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  Stephen Hurry: Here’s the nucleus   
 with this nuclear membrane around it.

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  The only structure that can be   
 seen are these dark objects here.

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  These are called nucleoli. They   
 have no function in cell division.

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  Notice that the rest of the   
 nucleus contains apparently nothing special,

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  but chemical activity is going on   
 here and it’s at this stage…

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  ..in the division process, that   
 the DNA is duplicated.

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  This stage is called Interphase.  

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  What happens next? Well, inside   
 the nucleus the chromosomes become apparent.

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  The nucleoli vanish and the   
 nuclear membrane bursts apart.

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  Watch it here. We’ve made a jump   
 so this is rather late in the process.

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  You can see the chromosomes, now   
 they become free in the cytoplasm.

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  Here we are, here’s the same cell   
 again.

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  Here are the chromosomes and you   
 can see on this one, and on this one…

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  ..over here that the chromosomes   
 are double along their whole length.

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  This is a consequence of the   
 duplication that took place at the Interphase stage.

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  The doubleness of the chromosomes   
 extends down their whole length…

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  ..except for one special region,   
 here is one such region…

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  ..and here on this chromosome another.  

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  These special regions are called   
 centromeres and they are in fact…

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  ..holding the double chromosome   
 together. This stage is called Prophase.

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  What happens next is that the   
 chromosomes move together in the…

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  ..centre of the cell and will line  
  up across this equator.

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  The centromere divides, setting   
 the doubled chromosomes free in the cell.

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  Let’s see it happen.  

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  Here you are, the chromosomes are   
 unravelling, becoming shorter and thicker,

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  and are now beginning to line up.  

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  There. Now here’s the same cell   
 again and there’s the equator…

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  ..along which the cell, the   
 chromosomes are aligned.

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  The centromeres divide, though you  
  can’t see that on the photograph,

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  and this stage is called Metaphase.  

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  The next stages happen quite quickly.  

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  The now separated parts of the   
 chromosome move,

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  one to this end, and one to that   
 end of the cell.

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  At the same time, a new cell wall   
 will become visible forming across the equator.

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  And also around the chromosomes at  
  the ends of the…

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  ..daughter cells a new nuclear   
 membrane will appear.

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  Now you can see this if you watch   
 not only this cell but this one…

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  ..and this one, all three at the   
 same time, for in these two cells…

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  ..the process is slightly in   
 advance of the process in this big cell.

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  So let’s see that happen.  

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  Now the chromosomes are separating  
 , some of them…

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  ..fairly reluctantly as if the   
 chromosomes were sticking together.

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  There they go and the last one. An  
  arrow will appear in a moment…

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  ..simply to show the direction of   
 movement. There it is.

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  Now you can begin to see the   
 beginnings of the cell wall…

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  ..forming across the middle,   
 growing inwards from the edges.

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  The cell wall’s very distinct now.  

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  Here are the last stages in the   
 division of the cell.

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  In this cell the chromosomes have   
 retreated to the ends of the daughter cells.

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  A new cell wall is forming between  
  them and…

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  ..in these two cells the final   
 stages can be seen.

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  Notice that the structure of the   
 chromosomes is being lost and…

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  ..in this lower nucleus, even less  
  of the chromosomes can be seen.

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  And around each, a new nuclear   
 membrane will be forming.

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  Daughter cells, each now with   
 their own nucleus and separated…

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  ..by a cell wall, so that we have   
 two cells where we started with one.