Studies of fat cells a d thyroid cells show that fat cells have fewer mitochondria than thyroid cells. a biologist would most likely infer that fat tissue

Think where mitochondria are found in the greatest numbers - they are found (for example) in liver cells, kidney cells, muscle cells etc. These tissues carry out a lot of work and thus require lots of energy. 

Fat is a storage product that sits there until required but the thyroid does lots of work involved in metabolism and therefore requires plenty of energy.

This should help :)

Streaks on the face of wave rock

That is false even though water expands when frozen nothing changes at all