Q.What is the anomeric carbon of glucose? Which carbon becomes the anomeric carbon when fructose cyclises, and why is it a different carbon from glucose's?

The anomeric carbon of a cyclic sugar is the ring carbon derived from the original open-chain carbonyl carbon, since it is the carbon that becomes a new stereocentre upon ring closure. In glucose, the carbonyl group in the open chain is an aldehyde at C1, so when the C5 hydroxyl attacks it during cyclisation, C1 becomes glucose's anomeric carbon.

In fructose, the carbonyl group in the open chain is instead a ketone at C2, so when the C5 hydroxyl attacks that carbon during cyclisation, it is C2 -- not C1 -- that becomes fructose's anomeric carbon. The anomeric carbon is always the carbon that was the carbonyl carbon before cyclisation, so which carbon it is depends entirely on where that sugar's own carbonyl group happens to sit.

Locate the carbonyl carbon in each sugar's open-chain structure -- that is the carbon that becomes the anomeric carbon once the ring closes.

Assuming the anomeric carbon is always C1 for every sugar -- it is C1 only for aldoses like glucose; for a ketose like fructose, it is the carbon bearing the ketone group, C2.