When you hold a mug of hot cocoa, you feel a change in temperature. how does the skin detect this change?

I think the skin has receptors that feel a change in the temperature from there it sends a message to the processing center of the brain called the hypothalamus, this center of the brain also has temperature receptors to detect a temperature change in the blood. 

Eukaryotic cells are theorized to have evolved from prokaryotes called the endosymbiotic theory. this explains that the most primitive eukaryotic cell engulfed a prokaryotic cell (by the process of phagocytosis) that is capable of cellular respiration and another prokaryotic cell that is capable of photosynthesis. these prokaryotic cells eventually became organelles and these organelles are the mitochondria and the chloroplast