There is a maximum number of times that a human cell can divide (roughly 50) before it dies.

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Like a key in a lock, EGF binds to a receptor on a cell's surface, sending off a signal to the cell to divide, grow and die.

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When they shrink beyond a certain point, that cell can no longer divide.

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There the toxins detach from the antibody, and they hurt the cell when it tries to divide, essentially halting the cancer in its tracks.

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Without an adequate supply of them a cell cannot grow big enough to divide.

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But getting stem cells to divide without them turning into other cell types is an even bigger problem.

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But critics of human cloning and stem cell extraction methods essentially believe a human egg that begins to divide for any reason should be considered an embryo, and a potential person, that deserves protection under the law.

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They then began to divide into embryos, but none grew past the six-cell stage.

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Scientists divide bacteria into so-called "gram positive" varieties like Strep, which lack rigid cell walls and can be stained with dye, and "gram negative" ones that have cell walls and aren't dyeable.

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