Can anyone help with Mitosis? (AS AQA B)

Hi everyone, I have been given a sheet for homework and having missed a lesson, i'm a little stuck with the stages of mitosis. I know the names but i'm not sure how they are relevent to the graph. Any help would be greatly appreciated on how to work out the answer. :smile:

Curve 1 on the graph (attached) shows the change in distance between the centromeres of the chromosomes and the poles of the spindles; curve 2 shows the change in distance between the centromeres of sister chromatids. At 0 minutes the chromosomes are lined up at the equator.

1) Name the stage of mitosis that is occuring at 0 minutes.

(The axis on the left-hand side label is Distance (um)

Mitosis.doc28.2KB

Reply 1

Iscariot

"At 0 minutes the chromosomes are lined up at the equator."

Therefore without even looking at the graph you can deduce the cell is at metaphase.

Reply 2

JellyBellyBaby

Thanks

2) Name the stage of mitosis that is occuring between 10 and 20 minutes.

Reply 3

Iscariot

Anaphase. The spindle fibres are contacting causing the distance to decrease, and the sister chromatids are pulled away from the equator of the cell so the distance increases.

Reply 4

JellyBellyBaby

3) Explain why the distance between the cenromeres and the poles of the spindles is getting shorter between 10 and 20 minutes.

4) From curve 2 estimate the distance between the two poles.

Reply 5

JellyBellyBaby

Any ideas on 3) and 4) ?

Reply 6

Iscariot

I just explained #3:

The distance between the centromeres and the poles of the spindles gets shorter because the centromeres are being pulled towards the poles of the spindle fibres as the chromosomes are moved to opposite sides of the cell.

Question #4:

40 micrometres. That's just 20 micrometres * 2.

www.wikipedia.com/mitosis - try reading that, it'll explain most concepts of mitosis in good, easy to read detail.

Reply 7

JellyBellyBaby

Would the stage that starts at 20 minutes be telophase?

Reply 8

Iscariot

No, the stage that marks zero would be the telophase.

There's a typo in my above link, http://en.wikipedia.org/wiki/Mitosis is the correct url.

Reply 9

JellyBellyBaby

I realised the typo but it re-directed me :smile:

So should I say the PC realised the typo lol! What stage of mitosis starts at 20 minutes?

Reply 10

MadNatSci

JellyBellyBaby

I realised the typo but it re-directed me :smile:

So should I say the PC realised the typo lol! What stage of mitosis starts at 20 minutes?

You've gone through prophase and anaphase so the next stage is telophase, which, yes, should be starting at 20 mins as this - according to your graph - is the time at which the distance between sister chromatids is at its maximum and the distance between the chromatids' centromeres and the spindle poles is at its minimum. In other words the groups of chromatids have been pulled as far apart as they're going to go, so now the cell can stick a nuclear envelope around each of the two groups and start the process of cutting itself in two.

If in doubt remember IPMAT: Interphase Prophase Metaphase Anaphase Telophase. The phases always go in that order.