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The mammalian blastocoel becomes yolk sac without yolk according to my professor. I have not found any evidence that such a thing happens in amphibians like frog.

I need to be able to compare and contrast cleavage and formation of blastula in amphibians and in humans. My thoughts raised another question. My friend says that blastula exists only when blastocoel exists.

2. Is the thing without blastocoel but with yolk sac the blastula?

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Amphibians are produced externally so they do not get proteins and ATP from the mother during their maturation and differentiation. This means that they must have some way to get those things to protect themselves and survive.

The way that they get these things is yolk. Amphibians start to have yolk-filled endoderm during blastulation, [page 9, Gilbert, Developmental Biology].

I am considering the frog here as an example of amphibian. To know that things need energy to survive and that they must get it somewhere, you can deduce this solution. So nutrition and external "hatching" or development outside of female is the key here.

The overall answer to the question: The organism must have a yolk sac, since it has yolk.

The second question seems to be an idealized one. Without blastocoele but with yolk-sac suggests me that the blastocoel has developed already to yolk-sac. If that is the case, then I would call the thing gastrula, since for instance some species' ectoderm develops into yolk-sac. I assume that the question refers with "yolk-sac" to complete yolk-sac, not to the developing one during gastrulation.

If it is about developing yolk-sac, I would say that the cell is still blastula but is developing to gastrula. The yolk sac is not ready until gastrulation is complete.

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    $\begingroup$ I'm not overly convinced about getting ATP from yolk. Perhaps glucose or other respiratory substrate but cellular metabolism is still internal? $\endgroup$
    – Rory M
    Feb 11, 2012 at 18:26
  • $\begingroup$ @RoryM You are correct. I am not either overly convinced about getting all of the ATP from yolk, probably some - do not know, need to verify. There must be glucose around to get it the most of ATP. Cellular metabolism should be internal, since no mother around, but do not know about possible bacteria or other culture helping the thing. - Need to verify. $\endgroup$
    – Léo Léopold Hertz 준영
    Feb 11, 2012 at 20:53
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    $\begingroup$ if you're happy with the answer that you have posted you should consider marking it as accepted =) $\endgroup$
    – Rory M
    Feb 20, 2012 at 22:50

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