This must be obvious. Is it really one single cell? What is all the extra material, beyond the DNA, mitochondria, etc. I assume it’s food for growth; is that true? If it is one cell, does it actually split into two yolks and albumins (sp?), etc.? Or is the actual reproducing part a reasonable size (i.e. very small) And in that case, I assume the actual cell is in the yolk; true?
It is one cell, with a big support system. No, the yolk doesn’t split, nor does the white. The yolk is the food source for the developing embryo, which starts microscopically on the surface of the yolk. The embryo grows, the yolk shrinks.
Technically, a chicken egg (or any other bird or reptile egg) is not a cell at all. The “amniotic egg” is composed of several parts which effectively allow for a fluid environment for the developing fetus.
The actual fetus (or the cell which will become the fetus) is housed in the amnion (thus the “amniotic egg” bit), a mebranous compartment within the egg. Other such compartments include the allantois (kind of a waste receptacle), the yolk sac (this houses the egg yolk), and the chorion, which encloses everything (this is the thin “skin” that you find on hard-boiled eggs, just inside the shell).
In a chicken egg, the yolk, of course, is the fluid-filled yolk sac, which is a nutrient source for the developing fetus. The fetus, when present, would be attached to the yolk sac (actually, the yolk sac is attached to the fetus, but you get the idea).
And those blood spots you sometimes find?
Those come from the yolk breaking out of the ovary (technically breaking out of follicular sacs of the ovary) before it moves through the oviduct to be fertilized and have the shell deposited. Usually, the yolks break through at areas of limited arterial involvement (called stigma) but occasionally a blood vessel gets in the way, and voila! Blood spot.
Since this occurs before fertilization, blood spots are poor indicators of fertile eggs. Just thought I’d share.
Excellent info; thanks all. So what is the purpose and destiny of the white of the egg? Is it cushion? Does it remain until hatching?
The egg-white, aka albumen, is essentially a protein soup which, in addition to the yolk, supplies proteins, vitamins, water, and minerals to the developing embryo. The yolk is primarily protein and fat.