gcseangel
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Report Thread starter 13 years ago
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Edit- mistake in title fragmentation not fractionation

I am doing some exam questions and need help:
Explain why the homogenate was filtered before spinning at a low speed in the centrifuge (2marks).
My answer is- To remove unbroken cells, but there is more to the answer since it is worth 2 marks can anyone elaborate more?

Explain why the organelles in sediment C (Nucleus) could be seen with a transmission electron microscope but not with an optical microscope?


Thanks anyone who can help me.
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Akkuz
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Report 13 years ago
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1) Firstly the suspension is spun at a low speed to seperate out the heavier parts e.g. nuclei. It might be filtered beforehand to seperate the solid from the liquid or may filtration seperates the liquid better/faster.

2) A transmission electron microscope uses a beam of electrons to create an image of the sample on a monitor. An optical microscope uses visible light and lenses to to magnify the sample.

Basically the transmission microscope is more powerful and produces a clearer image.

In this case, because the organelles found in the nucleus are very small and thin, an transmission electron microscope will be needed to create a more accurate image of the sample, therefore it can be analysed a lot easier/better.

Hope it helps.

(if anyone feels this is incorrect, feel free to edit it)
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14ahussain
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1)it is filtered, to remove larger debri or as you mentioned ‘unbroken cells’ to prevent mixing with the pellet which forms by only containing heavier organelles. If unbroken cells are present it could confuse one to assume it’s a heavy organelle such as the Nucleus2) Electron microscopes have a higher magnification and resolution compared to electron microscopes. Electrons fired from within the electron microscopes can target smaller organelles much more than wavelengths of light can. (Light waves may be too bigger than an organelle compared to the size of an electron)Hope that helps
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