Karl Bloxham, of Kings High School, asks :-

Why is muscle heavier that Fat?

Peter Hurst, of the Department of Anatomy and Structural Biology at Otago University, responded.

Fat is made up mainly of millions of large cells that contain fat molecules. These cells and molecules have a density (mass per unit volume) that is about 0.92 in humans and 0.95 in sheep. These figures are less than the standard figure of 1 for water and so fat will float to the surface of water.

Muscle is also made up of millions of large cells but by contrast here the main molecules are large proteins packed into the cells in such a way that means the cells can contract. These proteins have a density in the range of 1.20 to 1.53 and so they are heavier than water and fat and sink in water.

A piece of fat would therefore weigh less than the same sized piece of muscle.