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An Introduction to Zoology:  Chapter 6
An Introduction to Zoology: Chapter 6
Published by The Lone Ranger
08-07-2008
Default Fertilization

Fertilization:
Fertilization (also known as conception or syngamy) occurs when a spermatozoan and an ovum unite to form a diploid zygote. It isn’t quite as simple a process as you might think.

The terms “egg” and “ovum” are often used as if they’re interchangeable, but they aren’t, really. An “egg” consists of an ovum plus various supporting structures. In mammals, for instance, the ovum is surrounded by a clear layer of glycoproteins known as the zona pellucida. Surrounding the zona pellucida is a layer of cells known as the corona radiata. These structures that surround and support the ovum can make things difficult for spermatozoa, since a spermatozoan must penetrate them in order to fuse with the ovum.

That’s one of the reasons that many, many spermatozoa must be produced per ejaculation. First of all, since it lacks most of the organelles that a cell needs in order to survive for any length of time, a spermatozoan has a short life expectancy. Second, if fertilization is internal, the female’s reproductive tract (which is typically rather acidic) can be a rather hostile place from the perspective of spermatozoa. (By some estimates, more than half the spermatozoa deposited into a woman’s vagina when her partner ejaculates are killed within a minute.) Finally, it usually takes the combined actions of several spermatozoa to penetrate the corona radiata and zona pellucida.

If all goes well, however, a spermatozoan penetrates into the ovum and fertilization occurs.

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  #1  
By monruw on 03-30-2011, 01:55 PM
Default Re: An Introduction to Zoology: Chapter 6

why it's called animal-vegetal axis? sound like kinda food, meat and vegetable or what else~ any story behind this?
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  #2  
By The Lone Ranger on 05-22-2011, 01:35 AM
Default Re: An Introduction to Zoology: Chapter 6

"Vegetal," is related to "vegetable." Many plants can reproduce asexually, whereas virtually all animals reproduce sexually.

Probably for this reason, "vegetal" came to refer to processes in living things that are "plant-like," especially processes that do not occur through sexual reproduction. More to the point, perhaps, plants generally grow much more slowly than do animals. So the "vegetal" pole of an egg gets its name for the fact that the cells in this region grow and divide much more slowly than do the cells in the "animal" pole.


Cheers,

Michael
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