspores)
Out of these 4 MEGASPORES, 3 degenerate & only one becomes functional MEGASPORE.


FATE OF FUNCTIONAL MEGASPORE

For further Clarity I am also attaching a link of above process of Megasprogenesis below. I will also send you on watsapp the YouTube video link to watch for concept clarification. 

Well this is all for today. Kindly complete all the notes in your register. 

I will see you tomorrow again at the same time. Kindly do write your comments under the blog for your ATTENDANCE. 

https://images.app.goo.gl/8bFXuXUVbPzn68Z6A