How can you explain the difference in number of mitochondria in these types of cells?

Organs which need alot of energy to function properly have a greater number of mitochondria

Explanation:

Mitochondria are sites for respiratory enzymes which yield energy for the cells thus skeletal muscles which need alot of energy have more mitochondria than liver and liver due to doing more activities than skin has more mitochondria than the skin.

Skeletal muscle cells have a very high amount of mitochondria as well as liver cells because they need high amounts of energy to carry out their functions, whereas skin cells don't need high amounts of energy to function.

Explanation:

The Precambrian covers almost 90% of the entire history of the Earth. It has been divided into three eras: the Hadean, the Archean and the Proterozoic. The Precambrian Era comprises all of geologic time prior to 600 million years ago.