Greasy pots - answers page

Fig 7.6

Fig. 7.7


1. In Fig. 7.6, which fatty acid came out fastest, C16 or C18?

Fatty acid C16 came out about 4 minutes before C18

2. In Fig. 7.7 the carbon 13 isotope levels form a 45 degree line. Why is this?

The C16 and C18 fatty acids are from the same animal for each data point. So plotting C16 against C18 will give almost equal results and an x=y line at 45 degrees. The exception is ruminant milk.

3. In Fig. 7.7 why are fresh water fish lower in carbon 13 than marine fish? Are there any fish that could mess up results for freshwater fish?

Marine fish take up more carbon 13 because it there is a higher level in sea water. Salmon migrate up fresh water rivers to spawn, but they spend most of their lives at sea. They could be part of the diet of people living inland.


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Fig. 7.1 Food crust on ancient pottery


Fig.7.2 Paper chromatography separates molecules from a mixture. You may have done this with ink at school using filter paper.
The paper is called the "stationary phase". The water carrying the molecules is the "mobile phase".

Fig.7.3 In gas chromatography (GC) the stationary phase is a long fine silica tube with a special coating inside. This one is 60 metres long. The coating is the stationary phase and gas is the mobile phase.