Structure of stamen & Microsporogenesis

Today we will start with our second chapter of Unit VI.
We will cover the following learning Outcomes :-
I) Students will be able to draw & label the parts of a L. S section of flower.
II) Students will be able to Elaborate on the structure of stamen & pollen grains.
III) Students will be able to List the importance of Tapetum.
IV) Analyse the mechanism of Microsporogenesis.


So I will show you an image on watsapp group, where you will be asked to label the missing parts of the flower.
I will expect all the students online to type the labels as I ask you all. This is just a revision quiz I want to see how many of you remember what I've taught you all in class 11.

STRUCTURE OF  ANTHER

We know that the male part of a flower is called stamen / Androecium. It consists of  filament, connector & bilobed anther.
Bilobed anther have two theca ( layers) on it, thus they are also called Dithecous.
This is a typical 3D structure of an anther.
The Line of Dehiscence is very important as the pollens mature, these lines which runs through theca , dehydrates and allow the anther lobes to rupture, this makes pollen available for pollination.

https://images.app.goo.gl/sbviqKXzpHMbK6DL9

The above link will show how the walls of anther lobes are formed & how the sporogenous tissue/microspore mother cells are formed.

The above diagram is detailed view of T. S ( Transverse Section) of Microsporangium. 


1. The outermost layer of microsporangium is called EPIDERMIS. 
2.Followed by ENDOTHECIUM & three layers of Middle layer. All these layer function as protective layer & helps in dehiscence of anther to release the pollen. 
3. The innermost layer is called TAPETUM. The cells of tapetum have dense cytoplasm & have more than one nucleus. 

FUNCTIONS OF TAPETUM


4. SPOROGENOUS TISSUES is capable to give rise to a Microspore Tetrad. The process of formation of microspores from pollen mother cell through Meiosis is called MICROSPOROGENESIS.
The steps are explained through the link below.


https://images.app.goo.gl/2RyNS1mW6yCFEckJ9


STRUCTURE OF POLLEN GRAIN.
1. Has prominent two layered wall.
2. Hard outer layer called Exine - It is made up of SPOROPOLLENIN which is one of the most resistant organic material. It can withstand high temperature, strong acids & Alkali. The exine layer has prominent apertures called GERM PORE ( where sporopollenin is absent).
3. Inner wall or pollen is called INTINE - It is made up of cellulose & pectin. The cytoplasm of pollen is surrounded by plasma membrane.
4. When pollen grain matures it contains 2 unequal cells due to asymmetric spindle formed during cell division. The big cell is called VEGETATIVE CELL and the small one is called GENERATIVE CELL.

( Around 60% of angiosperms, she'd pollen grains in this 2celled stage.
In remaining species, the generative cell divides mitotically to give rise to two male gametes before pollen grains are she'd I. E 3 celled stage.)


 With this we come to an end of today's lesson.
I leave you all with one question to answer in comments of this blog:-
What is pollenkit. How is it useful?

I will share with you all a YouTube video related to the whole process. Watch it & complete your notes for today. Kindly do post your doubts in comments or on our official watsapp group. 

Comments

  1. Har.shaved25 March 2020 at 09:57

    A part of the tapetum made up of lipids and carotenoids, it's an insect attractant and shields the pollen grains from uv rays

    ReplyDelete
  2. amaanlopez yuh25 March 2020 at 09:57

    Pollenkit is a sticky layer present on the exine of pollen grains. It facilitates pollination by sticking to fur/hair of animals like honey bees.

    Do we copy what's on this blog for notes?

    ReplyDelete
  3. Ashwin25 March 2020 at 18:36

    Pollenkit is a sticky substance present around the pollen grains i.e. exine of pollen grain.
    Uses :-
    i) Provides specific odour to the pollen.
    ii) Helps in insect pollination.

    ReplyDelete
  4. Gauravya25 March 2020 at 19:36

    Pollenkit is a covering found on the pollen grains of plants that are pollinated by insects. The pollenkit is sticky in nature and yellowish-orange in colour. This is because of the fact that pollenkit is made up of lipids and carotenoids. At times, the pollenkit can have a specific odour. This odour is essential in attracting insects which carry out pollination for that particular plant. The sticky nature of this film also allows pollen grain to stick to the appendages of the insects.

    ReplyDelete

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