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An Introduction to Zoology:  Chapter 6
An Introduction to Zoology: Chapter 6
Published by The Lone Ranger
Default Anatomy of Spermatozoa and Ova

Spermatozoa are specialized for movement; they seek out and swim toward ova. This doesnít mean that the ovum is a passive participant in the process, however; it secretes chemicals to attract the spermatozoa.

A typical sperm cell has three main regions: a head, a midpiece, and a tail. The head is capped with an acrosome, which contains digestive enzymes. These chemicals partially dissolve the tissues that surround the ovum, allowing the spermatozoan to penetrate and fertilize the ovum. The head of a spermatozoan also contains the nucleus, which has one set of chromosomes. If a spermatozoan successfully unites with an ovum, only the head actually penetrates all the way into the ovum. The nucleus of the spermatozoan unites with the nucleus of the ovum, and a diploid zygote is formed.

The midpiece of a spermatozoan is packed full of organelles known as mitochondria. The mitochondria break down carbohydrate molecules to produce energy, which powers the spermatozoan as it swims toward the ovum.

The tail of a spermatozoan is a flagellum. Powered by the mitochondria in the midpiece, the tail rapidly beats back-and-forth, propelling the spermatozoan forward.

Anatomy of a spermatozoan: A spermatozoan
is a very simple cell Ė basically, itís just genetic
material with a motor attached.

A human egg: the ovum (
oocyte) is surrounded by a clear layer of glycoproteins
known as the
zona pellucida and by cells collectively known as the corona radiata.


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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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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.


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