Like in the eye for example how do the cells know to start curving around into an orb. How do the ones in the eyelid know that it’s the last one and doesn’t grow to big or too small of a eyelid?
In: Biology
[Morphogens](https://en.wikipedia.org/wiki/Morphogen)
When an embryo develops, new structures form as follows. A cell or group of cells at the right spot produce a chemical called a “morphogen” that diffuses (spreads out) a bit and so mark the area where the structure should form,
So, in your example, some morphogen the signals “skin cells needed here” tells all the cells growing there that they should turn into skin cells. And the cell at the border of the eye lid noticed that it should be the last cell to do so because it only gets very little of the morphogen.
Of course, this is all a complicated machinery, because some morphogens will cause other cells to turn into morphogen-producing cells, and some things only happen if different morphogens coming from different directions meet at the right concentration ratio and so on.
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