What is the function of structure B ?

Mitochondria

The most prominent roles of mitochondria are to produce the energy currency of the cell, ATP (i.e., phosphorylation of ADP), through respiration, and to regulate cellular metabolism.[17] The central set of reactions involved in ATP production are collectively known as the citric acid cycle, or the Krebs cycle. However, the mitochondrion has many other functions in addition to the production of ATP.

Active site is where they touch.

From our previous experiment, we examined how many drops a penny can hold - and place drops of salt water on the penny after recording 5 trials each, take the average of each solution.