What you Need
What to do
Put the food colouring or ink from a pen into some water. Now try adding some oil.
Does anything happen to the colour?
Now try extracting some colour from some grated carrot. Try this in two jars one with a little water and another with a little oil.
Add some grated carrot to each jar and shake them vigorously.
Separate off the oil and the water and look at them.
Now try adding some oil to the water and water to the oil and shaking.
You can try the same thing with other colours like the red in tomato skins.
What may happen
Why does it happen?
The felt pen is very soluble in water but not in oil.
The orange pigment in carrot (beta carotene) appears to be soluble in both oil and water, but if you look closely at the water or leave it to stand for a long time the orange tends to settle to the bottom as it is mostly in small lumps of carrot.
This means that if you shake the carrotey water with oil, the beta carotene can still dissolve in the oil, but if you shake the carrotey oil with water the beta carotene can't dissolve so the water stays clear.
This is a really important process in chemistry. Many reactions produce lots of byproducts and waste products, and your starting materials may not have been pure anyway, and you want to produce a pure product. One of the most straight forward ways to do this is to find a solvent which will dissolve your product but not the other chemicals. You then shake the two solvents together, wait for them to separate and extract the solvent you want. It is then just a matter of removing the solvent from your product.
What has this got to to with cells?
A cell is made up of lots of important pieces, the cell membrane, the DNA in the nucleus, fats, proteins etc. But under a microscope they all look very similar, you need an agent to make them look different, these are called stains.
Stains with similar properties to the beta carotene will stain oily cell membranes, other stains will stick to DNA (and are therefore quite good at causing cancer) or particular proteins. So with the right stains it is much easier to tell the parts of a cell, or even see damaged cells which may become cancerous.