How does the ovule develop?

HOW OVULES ARE FORMED

Where Does the Ovule Develop?:

Whilst the pollen grains develop in the anther of the flowering plant, the ovule develops in the bud of the early growing flower. Can you locate the ovule on the diagram to the right?

[1]

The Formation of an Ovule

***All underlined words will have corresponding definitions found at the bottom of this page***

STEP 1: MEIOSIS, MEIOSIS,& MEIOSIS!

The journey of a female gametophyte begins inside the ovule with cells known as a megasporocytes

Beginning as a single microspore within the ovule, through meiosis it produces 4 megaspores. Soon after, 3 will disappear leaving the sole survivor to go through three successive divisions.  

The one remaining megaspore will divide once to become 2, once more to become 4, and once more. There are now 8 megaspore nuclei within the ovule!  

Please see the image to the right for a visualization of this process! 

STEP 2: THE MEGAGAMETOPHYTE

Once the 8 megaspore nuclei are created, they then rearrange to form what is called a megagametophyte. With its formation, the development of the female gametophyte is almost complete! 

Visualization: 

If you look at the picture to the right, you will see a red square. Within this square is the megagametophyte and each of its labeled components:

A. Antipodals

B. Synergids

C. Egg

D. Central Nuclei

STEP 3: THE FINAL STAGES

With a few more small changes not mentioned in detail here:

A. Growth of integuments(layers that protect the ovule) 

B. Development of the micropyle

C. Cell wall development around some of the eight nuclei

D. Fusion of joining of the two central nuclei(in most cases)

After these last four steps, we now have a female gametophyte that is ready to undergo pollination and fertilization! 

Please refer to the ANGIOSPERM section of the image to the right for a complete visualization! 

[2]

DEFINITIONS

TERMDEFINITION
AntipodalThree cells that lie opposite the synergid cells and the egg. Their main function is to provide nutrients for the endosperm
Female GametophyteFemale element that is required for pollination and fertilization(sexual reproduction stage)
MegagametophyteThe resulting creation from the development of a megaspore(female)
MegasporeA spore that is larger than the previous microspore which will eventually transform into a megagametophyte
MegasporocyteCells in the ovule that will become a megaspore through the process of meiosis
MicropyleA very small opening on the ovule where the pollen tube will enter
OvuleA structure found within the ovary that will eventually become a seed after being fertilized by pollen
SynergidCells that are able to guide the pollen tube to the female gametophyte