Cliff Notes question about embryo sacs in fertilization of angiosperms

[510586]

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Hi everyone. So on page 157 of the 3rd edition of cliff notes, on the second bullet point from the top of the page, it says, "six of the nuclei undergo cytokinesis and form plasma membranes. The result is an embryo sac". But on the diagram/picture on page 156, the embryo sac is labeled before cytokinesis occurs. I was wondering if there was any discrepancy and which part is incorrect if any?

https://books.google.com/books?id=N...gure 10-1 reproduction in angiosperms&f=false

 

[DAT Destroyer]

The diagram is slightly misrepresented

Only one megaspore survives, the remaining three are absorbed by the ovule. The remaining megaspore enlarges and undergoes several mitotic divisions to produce 8 haploid nuclei that are enclosed in embryo sac. One of those nuclei is the egg, 2 become polar nuclei, 2 are in synergid cells and 3 will be in antipodal cells.

Hope this helps

 

[510586]

The diagram is slightly misrepresented

Only one megaspore survives, the remaining three are absorbed by the ovule. The remaining megaspore enlarges and undergoes several mitotic divisions to produce 8 haploid nuclei that are enclosed in embryo sac. One of those nuclei is the egg, 2 become polar nuclei, 2 are in synergid cells and 3 will be in antipodal cells.

Hope this helps

So the three circles to the left of the "surviving megaspore ( n )" aren't really there in reality, right? They form the embryo sac (by being absorbed into ovule?). What are the things that form plasma membranes if the 8 haploid nuclei are used to form egg, polar nuclei, etc? Because in the textbook, it says the 6 nuclei undergo cytokinesis to form plasma membranes, not that they become the antipodal cells and stuff. Would this plasma membrane be included in the embryo sac along with the 3 absorbed megaspores that didn't survive? I really appreciate the help by the way 🙂

 

[DAT Destroyer]

You are right. The plasma membrane was there during the division of megaspores. The embryo sac does not include others absorbed. Megaspore is a haploid cell with a nucleus. So that gave the cell membrane for the embryo sac along with 8 nuclei.

 

[510586]

Oh ok so I think I am kind of getting it.
1. When the surviving megaspore undergoes mitosis 3 times, it produces the 8 nuclei as shown in the picture, and its cells around the nucleus form the cell membrane for the embryo sac (NOT the plasma membrane which was already there), correct?
2. And the 3 megaspores that did not survive just disappear (do not help form the embryo sac)?
3. What is the difference between the plasma membrane and the embryo sac?

Sorry for so many questions and once again thank you for the help.

 

[DAT Destroyer]

Yes. The difference between plasma membrane and embryo sac is mainly the contents and composition of the membrane.

 

[510586]

Alright awesome thank you so much!

 

[510586]

Yes. The difference between plasma membrane and embryo sac is mainly the contents and composition of the membrane.

So in the diagram, the ovule does not have a nucellus and integuments before meiosis. Do those structures arise after meiosis, or are they already there to begin with?

 

[DAT Destroyer]

So in the diagram, the ovule does not have a nucellus and integuments before meiosis. Do those structures arise after meiosis, or are they already there to begin with?

Membrane is before mitosis. Nuclei after mitosis.

 

[510586]

Membrane is before mitosis. Nuclei after mitosis.

Oh I meant nucellus not nuclei. So integuments arise before mitosis right? Since integuments are an outer protective layer? And nucellus comes after mitosis because it is the part containing the embryo sac, and the embryo sac is formed after cytokinesis of the 6 nuclei that arose from the mitosis of the original haploid nuclei?

 

[DAT Destroyer]

Oh I meant nucellus not nuclei. So integuments arise before mitosis right? Since integuments are an outer protective layer? And nucellus comes after mitosis because it is the part containing the embryo sac, and the embryo sac is formed after cytokinesis of the 6 nuclei that arose from the mitosis of the original haploid nuclei?

That is correct.

 

[510586]

That is correct.

Do integuments arise before meiosis of the megaspore too? And when does the micropyle form? Man I checked the campbell 9th edition on this section and they didn't even mention stuff like nucellus. Ferali's notes go along with the cliff notes too.

 

[DAT Destroyer]

This is graduate school material. It is sort of a complicated process. Campbell does not mention it is because it is a topic usually not discussed in first year Bio. This is a topic in 300-400 level Botany course.

 

[510586]

This is graduate school material. It is sort of a complicated process. Campbell does not mention it is because it is a topic usually not discussed in first year Bio. This is a topic in 300-400 level Botany course.

Would you consider it worth it to buy a textbook that maybe explains it better for the DAT? I feel like I am being nitpicky, but I would hate to miss a question on it or be unclear while learning.

 

[DAT Destroyer]

Would you consider it worth it to buy a textbook that maybe explains it better for the DAT? I feel like I am being nitpicky, but I would hate to miss a question on it or be unclear while learning.

You can try Schaums outlines or Campbell. That is more than you need for the DAT. If it is not there, then do not go into that topic.

Good luck in your studies!

 

[510586]

Alright thank you so much again orgoman!

 

[DAT Destroyer]

Alright thank you so much again orgoman!

Your are welcome, 510586, All your hard work will pay off..

Don't hesitate to ask questions, I will always my do best to answer asap.

🙂

 

[510586]

That is correct.

http://media-3.web.britannica.com/eb-media/12/5612-004-B7054A15.jpg So I think I found a better picture for the nucellus anyway. The nucellus is there before meiosis actually, and the embryo sac forms after mitosis like you said.